Physiology of Forage Maize (Zea Mays L.) in Relation to Its Production and Quality

Physiologyo f foragemaiz e (Zea mays L.) inrelatio n toit sproductio nan d quality

0000002 0 Promotor :ir .M.L . 'tHart ,oud-hoogleraa ri nd elee rva nd elandbouw plantenteelte nhe tgraslan d Co-referent:dr.ir .B .Deinum ,wetenschappelij k hoofdmedewerker jiMJoB701,75 0

P.C. STRUIK

PHYSIOLOGY OF FORAGE MAIZE (ZEA MAYS L.) IN RELATION TO ITS PRODUCTION AND QUALITY

Proefschrift terverkrijgin gva nd egraa dva n doctori nd elandbouwwetenschappen , opgeza gva nd erecto rmagnificus , dr.C.C .Oosterlee , hoogleraari nd eveeteeltwetenschap , inhe topenbaa rt everdedige n opvrijda g 16septembe r198 3 desnamiddag st evie ruu ri nd eaul a vand eLandbouwhogeschoo lt eWageningen .

hUîLlOTHEBK [>KR LANUBOU W H< »GKSCHOOL WAGEMN&EM

ISl/t tffjXilo^oz ABSTRACT

Struik,P.C. , 1983.Physiolog y of foragemaiz e (Zea mays L.) inrelatio nt o itsproductio n andquality .Doctora l thesis,Wageningen , (IX)+ 9 7p. ,7 tables , 12figs ,32 9refs ,Eng .an dDutc h summaries,plu s 6paper spublishe din : Mededelingno .64 ,Vakgroe pLandbouwplantenteel t enGraslandkunde ,Landbouw hogeschool,Wageninge n (1982),2 8p. ,7 tables ,9 figs,4 1 refs,Eng .summary ; Meded.Landbouwhogesch .Wageninge n 83-3 (1983),4 1p. ,1 2tables ,1 6figs , 93refs ,Eng .summary ;Neth .J . agric.Sei .3 0 (1982)2 0p. ,9 tables ,4 figs , 36refs ,Eng .summary ;Neth .J . agric.Sei .3 1 (1983),2 4p. ,6 tables,1 1figs , 12refs ,Eng .summary ;Neth .J . agric.Sei .3 0 (1982), 15p. ,3 tables ,6 figs, 27refs ,Eng .summary ;Meded .Landbouwhogesch .Wageninge n 83-2 (1983),2 7p. , 9 tables,4 figs,6 0refs ,Eng .summary .

This thesis describes anddiscusse s thequantitativ e effectso fchange si n temperature,ligh t intensity andphotoperio d on thedevelopment ,dry-matte r production,dry-matte rdistribution ,digestibilit y anddry-matte r contento f foragemaize .Cultivatio n techniques andhybri d choice areals odiscussed . Theproductivit y ofmaiz e inNorth-Wes t Europemainl y dependso n therat eo f development duringearl y seedlinggrowth .Yet ,development ,productivity , maturation anddigestibilit y areals ostrongl y affectedb y climatic conditions during laterstage so fgrowth .Moreover ,significan t aftereffectso fadvers e conditions areofte n found.Som estep s inth eplant' sdevelopmen t are especially sensitive,e.g . tassel initiation,silkin gan d grainset . Digestibility was found tob e lessvariabl e thanyiel d anddry-matte rcontent . Climatic factorsaffecte d digestibility mainly through theireffect so nth e proportiono f (lessdigestible )structura lmateria l inth eorgani cmatter . Onlyprolonge dhig h temperatures caninduc e largedepression s infina lcell - walldigestibility .Sinc e theproductio no fcell-wal l components doesno t develop overtim e inth esam ewa y asth eproductio n ofcel lsolubles , digestibility isno t always affected inth esam edirectio n asyield . Differences betweenhybrid swer epredominantl y causedb ydifference s incell-wal ldigesti bility.Therefor e selection forimprove d digestibility shouldb epossibl e without affecting earliness oryield . Thesuitabilit y of theDutc h climate forgrowin g foragemaiz e isevaluated . Furthermore,th eidea lweathe r and theidea l genotype forNorth-Wes tEurop e aredescribed .

Freedescriptors :development ,yield ,digestibility ,cel lwall ,dry-matte r content,dr ymatte rdistribution ,temperature ,ligh t intensity,photoperiod , hybrid,cultura lpractice ,ideotype .

Reference toth econtent so fChapter s 1u p toan dincludin g6 shoul db emad e by citing theorigina lpublications .

Printedb yPUDO C (CO),Wageningen ,Netherlands .

Cover illustration:Pita oCozobi ,Collectio nMusé ed el'Homme ,Paris . fOM o¥?o^ {°\^b

STELLINGEN

1. InNoordwest-Europ a isd evariati e inverteerbaarhei d vansnijmaï s bijnormal e teelttechniek geringmaa rnie tonbetekenend .

Ditproefschrift .

2. Deontwikkeling ,groe ie nomvan gva nd ekol f zijnvoo rd eopbrengs te n kwaliteitva nsnijmaï si nNoordwest-Europ abelangrijke r dand elaatst e jaren werdaangenomen .

Ditproefschrift .

3. Hetaanta lbladere nda tee nmaïsplan taanleg ti safhankelij k vankli maatsfactoren tijdensee n zeerkort eperiod evoo r deaanle gva nd epluim . Dezekort eperiod ei sdaaro mva nwezenlij k belangvoo rd eproduktivitei te n deverteerbaarhei d vansnijmaïs .

Ditproefschrift .

4. Voorhe tontstaa nva nverschi li ncelwandverteerbaarhei d isstrekkings - groeiva nplantecelle nnoodzakelijk .

Ditproefschrift .

5. Bijhe tonderzoe knaa rd eeffecte nva nklimaatsfactore n opd everteer baarheidva ncelwande ndien td echemisch ee n fysische stabiliteitva nd e celwand inbeschouwin g teworde ngenomen .

Ditproefschrift .

6. Maïsgenotypen zijnslecht sda ndaglengteneutraa l alsdaglengt e geen invloedheef to phe ttijdsinterva ltusse nmannelijk e envrouwelijk ebloei .

Ditproefschrift .

7. Degenotypisch e variatieva nsnijmaï si ndroge-stofopnam edoo rherkauwer s isvee lgrote re nbelangrijke r danzij ngenotypisch evariati e inverteerbaar heid.

On;ZU i^tf 8. Ontmenginge nonbedoeld e selectie,optreden dbi jhe thakselen ,male ne n bemonsteren van snijmaïs,vorme nvaa kd egrootst ebronne nva n fouteni nhe t onderzoekme tdi tgewas .

9. Hetbewij sva nSmit h (1981)voo rhe tfei tda tbi jmaï sP nietd e actievevor mva n fytochroomka nzijn ,i swankel .

Smith,Natur e 293:163-16 5 (1981).

10. Thiagarajah &Hun t (1982)neme nwaa rda tbove n 24C d esnelhei dwaarme e debladere nbi jmaï sworde naangeleg dnie tmee r toeneemtbi jee nstijgin g vand etemperatuur .D everklarin gdi e zijvoo rdi tverschijnse l geven,i s onjuist.

Thiagarajah &Hunt ,Can .J .Bot .6 0 (9):1647-165 2 (1982).

11. Zelfsbinne néé nstolo ngeld tnie tda td eeers taangelegd e aardappelknol bijd eeindoogs tautomatisc h degrootst e zalzijn .

12. Deindexerin gnaa rhe tprijspei lva nd egezinsconsumpti e van 1980wa s reedso phe ttijdsti pva ninvoerin gachterhaald .D egezinsbestedinge n zijn immerssind s 1980ster kveranderd .

13. Geweldlozeburgerlijk e ongehoorzaamheid leidtnie tto tuithollin gmaa r eerderto tverrijkin gva nd edemocratie ,omda tdez evor mva nverze ttege n meerderheidsbeslissingen aanleiding geeftto twegin gva nstemme nnaas t loutertellin gervan .

14. Dehuidig e teruggangva nhe tledenta lva nvee lprotestants ekerke ni s vooree naanzienlij k deel tewijte n aanhe tgebre kaa neigentijds e goede kinder-e n jeugdbijbels invorig egeneraties .

15. Heti sbete r rood testaa nda n zwartt ebezitten .

Proefschriftva nP.C .Strui k Physiologyo f foragemaiz e {Zea mays L.)i nrelatio n toit sproductio nan d quality Wageningen, 16septembe r 1983 WOORDVOORA F

Ditproefschrif tbeschrijf te nbespreek td eresultate nva nonderzoek ,da t isuitgevoer dbi jd eVakgroe pLandbouwplantenteel te nGraslandkunde .Vele n hebbendaadwerkelij k enmoree lbijgedrage n totd etotstandkomin gva ndi tproef schrift.Mij nerkentelijkhei d hiervoorbeperk tzic hnie tto td epersone ne n instellingendi ei khieronde rme tnam ewi lnoemen . Heti svoo rmi jee ngrot eee rt emoge npromovere nbi j professorir .M.L . 'tHart .I kbe nhe mzee rerkentelij kvoo rd estimulerend ewijz ewaaro phi jhe t onderzoek enhe to pschrif tstelle nerva nbegeleidde ,zij nveelzijdig e landbouw kundigekenni se ngroo tkritisc hvermoge nbleke n telkensonmisbaar . Dr.ir.B .Deinum ,mij nco-referent ,i ssteed szee rnau wbi jdi tprojec t betrokkengeweest .Hi jverrichtt ehe tvooronderzoek ,formuleerd ehe tvoorste l voorhe tpromotie-onderzoe k enwa smij ndagelijks ebegeleide r enstimulator . Zijnkenni sva nhe tgewas ,d eanalysetechnieke n end edier -e nplantenfysiolo - gischeachtergronde nvormde nee nvoortdurend etoetsstee ne nbro nva ninspiratie . Prof.ir.L.J.P .Kuper swa sal sadviseu rbi jhe tonderzoe kbetrokken .Zij n grondigekenni sva nd eplantenteel te nd egewasfysiologi e leverdenvaa knuttig e adviezene nideeën .Teven sbe ni kprof .Kuper sdankbaa rvoo rd eruimt edi ehi j ind ebeginperiod eva nmij nnieuw e functiebood ,waardoo rdi tproefschrif t versneldko nworde nafgerond . Dediscussi eme tvel eandere nbinne ne nbuite nd eLandbouwhogeschoo lheb benaanzienlij kbijgedrage n totd etotstandkomin gva ndi tproefschrift .Hierbi j denk iko.a .aa nir .J.P.M .Bink ,prof.dr .J .Bruinsma ,prof.ir .J.G.P .Dirven , dr.ir.O .Dolstra ,prof.dr.ir .A.J.H ,va nEs ,dr.ir .ï .va nde rHoning ,ir .H.A . teVeld ee nprof.dr.ir .S.J .Wellensiek . Mevr.L.M . vanRavenswaaij-Bou w is2* sjaa rnau wbetrokke ngewees tbi jhe t onderzoek.Me tgrot eprecisi ee nvee lgedul dheef tzi jtalloz ebepalinge nver richte ngegeven sverwerkt ,di talle sme tee nbewonderenswaardig e evenwichtig heid.Haa raanstellin gwer dmogelij k gemaaktdoo r financiëlesteu nva nhe t NederlandsGraa nCentrum .Dez e stichtingbe ni kdaarvoo rzee rerkentelijk . Deaanle ge nbewerkin gva nd eveldproeve nwa si nd ebekwam ehande nva n dehee rL.A .Mo le nzij nmedewerkers .Me tnam ed ebeschaduwingsproeve n vergden veelaandacht .D efytotron-proeve nwerde nuitsteken dverzorg ddoo rd ehee r J.C.M,va nde rPal . Ook aand ehee rJ.A .Möhrin ge nmedewerker si svee ldan kverschuldigd . daarzi jbi jfytotron-proeve ne nbi jd edaglengte-proeve ni nhe tvel dd e technische installatiese nhulpapparatuu raanlegden ,verzorgde ne ndraaiend e hielden. Biologischee nchemisch e analysesva nd esamenstellin gva nhe tplant - materiaalvormde nee nwezenlij k onderdeelva ndez estudie .D etienduizende n analyseswerde nuitgevoer d doormevr .W .va nHeusden ,mevr .C .d eWit-Krechtin g enmevr .I.A.M .Reurink-va nEttinger ,terwij lmevr .J.G.M .Miechels-d eBeije r enmevr .L.M .va nRavenswaaij-Bou windie nnodi gbijstan dverleenden .He t analysewerk gebeurdenie tallee nuiters tvakkundig ,maa roo kme tee ngezonde , kritischeopstellin gte naanzie nva nhe tverkrege nresultaat . Inhe tkade rva nhu ndoctoraalstudi eo fal sstagiai rhebbe nd evolgend e studentenvoo r langere tijdaa nd eproeve no fd everwerkin g daarvanmeegewerkt : HelmyAsfour ,Lubber tva nde nBrink ,Barbar aFrischknecht ,Harri ed eGraaf , PabloHarri ,Roe lHoekstra ,Ger tJa nHoornenborg ,Aal tva nd ePol ,Tree sd e Vent,Ber tWassin ke nJa nd eWilt .Daarnaas twerkt eee ngroo taanta lstudenten , stagiairse nvakantiehulpe nvoo rkorter e tijdmee .Teven sheef td ehee rJ . Knoppersal sassisten tva ndr.ir .B .Deinu mee nbelangrij k aandeeli nhe twer k gehadi nd ebeginfas eva nhe tonderzoek . Verschillende firma'se ninstellinge nhebbe n zaadbeschikbaa rgestel d tenbehoev eva ndi tonderzoek .Va nhe nwi li kme tnam enoeme nhe tStatio n d'Amélioration desPlante sfourragère s (INRA,Lusignan ,Frankrijk) ,he t KoninklijkKweekbedrij fe nZaadhande lD.J .va nde rHav eB.V .t eKapell ee n hetKweekbedrij f ZelderB.V .t eOttersum . Ir.H.A .t eVeld e (RIVRO)be ni kdankbaa rvoo rd egegevens ,di everwerk t zijni nd einleidin gva ndi tproefschrift . Dehee rJ.C .Rig gcorrigeerd eo pkundig ewijz ed eEngels eteks tva n hoofdstuk 5.Mevr .J .Burrough-Boenisc h redigeerdenie tallee nbekwaa md e overige tekst,maa r trokoo kvee ltij dui tvoo rd ebesprekin gervan .Daardoo r hebi kvee lva nhaa rkunne nleren . Dhr.G.C .Beekho fverzorgd eo pnauwkeurig ewijz ed etekeningen ,terwij l hetmanuscrip t zorgvuldiguitgetik twer ddoo rmevr .T .va nRoosendaal-va nHal . Deredacti ee nd edrukke rva nhe tNetherland sJourna lo fagricultura lScienc e beni kerkentelij kvoo rd evlott ewijz ewaaro pme tnam ehoofdstu k 4voo rop namei ndi tproefschrif tbeschikbaa rkwam .Di tproefschrif twer do psnell ee n bekwamewijz egedruk tdoo rCentral eOffsetdrukkeri jPUDO Ct eWageningen . Tenslottewi li kmij nouder sdanke nvoo rd ekansen ,di ezi jmi jboden . Mijnvrou we nzoo nbe ni kvee lverschuldig d voorhe tgedul dda tzi jgetoon d hebbene nvoo rhu nmorel emaa roo kdaadwerkelijk esteu nbi jhe tvolbrenge n vandi twerk . CURRICULUM VITAE

PaulChristiaa nStrui kwer d geboreno p2 7novembe r 1954t eNieu wVenne p (gemeenteHaarlemmermeer) .Vana f 1967bezoch thi jhe tChristelij kLyceu m Dr.W.A .Visse r 'tHoof tt eLeiden .I n 1973behaald ehi jhe tdiplom aGymnasiu m ß. Inseptembe rva ndatzelfd e jaarwer dbegonne nme td estudi eaa nd eLand bouwhogeschool teWageningen .I nseptembe r 1978studeerd ehi jme tlo fa fi n derichtin g landbouwplantenteelt.Doctoraalvakke nware nd e leerva nhe t grasland,d elandbouwplantenteelt ,d efysiologi ede rplante ne nd eerfelijk heidsleer.Va noktobe r 1978to toktobe r 1981wa shi jwerkzaa m alspromotie assistentbi jd eVakgroe pLandbouwplantenteel te nGraslandkund eva nd e Landbouwhogeschool.I ndez eperiod ewer dhe tonderzoe kverrich tda tgelei d heeftto tdi tproefschrift .Sind s 1januar i 1982i sd eauteu ral swetenschap pelijkambtenaa rwerkzaa mbi jdezelfd evakgroep .Hi jverrich tdaa ronderzoe k naard efysiologisch e aspectenva nd eknolsorterin gbi jeetaardappelen . Hiji sgehuw de nheef tee nzoon . CONTENTS

Page General introduction 1 1.Botan yo f Zea mays L. 1 2.Origi n anddevelopmen to fmaiz ea sa majo rcro p 4 3.Ai mo fth epresen tstud y 7 4.Som enote so nanalytica lprocedure s 12 4.1.Dry-matte ranalysi san dsamplin gproblem s 12 4.2.Evaluatio no fqualit y 20 4.2.1.Introductio n 20 4.2.2.Restriction so fth ei nvitr odigestibilit y technique 22 5.Reference s 24

Chapter 1.Productio npattern ,chemica l compositionan ddigesti bilityo f foragemaiz e (Zeamay s L.). P.C.Struik , Mededelingno .64 ,Vakgroe pLandbouwplantenteel te n Graslandkunde,Landbouwhogeschool ,Wageningen ,pp . 1-28 (1982) 28

Chapter 2.Effec to ftemperatur eo ndevelopment ,dry-matte rproduction , dry-matterdistributio n andqualit y offorag emaiz e (Zea mays L.). Ananalysis .P.C .Struik ,Mededelin gLandbouw hogeschoolWageninge n83-3 ,pp . 1-41 (1983) 56

Chapter 3.Effect so fligh tintensit yafte r floweringo nth eproduc tivity andqualit yo fsilag emaize .P.C .Strui k &B .Deinum , Neth.J . agric.Sei .30 :297-31 6 (1982) 97

Chapter4 .Th eeffect so fshor tan dlon gshading ,applie d during differentstage so fgrowth ,o n thedevelopment ,productivit y andqualit yo f foragemaiz e (Zeamay s L.). P.C.Struik , Neth.J . agric.Sei .31 :101-12 4 (1983) 117 Page Chapter5 .Effec to fa switc h inphotoperio do nth ereproductiv e developmento ftemperat ehybrid so fmaize .P.C .Struik , Neth.J .agric .Sei . 30:69-8 3 (1982) 141

Chapter6 .Th eeffect so fswitche s inphotoperio do n cropmorphology , productionpatter nan dqualit y offorag emaiz e (Zea mays L.) under field conditions.P.C .Struik ,Mededelinge n Landbouwhogeschool Wageningen 83-2,pp . 1-27 (1983) 156

Generaldiscussio n 183 1.Influenc eo fclimat e andweathe ro nth eyiel dan dqualit yo f foragemaiz e inTh eNetherland s 183 1.1.Evaluatio no fth e suitabilityo fth eDutc h climate for growingforag emaiz e 183 1.2.Evaluatio no fth eeffect so fweathe ro n thedevelopment , productivity andqualit y offorag emaiz e 191 1.3.Idea lweathe rcondition s forgrowin g foragemaiz ei n TheNetherland s 202 1.4.Implication s 203 2.A nideotyp eo f foragemaiz e forNorth-Wes tEurop e 207 3. References 230

Summary 243

Samenvatting 248 GENERAL INTRODUCTION

1.BOTAN YO F ZEA MAYS h.

Iti sdifficul tt odiscus sth eecophysiolog y offorag e maizewithou t havinga clea rpictur eo fth edevelopmen tan dth ehabitu so fth eplant .There fore,i nth efollowin g sectionthes ewil lb edescribe d anda tth esam etime , thebotanica l termsuse d inthi sthesi swil lb edefined .

Maize isa tall ,vigorousl y growingannua lo fth eGraminea e (orPoaceae ) family. A fullygrow nplan tbear sa tleas teigh tleave so nth emai nstal k (Duncan, 1975).Hybrid sgrow ni nTh eNetherland s generallyproduc e 13-17 leaveso naverage .A tlowe rlatitudes ,a maiz eplan tnormall yha sman ymor e leaves (upt o48) .Th eleave sar esessile ,wit h rigidsheath ssurroundin gth e steminternode .Th esheat han d laminamee ta ta definit ecolla ro nwhic ha small,thi nligul edevelops .Th e firstlea fo fth eseedlin gi sspatulate ; subsequentleave sar elong ,sword-shape do rlinear-lanceolate ,acuminate-pointed , andhav eprominen tmidribs .Th e leafblade s (usuallycalle d 'leaves')ar e mostlycurving .Bot h leafangl ean dinclinatio nar evariable .Som egenotype s evensho werect ,stif fuppe rleaves .Th euppe rsurfac eo fth eblade si s pubescent,whil eth elowe rsurfac ei sglabrous . Thesurfac eare ao fth esuccessiv e leavesincrease sexponentiall y upt o 2 theleave s fromth emiddl eo fth estalk ,whic hca nexcee d 1000c m .Furthe r upth estal k theare ao fth eindividua l leavesdrop ssharply . Thealternat e leavesar eusuall yarrange di ntw oopposit eorthostiches , althoughpronounce d torsionma yoccur .However ,genotype swit ha decussat e leafarrangemen thav eals obee nreporte d (Blanco, 1976). Duringearl yvegetativ e growth theshoo tape xelongate san d tassel-branch primordiainstea do flea fprimordi aar einitiated .A tthi sstag e thenumbe ro f leavesi sfixed . Theshoo tma yfinall y reacha heigh to f 7m ,dependin go f thenumbe ro f leaves (andthu snumbe ro fste minternodes )an d factorsdeterminin g thelengt h ofeac hindividua lphytomere .Th eusua lheigh to fth este mi ntemperat e regionsi s20 0- 30 0cm . Unlikemos tothe rgrasses ,th estalk so fth emaiz eplan tar efille d withparenchymatou s tissue called 'pith'.Thi s tissue,i nwhic hsom evascula r strandsar eembedded ,add sstrengt h toth estal k (Zubere tal- , 1980)an d enlarges thecapacit y tostor enon-structura l carbohydrates.Th etissu e enclosing thepit h isver y fibrousan di scalle d 'rind'. Inadditio n toth eradicle ,th esemina lroot san d thenoda lroots ,maiz e mayals oproduc e aerialo r 'brace'roots .Aeria lroot sappea ro nth elowe r stemnode sa tth een do fth evegetativ egrowth .I fthes eaeria lroot sreac h thesoil ,the ydevelo pint onormall y functioningroots .Plant sbearin g these rootsar ebette rprotecte dagains troo tlodging . Maize alsodiffer s frommos tothe rgrasse si nhavin g unisexual inflorescences,althoug hth especie si smonoecious .Th emal ean dfemal e inflorescences areborn eapart .Th estaminat e inflorescence isa panicle , called 'tassel'.Th etasse lterminate sth emai nshoot .Th etasse lbranche s carry spikelets,occurrin gi npairs :on emembe ri spedicellat e and theothe r issubsessile .Eac hspikele tcontain stw oflower san deac hstaminat eflowe r contains threeanthers .Th eglume so fth espikelet s arerobust ;th e lemmasan d thepalea so fth estaminat e flowersar eals owel ldeveloped .Sinc eeac hanthe r produces about250 0polle ngrain san dsinc eth etasse lo fa norma lplan tgrow n undertemperat econdition sproduce sabou t40 0spikelets ,a maiz eplan tproduce s approximately6,000,00 0polle ngrains .Kiesselbac h (1949)estimate d thata n average-sizedplan tgrow nunde rAmerica ncondition seve nproduce s25,000,00 0 pollengrains . Duringearl yste mdevelopmen ta shoo ti sinitiate di nth eaxi lo feac h present leaf.Suc h axillary shootsi nth emid-sectio no fth este mnormall y developint oa nea rshoot .Ea rshoot sar ecompose do fa ver yshor tstal k (called 'shank')bearin g anumbe ro fleaves ,th esheath so fwhic h arewel l developed,bu twhos e laminaear emostl y rudimentary.Thes e leavesar ecalle d 'husks':the yenvelo pan dprotec tth epistillat e flowers.Th eea r shootsar e terminatedb y anear . Earsconsis to fa robus trachi s ('cob'),bearin g 4-30 rowso falmos t sessile spikelets.Ther ei salway sa neve nnumbe ro frows ,becaus e spikelets arearrange di npairs ,a si nth etassel .Althoug h twoflower sar eproduce d ineac h female spikelet,onl yth euppe ron eusuall ydevelop sint oa functional flower.Th epistil so fthes e flowershav ever y longstyle scovere d with stigmaticbranches .Th e style,includin g stigmaticbranches ,i scalle d a 'silk'an d theproces so fextrusio no f thesesilk sou to fth ehus kenvelop e iscalle d 'silking'.Th etw oglume so fth efemal espikele tenclos e theovary , butth esil kextend sbeyon d theman d canreac h anenormou s length ifi ti sno t pollinated .Th eglume sar eto osmal l toenclos e thecaryopsi swhe n itha s reached itsmaximu mvolume ;th etw olemma san d the twopalea so feac h female spikeletar eeve nshorte r thanth eglume s (Miller, 1919). Matur ecaryopse s arethu sno tindividuall y enclosed. Atfirs tal lth e flowerso fth e tasselan do fth eear so nth emai nste m showprimordi ao fbot h staminaan dpistil s (Bonnett, 1966). Phytohormone san d environmental factors (e.g.temperature ,photoperiod ) regulate these x expressiono feac hflower . Self-pollination ispossibl ebu twin dan dprotandr y stimulatecros s pollination.Th e fertilizedovar y developsint oa caryopsi s called 'kernel' or 'grain'. Anaxillar ybu d ispresen ti nth eaxil so fal lhusks ;thi sma ydevelo p intoa secondar yea r (alsocalle d 'axillaryear 'o r 'shank ear').A sthes e earsar eenvelope db yhusk swit h theirow nbuds ,a ste minternod ema ybea r many ears.Sinc e each steminternod e (exceptperhap s the 3-7 internodes immediatelybelo w thetassel )ar epotentiall y capableo fproducin gea rshoots , thenumbe ro fear spe rplan ti salmos tindeterminate . Normallyonl yon eo r twointernode sbea ron eea rshoot .Unde rDutc h conditions,approximatel y 400 floretso fth eto pea rwil lextrud esilks .Thu s 15,000polle n grainsar eavailabl e foreac hsilk . Theaxillar ybud so f the lowerleave sma ydevelo pint otiller srathe r thanint oea rshoots .Th e tendency totille ri ssmal li nmoder nhybrids : tilleringonl yoccur swhe nplan tdensit yi slow .Tiller susuall ybea ra hermaphrodytic topinflorescenc e onwhic h roundkernel sar ese to ntasse l branches,no tprotecte d byhusks . The shapeo fth ekernel so nth eea rshoo tan d thecharacteristic so f theendosper m arever yvariabl ean d formth ebasi so fa classificatio n into differentcommercia l types:dent ,flint ,flour ,waxy ,po pan d sweet('sugary' ) corn.Numerou sothe rendosper mmutants ,suc ha sopaque ,amylose-extender , brittle,dull ,sof tstarch ,an dshrunken ,hav en oo ronl yver y limited commercialvalue .A specia l typeo fkerne lmutan ti spo d corni nwhic hth e glumesar eno tvestigia lbu tenclos e thekerne l likechaf fdoe si nothe r cereals.Commercia l forage-maizehybrids ,grow ni nTh eNetherland s areal l flint,dent ,o r flint/denttypes . Thekerne lmainl y consistso fendosperm ,th emajo r componento fwhic h isstarc h (amylosean damylopectin) .A specifi c characteristic ofth ematur e maizekerne li sth epresenc eo fa closin glaye rbetwee nth ebasa lendosper m and thevascula rregio no f thepedice l (Kiesselbach& Walker , 1952). This plateo ftissu e several cellsthic kdevelop searl yi nth ekerne ldevelopmen t buta tth een do fth egrain-fillin gperio di scompresse d andthe nappear sa s ablac k layer.Thi s 'black-layerformation 'serve sa sa nindicato ro f physiologicalmaturit y inmaiz e (Daynard& Duncan , 1969).Unde rDutc h conditionso fgrowin gsilag emaize ,blac k layersonl ybecom evisibl ei nti p kernelsi nwhic h theaccumulatio no fdr ymatte rha sbee n startedbu tha sonl y lasted fora shor twhile .Onc e compressed,th eblac k layerprevent sth e passageo fchemica l compounds.I nthi swa yth eplan tadjust sit snumbe ro f dry-matteraccumulatin gkernel s toth eprevailin gconditions .Th eproces so f adjustmenti sreferre dt oa s 'kernelabortion' .

2.ORIGI NAN DDEVELOPMEN TO FMAIZ EA SA MAJO RCRO P

TheC -plan tmaiz eha sbee nknow nthroughou tNorth ,Centra lan dSouth - Americasinc eprehistori c times.Ancien tIndia ncivilizations ,lik ethos eo f theIncas ,th eAztec san dth eMayas ,wer e foundedo nmaize .Th edependenc eo n maize forstapl e foodwa ss ocomplet e thatth eplan tplaye da nimportan trol e inth ereligion so fthes epeoples .Th epresenc eo fspecia lgodhead s formaize , e.g.Pita oCozob i (seecover) ,illustrate s this. Maize isa cro pmad eb yman .Galina t (1971)state d thatth emoder nmaiz e earha sa Darwinia n fitnessapproachin g zero.Maiz eonl ysurvive d thankst o thedomesti cpropagatio nb y theIndians .Al lit scloses trelative sbecam e extinct.Moder nscientist sar estil ltryin gt otrac eth eorigi no f Zeamay sL . andd ono teve nagre eabou tth etaxonom yo fth etrib eo fth eMaydea e (or Tripsaceae),o fth ever ysmal lgenu s Zeaan do fth esubspecie so fmaize . Todaymaiz ei son eo fth emai ncrop so fth eworld ;i tha sa ver ywid e ecologicalrange .Lik eman yothe rcultivate dplants ,e.g .peanut ,potat oan d tobacco,th eplan twa ssprea dove rth eworl dafte rth e 'discovery'o f Americab yColumbus .Toda y themai nmaize-growin g regionsare :th eU.S .Cor n Belt (centredi nIow aan d Illinois),th eDanub eBasin ,th eP oValley ,th e plainso fnorther nChina ,north-easter nArgentina ,south-easter nBrazi lan d southernAfrica .Th enorther n limitso fth erang eo fgrai nmaiz e runthroug h southernCanada ,centra lEurope ,souther nU.S.S.R . andChina .Thes e limits areshiftin gnorthwards ,becaus ebreeder sar esucceedin gi ndevelopin g productivehybrid stha tmatur ewit heve rlowe raccumulate d temperaturetotals .

The traditionalmaiz earea si nEurop ear echaracterize db ya mea n temperatureo f 17C o rmor edurin gth eperio d from 1Ma y to 30September . Atpresent ,grai nmaiz ei sals ogrow ni narea swit ha seasona lmea n temperature ofapproximatel y 15.5C (Bunting, 1980). Severaltime sdurin gthi scentur y theare ao fgrai nmaiz ei nTh e Netherlandsha sreache da substantia lsiz e (Becker, 1976),mainl y during periodso feconomi c crisis,wars ,o rwhe ngrai nprice shav ebee nextremel y high. Themea nseasona ltemperatur e inTh eNetherland s (approx. 14.5C) , however,i sstil lmuc h toolo wfo rgrai nmaiz et ob egrow nprofitabl yi n normaltimes ,i nspit eo fsubsidie s fromth eCommo nMarket .

Inearl yday smaiz ewa sno tuse da sa forag ecrop ,bu tth eEuropea n colonistsi nAmeric asoo ndiscovere d thatth estove rwa sa usefu lroughag e forthei rlivestock .Th etemperatur e requirementso f foragemaiz ear elowe r thanthos eo fgrai nmaiz ebecaus eth e foragecro pi sharveste d beforegrai n maturity.Forag emaiz eca nb egrow ni narea swit ha mea nseasona l temperature of 13.5C an dabove .Considerabl e areaso f foragemaiz ear eeve nfoun di n Scandinavia. InTh eNetherland sa revolutionar y developmento fth eare ao fforag e maizestarte di nth eearl y 1970s (Fig. 1;source :C.B.S.) , initiallymainl y onth esand ysoil so fth esouther nan dth eeaster npar to fth ecountry ,bu t laterals omor et oth enort han deve no nth eFrisia nIslands .

areai nha/yea r (*1000) 160r

140

120

100

0 1960 1965 1970 1975 year Fig.1 .Developmen t overtim eo f the areao f foragemaiz e inTh eNetherlands . 5 By 1982,forag emaiz ewa sth esecon darabl ecro p (interm so farea )i n TheNetherlands .Th e samedramati cdevelopmen twa sfoun di nneighbourin g countries (Table 1).

Table 1.Are ao f foragemaiz e innorther nEurop e( *100 0ha) ,excludin g corn-cobmix .

year 1965 1970 1975 1980 1982 country Netherlands 3 6 77 139 147 Belgium 5 18 66 90 92 W.German y 100 190 430 700 775 France 360 400 870 1140 1280

Therear eman yreason s forth erapi dincreas ei nth e forage-maizearea .Som e ofthes eare :

characteristics of the maize crop . maizeyield sar ehigh ,partl ybecaus e well-adaptedhybrid sar eavailabl e .maiz ei sa good-qualit y roughage (highenerg y content,tasty ,ver ydigestible) , suitable formea tan dmil kproductio n and forth erearin go fyoun gcattl e . thecompositio n isfavourabl e forensiling :a hig hproportio no f fermentable carbohydratesan da lo wbufferin g capacity .maiz eca ntolerat ever yhig hgift so fslurr yan dmanure ,whic har eproduce d inenormou squantitie so npig ,chicke nan ddair y farms

cultural factors .wee d controlha sbecom eeas ya sa resul to fth eus eo fchemicals ;th e chemical controlo fcertai nweeds ,however ,i sgettin gmor etroublesom e . therear en osever edisease so rpest stha treduc eth eforag eyiel dt oa greatextent ;continuou s croppingo f foragemaiz ei sstil lpossibl ewithou t severeyiel d depressions . thesoi lcondition s (e.g.pH )demande db y foragemaiz ear eno ta sexactin g asthos erequire db yothe r foragecrop s (e.g.fodde rbeet ) . themaiz ecro pshow sa lo wwate rdefici tcompare dwit hothe r foragecrop s growni nTh eNetherlands ;therefor emaiz e cangiv establ eyield so nsoil s with lowwater-bearin g capacity socio-economical factors . cultivation,harvest ,ensilin g and feedingar ecompletel y andefficientl y mechanizable;cultivation ,harves tan densilin g aremainl y doneb y contractors .productio n costspe r feedinguni tar elo w .becaus eo flo wlabou rinput ,maiz e caneasil yb egrow no n fieldsa lon g distance fromth e farmstead . the trend frommixe d farmingtoward scattl e farmswit h alarg enumbe ro f animalspe rhectar e . foragemaiz e isno tonl ya forag e cropbu tals oa commercia lon e . theknow-ho wnecessar y forgrowin g foragemaiz equickl ybecam e available

The cultivationo fmaiz e forcorn-co bmi x (CCM)an dhigh-moistur e grain (feedsmainl y used forrearin gpig si nNorth-Wes tEurope )ha sals obecom e increasinglypopula rdurin grecen tyears ,mainl y inFrance ,Belgiu man d W.Germany .T odat e thisdevelopmen tha sno tbee no fgrea timportanc ei n TheNetherlands .Thi s lacko finteres tno tonl yreflect sadvers e climatic conditionsbu ti sals obecaus e theDutc hcompound-fee d industryi shighl y developed.

3.AI MO FTH EPRESEN TSTUD Y

Foragemaiz ei sgrow nt ofee dth elivestoc k thati sreare dfo rmea t andmil kproductio n andi suse despeciall y duringwinter .Th evalu eo fa maizecro pi stherefor eno tonl ydetermine db y factorsaffectin gdry-matte r yield,bu tals ob y factorsaffectin g dry-matterdistribution ,ageing , preservation and theefficienc yo fth econversio n tovaluabl eanima lproduct . Fig.2 indicate sth e factorsinvolve di nth eagronomi cvalu eo fa forage-maize crop.Th epresen tstud ywa s focussedo nth e factorswritte ni n italics. Theaverag eincreas e indry-matte ryiel d inth evariet y trialscarrie d outb y theGovernmen tInstitut e forResearc ho nVarietie so fCultivate d Plants (RIVRO)i nth eperio d 1954-1981wa sapproximatel y 160kg.h a .year (teVelde , 1983).Thi sincreas ei sproportionall y largertha nth ecorrespondin g increase inmos tothe r crops (Scheijgrond, 1978)bu tagree swit h the findingso f Schustere tal . (1977)o n foragemaiz ei nW .Germany .Thes e largeincrease s inforage-maiz eyield smus tpartl yb eattribute d toimprove d cultivation techniquesan dpartl yt oth eintroductio no fne wvarieties .Fig .3 show stha t Fig.2 .Factor s affecting the agronomic valueo fa forage-maiz e crop.Th e factorswithi n one frame areinterdependen t or interact.Th e factorsi n italicswer epar t of thepresen t study.

theyiel d increaseo f foragemaiz e resulting fromplan tbreedin gdurin gth e lastthre edecade sha sbee napproximatel y 1.0% (i.e.approx . 125kg.h a year ).Th eincreas ei naverag eyiel do fth evarietie suse db ygrower si n theperio d 1954-1981 (averageweighte d according toth eare ao fth edifferen t -1 -1 -1 hybrids),however ,wa sonl y6 9kg.h a .year (i.e.0.54%.yea r ;t eVelde , 1983;t eVelde ,persona lcommunication) . Inth esam eperio dsevera lothe rrelevan tagronomi cpropertie so fth e collectiono fhybrid s listed onth edescriptiv evariet y listproduce db yth e RIVROhav e improvedslowl y (Fig.4) .Difference s inproportio no fea rbetwee n thehybrid s listed,however ,declined .Fig .4 clearl y showstha tth ebreeders ' relative dm yield

130 .Splend a •Markan t 125 Dorina 120 Fronica 'irla

115 Brutus ll ^ °. LG11 And 110

105 .Protor(CIV7) ,, ... •rCalder a56 1 •Pionee r39 5 100 p=1 6 .Caldera40 2 r=0.950(P<0.001 ) .Goudster b=095% ,year" 1 95h •CIV6 U.A 1 L '54 '58 '62 '66 '70 '74 '78 '82 firstyea ro ftestin ga sforag emaiz e

Fig. 3.Relativ edry-matte ryiel do f forage-maize hybrids,tha thav ebee no r arebein ggrow nb y farmerso na larg escale ,i nrelatio n toth e firstyea ro f testinga sforag emaiz eb y the Government Institute forResearc ho nVarietie s ofCultivate d plants (RIVRO).Pionee r 377Aha sbee nexclude d sincei twa s only recommended forgrowin g asfres h forage.Dat akindl yprovide db y Ir.H.A . teVeld e (RIVRO).Th emetho do fanalysin g thedat aha sbee ndescribe db yt e Velde (1983).Thi smetho d enableshybrid st ob ecompare deve nthoug h theywer e testedi ndifferen tyears ,a tdifferen t locations andunde rdifferen t cultivation techniques.

interestwa smainl y focussedo nimprovin gdry-matte ryield . Acompariso nwit h datarecorde d inth edescriptiv e variety listso fth elas t twodecade s (RIVRO,196 3u pt oan dincludin g 1983),however ,show stha tbot h dry-matterconten to fth ewhol ecro pan dproportio no fea ri nth edr ymatte r increased steadily asa resul to f improved cultivation techniques.On eo fth emos t drastic changesi ncultura lpractic ewa sa reductio n inth eplan tdensit y from 2 14t o 10plants/ m. Inadditio n toth equalit y characteristics mentioned inFig .4 ,RIVR O alsopai d someattentio n tofeedin gvalue .Comparison so ffeedin gvalu ewer e based oncrude-fibr e and ashcontent .Maiz equalit yhardl yvarie s betweenhybrid s according tothes e chemicalanalyses :clos erelationship swer etherefor efoun d proportion of ear in dry matter

• Goudster ^Blizzard .GoaJ .Irla Brutus •Markant •Fronica -Splenda • CIV« •Caldera 402 Dorina • Capella

'Caldera 561

.ProtorlCIW] n.16 r .0543 (P< 0.05) b .0.12 •/..year"1 • Pioneer 395

i I i i i '68 '66 '70 '74 '78 '82 first year of testing as forage maize

dry-matter content whole crop (%) 32 -

• Splenda Brutus . • .Irla . Capella Blizzard u . L . .Goal 'Markant .Caldera 402 •Ca!dero56 1 Fronica 'Dorina 'CIV 6 Î Protor ICIV7 1 n= 16 Pioneer 395 r -0.602 (P<0.05) b=0.07 '/..year-1 ^ '62 '66 '70 '74 '78 '82 first year of testing as forage maize

Fig.4 .Dry-matte r content of thewhol e crop (a)an dproportio n ofea r inth e drymatte r (b)i nrelatio n toth e first yearo f testing asforag emaiz efo r thesam ehybrid s asi nFig . 3.Dat akindl yprovide db y Ir.H.A . teVeld e (RIVRO).Metho d asmentione d underFig . 3.Not etha t theabsolut evalue si nthi s figure are lowcompare d toth edat a inrecen t varietylists .

between relativedry-matte ryiel d andrelativ e starch-equivalentyiel do r relativeVE Myield ,calculate d fromcrude-fibr e andas h content (e.g.Ebskamp , 1981). Deinum& Bakke r (1981),however ,showe d thatsignifican tgeneti c differences indigestibilit y betweenhybrid s fromth ecollection s submitted foragronomi c testingdi dexis ti fdigestibilit ywa sestimate db y thei nvitr o disappearance oforgani cmatter .Recen tresearc h indicates thatth enarrow - senceheritabillt y offorage-maiz e digestibility mayb ehig h (Beerepoot, 1981; Deinum& Struik , 1982)an d thatth eexistenc e ofgeneti c differencesi n

10 apparent digestibility found by means of in vitro digestion of fresh material can be confirmed by in vivo digestion trials on ensiled products (Deinum & Struik, 1982). Therefore RIVRO decided to present new figures on relative feed-unit yields, based on in vitro digestibility data (RIVRO, 1983).

Fig. 5 shows that the widespread lack of interest in the quality differences of forage maize and the use of misleading feed-evaluation techniques have resulted in new introductions having slightly but continuously lower digestibility values,wherea s other characteristics have steadily improved.

relativeD ol LG1 1=10 0 <%) .Leopard LG11 100 ,Camp o •Circe '

96 n= 1 9 r=-0.66 0(P <0.0 1) EtaIph o Markant 94 b=-Q2 3"/..year -1

•68 '70 72 '74 '76 '78 '80 '82 'S« yearo fintroductio n

Fig. 5.Reductio no frelativ e digestibility of theorgani cmatte r (D ) on resulting fromth eintroductio n ofne wvarieties .

Yeti ti spossibl e toimprov e thedigestibilit y of foragemaiz eb y breeding,withou tsacrifyin gmuc hyiel d (Gallaise tal. , 1976;Deinu mS Bakker, 1981), althoughRot he tal . (1970),Beerepoo t (1981)an dGallai s& Vincourt (1983)reporte d significantnegativ ecorrelation sbetwee n dry-matter yieldan ddigestibility : theseresul tfro mth enegativ e correlationbetwee n yieldan dearlines s (i.e.positiv e correlationbetwee nyiel dan d cell-wall content). Ifbreedin gprogramme sar et oimprov edigestibility ,specia laspect s ofth emorphology ,anatom yan dphysiolog yo fth emaiz eplan tmus tb eknown . Muchinformatio no nth eeffect so fphysica l factorsinfluencin g thequalit y of foragesfro mth eGraminea e familyha salread ybee ncollecte d (seee.g . reviewsb yDeinum , 1981;Wilson , 1982).Silag emaize ,however ,need sspecia l attention,becaus eit sphysiology ,productio npatter nan dchemica l composition

11 deviate fromal lothe r foragescommonl yuse di nNorth-Wes tEurope ,an dar e not fullyunderstood . This research aimed to gain insight into the ecophysiology of the plant, its development, its production, its distribution of dry matter and of chemical components, and the trend in whole-crop quality {dry-matter content, proportion of ear in the whole plant, digestibility). The possible inter relations and interactions between these factors were also studied. These plant phenomena were investigated under controlled climatic conditions, with selected hybrids and certain cultural practices (cf. Fig. 2). Onth ebasi so fdat a fromth eliteratur ean dth eresult sdescribe di n Chapters 1u pt oan dincludin g6 ,th emorphologica lan dphysiologica lcharac teristicso fa nidea lforag emaiz e ('ideotype')fo rNorth-Wes tEurop ewil l bedescribe dan dth esuitabilit yo fth eclimat eo fthi sare afo rth eproductio n of foragemaiz eo fhig hqualit ywil lb eevaluated . Thesepaper san ddescription s should contributet oknowledg eo fth e physiology,productivit yan dqualit yo fforag emaiz ei nmargina lan dsubmargina l regions,t oth eunderstandin go fcultura lmeasure snecessar yt omaximiz eth e crop'spotentia lan dt odevelopin g selection criteriafo rbreedin gmaiz e hybridsfo rforag eproductio ni nNorth-Wes tEurope .Moreover ,the yindicat e thatlarge-scal e evaluationo fth efeedin gvalu eo fmaiz esilage sfo r practicalus eca nb ereplace db ya predictio nbase do nclimati c dataan d cultivationpractice .

4.SOM ENOTE SO NANALYTICA LPROCEDURE S

4.1. Dry-matter analysis and sampling problems Thissectio ndescribe sth eprocedure suse di nfiel dexperiments . Phytotronexperiment sar eno tdiscusse dbecaus esom estep swer eno tnecessar y andther ewer e fewersamplin gproblem sbecaus eth eplant swer eanalyse d quantitatively.Th emai nsourc eo fvariatio ni nphytotro nexperiment sthere forewa splant-to-plan tvariability .

Thecomplet eprocedur eo fprocessin gan danalysin gmaiz ei nth efiel d researchwa sa sfollow s: 1. harvest,i.e .cuttin gof fan dcollectin gth emaiz eplant s 2. transportan dstorag e 3. separationint omorphologica l fractions 4. determining freshweigh to fth efraction s

12 5. chopping 6. sampling 7. weighing the freshsample s 8. drying 9. weighingth edrie d samples 10.bulkin g 11.grindin g 12.samplin gan dstorin go fth egroun dmateria l 13. subsamplingan dchemica lanalysi so fth egroun dmateria l

Steps4 ,7 an d9 ca nb ecarrie dou twithou tnoticeabl e errorsan dthere forewil lno tb ediscussed .Al lth eothe rstep si nth eprocedur ear eafflicte d witha nerror ,sometime smainl y systematic,sometime smainl y random.Th e relevanceo fthes eerror si spresente d inTabl e2 an ddiscusse dbelow .

Step 1.Harves t Plant-to-plantvariabilit y ofmaiz e isgrea t (e.g.Deinu m sStruik , 1980)especiall y innorther n latitudes (Breeze& Milbourn , 1981),bu ti ti s similart otha ti nsuga rbee tan dothe rnon-tillerin g species.Th evariability , especially forea rcharacteristic s generally increaseswit h increasingplan t densities (Glenn& Daynard , 1974;Edmeade s& Daynard , 1979;Breez e &Milbourn , 1981).Th e frequencydistributio no fvariou splan tparameter sbecome sbimoda l insteado fnorma la thig hplan tdensitie s (Edmeades& Daynard , 1979;Daynar d &Muldoon , 1983). Standarddeviation sincreas ea scro pdevelopmen tprogresse s butcoefficient so fvariatio n_(CV ) decline (Daynard& Muldoon , 1983).Th e declinei nC Vi sals oillustrate d inFig .6 fordry-matte ryiel dpe rplan t (glasshouseexperiment) ,plan theigh t (fieldexperiment ) anddry-matte ryiel d perplo t (twofiel dexperiments) .A tth een do fth egrowin gseason ,16-6 4 plantsmus tb eharveste d toreduc eth eC Vt o5% .M yunpublishe d datasugges t thatth eplant-to-plan tvariabilit y indigestibilit yo fth eorgani cmatte r isver ysmal li na unifor mcro p (CV= 1.55%,n = 10) . Becauseo fth elarg eplant-to-plan tvariability ,a considerabl e amount ofplan tmateria lmus tb ecollecte di neac hplo to neac hsamplin gdate . Thereforeplot smus tb e large.I naddition ,plot smus tb ea shomogeneou sa s possiblean dno tb eaffecte db ysurroundin gplot so rb yvacan tsite slef t frompreviou ssampling s (cf.Deinu m &Struik , 1980).Th e latterrequiremen t demands'.largeborder s (mostly 70-95%o fth eexperimenta l area).Th edesire d plotsiz etherefor e limitsth enumbe ro fplot stha tca nb ehandle dpe r

13 ai

•rc4 A U 0c <-*• H •rii G 4J £> 01 C U S! •a 0) 01 144 •rai 0) 1H •0 3 •H (1) 10 •a 10 Ü

4-1 o o ai +1

J3 c o 4J u> + 1 1 o n +1 +1 + +1 +1 +1 ai ai H a. ai

ai o 01 0 01 II) u C ai 0 u •o ft •H 0 a >i •P M d £) •H ft +1 +1 +1 +1 + 1 •0 c Di ai 0 c P ai Ü •H C 3 M 10 id u 3 4J 0 0 •a u 4-1 0 C 10 ftS 4J •H 1-1 H 0 & O 01 •raftH u > ai II II a +1 I + o + + •o + + a

(0 a •H 0c •H ai io 4J en •H u 10 to 0 Si 10 M >i u u 0 H • ai »10 14-1 4-1 10 S u -4 n 10 C -H 0 a 0 0 B) T3 4-1 •p TS 4J •cH <1) oi c G >S-l . C 5 Ü •H 10 + 4J 10 BS 0 Oi 01 10 iH + c Oi e >01 Q, 4-1 0 C •H -H 10 14 -H D> o> e> •H H •0a1 01 >1 c; 4-1 0 P c c 0> c H fi U 10 •H oi 10 •H •r4 Cn C •H & 0 H rH ai ft10 U .-H C •H T3 & (Ö t-l Q, c 10 ft -r4 a 1a0 œ ft a ai u> 10 ft0 Bft >1 H.* M 01 II II •u 10 u ftai fl 10 H 3 n 01 3 w fi 4-1 oi 0 01 -a A Ol u W 1 +1

14 experimentan dmake sdemand so nth efacilitie san dman-powe r available.I n theexperiment sreporte d inthi sthesis ,plo tsiz e (excluding separation 2 2 betweenblocks )range d from60-9 0m .A tleas t4. 5 m washarveste dpe r samplingdat e andpe rplot .Th enumbe ro freplicate s ranged from4-8 . Stubbleheigh tmus tb ever yuniform .I nth ereporte dexperiments ,plant s werecu tof fjus tabov e soil level,thu sexcludin gvariatio n instubbl eheight . Fallenleave san dsmal ltiller swer eals ocollected . Conditionsdurin gharvestin g (e.g.rainfall ,dew )influenc e absolute valueso fplan tcharacteristic s sucha sdry-matte r content.Th erelativ e differencesbetwee ntreatment swer ehardl yaffecte db y thesecondition ssinc e theharves t took little timean dbecaus eplot swer e sampledreplicat eb y replicate. coefficient of variation M.) Hybrid LG 11

whole-plant yield ,n=40,(o)n=30: glasshouse experiment

plant height,n=98,field experiment

plot yield; n=8; field experiment«

plot yield;fi=8,fiel d experiment

100 110 120 130 140 days after emergence

Fig.6 .Developmen t over timeo fth e coefficient ofvariatio n indifferen t experiments.Pe rplo t4. 5m 2 washarveste d (i.e.approx .4 5plants) .

15 Step2 .Transpor tan dstorag e Allfiel dexperiment swer e laiddow nwithi na radiu so f 7k m fromth e laboratory.Losse sdurin gtransportatio nwer e thereforesmall . Inorde rt opreven tlosse so fdr ymatte ran do fwater ,intac tplan t materialwa sstore d ina larg ecol dchambe r (temperature 2- 3C )durin g furtherprocessing . (Choppedmateria l shouldeve nb estore d ina dee pfreezer , since fermentationan drottin gprocesse s causesever e lossesi nthi smateria l within aver y shorttime ,eve na ttemperature s justabov e freezingpoint. ) Respiration lossesan dlosse so fwate rdepen do nth etreatment sapplie di n theexperiment ,a streatment saffec tth emas s fractionso freadil y respirable and fermentable assimilates ando fwater :therefor e theduratio no fstorag e waskep tminimal .I naddition ,wheneve rpossibl eea rsample swer etreate d afterstove ran dhus k+ shan k samples,sinc eea rsample slos ewate ran d drymatte ra tth eslowes trate .

Step 3.Separatio nint ofraction s Separationint oplan tfraction s (mostlystover ,to pear ,lowe rears , husk +shank )ca nb e carriedou twithou tlarg eerror si fth ecriteri afo r separationar estrict .Separatio nwa stherefor ea ver ymino rsourc eo f variationi ndry-matte ryiel do rqualit yo fth efractions ,excep tperhap s forth elower-ea rfraction .

Step5 .Choppin g Choppingi snecessar y forprope rsampling . Ear samples werechoppe d ina stron gvegetabl e cutter (0.7kW )int o particleso f0. 5 - 1.0cm .Thi scutte rhomogenize sth emateria li na horizonta l direction,bu tvertically ,differentia l sedimentation occurs.I naddition , inearl y stageso fea rdevelopment ,materia lwit ha ver ylo wdry-matte rconten t mayaccumulat e inth ehea do fth emachin etha tprotect s theknives .I nver y latestage so fea rdevelopmen tkernel sca nremai nunchoppe do reve nb eswun g outo fth ecutter .B ychoppin g fora lon gtim ean dcoverin g thebowl ,thes e problemsmigh tb eminimized . Thecapacit yo fthi svegetabl e cutteri sto osmal lfo rlarg esamples . Toovercom e thisproblem , samplesiz emus tb e reducedb y randomly selecting completeears .

Stover and husk + shank samples were choppedwit ha tractor-mounted , stationary,1-ro wchoppe r (FAHRM H 70;se eFig .7) .Sample so fplant s

16 harvestedbefor e silking,canno tb echoppe dwit h thischopper , sincever ywe t materialstick si nth emachine .Th erat eo finput ,th epowe r andth esharpnes s ofth eknive sdetermin e theparticl e size.Optimu mparticl e size forth e stoveri s0. 5 -0. 8 cm.Particle smus tb ea sspherica la spossible .Dea d leaves,however ,remai nuncut ;pit h iscu tint osmall ,spherica lparticles , whichar ever ylight ,wherea s therin di schoppe dint o thin,filamentous , oblongpieces .I fth emateria li sto owet ,smal lamount so fth egree nleave s mightlodg esomewher ei nth emachin eo nthei rwa y fromth eknive s toth een d ofth ecyclone .Usuall y thiseffec ti sno tver y relevant.Hus k+ shank samples areno tchoppe dwell ,especiall ywhe nth emateria li sver ydry .Th eeffec t ofchoppin gi sthe nrestricte d to looseningth ehusk san dchoppin g the (moister) shank.

Step6 .Samplin g Themaiz eplan ti scompose do fvariou sdifferentiate d structures,organ s andtissues ,eac hwit hit sow ndry-matte rcontent ,nutritiv evalue ,resistanc e tochoppin gan dothe rphysica lo rchemica l characteristics (seee.g .Struik , 1982).Choppe dmaiz ei stherefor ea conglomeratio no fparticle svaryin gi n shape,specifi c gravity andcomposition .Thi svariatio nwithi n theplan t placesconstraint so nprope r sampling.Th ebia sintroduce db yth esample ri s particularly large.Thes e constraints canb ereduce dconsiderabl yb y separating theplan tint oth e fourfraction smentione dearlier ,an d thenchoppin gan d samplingthe mseparately .However ,whe ndiscussin gste p5 i twa salread ynote d thatth echoppin gproces s itselfselects ,fractionate s andcause s differences inshape ,siz ean dspecifi cgravit yan dthu seve nrelativel y uniformmateria l isdifferentiall y sedimented.Thi seffec to fchoppin gi smos tpronounce d for stoversample sbu tals ooccur swhe near sar echopped .Carefu lmixin go fth e materiali stherefor e crucial.I nthes eexperiments ,ea rsample swer emixe d byth evegetabl e cutteritsel f (seeabove) .T oeliminat e theadvers eeffect s ofth ecutter ,th ewe tmateria li nth ehea do fth emachin emus tb eredistri butedan dsample smus tconsis to fa complet e segmento fth econtent so fth e bowl. Ifsample sar etake nthi sway ,n oproblem s shouldarise .However , sampleso fstove ran dhus k+ shan kmus tb emixe dafte rchopping .I nth e procedure used inth epresen ttrial sthi swa sdon eb yusin ga concret emixer . Thechoppe dmateria lwa s transported fromth ecyclon eo nth echoppe rint oth e concretemixe rb ya conveyo rbel tmodifie d forthi spurpos e (seeFig .7) . Samplesmus tb etake n fromth estrea mo fmateria lwhil e themixe r isbein g emptied,t oavoi d discriminationb yhandpicking .

17 Sample sizei sa compromis ebetwee n dryingcapacit yan daccuracy .Larg e samplesreduc e randomerror sbu tincreas e systematicerror sdurin gdryin gan d reduce drying capacity.I fmixin g isdon eproperly ,th eidea lsampl e sizei s approx.50 0- 75 0g fres hweight .

Fig. 7.Choppin gprocedur e forsample so f stoveran dhus k +shank . 1 =balance ;2 = input ;3 = transpor to fchoppe dmateria lb y jeto fair ; 4 =cyclone ;5 = conveyo rbel t 1;6 = concret emixer ;7 = conveyo rbel t2 ; 8 =waggo n forwastes . (Photographb yDr.ir .B .Deinum )

Step 8.Dryin g Dryingi nth eove nmus tb e rapidt opreven tbiologica lprocesse s changing the chemical composition and reducing thedr yweigh to fth esample . The temperatureo fth ematerial ,however ,shoul dno texcee d 70C i fcertai n chemical analysesar erequired .Sample swer e thereforeplace d inpre-heate d ovensimmediatel y afterfres hweighin go feac h individual sample.B yspreadin g thesample sthinl yove rlarg ealuminiu m trays,maximu mcontac twit hth eho t airwa sachieved .I fnecessary ,th emateria lwa sshake nabou t duringdrying .Th e temperatureo fth eove nwa schecke d regularly.Eac h driedsampl ewa sweighe d assoo na si tha dbee n takenou to fth eheate doven .Thu sn o acclimatization toth eai roccurred .Sinc e sampleswer eweighe d afterreachin g constant weighta t7 0C ,th edry-matte r contento fth esample sdurin gweighin gwa s approximately99% .

Step 10.Bulkin g Toreduc e thenumbe ro fsample s forchemica l analysis,sample so fth e replicateswer ebulke dpe rtreatmen t andpe r fractionafte rassessin gth e dryweight .Th e sample sizemus tb eunifor mt opreven toverrepresentatio n of certainreplicates .Thi si sonl y relevanti fbloc k effectscanno tb e ignored.

Step 11.Grindin g Sampleso fa certai n fractionmus talway sb egroun do nth esam emill , since theshap ean dsiz eo fth eparticle s areimportan t characteristics for subsamplingan dchemica lan dbiologica lanalyses . Duringgrinding ,sample smus tb edry .I fthe yar etemporaril y stored before grindingthe y shouldb ere-drie d toenabl e grindingwithou tundesire d heatgeneration .Re-dryin g ispermissibl ebecaus e thedr yweight s arealread y determined anddry-matte r contentsar ere-assesse d inth echemistr y laboratory. Rateo finpu ti sver y importantt opreven thea tgeneration ,t oreduc e fractionation andt oobtai nunifor man dsmal lparticles .Grindin gshoul d notb eto oshort ,i.e . should lastunti lth emil li scompletel yempty . Standardizingo fth eduratio no fgrindin gproduce s systematicerrors ! Liketh echoppin gmachines ,th ehamme rmill suse d forgrindin gselec tan d fractionate.Differen t structures andtissue s showdifferen t resistance togrinding .Cobs ,midribs ,shank san d rind arehar d togrind ,wherea slea f mesophyllan dpit hpas s through the 1m msieve sver yrapidly .I naddition , differential sedimentation occursbecaus eo fdifference s inspecifi cgravity . Before resampling thisselection ,fractionatio n anddifferentia l sedimentationmus tb eovercom eb ymixing .

Step 12.Samplin gan dstorag eo fth egroun dmateria l Carefulmixin go fth emea lafte rgrindin gi snecessary .Whe n thebul k ofmea li sto olarg ean di fth emea li sno tto odusty ,i tca nb e subsampled usinga prope rdividin gdevice . The samplebag so r flasks shouldb emad eo fa niner tmateria l impervious

19 toal lchemica lcomponents .Th esample sshoul db estore d inchamber swit hlo w relativehumidit y ofth eai ran dfre efro mpest san dothe rkind so fdamagin g organisms.I flong-ter m storage isdesired ,th echamber s shouldb e decontaminated regularlywit h gaseousdisinfectants .Insect sar eparticularl y selectivei n theirchoic eo fsample s toinfest :starc h content,fo rexample ,prove d tob e predictable onth ebasi so fth enumbe ro flarva ei nth esampl eafte rprotracte d storage inseale dplasti cbags .

Step 13.Subsamplin gan dchemica lanalysi s Anothercrucia l stepi nsubsamplin g iscarrie dou ti nth echemistr y laboratory.Th e shape,volum ean ddegre eo f fillingo fth esampl ebag so r flasksdetermin e thepossibilit y ofmixin gan dtherefor e affectth eaccurat e subsamplingo fth emeal .Th eerro rmad edurin gthi sfina lsubsamplin gi s probablypredominantl y random. Mosto fth eanalyse swer e finallydon ewit h0. 5 go fmaterial .Thi s 0.5 gi sbelieve d tob erepresentativ eo fdozen so fkilogram so fharveste d material.I ttherefor egoe swithou tsayin gtha tal lstage so fsamplin grequir e greataccuracy ,alertnes san dcontinuou s criticism:samplin gi scertainl y themajo rsourc eo ferror san dinaccuracie s inth eentir eprocedure .Th erando m errorsmad edurin gchemica l andbiologica lanalyse s arever ymino ri n comparisonwit hothe r sourceso fvariation .Som esystemati cerror sma yb e made,e.g .durin ganalysi so fcell-wal l components (seee.g .Va nSoes t& Robertson, 1980), contento fnon-structura lcarbohydrate s andorganic-matte r digestibility.Th elatte rwil lb ediscusse d inth enex tsectio no fthi sthesis .

4.2. Evaluation of quality

4.2.1. Introduction Theevaluatio no f forages forthei rqualit y ismostl ybase do nmethod s ofestimatin g theindigestibl emas s fraction.Th eabsolut e digestibility canonl yb eascertaine db ymean so fdigestio n trialswit h animals.Thes e trialsar eexpensive ,laboriou s andtime-consuming ,an dth eamount so fforag e requiredar elarge .I naddition ,standar ddeviation sar ehigh ,especiall y in thecas eo fforag emaize ,becaus eo f largevariatio nbetwee nanimal s (Deinum etal. , 1983). Therefore,numerou s laboratoryprocedure shav ebee ndevelope dt o estimateth eindigestibl e fraction.Belo w Ishal ldiscus swh y Imainl y evaluatedqualit y interm so fi nvitr odigestibilit y andcell-wal lcontent .

20 Aplan ti scompose do fcel lwall san d cellularcontents .Th e cellular contentsar ealmos tcompletel y digestible (e.g.Va nSoest , 1967); thi smean s thatth eindigestibl ematte ri slocate d inth eplan tcel lwall .Digestibilit y cantherefor eb eestimate db ychemica lanalyse sinvolvin gcrud e fibre,cel l wallso rcell-wal lcomponents .O fthes eanalyses ,determination s ofacid - detergent fibregiv eth ehighes tcorrelation swit hdigestibilit y (e.g.Va n Soest, 1965;Mertens , 1973;Marte ne tal. , 1975).B ymean so f regression modelsusin g summativecalculation s afai restimat eo fcro pqualit y canb e made (Lucase tal. , 1961;Va nSoest ,1967 ;Deinu m& Va nSoest , 1969;va nde r Koelen& va nEs , 1973).Becaus eo fth enumerou s analyses involved,thes e methodsar eunpractica l:the yar eno tsufficientl yaccurat e tob eapplie d forqualit ypredictio n inthi sstudy . However,chemica lanalysi scanno trevea lth edigestibilit y ofa forage , sincether ei sn ochemica lmetho d thatwil l fractionate thecarbohydrate s ofth ecel lwal lint odigestibl e andindigestibl e fractions,an dsinc e structural featureso fth ecel lwal lals oaffec tth edigestibilit y (VanSoest , 1976). Thereforebiologica lprocedure s involving thei nvitr oincubatio no f foragemateria li nrume nliquo rhav ebee ndevelope denablin g foragedigesti bility tob eaccuratel ypredicted .Th emos tpopula r techniquesar ethos eo f Tilley &Terr y (1963)an dVa nSoes te tal . (1966).Bot h systemsnee d calibration asdescribe db yva nde rMee r (1980). Themetho do fVa nSoes te tal .i sth e mostelegant ,fo ri tyield sth eindigestibl e fractiono fth e cellwall san d thusth e truedigestibilit y ofth ecel lwall sca nals ob eestimate dwhe n cell-wallconten tan das hconten tar eknown .I nvitr orume n fermentation methodshav ebee nrecognize da sth emos tsuitabl emethod s forpredictin g inviv odigestibilit y (e.g.Deinu m &Va nSoest ,1969 ;va nde rKoele n &va nEs , 1973; Schmide tal. , 1975;Va nSoest ,1976 ;Aert se tal. , 1977;va nEs ,1979 ; Marten &Barnes , 1980).However ,th ei nvitr otechniqu e results ina fina l value forcro pqualit y thatgive sn oinklin go fth eorigin so fth edifference s indigestibilit yobserved .Furthe rchemica lanalysi smus trevea lthes ecauses . Moreover,a thig h levelso f feedintake ,fee defficienc yan drat eo fdigestio n aremor erelevan ttha npossibl eexten to fdigestion .Intak e isrelate dmor et o thecell-wal lconten t (e.g.Va nSoest ,1965 ,1976 ;Va nSoes t& Robertson , 1980; Waldo &Jorgensen , 1981),rat eo fdigestio n (Donefere tal. , 1960;Va n Soest,1976 ;Va nSoes te tal. , 1978;Wald o &Jorgensen , 1981)o rcell-wal l bulkdensit y (vande rAa re tal. , 1981)tha nt oth eexten ttha tth efeedstuf f isdigeste d (i.e.it sdigestibility) .

21 Newdevelopment s inth eevaluatio no f feedqualit yare : - theus eo fenzym epreparation s (e.g.McQuee n &Va nSoest ,1975 ;Jones ,1976 ; Barthiaux-Thille tal. , 1980a,b;Marte n &Barnes ,1980 ;Dowma n& Collins , 1982) -near-infrare d reflectance (e.g.Norri se tal. , 1976;Shen ke tal. ,1979 ; Barton &Burdick , 1981;Shen ke tal. , 1981;Templeto ne tal. ,1981 ) - gasproductio ndurin gincubatio nwit hrume n liquor (Menkee tal. ,1979 ; Dinkelakere tal. , 1980). Themerit so fthes eprocedure snee d furtherevaluation . Because iti saccurate ,elegant ,reliabl ean dtried ,I use d themetho d ofVa nSoes te tal . (1966)a sth ebasi c technique forevaluatin gquality .

4.2.2.Restriction so fth ei nvitr odigestibilit y technique Thesamplin gproblem sdescribe d in4.1 .ha d tob eovercom et oensur e thatth eresult so fchemica lan dbiologica lanalyse swer ereliable .I n addition,al lprocedure sha d tob eprecisel y standardized.Nevertheless ,som e sourceso fvariatio n andinaccurac yprobabl yremaine dan d limited thereliabilit y ofth edat ao ndigestibility : - Differencesbetwee n invitr oruns . Topreven t this,al lsample so fa harves thav e tob eanalyse dwithi non erun . Sometimesa small ,bu tsignifican tdifferenc ewa s foundbetwee nth evalue s ofcertai n samplesanalyse d indifferen truns ,eve nafte rcalibration . - Differenceswithi n invitr oruns . Standard sampleso fknow n inviv odigestibilit y shouldb ere-analyse d several timesthroughou ton erun .I twa s found thatvalue so fthes estandar d sampleswer e sometimes lowera tth een do fth eru ntha na tth ebeginning , especially forsample swit ha lo wdigestibility .Repeate danalysi so fon e sample1 0time sthroughou ta ru nshowe d thatdifference swithi na ru nar e notconsistentl y relevant (CVonl yapprox . 1.5%;n = 10).Nevertheless ,th e effectso fsuc hsmal ldifference s forth ecalibratio n curveca nb e considerable. - Standarddeviation so fdigestibilit y ofth eorgani cmatte ro fpoorl y digestible sampleswer e oftenlarge rtha nstandar ddeviation s foundfo r verydigestibl e samples.Th eopposit ewa s truefo rdigestibilit y ofcel l walls,sinc e thisi scalculate d fromth eresidu eo fundigeste d cell-wall components.Thi sresidu e issmal l- an dthu safflicte dwit ha grea t relativeerro r- whe ndigestibilit y ishigh . - Standard samplesan dexperimenta l samplesshoul db e fromth e sameplan t

22 species;Standar d samplesshoul dcove rth eentir e rangeo fth eexperimenta l samples.Unfortunately ,thi si sno talway spossible . -A tleas tfiv e (reliable!)standar d samplesshoul db eanalyse d ineac hrun , preferably intriplicat e orquadruplicate . - Severecontaminatio nwit h soil (e.g.occurrin gi nharvest so fver yyoun g plants)ma yresul ti na smalle rreproducibility . - Therati oo fsampl esize :amoun to finoculum ,an d themea nparticl esiz e andth eparticle-siz e distribution mayaffec tth erat ean dexten to fdigestion , especially inver y fibrousmaterial .

Nevertheless,i fth eregressio n linebetwee n invitr oan di nviv o digestibility canb eassesse d accurately,th ei nvitr odat awil lb emor e reliablean dmor ereproducibl e thenth ei nviv odata .I ti stherefor e essential tohav eman ystandar d sampleswhos e inviv odigestibilit yi s indisputable.

23 5.REFERENCE S

Aar,P.J . vander ,H .Boer ,B .Deinu m& G .Hof ,1981 .Bul k volume:a paramete r formeasurin g foragequalit y and itsinfluenc eo nvoluntar y intake.In : J.A.Smit h& V.W .Hay s (eds.),Proc .XlVt h int.Grassl dCongr. , Lexington,Ky ,pp .502-505 . Aerts,J.V. ,D.L .D eBrabander ,B.G .Cotty nS iF.X .Buysse ,1977 .Compariso no f laboratorymethod s forpredictin g theorgani cmatte rdigestibilit yo f forage.Anim .Fee dSei .Technol .2 :337-349 . Barthiaux-Thill,N. ,R .Bisto n &J .Fabry ,1980a .Estimatio n invitr od el a digestibilité del'herb ed eprairi epermanent e par lacellulase .1 . Examen dequelque s facteurs susceptibles demodifie r l'importance de l'attaque cellulasique.Bull .Rech .Agron .Gemblou x 15:277-296 . Barthiaux-Thill,N. ,J .Fabry ,R .Bisto n& M .Boukharta ,1980b .Estimatio n invitr od el adigestibilit é del'herb ed eprairi epermanent e parl a cellulase.2 .Corrélation s avec ladigestibilit émesuré e inviv oo u estimée invitr oselo nTille y etTerry .Bull .Rech .Agron .Gemblou x15 : 297-308. Barton,F.E . II& D .Burdick , 1981.Predictio n of foragequalit ywit hNI R reflectancespectroscopy .In :J.A .Smit hS iV.W .Hay s (eds.),Proc .XlVt h int.Grassl dCongr. ,Lexington ,Ky ,pp .532-534 . Becker,W.R. , 1976.Mais .Ee nhandleidin g voord eteel t vankorrel -e nsnijmais . P.A. publicatie nr.21 ,pp .1-84 . Beerepoot,L.J. , 1981.D egenetisch e variatie inverteerbaarhei d vansnijmais . ScriptieVakgroe p Landbouwplantenteelt &Graslandkunde ,Agric .Univ. , Wageningen,pp .1-43 . Blanco,J.L. , 1976.Selectio nobjective s formaximu m yieldso f feedwit hhybri d maize.Anim .Fee dSei .Technol .1 :245-250 . Bonnett,O.T. , 1966.Inflorescence so fmaize ,wheat ,rye ,barle y andoats : theirinitiatio n anddevelopment .Univ . 111.agric .Exp .St nBull .721 , pp.5-30 . Breeze,V.G .& G.M . Milbourn,1981 .Inter-plan t variation intemperat ecrop s ofmaize .Ann .appl .Biol .99 :335-352 . Bunting,E.S. ,1980 .Histor y of themaiz e cropi nN.W .Europe .In :E.S .Buntin g (ed.),Productio n andutilizatio no fth emaiz e crop.Proc .Firs tEuropea n MaizeCongress ,Cambridge ,England ,Herewar d &Stourdal ePress ,Ely ,pp . 3-13. Daynard,T.B .& W.G .Duncan ,1969 .Th eblac k layeran d grainmaturit y incorn . CropSei . 9:473-476 . Daynard,T.B .& J.F .Muldoon ,1983 .Plant-to-plan t variability ofmaiz eplant s growna tdifferen t densities.Can .J .Plan tSei .63 :45-59 . Deinum,B. ,1981 .Th e influenceo fphysica l factorso nth enutrien t content of forages.Mededelinge nLandbouwhogeschoo l Wageningen 81-5,pp .1-18 . Deinum,B .S iJ.J . Bakker,1981 .Geneti cdifference s indigestibilit y of forage maizehybrids .Neth .J . agric.Sei .29 :93-98 . Deinum,B. ,A .Ste g& G .Hof ,1983 .Measuremen t andpredictio no f digestibility of foragemaiz e inTh eNetherlands .Anim .Fee dSei .Technol .8 (inpress) . Deinum,B .& P.C . Struik,1980 .Harvestin g fieldexperiment s forsilag emaize . In:J .Dijkstr a& A .va nSante n (eds.),Proc .5t hint .Conf .o n Mechanization ofFiel dExperiments ,Wageningen ,pp .231-236 . Deinum,B .& P.C .Struik ,1982 .Productivit y andnutritiv evalu eo f foragemaize . In:H.J .Oslag eS tR .Daccor d (eds.),Proc .Semina ro nCOST-PROJEC T8 2 'Maizea sbasi c feed forbee fproduction' ,Grangeneuve ,Switzerland , pp. 8-16. Deinum,B .S iP.J . VanSoest ,1969 .Predictio no fforag edigestibilit y from somelaborator y procedures.Neth .J . agric.Sei . 17:119-127 .

24 Dinkelaker,J. , K.H.Menke ,F .Gross ,W.G .Pollme r& D .Klein ,1980 .Evaluatio n ofth efeedin gvalu eo fmaiz e forsilag eus eb y thega sproductio nmethod . Preliminary results.In :W.G .Pollme r& R.H .Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai nan d silageuse .Martinu sNijhoff , TheHague ,pp .477-489 . Donefer,E. ,E.W .Crampto n& L.E .Lloyd ,1960 .Predictio no f thenutritiv e value indexo fa forag e fromi nvitr o rumen fermentationdata .J .Anim . Sei. 19:545-552 . Dowman,M.G .& F.C .Collins ,1982 .Th eus eo fenzyme st opredic t thedigestibilit y ofanima l feeds.J . Sei.Foo dAgric . 33:689-696 . Duncan,W.G. ,1975 .Maize . In:L.T .Evan s (ed.),Cro pphysiology .Som ecas e histories.Cambridg e UniversityPress ,London ,pp .23-50 . Ebskamp,A.G. ,1981 .He tcultuurwaardeonderzoe kva nsnijmaisrasse ni nNederland . (II).Criteri abi jd ebeoordelin g vansnijmaisrassen .Bedrijfsontwikkelin g 12:269-275 . Edmeades,G.O .& T.B .Daynard ,1979 .Th edevelopmen t ofplant-to-plan t variability inmaiz e atdifferen t densities.Can .J .Plan t Sei.59 : 561-576. Es, A.J.H,van ,1979 .Internationa lworksho po nth estandardizatio no f techniques infeedingstuff s analysis,Ottawa ,12-1 4Marc h 1979.Inter n Rapportno .129 ,I.V.V.O . 'Hoorn',Lelystad ,pp .1-15 . Galinat,W.C. ,1971 .Th eorigi no fmaize .Ann .Rev .Genetic s 5:447-478 . Gallais,A. ,M .Pollacse k &L .Huguet ,1976 .Possibilité s desélectio nd umaï s entan tqu eplant e fourragère.Ann .Amélior .Plante s26 :591-605 . Gallais,A .& P . Vincourt, 1983.Possibilité sd'amélioratio n durendemen te n matière sèched umaï sensilage .Colloqu e 'Physiologie dumaïs' ,Roya n 15-17Mar s1983 . Glenn,F.B .& T.B .Daynard ,1974 .Effect so fgenotype ,plantin gpattern ,an d plant densityo nplant-to-plan t variability and grainyiel do fcorn .Can . J.Plan t Sei.54 :323-330 . Jones,D.I.H. , 1976.Funga lcellulase s andhemicellulase san d theirapplicatio n toth eanalysi so f forage.In :Carbohydrat e research inplant san d animals.Misc .Paper sno .12 ,Agric .Univ. ,Wageningen ,pp .67-77 . Kiesselbach,T.A. , 1949.Th estructur e andreproductio n ofcorn .Res .Bull . Univ.Nebr .agric .Exp .St n161 . Kiesselbach,T.A . &E.R .Walker ,1952 .Structur eo fcertai n specialized tissuesi nth ekerne lo fcorn .Amer .J .Bot .39 :561-569 . Koelen,C.J . vande r& A.J.H ,va nEs ,1973 .A compariso no f somelaborator y techniques forth eestimatio no f thedigestibilit y of theorgani cmatte r inforag esamples .Neth .J . agric.Sei .21 :199-205 . Lucas,H.L. ,Jr. ,W.W.G .Smart ,Jr. ,M.A .Cipollin i &H.D. Gross,1961 . Relationsbetwee ndigestibilit y andcompositio no f feedsan dfoods . S-45Report ,Nort hCarolin aStat eColleg e (Mimeo). Marten,G.C .& R.F .Barnes ,1980 .Predictio n ofenerg ydigestibilit y of forageswit h invitr orume n fermentation and fungalenzym e systems.In : W.J.Pigden ,C.C .Balc h& M .Graha m (eds.),Proc .Worksho pOttawa . Standardization ofanalytica lmethodolog y forfeeds .IDR C- 134 eInt . Develop.Res .Centre ,Ottawa ,pp .61-71 . Marten,G.C , R.D.Goodrich ,A.R .Schmid ,J.C .Meiske ,R.M .Jorda n& J.C .Linn , 1975. Evaluationo flaborator ymethod s fordeterminin gqualit yo fcor n andsorghu m silages.II .Chemica lmethod s forpredictin g inviv o digestibility.Agron .J .67 :247-251 . McQueen,R.E .& P.J . VanSoest ,1975 .Funga lcellulas e andhemicellulas e predictiono f foragedigestibility .J . DairySei .58 :1482-1491 . Meer,J.M . vander ,1980 .Determinatio n of the 'invitro 'digestibilit y for thepredictio no fth e 'inviv oorgani cmatte rdigestibilit y coefficient' of feeds forruminants .Documentatio n reportno .67 ,I.V.V.O . 'Hoorn', Lelystad,pp .1-12 .

25 Menke,K.H. ,L .Raab ,A .Salewski ,H .Steingas s& W .Schneider ,1979 .Th e estimation ofth edigestibilit y andmetabolizabl eenerg yconten to f ruminant feedingstuffsfro m thega sproductio nwhe n they areincubate d with rumen liquori nvitro .J . agric.Sei. ,Camb .93 :217-222 . Mertens,D.R. , 1973.Applicatio n of theoretical mathematicalmodel st o cell-wall digestion and forage intake inruminants .Ph.D .thesis , Cornell Univ.,Ithaca ,N.Y . Miller,E.C. ,1919 .Developmen t of thepistillat e spikelet and fertilization in lea mays L.J . agric.Res .28 :255-265 . Norris,K.H. ,R.F .Barnes ,J.E .Moor e& J.S .Shenk ,1976 .Predictin g forage quality by infrared reflectance spectroscopy.J .Anim .Sei .43 :889-897 . Rijksinstituut voorhe tRassenonderzoe k vanCultuurgewasse n (RIVRO),196 3 upt oan d including 1983.38 e t/m 58eBeschrijvend erassenlijs tvoo r landbouwgewassen,Leiter-Nypels ,Maastricht . Roth,L.S. ,G.C .Marten ,W.A .Compto n &D.D .Stuthman ,1970 .Geneti c variation ofqualit y traits inmaiz e forage (Zea mays L.). CropSei . 10:365-367 . Scheijgrond,W. ,1978 .Ontwikkelinge n inhe trassensortimen t vanlandbouw gewassen sedert deoprichtin g vand eStudiekrin g voorPlantenveredeling . Zaadbelangen 32:226-231 . Schmid,A.R. ,R.D .Goodrich ,G.C .Marten ,J.C .Meiske ,R.M . Jordan& J.L . Halgerson,1975 .Evaluatio n oflaborator ymethod s fordeterminin g quality ofcor n andsorghu m silages.I .Biologica lmethod sfo r predicting inviv odigestibility .Agron .J . 67:243-246 . Schuster,W. ,W .Schreine r& G.R . Müller,1977 .Übe rdi eErtragssteigerun g beieinige nKulturpflanze n inde n letzten2 4Jahre n inde rBundes republik Deutschland.Z .Acker -u .PflBa u145 :119-141 . Shenk,J.S. , I.Landa ,M.R .Hoove rS tM.O .Westerhaus ,1981 .Descriptio nan d evaluation ofa Nea r InfraredSpectro-Compute r forforag e andgrai n analysis.Cro pSei .21 :355-358 . Shenk,J.S. ,M.O .Westerhau s &M.R .Hoover ,1979 .Analysi so f foragesb y infrared reflectance.J .Dair y Sei.62 :807-812 . Struik,P.C. , 1982.Productio npattern ,chemica l composition and digestibility of foragemaiz e (Zeamay s L.). Mededelingno .64 ,LH ,Vakgroe pLandbouw plantenteelt &Graslandkunde ,Wageningen ,Netherlands ,pp .1-28 . Templeton,W.J. ,Jr. ,J.S .Shenk ,K.H .Norris ,G.W . Fissel,G.C .Marten ,J.H . Elgin,Jr .& M.O .Westerhaus ,1981 .Forag e analysiswit hNear-Infrare d ReflectanceSpectroscopy : Statusan doutlin eo fnationa l research project. In:J.A .Smit h& V.W .Hay s (eds.),Proc .XlVt h int.Grassl d Congr.,Lexington ,Ky ,pp .528-531 . Tilley,J.M.A .& R.A .Terry ,1963 .A two-stage technique forth ei nvitr o digestion of forage crops.J .Brit .Grassl dSoc .18 :104-111 . VanSoest ,P.J. , 1965.Symposiu mo n factorsinfluencin g thevoluntar y intake ofherbag eb y ruminants:Voluntar y intake inrelatio n tochemica l composition anddigestibility .J .Anim .Sei .24 :834-843 . VanSoest ,P.J. , 1967.Developmen to f acomprehensiv e systemo f feed analyses andit sapplicatio n toforages .J .Anim .Sei .26 :119-128 . VanSoest ,P.J. , 1976.Th eestimatio no fdigestibilit y fromchemica l composition. In:Carbohydrat e research inplant san danimals .Misc . Papersnr .12 ,Agric .Univ. ,Wageningen ,pp .137-145 . VanSoest ,P.J. , D.R. Mertens& B .Deinum ,1978 .Preharves t factors influencingqualit y ofconserve d forage.J .Anim .Sei .47 :712-720 . VanSoest ,P.J . &J.B .Robertson ,1980 .System so fanalysi s forevaluatin g fibrous feeds.In :W.J .Pigden ,C.C .Balc h& M .Graha m (eds.), Standardizationo fanalytica lmethodolog y forfeeds .IDRC-134 eInt . Develop.Res .Centre ,Ottawa ,pp .49-60 .

26 VanSoest ,P.J. , R.H.Win e& L.A .Moore ,1966 .Estimatio no f true digestibility of foragesb y the invitr o digestiono fcel lwalls .Proc . Xth int.Grassl dCongr .Helsinki ,pp .438-441 . Velde,H.A . te,1983 .Constraint so nmaiz eproductio n innorther nlatitudes . Proc. 2nd int.Summe rSchoo l inAgriculture ,"Cerea lproduction" . (ed.)E .Gallagher ,Roya lDubli nSociet y (inpress) . Waldo,D.R . &N.A . Jorgensen,1981 .Forage s forhig h animalproduction : nutritional factors andeffect so f conservation.J . DairySei .64 : 1207-1229. Wilson,J.R. , 1982.Environmenta l andnutritiona l factorsaffectin gherbag e quality. In:J.B .Hacke r (ed.), Nutritional limits toanima lproductio n frompastures .Farnha mRoya lU.K. ,Commonwealt hAgricultura lBureaux , pp.111-131 . Zuber,M.S. ,T.R . Colbert &L.L .Darrah ,1980 .Effec to frecurren t selection forcrushin g strengtho n several stalk components inmaize .Cro pSei . 20:711-717 .

27 CHAPTER1 PRODUCTION PATTERN, CHEMICAL COMPOSITION AND DIGESTIBILITY OFFORAG EMAIZ E (ZEA MAYS L.)

P.C.Strui k Department ofFiel d Cropsan dGrasslan dScienc e AgriculturalUniversit y Wageningen,Netherlands .

Keywords :forag emaize ,productio npattern ,yield ,chemica lcomposition , quality,digestibility ,sowin gtime ,hybrid ,brow nmidri b

Summary Foursilage-maiz e hybrids,differin g inrat eo fgrai n fillingan dwhole-cro p digestibilitywer e sowno ntw odates .Productio n andqualit ytrait swer e estimated fivetime s duringth egrowin g season.Difference s inyiel dbetwee n hybridswer erelativel y small.Difference s inqualit ywer e causedb y differences incell-wal lqualit y andaros edurin gth econstructio n ofth e vegetative organs.Difference s inyiel d andqualit ybetwee n thecrop ssow n onth etw osowin gdate swer emainl y causedb y differences inth eamoun to f carbohydratesproduce d inth epost-silkin gperiod .Thi sperio dwa s approximately twoweek s shorter forth elater-sow ncrops . Ina concomitan t trial,tw ocontrastin g commercialhybrid s andthre ebrown - midrib (bm,)hybrid swer e grown.Th eplant swer e separated intote nmorpho logical fractions,whic hwer e analysed fordry-matte r content,yiel dan d quality.Th e dry-matter content ofth e fractionsvarie d greatlywithi non e plant andbetwee nhybrids .Inter-hybri d differences inth eproportio n of drymatte r inth e fractionswer e ofmino r importance forth equalit yo f thewhol e crop.Excep t forth ekernels ,th e in-vitro digestibility ofth e organicmatte rdiffere d greatly foral lfraction s andwa smostl ybes tfo r bm genotypes.Difference sbetwee nth etw o commercialhybrids ,however , were alsorelevant . These differences resultedfro mdifference s incell-wal l content and cell-wallquality .Th edigestibilit y ofth ecel lwall swa sth e main factortha t determinedth ewhole-cro p digestibility ofeac hhybrid , although differencesbetwee nbrown-midri b genotypeswer e completely attributable todifference s incell-wal l content. In—vivo digestion trials confirmedthes eresults .

28 Introduction Theare aunde r foragemaiz e hasexpande d rapidly inNorth-Wes tEurop ei n recent decades.Initially ,al lth ehybrid s availablewer e forgrai n production.Eve nnow ,severa lEuropea n countries dono thav e special variety lists forforag emaize .Ye t therequirement s fora grai n cropar e notth e samea sthos efo ra forag e cropbecaus ethe y areuse d forver y differentpurpose s andthe y aregrow n indifferen tways .Muc h attentionha s beenpai dt oth erelevanc e ofea rdevelopmen t andgrai n filling forth e yielding ability andqualit y (dry-matter content,digestibility ,fee dintak e etc.)o fforag emaiz e (Bunting, 1975,1976 ,1977 ;Deinu m& Knoppers ,1979 ; Gross, 1980).Thes e studies suggesttha t theeffect s ofgrai n fillingo n yield aremino r inmos tyears ;th ewhole-cro p digestibility ofa grainles s cropma yb e lower,an dth e dry-matter content ofth ewhol e cropi spositivel y influencedb y grain filling.Ea rdevelopmen t andsubsequen t grainfillin g areles simportan t inNorth-Wes t Europe than inth eU.S.A . ori ntropica lo r subtropicalregions .Th erati oo fnon-structura l carbohydrates to structural material,whic h is affectedb y cell-wallproductio n andtota lproduction , changes during grain filling.Becaus e the digestibility ofth enon-structura l carbohydrates isalmos t 100%an dth edigestibilit y ofth estructura lmateria l (cell-wall constituents:hemicellulose ,cellulose ,ligni nan dsilica )i s much lower,thi s couldhav e agrea t impact onth edigestibilit y ofth ewhol e crop.Bu tth equalit yo fth e structuralmateria l isno t constant.Cell-wal l digestibility isstrongl y affectedb y climatic factors (mainlytemperature) , cutting date,genotyp e and culturalpractice .Fig . 1show sa nexampl eo fth e development overtim e ofth emai nplan t characterstha t influencewhole-cro p digestibility.

Cell-wall content increasesunti lflowering ,remain s constant fora whil e afterthi s stagean ddecrease s during laterstage s ofgrai n filling.Th e digestibility ofth eorgani cmatte rdecline srapidl y inth epre-silkin g period andthen ,i nthi s example,increase s slightly.Th edeclin e incell - wall digestibility isles s afterflowerin g thanbefore .I nFig. 1 this decline is compensated forb y theincreas e inea rcontent ,whic h causesth e content ofth eles sdigestibl e cellwall st odecrease .Genotypi c differences inthi s pattern arelikely . Recently,breedin gprogramme s toimprov eth equalit y ofth evegetativ epart s ofmaiz e havebee n startedi n several countries.Strikin g resultshav ebee n obtained fromth ebrown-midri b genes,whic h lowerth e lignin contentan d therefore improveth edigestibilit y ofth ecel lwalls . Inth eNetherlands ,

29 % 100 r

50% ç flowering 90

o—, 70 +—+ cwc 60

0L\ + 710 710 time

Fig. 1.Ea r content (ear?),cell-wal lconten t indr ymatte r (cwc?),apparen tdi gestibility oforgani cmatte r (D )an d cell-walldigestibilit y (D )a s a functiono ftime .Hybri dL G 11;locatio nAchterberg ,Netherlands ;yea r _2 I98O;plan t density 10m .

30 aresearc hprogramm e hasbee n startedt oinvestigat e therelationshi pbetwee n productionpatter n andqualit y offorag emaiz eunde rdifferen t climatic conditions.I non eo fth efirs t trials,w e investigated howproductio n and quality developeddurin gth egrowin gseaso ni nfou rhybrid ssow no ntw o different dates.A tth esam elocation ,tw o commercialhybrid s andthre eb m syntheticswer e grown and separated intoa numbe r ofmorphologica l fractions sotha tth emos t important quality differences couldb eidentified .Thi s paper reports onthes etrials .

Materials andmethod s Trial 1. Fourhybrid swer e selected onth ebasi s ofthei rwhole-cro p digestibility anddry-matte r content ofth eear .Fo rman yyear s LG 11an d Fronicawer e the dominantvarietie s inth eNetherlands .Et aIph oi suse d onlimite d scale.Nicc oi sno to fan ypractica limportanc eunde rDutc h conditions,sinc eth edry-matte r content ofth ewhol e cropi snormall yto o lowt omak egoo d silage.Al lfou rhybrid s aredescribe db yth eBundessorten amti n 1980.Th ehybrid swer e sowni nsand y soilo ntw odates :2 6Apri lan d 28Ma y 1979,i na split-plo t design,wit h sowingtim e asmai ntreatmen t and with sixreplicates .Fertilizatio n (bothorgani c andinorganic) ,wee dan d disease controlwer eoptimum . Originally theplan t densitywa s 16m (row _p distance 75cm) .Th enumbe ro fseedling swa sreduce dt o 10m 3- hweek s afteremergence .Th eplant stha tha dbee n removedwer euse d forth efirs t 2 sample.O n fourothe rsamplin g dateson ero w6 m lon g (i.e. h.5 m orabou t h5 plants)wa sharveste d fromeac hplot .Plo t sizewa s9 m x 10m wit htw o borderrow sor .bot hside s ofth eplo t andon ero wseparatin g therow s intended forsampling .On eextr ane tro wwa suse d foradditiona lmeasurement s atfina l sampling. Before theestimatio n ofth efres hweight ,sample swer e separated intofou r fractions:to pear ,lowe rear s ifvisibl e inth eaxil so fth elea fblades , husks+ shanks ,an dstove r (stem,tasse l andleaves) .Wit hearlie r samplings wholeplant swer e choppedwit h avegetabl e cutter.Wit hlate rsampling sth e earswer echoppe dwit hth esam emachin ebu tth ehusk s+ shank san dth estove r were choppedwit h astationar y ordinary 1-rowFah rM H7 0choppe r (tractor- mounted). Thechoppe dmateria lwa sblow n ina je to fai rove ra conveyo r belt,whic htransporte di tint oa concret emixer .Subsample swer etake nfro m thestrea mo fmateria lwhil eemptyin gth emixer .Althoug htime-consuming , thismetho dgav eminima lrando man d systematicalerror s inestimatin gth e

31 dry-matter contento fth ewhol e crop (seeDeinu m& Struik ,1980 )an d providedmuc h additionalinformation . After subsampling,th emateria lwa s driedt oconstan tweigh t inforce d ventilatedoven s at7 0 C.Sample so fth esi xreplicate swer ebulke dpe r plantpar t andpe rtreatmen t andgroun d inhamme rmill swit h 1m msieves . Sampleswer e analysed fortru e digestibility in-vitro ofth eorgani cmatter , using themetho d ofVa nSoes t etal . (1966).B yrecours et oa serie so f standardmaiz e sampleswit hknow n in-vivo digestibility forsheep ,conversio n couldb emad et oapparen t digestibility oforgani cmatte r (D ).Cell-wal l om constituents (cwc)wer eestimate d accordingt oVa nSoest' s (1977)method . Cell-walldigestibilit y was calculated fromtru edigestibility ,cell-wal l content andas hcontent . Further analysisreveale dth econtent s of crudeprotei n (N %x 6.25) ,water - soluble carbohydrates (withferricyanide) ,tota lnon-structura l carbohydrates (starch+ water-solubl e carbohydrates),Ca ,P ,K an dresidu e (l00-(crude protein +as h+ tota lnon-structura l carbohydrates +cel lwalls)) . Some additional informationwa s collecteddurin gth egrowin gseason .Lea f areawa smeasure d atsilking ,usin gth elengt h* maximu mwidt h* 0.7 5metho d (Montgomery, 1911).Becaus eth e areao fal llea fnumber swa sestimated ,th e post-silking duration oflea fare acoul db eestimate db y countingth enumbe r ofgree n leavesweekly . Leafangle swer eestimate dwit h aclinomete r (Whigham& Woolley , 197^)- Plantheigh t andnumbe r ofleave swer emeasure dweekly .Lengt han dmaximu m widtho fth eto pea rwer e estimatedonc edurin ggrai nfilling .

Trial 2.A tth esam elocation ,larg eplot so fth efollowin ggenotype swer e sowno n2 6April :Et aIpho ,Circ é (bothdescribe db yRijksinstituu t voorhe t Rassenonderzoekva nCultuurgewassen , 1982),INR A2U 0bm, ,INR A 188b m and LG 11b m .See do fth ebm _ genotypeswa skindl yprovide db yD rA .Gallai s (INRA,France) . Forth edescriptio n ofthes egenotypes ,se eGallai s et al., 1980. Thedensit ywa s 7pi. m .Fo reac hgenotyp e2 0plant swer eharveste d on1 1 October andseparate d intotassel ,kerne lo fth eto pear ,rachi so fth eto p ear,kerne lo flowe rears ,rachi so flowe rears ,hus k+ shank ,lea fmidribs , resto flea fblades ,lea fsheath ,ste mrind ,ste mpit han dtiller .Materia l was chopped ina vegetabl e cutter and drieda t7 0 C.Drie d sampleswer e treated asdescribe d forTria l 1.To pear san dlowe rear swer eanalyse d

32 separately,bu t theresult swil lb epresente dtogether . Thecrop slef to nth eplot s aftersamplin gwer euse d formakin gsilag efro m EtaIpho ,Circ éan dbm -materia lfo r in-vivo digestionstudies .

Results anddiscussio n Weather. The 1979seaso nwa s coolwit h excessiverai n duringMa y andJun e (Table 1).Moreover ,th eprecipitatio n inJun ewa s concentrated inshor t periods (once 100m mfel l in2 days). Theothe rmonth swer edry .Radiatio n was about average.Damagin gfrost s didno toccu ra tth etria lsite .

Table 1.Weathe ra tWageninge ni n 1979an dmean sove rth eperio d 1931-1960 at DeBilt .

Month Solarirradianc e Average temperature Rainfall •2 o„ J.c m mm mean 1979 mean 1979 mean 1979

May 51779 51593 12.1+ 11.7 52 75-7 June 53108 1+9272 15.5 15.0 57 11*8.1+ July U775^ U6118 I7.O 15.8 78 31.1+ August 1*1525 1+0918 16.8 15.3 89 81». 8 September 30390 33225 1U.3 13.2 71 17.8 October 17707 19399 10.0 10.8 72 36.6

Trial1 Plant measurements: Early development,a sexpresse db y numbero f visible leaves andplan theight ,wa sfaste rfo rEt aIph oan dFronic atha nfo rL G1 1 andNicco .Tabl e 2show s someplan t characteristics.Difference sbetwee n sowingdate s areno to fgrea t relevance forthes e characteristics except forth eea rsize .Et aIph oappeare dt ob e atal lgenotyp ewit h smallears ; thiswa s especially apparent inth elater-sow n crop.Th elea fare awa s rather small.It suppe rleave sha drelativel ylarg elea fangle s andwer e stiff.Et aIph othu sshowe dth etypica l leafarrangemen t ofth eideotyp e describedb yMoc k& Pearc e (1975).L G 11wa sshor twit h asmal llea farea . Sinceth eleave s ofthi shybri d alsodie dearlier ,th epost-silkin g duration oflea fare awa smuc h shorter forL G 11tha n forth eothe rhybrids .Fo rth e later sowing datethes edifference swer e lesspronounced .Fronic awa stal l

33 andha d alarg e leafare aan dshowe d aslo wbu tgoo d eardevelopment .Nicc o proved tob ea stock yhybri dwit hwid e leaves and largeears .

Table 2.Fina lplan theight ,numbe ro fleaves ,lea fare aan d earsiz eo f fourhybrid s sowno n2 6Apri lan d 28May . hybrid EtaIph o LG 11 Fronica Nicco

Sowing date:26/1 +

Plant height (cm) 238 217 238 208 Number ofleave s Ht. 5 1 U. 2 15.2 11+.1+ Leafare aa tsilkin g (m/ m) 3.73 3.1+8 1+.78 1+.28 Post-silking duration oflea fare a (m/ m .days) 20*+ 201+ 153 227 203 Length ofto pea r (cm) 16.2 17.0 16.6 18.0 Maximumwidt h ofto pea r (cm) 1+.1 1+.3 1+.6 1+.7

Sowingdate :28/ 5

Plantheigh t (cm) 232 2lU 236 207 Numbero fleave s 11+.1+ 11+.0 15.0 11+.1 Leafare aa tsilkin c (m2/m2) 3.88 3.81+ 1+.80 1+.25 n of leaf area (m2/m2.days) 182 176 228 199 Length ofto pea r (cm) m) 11+.9 16.6 16.8 18.6 ear (cm) 3.8 1+.1 1+.1 1+.5

One ofth e original criteriafo rselectin g hybrids forthi stria lwa sth e dry-matter content ofth eto pear .Fo reac ho fth e sowing dates,th esam e pattern indry-matte r content ofth eto pea rwa s apparentwit hEt aIph o achieving thehighes t dry-matter contentan d Niccoth e lowest,i nbot h treatments (Fig.2) . Table 2show sth emaximu m diameter andlengt ho fth eto p ears.Th evolum e ofth eto p ear canb e roughly estimatedusin gth e formula 1/3.T T .{ï *width ) length.Th evolume s correlated negativelywit hth edry-matte r contents 2 presented inFig .2 . (atfina lsampling :r =0.9 7 forearl y sowingan d 2 r =0.9 5 forlat e sowing).Therefor eth e dry-matteryield so fth e earwer e not significantly different forth ehybrid so nan y samplingdate .Thi s agreeswit hth eofficia lvariet ytest so f1979 -

34 dry-matter content top ear (%)

• =Et a Ipho 20 o= L611 x = Fronica A= Nicc o 10 = sowno n 26/4 =sowno n 28/5 J_ _L 2 2 \ Vo "/I1 0 time

Fig.2 .Cours e ofth edry-matte r content ofth eto pea r forfou rhybrids , sowno ntw odates .

35 Sowing dateha d aconsiderabl e effect:a tfina lsamplin g (22October )th e difference indry-matte ryiel dbetwee n theearl y andlat esow n cropswa s stillabou t2 Mg.h a foral lhybrid s (hybridmean swer e9-1 7Mg.h a at early sowingan d7-0 8Mg.h a atlat e sowing).

Production pattern: Asstated ,th efou rselecte dhigh-yieldin ghybrid s showedn odifference s inea ryield .Th eresult s fromthi stria l suggesttha t theclimati c conditions influenced therat eo fassimilat e flowt oth eear , regardless ofea rvolum e andgenotype .Extendin gth egrain-fillin gperio d bypostponin gth e finalharves t datewoul dprobabl yhav e resulted inNicc o achievingth ehighes t earyields . Totaldry-matte ryield swer e significantly differentbetwee nsowin gdate s andhybrid s on allbu tth elas t sampling date.A tth e endo fOctober ,n o significanthybri d effect couldb ediscerned ,bu tth esowing-tim e effect was stillver y significant.Earl y samplings showedhybri d effectso nyield , becauseo fa neffec t onyiel d ofstove ran do fhusk s +shanks .Fo rbot h sowingdate san do nal lsamplin g dates,Fronic agav eth elarges t stover yield andNicc oth elarges thus k +shan kyield .I nth epre-silkin gperiod , Fronicaha dth ehighes tproductio n rate.Nicc oha dth ehighes tpost-silkin g production capacity.Th eflowerin gdate s ofal lth ehybrid swer ever y similar Althoughth elat esowin gwa s 32day s latertha nth eearl y one,later-sow n crops achieved 50% emergence only 19day slate rtha nearly-sow n crops.Th e anthesis andsilkin go fth elater-sow n cropswer e delayedb y only Thdays . Theeffect s ofsowin gdat ewer eles stha nhav ebee npreviousl y reported (Becker, 1976),probabl ybecaus e ofth elo wtemperature s duringMa y andth e useo fmoder nhybrid s inthi sexperiment . Toillustrat e thegenera lproductio npattern ,Fig .3 show sth edistributio n ofth e drymatte r inL G 11fo rth etw osowin gdates .Afte r floweringth e yield ofth enon-reproductiv epart s continuedt oincrease ,bu tdurin gth e last fourweeks ,grai nfillin goccurre dpartiall y atth eexpens eo fdr ymas s (probablymainl y carbohydrates)store d inth e stover,husk s and shanks.Thi s is anorma lpatter nunde rDutc h conditions.Th eproductivit y ofth elater - sown cropwa shighe rdurin gth elas t fourweeks ,becaus e itsremainin glea f areawa slarge r andmor eproductive .Th epatter nwa s exactlyth e samefo r allhybrids . So,despit e differences inplan ttrait s (earvolume ,plan theigh t etc.), production anddistributio n ofdr ymatte r only showed slight differences betweenhybrids .

36 dry-matter yield LG 11 (Mg.ha-1) 16 sowno n 26/4

14 LOWER EARS 12

10-

8 -

6 -

0L 26, 27, 22, time % h '8 79 '10 dry-matter yield 1 L61 1 (Mg.ha" » 14 sown on28/ 5

12 LOWER EARS 10

0L // 24/ 22/ time % % 27 '8 79 '10 Fig.3 .Productio npatter nfo rL G11 ,sow no ntw odates .I indicate s 50$p flowering .

37 Quality. Bywa yo fexample ,th eyield s ofth edifferen t chemical constituents ofth e drymatte ri nL G 11hav ebee nplotte d againsttim e (Fig. h). Cell-wall production stopped sometim e after flowering forth eearl y sowing,bu t seemed nott ohav ebee n completed atth efina lsamplin go fth elat esowing .Th e amountso fwater-solubl e carbohydrate,as han dcrud eprotei nwer ea tthei r peak on2U/9 • Most ofth enon-structura l carbohydrateswer eproduce d after flowering.Th emarke d decline inth eamoun t ofwater-solubl e carbohydrates clearly illustrates theredistributio n ofshor t carbohydrates fromth e non-reproductive partst oth eear ,wher ethe y areconverte dt ostarch .Thi s redistribution occurredi nbot hsowings .Th epatter n showni nFig . hwa s alsotru e forth e otherhybrids . Theproportion s ofth edifferen t constituentspresen twer ever ysimila ri n allth ehybrid s oneac hsamplin g date.Th ehybri drange s inyield so fth e constituents areliste di nTabl e 3.Th erange s aresmall ,excep t forth e estimatedresidue ,whic hi ssubjec tt oth egreates t error.Th eyield so f allconstituent s arelowe rfo rlat esowing ,excep tfo rthos eo fwater-solubl e carbohydrates (becausegrai n fillingwa sles sadvanced )an dthos eo fth e residue (because ofa smalle rdecreas ei nlea farea) . Themea neffec t ofsowin gtim eo ndry-matte ryiel d atfina lsamplin gwa s 1.67Mg.h a .Thi sdifferenc emainl y resulted fromth edifferenc e inyiel d ofnon-structura l carbohydrates (about 1U0Okg.h a ):i tdecrease db y 1Mg.ha - duringth elas t fourweeks .

Table 3.Range s inyield s ofconstituent s atfina lsamplin g (Mg.ha-) .

Sowingtim e * 26/U 28/5

Drymatte r 15.1- 16.T 13-9- 15. 0 Cell-wall constituents 6.25 -6.9 1* 6.16- 6.69 Water-soluble carbohydrates (CgH Cv) 0.50 -0.7 7 0.83 -1.2 U Starch (CgH^O^ 5.^2- 5-9 9 3.91 -U.0 9 Totalnon-structura l carbohydrates 6.17 -6.6 6 U.90- 5-1 8 Ash 0.70 -0.8 U 0.6U- 0.76 Crudeprotei n 1.20-1.1+0 1.08-1.25 Residue 0.61 - 1.18 0.80 - 1.33

Table h shows somequalit y factorsa tfina lsampling .Et aIph owa s considerably

38 yield (Mg.hcT1) 16 L6 11 sown on 26/4 ffoF|\DUEIIl * 14 CP = crude protein

|* WSC= water-solubl ecarbo 6 hydrates

4 CWC= cell-wal lconstitu 2 ents

0L 27 2 me ^ "' /8 H V residue includesorgani c acids (inleaves) ,fat san doil s (inears )an destimatio n errors

2/ 26/ 27/ 24/ 22/ time n H 78 '9 710

Fig. h. Dry-matter composition overtim e forL G 11.Î indicates 50%9 flowering .

39 less digestible thanth eothe rthre ehybrids .Thi sgenotypi c differencewa s mainly effectedb y differences incell-wal ldigestibility ,bu twa s also amplifiedb y differences incell-wal l content,especiall y inth elate rsowing . Sowingdat eonl y showed slight effectso ndigestibility :th ehighe r cell-wall contents forlater-sow n cropswer e compensated forb yth ehighe r cell-wall digestibilities. Both cell-wall contentan dcell-wal ldigestibilit y arerelate dt ophysio logicalage .Fig .5 show stha t inthi stria lth e cell-wallqualit y ofbot h sowingdate swa s completelycomparabl e iftim e isexpresse d inday safte r 50$emergence .I ti sals oeviden ttha tth epoore rdigestibilit y ofth ecel l wallso fEt aIph oresult s fromth emor erapi d decrease inqualit y during the formation ofth elarg eleave s (withthei rthic k midribs)an dste m elongation.Durin gthes eprocesse sth erat eo fcell-wal lproductio n isver y rapid andth equalit y ofth e cellwall sproduce d ispoorer .Thi s iswh y genotypic differences arisei nthes e stages.Similarly ,th ecel lwall s produced inth eea rpart so fEt aIph oafte rflowerin gwer e ofpoore rqualit y andagai nthes edifference s arose duringth erapi delongatio n ofth ecob . The cell-walldigestibilit y ofth ehusk s +shank s depended onth ephysio logical stageo fth eear .

Table h. Dry-matteryiel do fth ewhol eplan t (dmyield) ,ea rconten t (ear%), apparent digestibility oforgani cmatte r (D ),percentag e ofcell - om wall constituents indr ymatte r (cwc$),cell-wal ldigestibilit y (D )an ddry-matte r content o n 22/10. cwc J (dm%)

sowno n26/1 * sowno n28/ 5 EtaIph o LG 11 Fronica Nicco EtaIph o LG 11 Fronica Nicco dm yield (Mg.ha-1) 16.15 15.11 16.21 16.66 13.97 13.87 15.02 11*.61 earf {%) 57-5 59-2 56.1+ 56.6 50.I* 51.2 1*7.8 1*8.6 D™ W 70.3 Ik.2 73.1+ 75.0 69.5 7U.2 71*.U 71*.6 cwc# {%) 1*2.7 1*1.1* U2.0 1*1.6 1*6.6 1*1».l» UU.6 1*3.1* D {%) 58A 65.6 6U.2 60.2 67.8 68.3 68.0 cwc 67.5 dmjS {%) 38.2 38.9 33.8 31.1* 29.7 27.3 25.7 23.6

Thus inthi strial ,th ehybrid s differedmainl y inth eyiel do fth enon - reproductive organs,i nth e dry-matter contentso fth eear san do fth ewhol e

40 CO LD CM r-. o CM II m + C + 17 '2 {/) 00 M3 C a> , ON ai t*. "O O II 5 s " c= CM 4J CM *- M3 £_ c -rH m ai Ol Ol -* cd .ç c i GO ai «- t. n i Ol •a tu ai u ^~ t_ a) / ai 5 •p u / E 0

en flo w ai .-H

flo w a

win g ^ c CT) jwin g o a S e «/> o O o s o y £ W to "s Jï-aiôÇ S? / o ai / LTI 4-1 o Ol / _>•. c_ -a "i— c / ai a > 0 ai / O ai 's • O S Ipho,ea r Ipho,la t o

cate s 5 0 l y sowin g cate s 50 ' l/l t/> c ai o o -a •= -o 0 .D in a _j _i •*Q-j •*LU- •c— HO l c•_ _g T3 c n n Il II II II s O 0 O • a m -*• => - Ol 01 s 0 XI m o •a o -H XI >1 ss

>1 .-) o M oo m ai 0 5 0 o vO ê ai Q u c —' 0 >i 4-> &n -H O rH 1 -J- •H ai XI •H <*> •P o U) m cai •H ai O 13 •p CM rH « m >i S a .-H •a H a) «H o u 0

rsi rV CO GO oo o ••O oo r— LTI

41 crop,an di nth equalit y ofth e cellwalls .Th eeffect so fsowin g dateo n cropqualit ywer e connectedwit hth edifferenc e indat e ofemergenc e and wereno t causedb y differences inclimati c conditions during anystag eo f development.Withi n therang eo fgenotypi c variationpresent ,th epre-silkin g period appearedt ob e important forquality . Differences in digestibility were effected relatively quickly. Digestibility canb emodifie d afterflowering : itca nincrease ,decreas e orremai n constant,dependin g onth e climatebu tonl y slightly ongenotype . The course ofth e digestibility afterflowerin g inthi stria lwa sapproximate lyth e same foral lhybrids .I ntropica l climates,digestibilit yma y increase considerably afterflowering .Th e decline during stemelongatio n isgreat ,becaus eth ehig htemperature s stimulate lignification.However , high irradiance andgoo dea rdevelopmen twil l guarantee astron g"dilution " ofth e cellwalls . Inth esombr e autumn climateo fNorth-Wes t Europea decrease indigestibilit y iscommon .Digestibilit y is already goodbecaus e ofth egoo d cell-wallquality ,an dth eincreas ei nstarc h content cannot always compensate forth edecreas e incell-wal ldigestibilit ybecaus e starch ispartl y formed fromsucrose ,store dtemporaril y elsewhere inth eplant . Indeed,i nth eliteratur e increasing,decreasin g andconstan tpost-silkin g digestibilities havebee nreported ,dependin go nlatitud ean dyea r (Daynard& Hunter, 1975;Sheldrick , 1975; Andrieu ,1976 ,McAlla n& Phipps ,1977 ;Aert s et al., 1978;Phipps ,1978 ;Weave re t al., 1978;Deinu m& Knoppers ,1979 ; Gross, 1979;Phipp s &Weiler , 1979;Sheldrick ,1979 ;Whit e &Winter ,1979 ; Wilkinson &Phipps ,1979 ;Wermk e &Theune ,1980) .Thes edifferen t possibilities areillustrate d inFig .6 ,whic h showstha t grain filling iscrucia l forth e silage cropt ob eo fgoo dqualit yunde r tropical conditions,bu t isles s importantunde rtemperat e conditions.Variatio n inearlines s andi nduratio n oflea fare aafte rsilkin g areno ttake n intoaccoun t inthi sfigure .I nearl y genotypes,th e decline indigestibilit ybefor e silkingma yb e shorteran d therefore digestibility may increasemor erapidl y aftersilking .A hig hleaf - areaduratio n afterflowerin g (because ofearlie r floweringo rbette r longevity ofleaves )als o favourswhole-plan t digestibility,especiall y in thetropics .

Trial2 Dry-matter distribution. Thepercentage s ofdr ymatte r accounted forb y 10morphologica l fractions arepresente d inFig .7 ,togethe rwit hth e dry-matter contentso fthos e fractions.On eo fth emos t strikingphenomen a

42 1: ver y digestible hybridunde r temperate conditions Digestibility abrigh t autumn whole crop bnorma lautum n csombr e autumn 2:les s digestible hybridunde r temperate conditions a,b ,c se eunde r1 3:ver y digestible hybridunde rtropica l conditions h: less digestiblehybri dunde rtropica l conditions

L, Ç flowering time

Fig.6 .Hypothetica l course ofdigestibilit y overtim efo rdifferen t situations.

43 o

0) ^ fi ,p —, in o —' 1*}^ sg! 3m S v»S« g CI m 1-1 (l) Pi •rGt 13 P>- . al o C c (1) 6 ta) ,u

0) oo ao >H T~ C'' VU< H S 00 ui ° 'S H 00 •5 oi 5oi «M ei irt m oi po u> a Ü ** ** E (

rH >5 Ol P<5 t) S • H M •aH t>[l O •• — rH vi> in O t) C Ä s-i l) 3 Pi •H -H U P (1 ( ) o < E Fi at f)• * U C a Ü-1 (11 Pi 8-° •P M (U

at •P !>. -P ^) W D *H O v -P oaf ai P a! >> s vo S & „ D * •d ON •P op an .ri O «( rKn 2 r-= m Un i— (1) o e> m O •P JO JD S m " W3 g c « t— I i I I o o O o à) o^ 3 o •H s s (VI U. 2^

44 showni nthi sfigur e isth eenormou s range inth edry-matte r contentso fth e different fractionswithi n oneplant .Afte r freshmateria lha sbee n chopped, theshap e and specificgravit y ofth evariou s fractionswil lvar y sotha t stratification andselectio n are inevitable.Thi sillustrate s theproblem s encounteredwhe n attempting totak eadequat e samples from achoppe dmaiz e crop forestimatin gth edry-matte r content.Simila ro reve ngreate rproblem s areencountere dwhe ninvestigatin g qualitytraits . Theproportion s ofdr ymatte r didno tvar y greatlybetwee nth efiv egenotype s but: - shellingpercentag ewa shig h forbrown-midri b genotypes - INRA2^ 0b m had ahig hportio n ofhus k+ shan k ando flea fsheat h - Circéshowe d characteristics ofa lat ehybri d andha d athic krin d - LG 11b m was early;i tha da hig hproportio n ofgrai nbu t the amounts of pith andlea fblade swer elow . Inthi strial ,Et aIph oan dINR A2U 0b m yieldedmor etha n theothe rthre e genotypes.Th edry-matte r distribution ofEt aIph owa s similar inbot htrials . InTria l2 ,th ematurit y andth e dry-matter distribution ofL G 11b m were similart othos eo fit snorma lcounterpart ,whic hwa sgrow n atth esam e location andi nth esam eplan t density,bu tha sno tbee nmentione d elsewhere inthi spaper .

Quality. Thedigestibilit y ofth e fractionswa sver yvariabl ebot hbetwee n fractions andbetwee n genotypes (Table 5). Theapparen t digestibility ranged fromUU. 0 (thetasse lo fEt aIpho )t o88.9 $ (kernelo fINR A2U 0b m ).Thi s range iswide rtha nth erang eo fth estandar d samples,s oth eextrem evalue s mayb edeviation s thathav e arisenbecaus eth eextrapolate d relationship is not astraigh t line.Ver y lowvalue so fdigestibilit ywer enormall y repeatable within onin-vitr orun ,bu tno t alwaysbetwee n runs.Larg e inter-hybrid differences existed foral lfractions ,excep t forth ekernels .I nal lit s fractions,Circ ewa smor e digestible thanEt aIpho .Th ethre ebrown-midri b genotypesha dhighe r digestibility valuestha nth etw o commercialhybrid s except forth e "kernel"an d "resto fth elea fblade "fractions . InFi g .8 th edigestibilit y ofeac h fractionha sbee nplotte d againstth e cell-wall contento fth e drymatter .Ther ewa s awid erang eo fdigestibilit y ata give n cell-wallcontent ,especiall ywhe nth e cell-wall contentswer e high.Som eo fth edifference s indigestibility ,however ,ca nb eattribute d todifference s incell-wal l content (r2= 0.1*1+7; RSD= 9-12) .A tth esam e cell-wallcontent ,Et aIph o showsth elowes t D andbm. ,genotype s shows om 3

45 -p P< •H ö •KP Cl) o O m ä OJ CO PM .Ü PM a> •P ©S ai O OJ Va oo <-> Si •>H O » -P =H > «I 8 o g < + CO rH C *Vä—. O OJ + X o •H Ä •P •P X » o!» O 09 •H in — rt O Sn > rH + m Ü O LD J3 OJ Pi •éCD Ä u r-t o -p o o u c 1) c > CJ M rH a II II II II rH 1 «ri CD OJ « CJ H eu *H C li Ä -p h ,o {M -p •p a> cj M E £ a 0 oa CD CD Q o oj o J3 o (SI •H •P ri 3§| •!P» •H o. (N t- -D 0) § a OJ p w> o Ä h -P 'ai< < rr e o cd LD o •p a ïS •H 11 aj •H •P Ä •Ö II II

LO O in o in CD CO in S

46 Table 5-Apparen t digestibility ofth eorgani cmatte ro fte nmorphologica l fractions forfiv egenotypes ,expresse da s %.

Genotype Eta Ipho Circe INRA 2l*0 INRA 188 LG 11 Fraction bm- bm. bm

Tassel 1*1*.0 1*7.6 72.1 66.9 69.3 Cob 59-7 68.1* 78.1* 77.6 78.1* Kernel 88.1 88.6 88.9 87.0 87.3 Husk + shank 63.1 65.5 80.3 78.5 78.9 Midrib 1*6.1* 56.3 68.3 71.8 73.1+ Rest of leaf blade 71.6 76.7 75.3 76.5 77.1 Leaf sheath 1*7-7 55.6 68.7 69.2 68.3 Rind Ul*.9 5U. 1* 58.8 69.7 69.I Pith 65.3 73.6 80.7 82.7 79.7 Tiller — — 80.3 — 83.9

thehighes tD ,excep tfo rth ekernels .Difference sbetwee nhybrid swer e especially large formateria lwit ha high cell-wallcontent . Thus,cell-wal l contentinfluence dth equalit ynegativel ybu twa sno tth e only determinant;cell-wal lqualit ywa s alsovariable .I nFig .9 th edigesti bility ofth eorgani cmatte rha sbee nplotte dagains tth ecell-wal ldigesti bility.Th erelatio n islinea rwit h ahig h correlation anda relativel y low RSD. (Notetha tthes etw oparameter swer eno testimate d independently!).Et a Iphoan dCirc éha d predominantlylo wD values.Th elinea r correlation between cell-wall content andcell-wal ldigestibilit ywa srelativel y low (r =O.187) ,bu twa sals osignificant .Deinu m& Bakke r (1981)foun dhig h correlationsbetwee n cell-walldigestibilit y andth edigestibilit y ofth e organicmatte rwhe nexaminin g anumbe ro fhybrids . Inou rexperimen t fractions fromdifferen thybrid s alsoha da ver yhig h correlation,althoug hth erang ei ncell-wal lconten twa smuc hwider .I f thesehig h correlationsbetwee n cell-walldigestibilit y andorganic-matte r digestibility arecommo n (eveni fcell-wal lcontent svar ygreatly) ,the ni t willb e difficultt oestimat eth equalit y offorag emaiz e fromcrude-fibr e contento rfro m cell-wallcontent . Table6 show sth edifferen t characteristics forth ewhol e crop,calculate d fromth edat ao fth efractions .Not etha tEt aIph operforme ddifferentl yi n

47 si 01 -p 3 U o •P

,a cd 2 •H X) ai •P o 10 ai ai ai 00 p •H g •Ö rH* to O -P Ol rH a U ai sft ai h •p d o c P) c o ai •H ftai W) •P ai H -P >O 'M CO rH •cl 8*S a ai *"" U ai O ai bo !-ai. m m CO E E LO U CJ a! !> o\ a £ O rH co X3 -Q ~ o •H •H m o •P al o CJ •P o* —' Si co a -5 S ™- ° to a ai CL rH C*U* •H -p •-•• là CJ o rH •H o H * « +:•- zzq H M rH o 0) O s ce LU <—I .—i <—i —I ao Ü rH o il II II II II O > ai fi ••HP rHi O • X + < in .c P. O rH \+. •p S-, ai 01 t— O O > ai •H -P •p •p •H •p •Ö H S G m •H o .»1 al SD ,P u -Ö •H CM ai feS. •P rH o CO ai CJ o o ai •P U vO M a) •H —* •H O O -p a CO in •ti ai o 01 ^ ^ in .0 S eu g •p •d o o au] 0 « CO o ai G •H in ai !H o ai -H r>> ->p -p -P •P -4- Ö Ci -* in ai •p O •H ,a ai ai rH «* a SU •H c >, a CM ,£> oo o o •H •H •H rH -P -P 01 CO 3 cd ai c ai H bO M 60 ^ ai M ai •H E J_ i O J4 T3 in o in in o in o in « oo ao o m in

b0 •H

48 thetw otrial sbecaus eo fdifference s insamplin g date,plan t densityan d in—Ditro runs (compareTabl e6 wit hTabl e 't).Th e calculated digestibilities agreewit hth e in-vivo digestibilities estimatedfro m adultwether s feda t maintenance onsilage smad efro mth e samecrops .Thes e estimates ofdigesti bilitywer e doneb yth eInstitut e forAnima lFeedin g andNutritio nResearch , Lelystad,Netherland s (personalcommunication ,A .Steg , I980).Th eapparen t digestibilities ofth eorgani cmatte rwere :Et aIph o72. 6%; Circé75 .6%; mixtureo fbrown-midri b genotypes 80.1?.Th eimprovemen t inth equalit y attributable toth erecessiv ebm ,gen ei simpressive .Genotype svarie di n earliness,a sca nb e seenfro mdifference s in dm%an d cwc%.Regardles so f theircwc$ ,b m genotypes hada muc hbette rwhole-cro p digestibility than commercialhybrids ,becaus eo fthei rlarge rD .I naddition ,Et aIph owa s less digestibletha nCirce ,becaus eit sD waslowe r (seeals oDeinu m& ° cwc Bakker, 1981),an dINR A2^ 0b m wasles sdigestibl etha nth eothe rb m genotypes,becaus e itscell-wal lconten twa s greater.Th erelativel ylo w digestibilitieso fit srin dan dmidrib s indicatetha tth edigestibilit yo f INRA2U 0bm ,migh tb e improvedb y further alteration ofit sgenotype .Th e differencesobserve dar erelevan teve ni nth eNetherlands ,wher eth ecell - walldigestibilit y isalread y goodbecaus elignificatio n isles s extensive butwher eth ecell-wal lcontent s areals over ylarge .Improvin gth ecell - wallqualit yb ydecreasin g theligni n contenti seve nmor e importantfo r tropicalregions ,a slignificatio n ismor epronounce d inwarme r climates (Deinum, 1976).

Table6 .Dry-matte r content (dm$),apparen t digestibility ofth eorgani c matter (D ),cell-wal lconten t (cwc#)an dcell-wal l digestibility om (D )o fth ewhol ecro pfo rfiv egenotypes.calculate d fromth e fractions andexpresse d as%

Genotype aIph o Circé INRA2l* 0 INRA 188 LG1 1 bm bm bm

3U.8 29-3 32.7 33.3 38.8 cwc> 38.5 1*0. k 1(1. 7 33.2 36.6 D 71.8 T5.U 79-8 81.1+ 81.8 om D 62.6 70.7 81.1 80.1 83.O

49 Theagronomi c disadvantages ofbrown-midri b genotypes,however ,ar e considerable,an dimprovin g acommercia lhybri db y introducing ab mgen e isa time-consumin gproces s (Gallais et al., I980):therefor eth eyieldin g ability ofa brown-midri b hybrid isusuall y lesstha ntha t ofth elates t introductions. Thevariatio n inan dheritabilit y ofth e digestibility ofsevera lforag e crops inth eGraminea e family aregoo d (Ross et al., 1970;Burto n &Monson , 1972; Ross et al., 1975;Quesenberr y et al., 1978;Dang i et al.,1979 ; Monson &Burton , 1980;Pederse n et al., 1980;Voge le t al., 1981a,b) .A preliminary testha s showntha thig hheritabilit y values canb eobtaine d formaiz etoo'(Beerepoot ,1980 ;persona l communication).Ther e is sufficient unexploited geneticvariatio n toobtai ndigestibilit y values ashig ha s those ofth eb m genotypeswithou t recourset ob m genes,an dthu smayb e withoutthei r agronomic disadvantages.Firstly ,however ,i tshoul db e irrefutably establishedtha tth eknow n differences inqualit y havea positiveeffec t onth edigestibility ,intak e orfee d efficiency ofdifferen t classes oflivestoc k underpractica l feeding andproducin g levels.Method s mustb e standardized and-a s statedb y Gallais (198O)- international co-operationmus tb e establishedbecaus e ofth ehig h costsinvolved .

Mineral content and mineral uptake. InTria l 1n ogrea t differenceswer e foundbetwee nhybrid s inth euptak e ofN ,P ,K an dC aalthoug hNicc oshowe d a somewhat greater accumulation ofmineral s thanth eothe rthre ehybrids ; later sowingresulte d inles sminera luptak e (Table7 )hu tminera l contents were ashig h asfo rearl ysowing .

Table 7-Minera laccumulatio n inabove-groun dplan tpart s atfina lsampling , inkg.h a

Sown on 26/1+ Sown on 28/5 Mineral Hybrid range tiea n Hybrid range mean

H 192 - 225 203 172-199 184 P 25 - 32 29 23 - 25 2U K ll+8 - 19!+ 170 11+0-182 165 Ca 2h - 39 37 30 - 33 31

Total ash 701 - 839 758 61+3 - 760 706

50 Theminera l contentso fth e fractions fromTria l2 wer e alsoanalysed .Th e metabolic roles ofth edifferen tnutrient s determine inwhic hplan tpar t they accumulate.Accordin gt oPai n (19?8)th edistributio no fnutrient s can be summarized asfollows : -Nitrogen ,bein g anessentia l constituent ofprotein ,enzyme s andchlorophyll , reacheshig h levels inth eleaves ;a considerabl e amounto fN ,presen ti n vegetativepart s istranslocate d toth eea rafte rgrai nset . -Althoug hphosphoru s (animportan t constituent inth ecel lnucleus )i s initially fairlyuniforml y distributed inth edifferen tplan ttissues , translocation fromvegetativ epart st odevelopin gkernel soccurs . - Thoughno tincorporate d inan yorgani c compound ofth eplant ,maiz e requireslarg e amountso fpotassium . Potassium contributes toth e strength eningo fth esclerenchym ai nth efibre s andha sman y otherfunction si n transport,photosynthesis ,stomat aclosur e etc.A tth een do fth egrowin g season,potassiu mma y accumulate inste mparts . - Calcium isrequire d incell-wal l formation andi nneutralizin g organic acids.I ttend st oaccumulat e inth eleaves . Inconfirmatio n ofth e above,w efoun dtha t - theN contentwa shighes t inth emesophyl l - theP contentwa s fairlyconstant ,bu twa s lower infixe dorgan s sucha s cob,tassel ,rin dan dpit h - theK contentwa s relatively lowi nth eea rbu thig h inth epit han d midrib - Cawa sbarel y detectable inco ban dkernels ,bu t reachedhig hlevel si n tassel,lea fblade ,pit han drind . Caconten twa s significantly correlatedwit h cell-wall content.However , verylo wC acontent swer efoun d inth e cobs,althoug h cobswer eric hi n cellwalls .Th e absence ofC ai ncob-cel lwall s suggeststha tth estructur e ofth elatte ri sdifferent .

Concluding remarks Silagemad e fromwhol eplant so fforag emaiz e iscompose do fver y digestible plantpart swit h alo wcell-wal l content (kernels,pith )an do fplan tpart s withmuc hhighe r cell-wall contents andvariabl e cell-wall digestibility (e.g.rind ,tassel ,midrib) . It couldb e saidtha tth eforag eobtaine di s amixtur e ofroughag e and concentrates.Th eroughag e ismainl yproduce d during June,Jul y andAugust ,whil eth e concentrates aremainl yproduce d duringJuly ,August ,Septembe r andOctober .Moderat etemperature s during

51 early summeran da brigh tautum nencourag ehig hyield s of foragemaiz e and"boos tth eproportio n ofconcentrate s andth e quality ofth eroughage . Since cell-wall content andcell-wal l quality showa wid erang ewithi non e plant andbetwee ngenotype s and sinceth eproportio n ofth edifferen tplan t parts canb e changedb yselection ,breeder s areabl et oboos tth eproportio n ofth e concentrates andt oincreas eth e qualityo fth eroughage ,eve nwithou t undesirable repercussions onan yothe r agronomicproperty .

52 References

Aerts,J.V. ,B.G . Cottyn,D.L .D eBrabander ,Ch.V .Boucqu é &F.X .Buysse , 1978.Digestibilit y and feedingvalu eo fmaize .Proceeding s ofth e EuropeanMaiz eMeetin ghel d atLouvain-La-Neuv e (Belgium)ed . J.-F. Ledent,pp . 106-128 Andrieu,J. , 1976•Factor s influencingth e composition andnutritiv evalu e ofensile dtota lmaiz eplant .Symposiu m onth emaiz e cropa sa basi c feedfo rbee fproduction .Commissio n ofth eEuropea n Communities -Nov i Sad- Yugoslavi a Becker,W.R. , 1976.Mais .Ee nhandleidin gvoo rd eteel tva nkorrel -e n snij- mais. P.A. publicatie nr.21 ,pp .1-81 * Bundessortenamt, 1980.Beschreibend e Sortenliste 1980.Getreide ,Mais , Ölfrüchteun dHackfrücht e ausserKartoffeln .Alfre d StrotheVerlag , Hannover Bunting,E.S. , 1975- Thequestio n ofgrai nconten t andforag e qualityi n maize: Comparisonbetwee nisogeni c fertile andsteril eplants .J . agric. Sei.,Camb .85 :U55-U6 3 Bunting,E.S. ,1976 .Effect so fgrai n formation ondr ymatte r distribution and foragequalit y inmaize .Expl .Agric . 12:1*17-1*2 8 Bunting,E.S. ,1977 - Maizephysiolog y inrelatio nt obreedin g for anorther n climate.Ann .Appl .Biol . 87:25O-25I * Burton,G.W. ,& W.G .Monson ,1972 .Inheritanc e ofdr ymatte r digestibility inBermud agrass ,Cynado n dactylon (L.)Pers . Crop Sei. 12:375-37 8 Dangi,O.P. ,G.P . Lodhi &Y.P .Luthra ,1979 .Inheritanc e of invitr odr y matterdigestibilit y inforag e sorghum.Forag eResearc h 5:75-7 7 Daynard,T.B . &R.B .Hunter , 1975- Relationship amongwhole-plan tmoisture , grainmoisture ,dr ymatte ryiel d and quality ofwhole-plan t corn silage. Can.J .Plan t Sei. 55:77-81 * Deinum,B. , 1976.Effec t ofage ,lea fnumbe r andtemperatur e oncel lwal l anddigestibilit y ofmaize .In :Carbohydrat e research inplant san d animals.Misc .Paper snr . 12,Agric .Univ. ,Wageningen ,pp .29-1* 1 Deinum,B .& J.J . Bakker, 1981.Geneti c differences indigestibilit y of foragemaiz ehybrids .Neth .J . agric.Sei .29 :93-9 8 Deinum,B .& J . Knoppers,1979 - Thegrowt ho fmaiz e inth e cooltemperat e climate ofTh eNetherlands :Effec t ofgrai n fillingo nproductio no f drymatte r ando nchemica l composition andnutritiv evalue .Neth .J . agric.Sei . 27:116-13 0 Deinum,B .& P.C . Struik, 1980.Harvestin g fieldexperiment s forsilag emaize . Proc. fifth international conference onmechanizatio n offiel dexperiments , Wageningen,eds .J . Dijkstra &A .va n Santen,pp .231-23 6 Gallais,A. , 1980.Summarie sb y chairmen.In :Improvemen t ofqualit y traits ofmaiz e forgrai n andsilag euse ,eds .W.G .Pollme r &R.H .Phipps , MartinusNijhoff ,Th eHague ,p .1*9 3 Gallais,A. ,L .Huguet ,H .Berthet ,G .Bertin ,B .Broqua ,A .Mourgue t &R . Traineau,1980 .Preliminar y evaluation ofbrow nmidri bmaiz ehybrid s forthei rfeedin gan dagronomi c value inFrance .In :Improvemen to f quality traitso fmaiz e forgrai n and silageuse ,eds .W.G .Pollme r8s R.H.Phipps ,Martinu sNijhoff ,Th eHague ,pp .319-33 9 Gross,F. , 1979- Futterqualitä twir dbe i derErnt e festgelegt.Massnahme n zurVerbesserun g des Futterwertesun d derFutterqualitä t vonSilomais . Mais. Zeitschriftübe rForschung ,Produktionstechnik ,Verwertun gun d Ökonomik7 (1*): 12-13

53 Gross,F. , 1980.Conten tan di nviv odigestibilit y (sheep)o fnutrient si n maizevarietie s harvested atdifferen t stages forsilage .In :Improvemen t ofqualit y traitso fmaiz efo rgrai n andsilag euse ,eds .W.G .Pollme r& R.H.Phipps , Martinus."ijhoff ,Th eHague ,pp .U29- 1+1+5 McAllan,A.B .& R.H .Phipps ,1977 .Th eeffec t ofsampl edat e andplan t density onth e carbohydrate contento fforag emaiz e andth echange s thatoccu ro nensiling .J . agric.Sei. ,Camb .89 :589-59 7 Mock,J.J . &R.B .Pearce ,1975 - Anideotyp eo fmaize .Euphytic a 2k: 613-623 Monson,W.G . &G.W .Burton ,1980 .Forag equalit y evaluations inPear lMillet . 1980Agronom yAbstracts ,America n Society ofAgronomy ,Madiso n (WI), p. 127 Montgomery,F.G. ,1911 .Correlatio n studieso fcorn .Hebr .agric .Exp .Stat . Ann.Rep . 2k: 108-159 Pedersen,J.F. ,H.J . Gorz,F.A . Haskins &R.A .Britton ,1980 .Inheritanc e offorag e andsilag equalit ytrait s inforag e sorghumhybrids .198 0 AgronomyAbstracts ,Agronom y Society ofAmerica ,Madiso n (WI),p .12 7 Pain,B.F ., 1978 .Nutritiona l requirements offorag emaize .In :Forag emaize , eds.E.S .Bunting ,B.F .Pain ,R.H .Phipps ,J.M . Wilkinson &R.E .Gunn , Agricultural Research Council,London ,pp .87-11 6 Phipps,R.H. , 1978.Th equalit y ofmaiz e silage.Proceeding so fth eEuropea n MaizeMeetin ghel da tLouvain-La-Neuv e (Belgium)ed .J.-F . Ledent,pp . 7k-19 Phipps,R.H .& R.F .Weiler ,1979 - Thedevelopmen to fplan t components ando f theireffect so nth e compositiono ffres han densile d foragemaize .I . Theaccumulatio no fdr ymatter ,chemica lcompositio n andnutritiv evalu e offres hmaize .J . agric.Sei. ,Camb .92 :1*71-1*8 3 Quesenberry,K.H. ,D.A . Sleper& J.A .Cornell ,1978 .Heritabilit y and correlations ofIVOMD ,maturit y andplan theigh ti nRhode s grass.Cro p Sei. 18:8U7-85 O Rijksinstituut voorhe tRassenonderzoe kva nCultuurgewassen ,1982 .5 7 BeschrijvendeRassenlijs t voorLandbouwgewasse n 1982.Leiter-Nypels , Maastricht Ross,J.G. ,S.S .Bulli s& K.C .Lin ,1970 .Inheritanc eo fi nvitr odigestibilit y inSmoot hBroomegrass .Cro pSei . 10:672-67 3 Ross,J.G. ,R.T .Thade n &W.L .Tucker ,1975 - Selection criteriafo ryiel d andqualit y inbi gblueste mgrass .Cro pSei . 15:303-30 6 Sheldrick,R.D. ,1975 .Optimu mcuttin gperiod s forsilag emaiz ei nWester n Kenya.E .Afr .For .J . kO: 39^-399 Sheldrick,R.D. , 1979.Growin gmaiz e forsilage .Informatio n leafletno .6 . GrasslandResearc hInstitute ,Hurley ,pp . 1-8 VanSoest ,P.J ., 1977 .Modifie dprocedur e fordeterminin gplan tcel lwal lb y theneutra ldetergen tprocedure .Pape rpresente d atth eAnnua lMeetin g ofth eAmerica nSociet y ofAnima lScienc e VanSoest ,P.J. , R.H.Win e& L.A .Moore ,1966 .Estimatio no fth etru edigesti bilityo fforage sb yth e invitr odigestio no fcel lwalls .Proc . 10th int.Grassl .Congr . (Helsinki)pp .1*38-1(1( 1 Vogel,K.P. ,H.J . Gorz& F.A . Haskins,1981a .Heritabilit y estimates for forageyield ,i nvitr odr ymatte r digestibility,crud eprotei nan d headingdat e inIndiangrass .Cro pSei .21 :35-3 9 Vogel,K.P. ,F.A . Haskins &H.J . Gorz, 1981b.Divergen t selection fori n vitro drymatte rdigestibilit y inSwitchgrass .Cro pSei .21 :39-1( 1 Weaver,D.E. ,CE . Coppock,G.B .Lak e &R.W .Everett ,1978 .Effec to f maturation oncompositio n andi nvitr odr ymatte rdigestibilit y of cornplan tparts .J . ofDair ySei .61 :1782-178 8

54 Wermke,M . &H.H .Theune , I980.Influenc eo fvariety ,developmenta lstage , year andlocatio nupo nth equalit y ofsilag emaize .In :Improvemen t of quality traitso fmaiz e forgrai n and silageuse ,eds .W.G .Pollme r& R.H.Phipps ,Martinu sNijhoff ,Th eHague ,pp .1+11-1+2 7 Whigham,D.K . &D.G .Woolley , 1971*-Effec t oflea forientation ,lea fare a andplan t densities ofcor nproduction .Agron .J . 66: 1+82-1+86 White,R.P . &K.A .Winter , 1979.Effect s ofharves tdat eo nyield ,dr ymatte r content,plan tnutrien t content andin-vitr o digestibility of various partso f foragemaiz eplant s ina shor t seasonenvironment .Pape r presented atth eEuromai s Congress,1979 ,Cambridg e Wilkinson,J.M . &R.H .Phipps ,1979 - The development ofplan t components andthei reffec t onth e composition offres han densile dforag emaize . II. The effecto fgenotype ,plan t density anddat eo fharves t onth e composition ofmaiz e silage.J . agric.Sei. ,Camb .92 :1+85-1+91 .

55 from microbial degradation in the fore-stomachs of polygastric animals (see, e.g.: MINSON, 1976; AKIN and BURDICK, 1981, HARTLEY, 1981). In some forage species, plant silica may play the same role as lignin in the microbial degradation of cell walls (VAN SOEST and JONES, 1968; HARTLEY, 1981). There is, however, another temperature effect on cell-wall digestibility inde pendent of lignin content (DIRVE N and DEINUM, 1977; DEINUM, 1979).Thi s effect isprobabl y connected with the organization characteristics of the cell walls, such as the manner in which hemicellulose isassociate d with polyphenol esters (CHES- SON, 1982), the crystallinity of hemicellulose and cellulose (BAILEY et al., 1976; DEINUM, 1979), the interactions between hemicellulose and cellulose (BAILEY et al., 1976), the occurrence of O-acetyl groups (BAILEY et al., 1976), whether bacteria are physically impeded from adhering (cf. RICHARDS, 1976) or the avai lable surface of the cell walls and their fragility (SMITH et al., 1971). These two effects of temperature on cell-wall digestibility may be distin guished by estimating the potential cell-wall digestibility and the rate of cell-wall digestion. Lignin and silica affect the potential extent of cell-wall digestibility, but lignin content, the ratio of lignin to cellulose or of lignin to acid-detergent fibre do not correlate with the rate at which potentially digestible cell walls can be digested (SMITH et al., 1971; SMITH et al., 1972; WALDO et al., 1972; MERTENS, 1977). The rate of disappearance of digestible fibre is related to the morphologi cal and physical nature of the cell walls (MERTENS, 1977; GOODRICH and MEISKE, 1979), although SMITH et al. (1971) have stated that the content of cell solubles (or 100 - cell-wall content!) may also be relevant for cell-wall digestion kinetics during in vitro fermentation. Other factors limiting rates of degradation, such as the pH in the rumen, are not relevant in the in vitro technique.

Literature about the effects of temperature on maize digestibility is scarce. DEINUM (1976) found that higher temperatures caused a slight increase in cell- wall content, but a strong decline in the cell-wall digestibility of leaf blades, leaf sheaths and stems. Data on the effects of temperature on whole-plant diges tibility of forage maize have previously been based on comparisons made under uncontrolled conditions (e.g. CUMMINGS and DOBSON, 1973; ANDRIEU, 1976). This paper deals with the effects of temperature during certain stages of growth, partly in combination with low light intensity, on the development, production and quality of forage maize under controlled conditions.

MATERIALS AND METHODS

Three experiments were carried out in greenhouses in 1979, 1980 and 1981. To obtain high and relatively constant light intensities for all treatments during periods in which the area of green leaf was large, experiments were started in March or April. Four seeds were sown per plastic pot containing 101 of a mixture of equal volumes of sandy soil and peat. After emergence, the seedlings were reduced to 2 per pot. Nutrient solution, adjusted to soil type, and water were

58 Meded. Landbouwhogeschool Wageningen 83-3 (1983) provided adequately. Weeds were removed by hand or controlled by applying a low dose of atrazin. Plants (including their root systems) were kept as healthy as possible and were finally arranged in a density of 10 m 2wit h a row distance of 75 cm, a plant arrangement similar to cultural practice in The Netherlands. Thus it was possible to place 8 rows of 26 pots (i.e. 416 plants including the border rows)i neac h greenhouse. In early stages of growth, supplemental light was provided with 0.8 Philips HPLR 400 W mercury lamps per m2 for 14(197 9 and 1980)o r 16(1981 ) hours per day. During vegetative development, the photoperiod was extended to 16 h by means of 12 incandescent bulbs (100W ) per 40m 2, except for hybrid Dara in the 1979trial . Relative humidity was kept at 75%. Pollination ingreenhouse s may besuboptima l because aircurrent s are locally strong and always flow in the same direction. Therefore, pollen was collected and sprinkled over the silks by hand daily. The date on which silk extrusion was first visible was noted for each plant in all experiments. In the 1981experi ment the dates of the first visible extrusion of anthers were noted as well. Plants were checked twice daily every day. Prior to treatment, plants were rearranged to cancel out any differences that might have arisen in different greenhouses during pre-treatment growth. In 1979,th ehybri d Dara wassow n onewee kearlie r than Ula. In combination with different photoperiods, this ensured a better synchronized silking for the early and late genotypes.

Treatments Maize development can be divided into four physiologically distinct periods: 1. from sowing until the double-ridge stage of the shoot apex (approx. 6.5-leaf stage) 2. from double-ridge stage until 50%$ flowering 3. from 50%S flowering untilonse to flinea rdry-matte r accumulation inkernel s 4. grain-filling period. These phases differ greatly in duration. In this paper, experiments are described in which temperature was varied in period 2o r 4. Data from the literature or unpublished results on the influence of temperature during periods 1 and 3wil l be mentioned. Comparisons will be made with maize grown in the field under different conditions. In addition to temperature, light intensity was also varied during period 4 in the 1979 and 1980experiments . Each greenhouse was divided into two compartments, sepa rated by shading nets. The outer glass of low-light compartments was sprayed withtemperzo n (Hermadix).Car ewa stake n toensure ,tha t theligh twa sreduce d by the same amount in all temperature treatments. The hybrids were chosen according to the aims of the experiments. Only LG 11i s in current use in The Netherlands. Ula, LG 11 and Nicco have been described in earlier reports (STRUIK, 1982b;STRUI Kan d DEINUM, 1982).Dar a isa late ,den t hybrid registrat- ed in France. InTabl e 1, climaticcondition s are presented for each of thethre e experiments

Meded. LandbouwhogeschoolWageningen 83-3 f1983) 59 and for normal Dutch conditions. The data of normal conditions are based on average climatic data and on average rate ofcro p development. The treatments have been coded according to the day/night temperature during the period in which the temperature was varied and with the relative amount of light or ac cording to whether they were shaded or unshaded. Treatment 18/12 represents average temperature conditions in The Netherlands during periods 2, 3an d 4. Treatment 24/18 represents an extremely warm year, while treatment 30/24 re flects American and tropical or subtropical conditions. Average light intensity during period 4 was calculated as follows: cumulative outdoor irradiance in period 4 (J.cm" 2) _ „, duration of period 4 (days) in which 0.75 accounts for the light reduction, caused by the greenhouse itself a accounts for the light reduction obtained by shading. a = 1.00 for unshaded treatments and a = 0.40 (1979)o r 0.33 (1980)fo r shaded treatments. For Experiment 1 the same procedure was followed for period (3 + 4). Light intensity was relatively low for treatment 18/12 in 1981 and treatment 24/18 in 1980 and was relatively high for treatment 30/24 in 1979. In all years the radiation received by unshaded treatments exceeded or was similar to the amounts ofradiatio n maizecrop swoul d normally receiveunde rfield condition s in The Netherlands during grain filling.

Data oncrop development The number of visible leaves per plant and the plant height were estimated twice weekly to record and monitor rates of development in different green houses. The surface area of fully expanded leaves wascalculate d from the equa tion length x maximum width x 0.75 (MONTGOMERY, 1911). The maximum diameter of the middle of the second above-ground stem internode was mea sured with a marking gauge, to provide an estimate of stem thickness. Leaf an gles were estimated with a clinometer (WHIGHAM and WOOLLEY, 1974).A t each sampling date after female flowering, the ear length, number of unshrivelled kernels and total number of visible kernels or florets per ear were estimated for all ears arising from leaf axils. Plant height and flowering date were also noted. Light extinction was measured using a 97.5 cm long light meter containing silicon cells and calibrated against a solarimeter.

Yieldestimates Plants were cut off at soil level, separated into stover (i.e. tassel + stem + leaves + leaf sheaths), husk + shank, top ear and lower earsan d cut into pieces by hand. After recording their fresh weight, fractions were dried for each plant separately and without subsampling at 70° C in forced ventilation ovens. After reachingconstan t weight,the ywer ere-weighed . For theuppermos t ears,shellin g percentage (drygrai nweigh tdivide d bywhole-ea r weight)wa sestimate d in 1979

60 Meded. LandbouwhogeschoolWageningen 83-3 (1983) and 1980.I n 1980,th e root systems of sixplant s per treatment and per sampling date were also analysed. In Experiment 1,40plant s were harvested at the 6.5-leaf stage. For each tem perature treatment, 40 plants were harvested 4 times during period 2, at 50% c? flowering and 4 weeks after 50% <$flowering. Th e final sample was taken 8 weeks after 50%S flowering and comprised 30 plants. In Experiment 2, 32 plants of each hybrid were harvested prior to climate differentiation. 20 plants from each treatment were sampled some time there after and 20 plants were harvested at the first visible black-layer formation in normal kernels for Ula and the next day for Dara. InExperimen t 3, 36plant swer eharveste d at initiation oftreatment : 6harvest s

TABLE 1. Climatic conditions in Experiments 1, 2 and 3 and estimated normal conditions in The Netherlands.*

Experiment and Day/night temperatures (°C) Shading Estimated mean hybrid treatment light intensity period 1 period 2 period 3 period 4 during (J-cm _2.day~') period 4 during periods 3+ 4 < )r 4

18/12 1031 Experiment 1 (1981) 18/12 24/18 18/12 18/12 unshaded 1090 LG 11 (FAO 260) 30/24 1086

unshaded 1206 18/12 shaded 482 Experiment 2( 1979 ) ,» unshaded 1197 7n/ 20/15 20/15 24/18 Ula (FAO 190) ' shaded 479 unshaded 1305 30/24 shaded 522 unshaded 1202 18/12 shaded 481 unshaded 1178 Dara (FAO320 ) 20/15 20/15 20/15 24/18 shaded 471 unshaded 1300 30/24 shaded 520

unshaded 1107 18/12 shaded 365 Experiment 3( 1980 ) ~„... unshaded 1031 20/15 20/15 24/18 Nicco (FAO 300) ' shaded 340 unshaded 1080 30/24 shaded 356

Normal conditions period 1 period 2 period 3 period 4

2 Mean light intensity (J.cm" .day _1) 1650 1650 1350 1000 Mean air temperature (°C) 11.8 16.0 17.3 14.3

*Calculation s of normal conditions are based on climatic data (source: KNMI, The Bilt) and on the average rate of development of a standard crop.

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 61 of 20 plants from each treatment were taken after climate differentiation and the final harvest was at the end of the grain-filling period. The samples from one intermediate harvest of treatment 30/24wer elost , because ofa malfunction of the oven. Experiments 2 and 3 differed in frequency of sampling, hybrid choice (and thus crop structure and crop reaction), and light reduction for shaded crops.

Chemicalanalyses Sampleswer ebulke d per fraction and per treatment at each sampling, ground with hammer mills and subsampled. Subsamples were analysed for true digesti bility in vitro of organic matter, using the method described by VAN SOESTe t al. (1966).Thes e values were standardized and converted to apparent digestibil ity by means of a series of standard samples of fresh maize, ensiled maize and parts of the maize plant with known apparent in vivo digestibility (sheep). All the digestibilities of organic matter presented in this paper are standard ized values, unless otherwise stated. Digestibility of the whole plant wascalculate d from digestibilities of the frac tions and their proportions of organic matter. According to JOANNING et al. (1981) it is permissable to calculate the in vivo digestibility of a feed from the inviv odigestibilit y ofit scomponent s at feeding levelsbelo w 1.5-2 timesmainte nance. The calculations done by van DONSELAAR and STEG (1980) agree with this. Therefore I assumed that such calculations are permissable for the in vitro technique too. Organiccell-wal l content indr y matter (neutral-detergent fibre) after removal of the starch was estimated according to VAN SOEST'S (1977) method. In vitro cell-wall digestibility (Dcwc) was calculated from true digestibility (DtrUe), cell- wall content (cwc%) and ash content (ash%), using the formula:

D = 1Q0 (100-Dtrue) x (100-ash%) cwc cwc% Acid-detergent fibre, cellulose, lignin and insoluble ash were estimated accord ing to the methods described by GOERING and VAN SOEST(1970) . Hemicellulose was calculated as the difference between neutral-detergent fibre and acid-deter gent fibre. Rates of cell-wall digestion were estimated as described by SMITH et al. (1971) and GOODRICH and MEISKE (1979), assuming that the maximum extent of digestion was reached at a retention time of 96 h. For ear samples thisassumptio n wascertainl y true,a swa seviden t from thecalculation s ofmaxi mum extent of digestion done according to the method described by MERTENS and VAN SOEST (1972). For some stover samples, indigestibility was probably slightly overestimated. The potential extents of cell-wall digestibility after 96 ho f incubation in acertai n amount ofrume n liquor are thus not strictly compa rable with potential digestibilities after several weeks of incubation in mixed rumen microorganisms (see,e.g .PRIN Se tal. , 1981),o rwit hpotentia l digestibility after long-term incubation with refreshed inoculum (e.g. WILKINS, 1969).Water - soluble carbohydrates werecolorimetricall y determined with an automatic ana-

62 Meded. Landbouwhogeschool Wageningen 83-3 (1983) lysing device using ferricyanide. Toascertai n thetota l non-structural carbohy drates thesam e procedure was followed after hydrolizing thestarc h with amy- loglucosidase. N, P and Ca were determined after the dry material had been digested in a solution ofsalicyli c and sulphuric acid with hydrogen peroxide. Nan dP wer e measured colorimetrically; Ca was measured by flame-emission spectrometry. Crude-protein content was calculated asN content times 6.25.

RESULTS AND DISCUSSION

Period 1. Some unpublisheddata In this stage of growth, the growing point of the maize plant is still below thesoi lsurface . Thustemperature s inth euppe r soillaye rinfluenc e the processes in the shoot apex. Soil temperatures may increase bysevera l degrees centigrade under field conditions ifa plastic mulch isapplied . This technique hasalread y been practised by French growersfo rsom eyears .Muc h ofth e resulting increase in yield, however, consists of structural material, as is illustrated in Table 2. Thisincreas ei ncell-wal l yield may result because more plant cellsar e produced, especially in the vegetative parts of the plant. The effect on digestibility of a small risei ntemperatur e during early growth istherefor e variable. Inth etrial sdon eb yDEINU Man d STRUIK,th eplasti ccove rcause d thetempera ture in the upper soil layer during period 1t o rise by about 2°C. Therefore there were only slight differences inth enumbe r ofleave s (and thus the number ofste minternodes ) between mulched and unmulched treatments.I f temperature risesmor e than this during early stages ofgrowth , the increase incell-wal l yield will bemuc h greater, because ofa n increase in number ofste m internodesan d thus an increase in duration of the period ofcell-wal l formation. In that case, whole-plant digestibility mayeve n decline, especially ifcell-wal l digestibility is low.

TABLE 2. Dry-matteryield ,cell-wal lyiel d (cwcyield) , cell-wallconten t (cwc%), apparentdigestibilit y

(Dom) and cell-wall digestibility (Dcwc) of hybrid LG 11 with and without plastic mulch. (Field conditions; DEINUM and STRUIK, 1977;unpublishe d data).

Location and sowing date Wageningen 28Apri l Swifterbant 17Ma y

control mulched control mulched whole-crop yield (Mg.ha- ') 15.86 18.37 13.56 16.40 ear yield (Mg.ha-1) 7.19 8.95 5.51 7.13 cwc yield (Mg.ha-1) 7.28 8.22 6.56 8.06

Dom(%) 73.5 74.1 72.0 70.8 cwc%(%) 45.9 44.8 48.4 49.2 Dcwc(%) 65.4 65.7 64.1 62.0

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 63 Period2. Experiment 1.

Development In Experiment 1,th e effects of temperature on leaf number were deliberately avoided.Th e rateo fdevelopmen t increased dramatically when temperature rose (Table 3);ye tfinal difference s invegetativ edevelopmen t weresmall .Plan t height showed amaximu m in the24/1 8treatment , but wasno t affected much (cf. BLON- DON and GALLAIS, 1976). Stem thickness decreased markedly with a rise in tem perature. Thus stem volume declined if temperature rose. The cumulative area ofal l leaveswa ssomewha t greater in the24/1 8treatmen t than in theothe r treat ments. Leavesjus t below and above the top ear were smaller in treatment 30/24 than in the other two treatments but the uppermost leaves were larger when temperatures were higher (Fig. 1). This pattern is similar to the one described by ALLISONan d DAYNARD (1979),althoug h thedifference s found in Experiment 1 were smaller, possibly because the temperature differentiation occurred at a later stage. Although leaf areas only showed minor differences between treat ments, the maximum length and maximum width of the leaves differed greatly between temperature treatments.A tlowe rtemperatures ,leave swer eshorte r and wider. This difference in shape may alter the ratio of rib to mesophyll and there fore may affect digestibility (DEINUM, 1976). Reproductive development wasgreatl yaccelerate d athighe r temperatures but anthesis was hastened more than silking. In treatment 30/24 this resulted in a verylon ganthesis-to-silkin ginterval ,combine d with adelaye d ear development (cf. dry-matter content of top ear at final sampling) and in the severely limited development of second ears. The dominance of the terminal inflorescence is more marked at higher temperatures (BLONDON and GALLAIS, 1976)an d inhibi tion of reproductive axillary buds may be greater if climatic conditions are al tered in the very early stages of their development (STRUIK, 1982a). In addition, a high plant density may be unfavourable for a good synchronization (BUREN et al., 1974; EDMEADES and DAYNARD, 1979), thus emphasizing the effects of other adverse factors.

Dry-matter production At first, the rate of dry-matter production increased with temperatures, but dry-matter production was stimulated less than development. Maximum dry- matter production rates were found during tassel emergence and were similar for all treatments (Fig. 2a). Total dry-matter at 50%anthesi s correlated negatively with temperature (Fig. 2b).Climati ccondition sdurin gperio d 2affecte d production ratesafte r anthesis: the decline in rate of dry-matter production was more rapid if temperatures during period 2wer e higher, resulting in great differences between final whole- plant yields (cf. NELSON and TREHARNE, 1973). As a result of the above-men tioned effects of temperature on reproductive development, ear yields for treat ments 18/12 and 24/18 were the same, but the ear yield of treatment 30/24 was only half as much.

64 Meded. LandbouwhogeschoolWageningen 83-3 (1983) TABLE 3.Effec t of temperature treatment during the period from 6.5-leaf stage to 50%J flowering on vegetative and reproductive development.

Day/night temperaturesdurin gperio d 2 ( C)

18/12 24/18 30/24

Vegetativedevelopment rate of leaf appearance (leaves.day" l) 0.25 0.36 0.50 final number of leaves per plant* 14.85 14.80 14.80 finalheigh t of plant (cm)^ 291 300 284 stem diameter (cm)8 2.48 2.23 1.97 cumulative leaf area (dm2/pl)s 50.9 52.6 49.2

Reproductivedevelopment date of 50% anthesis (days after emergence) 73 57 50 portion of silking plants at 50%anthesi s (%) 81 50 15 date of 50% silking (days after emergence) 72 57 63 number of kernels (top ear)t 413 481 452 length of top ear (cm)1' 15.1 18.5 17.3 length of the second ear (cm)t 7.9 4.7 2.3 dry-matter content top ear at final sampling (%) 47.8 46.0 33.6

: average of 80plant s ^average of 70plant s s average of 20 plants leaf area (cm2) 800 ear leaves 1 * t 700 X o = 30/24 • • = 24/18 o ö 600 « = 18/12 1

500

400

300

200 -

100

® 0 _f_ _J_ _1_ _l_ _1_ _l_ 12 3 4 5 8 9 10 11 12 13 14 15 16 upper leaves lower leaves leaf number FIG. 1. Mean surface area of leaf laminae of plants grown at three different temperatures during period 2. Each point represents the mean of 20leaves .

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 65 dry-matter yield (g/pl) 220

200 - = 30/24 • 24/18 180 - • 18/12

160 rate of .30/24 140 dry-matter •• 24/18 production • 18/12 (g prVday"'] a __«_ 3.0 h 120

2.5 - 100

1.0 40

0.5 20

0.0 L\ 60 80 100 120 140 20 60 80 100 120 140 time in days after emergence time in days after emergence FIG. 2. Rate of dry-matter production (a) and dry-matter yield (b) in Experiment 1. Horizontal lines indicate the duration of the period, for which the production rate has been calculated. Arrows indicate 50% anthesis. The course of quality up to anthesis During period 2, maize generally shows a decline in the in vitro digestibility of the organic matter (Dom), because of an increase in cell-wall content and a decrease in thecell-wal l digestibility (STRUIK, 1982b). In thepresen t experiment, the increase in cell-wall content and the decrease in cell-wall digestibility were both stimulated by a rise in temperature, as occurs in other Gramineae (Table 4). This resulted in a marked temperature effect on Dom at 50% anthesis, as is shown in Fig. 3.

Temperature had a much greater effect on cell-wall digestibility than on cell- wall content, especially if ear shoots, including husks and shanks, are excluded (Table 4).Th echemica l composition of stover-cell wallswa sno t greatly affected by temperature, although therewer esmal l temperature-induced effects on ligni fication and on silica content (insoluble ash). Yet, the cell-wall digestibility dif fered greatly,especiall ybetwee n treatments 30/24an d 24/18.Unidentifie d physi cal/chemical factors must have been responsible for most of theobserve d effects on digestibility. Incidentally, it ismainl y these factors that prevent in vitro data being accurately extrapolated to in vivo parameters.

66 Meded. Landbouwhogeschool Wageningen 83-3 (1983) TABLE4 . Somequalit y parameters (all expressed as %o f organic matter or cell walls) of the whole crop and of the stover in Experiment 1 at 50%anthesis .

Day/night temperaturesdurin gperio d 2 ( C)

18/12 24/18 30/24

whole crop Dom 68.7 66.7 60.9 cwc% 59.5 61.3 62.9 Dcwc 68.2 66.1 58.7 stover Dom 67.2 65.4 60.3 cwc% 62.1 63.4 63.6 cell-wall composition: hemicellulose 39.4 38.9 38.3 cellulose 52.7 51.5 51.7 lignin 7.7 8.7 8.7 insoluble ash 0.2 0.9 1.3

Dc, 67.4 65.4 58.4

Dom(%) 88 h

o = 30/24 • = 24 /18 x * 18/12

80 90 100 110 120 130 time in days after emergence FIG. 3. Effect of temperature during period 2 on the apparent digestibility of the organic matter (Dom). Arrows indicate 50°0 J flowering.

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 67 but not in the same direction as the digestibility of cell walls produced before anthesis. Cell walls present in husks, shanks and ears were almost completely formed during periods 3an d 4, i.e. after the three temperature treatments were reduced to one. The digestibility of cell walls present in husks and shanks was not affected by the temperature treatments. The Dcwc of upper ears increased as temperatures rose during period 2. During periods 3 + 4 the stover Dcwc did not decline in treatment 30/24, but fell markedly in treatments 24/18 and 18/12 (Fig. 5).O n the basis of the whole crop, the most digestible cell-wall con stituents produced after anthesis were those from treatment 30/24. Differences in the Dcwc of the whole crop therefore faded in the post-anthesis period.

The digestibility of stover-cell walls appeared to be strongly correlated with plant height (Fig. 6). Theregressio ncoefficien t decreasedslightl y with increasing temperatures. However, the greatest deviations from the joint regression line were found at 50%anthesis , when mean plant height only ranged between 266 and 277cm ,bu t thedigestibilit y ofstover-cel lwall srange d from 58.4%t o67.4% . This relation ismeaningful : it indicates that the decline in stover Dcwc iscon nected with stem elongation and that this decline stops when stem extension has ceased (Fig. 6). The more rapid decline of the Dcwc with increasing plant height athighe r temperatures is caused byth eeffec t oftemperatur e on digestibil ity irrespective of morphological stage. For leaves,stem s and ears longitudinal growth exceeded growth in width and thickness at higher temperatures. FRIEND and POMEROY (1970) found for wheat that leaf length was stimulated by in creasing temperatures over a wide range and that length increase was mainly due to an increase in cell length. The number of cells along the lamina could even decline with increasing leaf length. Extrapolating these findings for wheat leaves to all plant parts in the present maize trial, wemigh t surmise,tha t athighe rtemperature s thestem ,leave san d cobsha d fewercell salon gthei r longitudinal (and perhapsals oalon gth elatera lan d radial)axes ,an dtha t thesewer elonger ,narrowe r and thinner. This would mean that the cell-wall content could be higher at higher temperatures since the ratio of surface area to volume increases when longitudinal growth dominates. This agrees with the data given in Table 4, but differences are very small, especially when the expected lower mass fraction ofwater-solubl e carbohydrates istake n into account. Thismean s that thecel l wallsmus t be thinner at higher temperatures. The possibilities for the formation of secondary walls are greater at lower temperatures since total area of cell walls is larger (because stem volume is larger and there are more cells).Thickenin g was also more pronounced at lower temperatures. Surface availability for microbial attack therefore declined when temperatures were lower during period 2.

TheQi ofo r lignin synthesis ishighe r than the Qiofo r the synthesiso f other cell-wall components. The lignin content is therefore higher at higher temperatures but the time lag between accretion of cellulose and hemicellulose and encrustation of lignin will also be smaller. A better synchronized ligninencrustatio n willgiv emor eopportunit y forth eformatio n oflinkage san d willtherefor e change the nature of the hemicellulose/cellulose fraction of the cell wall, especially when surface area of the primary cell wall is large. This structural effect will influence both potential digestibility and rate of cell-wall digestion and will be consistent throughout the growing season.

In an extra in vitro run, an attempt was made to gain more insight into these (partly hypothetical) influences of temperature by estimating potential digesti bility of cell walls and the rate of digestion of potentially digestible cell walls. Husk + shank sampleswer eno tinvestigated ,sinc etemperatur edurin gperio d2

70 Meded. Landbouwhogeschool Wageningen 83-3 (1983) o =30/24 • = 24/18 x = 18/12

—= whole crop =stove r

20 30 40 50 60 70 80 90 100 110 120 130 time in days after emergence

FIG. 5. Effect of temperature during period 2 on cell-wall digestibility (DCWc) of the whole plant and of the stover.

Dcwc of stover <%) 95r * »pre-treatment sampling 1: 0 00/24 y =-0135x » 95.66 (r 2 =0 986) 2 90 2: .=24/18 y= -0124x.964 7 (r .= 0983 ) 3: x=18/12 y= -0119x * 96.69 (r2 =0985) 4:Total(n=22) y=- 0125x« 95.91 (r2=0 954) 85

60-

55 40 60 80 100 120 140 160 180 200 220 240 260 280 300 plant height (cm) FIG. 6. Relation between plant height and cell-wall digestibility of the stover in Experiment 1.

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 71 did not affect their Dcwc. The data from ear samples will not be presented: theircell-wal l digestion showed aconsiderabl e time lag,bu t wasver yrapi d after 6hour s ofincubation , so that accurate estimation ofdigestio n ratewa simpossi ble. Stover samples taken about 2 weeks after temperature differentiation, at 50%£ flowering and 4an d 8week safte r anthesiswer eanalyse d and gaveworka bleresults .Fig .7 illustrate sth emetho d withstove rsampling sa t 50%( J flowering and gives the relation between rate of cell-wall digestion and sampling date.

true digestibility "cwc 7A 7B 100 100

80 80

60 60

0L 0 6 12 24 48 96 O 6 12 24 48 96 incubation time (h) incubation time (h)

• ) * 100 rate of digestion ("/*.h" 1) C/J 7C 7D

65 "V N. ,30/24 10 124/18

18/12

0 6 12 24 48 -56 -28 0 28 56 incubation time (h) ttmetdays after 50% 6* flowering)

FIG. 7. Illustration of method for estimating digestion rate of potentially digestible cell walls. 7A.Tru edigestibilit y in relation to incubation time;residue scontai n indigestiblecel lwall san d poten tially digestible cell walls that have not yet been digested. 7B. Digestibility of cell walls as a function of incubation time; Dcwca t 96 h is assumed to equal WC potential Dcwc. 1 - p at at, u indicates the fraction of the cell wallstha t have not been digested at time t, although they are digestible within 96h of incubation. 7C. Semilogplo t of fraction of potentially digestible cell walls that remained undigested versus incu bation time;th eregressio ncoefficien t isa n estimator ofth e rateo fdigestio n ofpotentiall y digestible cellwalls . 7D. Rates ofcell-wal l digestion plotted against samplingdat e(cf . Table6) .

72 Meded. Landbouwhogeschool Wageningen83-3 (1983) Table6 show sth epotentia l digestibilitieso fcel lwalls ,th e semilogregressio n equations and the correlation coefficients (all significant at P < 0.01;n = 5).

Potential digestibilitydepende d on content of lignin and silica but even more on thestructura lorganizatio n ofth ecell-wal lcomponents . Differences inpoten tial digestibility of cell walls achieved their maximum at 50% S flowering and decreased during the first weeks of the post-anthesis period. Although for final samplings only slight differences were recorded after 48 h of incubation (Table 5),th epotentia ldigestibilit yo fcel lwall sstil ldiffere d considerablybetwee n tem perature regimes.O n the other hand, stover samples from early sampling dates showed smaller differences in Dcwc (96 h) than in Dcwc (48 h).Thi s discrepancy iscause d by differences in rate of cell-wall digestion (Table6) . These digestion rates have been plotted against sampling date in Fig. 7D. Theeffec t oftemperatur e on lignification and structural organization apparent ly accelerated the maturity of the cell walls before flowering, which agrees with the above-described hypothesis. After anthesis, the content of cell solubles (i.e. 100-cwc%)increase dconsiderabl yi ntreatmen t 30/24,becaus eea rdevelopmen t wasinhibited .Thes eincreasin gcontent so fcel lsoluble scoul d havecompensate d for the normal declinei n the rate ofcell-wal l digestion. SMITHe t al. (1971, 1972) reportedver ysignifican t positivecorrelation sbetwee nth erat eo fcell-wal ldiges tion and content of cellsolubles .

TABLE 6. Potential cell-wall digestibilities (Dcwc after 96 h of incubation), and the regression equations and correlation coefficients (r) of the relation between (1 l-'cwc- tj ) x 100% and time Dcwc, 96 h of incubation, for stover samples taken on four sampling dates.

Temperature regime Dcwcafte r 96h o f Regression equation during period 2 C/C) incubation (%)

2 weeksafter temperature differentiation 30/24 76.1 y =-0.050 x + 4.544 -0.99 24/18 81.7 y = -0.062 x + 4.489 -0.98 18/12 84.5 y = -0.064x + 4.431 -0.96 at 50%<$ flowering 30/24 57.3 y =-0.050 x + 4.604 -1.00') 24/18 70.0 y =-0.053x + 4.643 -1.00 18/12 72.6 y = -0.058x +4.583 -1.00

4 weeksafter 50%<$ flowering 30/24 63.7 y = -0.050x +4.580 -1.00 24/18 65.3 y = -0.049x + 4.569 -1.00 18/12 69.6 y = -0.044x + 4.502 -0.99

8 weeksafter 50% $ flowering 30/24 63.2 y = -0.051 x + 4.591 -0.99 24/18 64.7 y = -0.041 x + 4.520 -0.98 18/12 70.0 y = -0.039x + 4.495 -0.99

') n = 4, since the potential Dcwc had already been reached after 48h of incubation.

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 73 Rates of digestion decreased for both other temperature treatments because ofchange si nth echemica l composition ofth ecel lwall safte r anthesi s(cf . Tables 4 and 5) and because of a reduction of the surface availability. These effects reduced therat eo fcell-wal ldigestio n tosuc ha nexten ttha t they overcompensated the still existing differences in physical structure. The method illustrated in Fig. 7clearl y reveals the effect of temperature on digestibility as caused by its effect on the organization of the cell-wall compo nents.

The dilution of cell walls with completely digestible organic matter was most efficient intreatmen t 24/18an d 30/24(Tabl e 5:A cwc%).Th erat eo fth edilutio n process wasdetermine d by thecell-wal l content present at anthesis,th e cell-wall production after anthesis and the production rate of cell contents.

Résumé:During period 2, themain processes that were dependenton temperature wereleaf appearance, stem growth andreproductive development.High tempera turesduring period 2 led to loweramounts of dry matter at 50% <$flowering and a lowerproductivity thereafter. Temperature affectedfinal digestibility by its ef fects oncell-wall content, cell-wall digestibility and amounts of cell wall. Its effects,, however, were limited, since cell-wall production after anthesis was reduced by higher temperatures before anthesis and since most of the difference incell-wall digestibilitypresent at anthesis subsequently disappeared. Considerabledifferences in potential digestibility of cell wallsremained atfinal samplings, but the rate of digestionof stover-cell walls was ultimately greater for thecrop that received higher temperaturesduring period 2. Thiseffect wasprobably partly causedby thehigh content of cellsolubles in thestover that resultedfrom poor eardevelopment.

Period3. Data andinferences from literature andunpublished research The period from anthesis to grain set is a very critical period in the develop ment of the maize crop. Stresses such as drought, low light intensity and heat produce very detrimental effects on ear development during this period. Al though inWester n Europehig h temperatures aregenerall yaccompanie d byhig h light intensity and high evaporation, in this discussion only temperature will be considered. High temperatures during pollination result in poor grain set because anther emergence is curtailed and pollen viability reduced (HERRERO and JOHNSON, 1980).Accordin g to these authors pollen viability remains almost unaffected up to 32°C. JOVANOVICan d JOVANOVIC(1963 )foun d that the success ofpollinatio n stronglydepende d on timeo fda yassociate d with the concomitant temperature and the concomitant atmospheric humidity. Poorest grain set was obtained by pollination at 1 p.m. when the temperature was 26.4°C and air humidity was 37%.Extremel y high temperatures during silking are rare in The Netherlands. However, it is known that both pollen shed and silk extrusion may be inhibited by a succession of cool days (F. DE WOLFF, 1982; personal communication). Tolerance ofcoo l weather during flowering showsgrea t genotypic variability.

74 Meded. LandbouwhogeschoolWageningen 83-3 (1983) The effects of successful pollination on dry-matter production and Dom are illustrated in Fig. 8. In this example both yield and quality are greatly reduced by partial sterility of the ear. Smaller effects of sterility, however, have also been reported (e.g. BUNTING, 1975; DEINUM and KNOPPERS, 1979). Fig. 4 illustrates that at least 43% of the cell-wall yield was attained after 50% anthesis. Much of this increase in cell-wall yield will occur during period

3. Thus during this stage too, an increase in temperature will reduce Dom by increasing the cell-wall content and reducing the cell-wall digestibility. The quantity of cell-wall constituents produced during period 4 will be little affected by the temperatures prevailing in period 3, unless adverse temperature reduces fertilization. In that case, cell-wall production during period 4 will be promoted (see above).

Period 4. Experiments 2 and 3

Developmental stage at climatic shift and climatic conditions In Fig. 9 the physiological stages at which climatic differentiations took place are illustrated for all three hybrids in Experiments 2 and 3. Ula was treated at a later stage of kernel development than Nicco and Dara. Rapid dry-matter accumulation in the kernels normally starts 12 to 18 days after silk emergence (JOHNSON and TANNER, 1972; DAYNARD and KANNENBERG, 1976; TOLLENAAR and DAYNARD, 1978), although cell division of the endosperm is not completed until 28 days after pollination (INGLE et al., 1965). Tip kernels

dry-matter yield (g/pl) Dom™

240

200 77 whole-crop yield-v . 160

75 120 73

- 71 40 - 69

40 60 80 100 °/ofertilize d grains FIG. 8. Ear yield, whole-crop yield and whole-plant digestibility asaffecte d byartificiall y prevented pollination. Plant density: 8.9m"2. (STRUIK, 1980; unpublished data).

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 75 TABLE 7. Length of the top ear (in cm) ± standard error of the mean, as affected by light intensity and temperature during period 4 (hybrid Nicco, 1980;mean s of 80plants) .

Day/night Lengtho fto pea r Length ofto pea r Meanlengt h temperatures (°C) at 100%rel .ligh t at33 %rel .ligh t ofto pea r intensity intensity

30/24 14.9 ±0.31 13.9 ±0.29 14.4 24/18 15.3 ±0.28 13.8 ±0.34 14.6 18/12 16.1 ±0.23 15.2 ±0.28 15.7

Mean length of top ear 15.4 14.3 treatments 18/12 and 24/18 were greater than differences between treatments 24/18 and 30/24. The shading treatment showed a prompt and strong effect on thenumbe r of active kernels at all temperatures; thefinal difference s between shaded and unshaded treatments were temperature-independent for Ula and Nicco, but not for Dara, where the shading effect was more pronounced at higher temperatures.

Leaf-area duration after grain set was temperature-dependent and was also affected byligh tintensity . Anexampl eo fth eleaf-senescenc e pattern ispresente d in Fig. 12. The pattern, however, varied between genotypes. The differences between light treatments in the number of green leaves per plant increased as temperatures fell.Thi swa stru efo r allgenotypes ,bu t thedegre eo fth e difference between the number of green leaves at final sampling for the shaded crop and the number of green leaves at final sampling for the unshaded crop depended on genotype. The difference was always large and positive for Ula. The differ ences were smaller, but still positive or zero for Nicco (Fig. 12). For Dara the difference declined from + 3.6 leaves at 18/12 to - 2.8 leaves at 30/24. These differences in type of reaction may beconnecte d with the physiological stage at which shading was applied (Fig. 9), or with genotypic background.

Dry-matter production Ear. The final ear yields of unshaded crops were always highest in treatment 18/12, slightly lower in treatment 24/18 and much lower in treatment 30/24. For Ula and Dara this was also true for shaded crops; for hybrid Nicco a very low ear yield was found for the shaded crop in treatment 24/18. The duration of grain filling increased as temperature fell; grain-filling rate increased as tem peratures rose, but not enough to compensate fully for the decrease in duration offilling. Th e growth rates ofear si n Nicco are presented inTabl e 8.Ea r growth can also be derived from Fig. 13. The penultimate harvest of the shaded crop intreatmen t 24/18gav ea n atypical high earyield ,tha t arosebecaus eth e average number ofaborte d kernelswa slo wi n that sample (seeals o Fig. 11).A t arelativ e light intensity of 100%, rate of ear growth was higher in treatment 30/24 than in treatments 24/18 and 18/12. For shaded crops, however, the growth rate was

78 Meded. Landbouwhogeschool Wageningen 83-3 (J983) K -400 number of active kernels 300

200 o o unshaded

100 shaded

10 20 30 40 50 60 time (days) >. «400 number of active kernels 24/18 300

200 unshaded

100 shaded

10 20 30 40 50 60 time (days) number of active kernels 18/12 300

200

100 shaded

10 20 30 40 50 60 time (days) FIG. 11. Decline in the number of active kernels at three temperatures and two light treatments during period 4 (hybrid Nicco, 1980;mean s of 20plants) . Day 0 = date of initiation of treatment. highesti ntreatmen t 18/12.Th ehighe r thetemperature , thegreate r thenegativ e effect of shading on the growth rate of earswa s(cf . the lower the temperature thegreate r thepositiv eeffec t of shading on leaf-area duration; seeabove) .Th e effects ofshadin g onduratio n ofea rfilling wer einconsisten t inthes etrials .

Thefinal shellin gpercentage s ofth eto pea rwer enegativel y affected bytem perature but unaffected byligh t intensity in Ula and Dara; inNicc on o signifi cant or consistent differences were found.

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 79 number of green leaves per plant 18/12 24/18 30/24 13 - unshaded o 12 shaded 11 10 *-^ 9 8 7 6 5 4 3 2 1

10 20 30 40 50 60 70 time(days) FIG. 12. Leaf senescence at three temperatures and two light intensities during period 4. Hybrid Nicco. Day 0 = date of initiation of treatment.

Inal lhybrids ,ea ryield swer eclosel yrelate dt oleaf-area duration duringperi od 4i f data from the two light treatments were pooled separately.

Stover and husk + shank. A large portion of the dry matter present in the earsi sproduce d after flowering.Thi sportio n mayb e 100%i nregion swit h abun dantirradianc ean d conditionstha t favour a longduratio n oflea fare a (ALLISON

TABLE 8. Correlation coefficients (r) and regression coefficients (b) of the linear relation between ear yield and timefo r Nicco,grow n under threetemperatur e regimesan d twoligh tintensitie s during period 4.

Day/night Relativeligh t n 90%interva lo f temperatures ( C) intensity confidence of (%) b(g.day_1)

30/24 100 5 0.99** 2.30 ± 0.42 33 6>) 0.99** 1.06 ±0.13

24/18 100 6 0.99** 1.91 ±0.34 33 6 0.92** 0.85 ± 0.38

18/12 100 6 0.99** 1.82 ±0.29 33 6 0.99** 1.16 + 0.17

') This treatment did not reach a constant level of ear yield. ** = significant at P < 0.01.

80 Meded. Landbouwhogeschool Wageningen 83-3 (1983) and WATSON, 1966). In many other regions a significant reduction in weight of stem, leaves, husks and shanks has been recorded (DAYNARD et al., 1969; GENTER et al., 1970; DEINUM and DIRVEN, 1971 ; ADELANA and MILBOURN, 1972; BUNTING, 1976; AERTS et al., 1978; PHIPPS and WELLER, 1979; DEINUM and KNOPPERS, 1979; LUCAS, 1981; STRUIK, 1982b). This reduction is caused by re distribution of soluble carbohydrates, minerals and nitrogenous compounds (HAY et al., 1953; HANWAY, 1963; DAYNARD et al., 1969; GENTER et al., 1970; BEAUCHAMP et al., 1976; BELOW et al., 1981; STRUIK, 1982b). The intensity of redistribution depends on the difference between the rate of ear growth and that of crop growth. Since high temperature stimulates kernel growth more than crop growth, redistribution will be more intensive at higher temperatures, pro viding the light intensity is the same. In addition, low light intensity will dramati cally increase the necessity for redistribution, unless complete ear abortion occurs. Table 9 shows the final increases in dry matter, non-structural carbohydrate (CbHttOf,) and protein (N x 6.25) in non-ear parts at the 6 combinations of temperature and light intensity in Experiments 2 and 3. The rates of decline in component yield differed even more than final absolute values. Kernel abor tion, induced by high temperatures or low light intensity, slowed down the re distribution of nitrogenous compounds (Table 9) and also of phosphorus (data not presented). Although the accumulation of N and P in the above-ground parts of the plant was reduced by shading (data not presented), the need for these minerals in the ear was reduced even more. If climatic conditions enable the plant to continue its ear growth successfully, N and P depletion in the stover occurs. This depletion may accelerate the senescence of the leaves under normal conditions. The Ca content was also estimated. Ca plays a role in cell-wall formation and neutralization of organic acids. It tends to accumulate in the leaves (PAIN, 1978) where the light-dependent and organic-acid producing nitrate reduction

TABLE 9. Constituent yield in non-ear parts at final sampling minus constituent yield in non-ear parts at the climatic shift in g per plant for six climatic regimes during period 4 (means of three hybrids).

Temperature 30/24 24/18 18/12 Mean regime( UC)

unshaded - 7.1 - 4.9 + 3.0 - 3.0 dry matter shaded -22.1 -20.4 -14.1 -18.8 Mean -14.6 -12.7 - 5.6 non-structural unshaded - 5.6 - 1.3 + 0.7 - 2.1 carbohydrates shaded -11.4 - 9.9 - 6.4 - 9.2 Mean - 8.5 - 5.6 - 2.8

unshaded - 3.8 - 4.5 - 5.0 - 4.5 protein shaded - 3.6 - 3.5 - 3.8 - 3.6 Mean - 3.7 - 4.0 - 4.4

Meded. Landbouwhogeschool Wageningen 83-3 (1983) UNSHADED

gdm/pl 30/24 gdm/pl 24/18 gdm/pl 18/12

180 180 180

0 140 - os£^~ 140 1401-

o' 1 (ear) 100 100 100 \

»NibonkJ 60 60 60 k

3 (stover) 20 20 20 h

i i i i 1 j L _L i L J_ • l I I I L 0 10 20 30 40 0 10 20 30 40 50 0 10 20 30 40 50 60 time (days) time (days) time (days)

SHADED gdm/p gdm/pl 18/12

180 h 180

140 140 V o^o -, o—o 100

"2 60 h

20[• _l__l I J- _L J 0 10 20 30 40 0 10 20 30 40 50 0 10 20 30 40 50 60 time (days) time (days) time (days) FIG. 13. Dry-matter production and distribution for all treatments in Experiment 3.Da y 0 = date of initiation of treatment.

82 Meded. Landbouwhogeschool Wageningen 83-3 (1983) occurs. The accumulation of Ca in the above-ground parts of the plant was reduced by shading during period 4, but the amounts of Ca in ears were very lowan d itwa sno t remobilized inth eplant .C adoe sno tpla ya rol ei nth eredistri bution pattern. Kernel abortion also decreases the amount of carbohydrates that has to be translocated from thevegetativ epart st oth eears .Th eredistributio n ofcarbohy drates,however , wasstil l intensive. Much of the fraction that wasno t identified asash , cellwall , non-structural carbohydrate orcrud e protein also left thevege tative parts if redistribution of other compounds was intensive.

Wholeplant. As an example, Fig. 13 illustrates the dry-matter production and distribution of Nicco. Although fewer sampling dates were available for Ula and Dara, the general pattern wasessentiall y similar. Since some data were deviant because there were few plants in the samples, curves were drawn using thecell-wal l yield asa standardizin g criterion. Final yieldsincrease d with falling temperature and increasing light intensity. Initially, the production rates of all hybrids in the unshaded treatments tended to increase with rising temperatures. If shaded, however, crop-production rate was highest in treatment 18/12. Low light intensity resulted in a strong reaction during the first part of the grainfilling, bu t dry-matter production ratewa shighe ri nth elate rpar t associat edwit ha decreas ei n rateo fredistribution .Thi si sespeciall yeviden t in treatment 18/12 (Fig. 13) but was also clear in Ula and Dara in treatments 24/18 and 30/24.Thi sphenomeno n ofhabituatio n toa growth-limitin g climaticfacto r dur ing a rather fixed, unplastic stage of the crop isconspicuous . The phenomenon might be explained by the hypothesis presented by STRUIK and DEINUM (1982), who stated that shading promptly curtailed root activity. Reduced root activity might have induced the observed kernel abortion. If abortion occurs early in the grain-filling period, a new balance might be obtained, since partial sterility favours translocation of sugars to the roots.Whe n this new balance is achieved, the plants may function better than expected on the basis of their previous per formance. Data from the root samples of Experiment 3tende d to support this hypothesis, but the difficulties of separating roots from root medium affected the reliability of the data. The linear correlation coefficient between non-struc tural carbohydrate content in the roots and number of active kernels, however, was highly significant (P < 0.01;n = 35).

Quality of the organic matter Fig. 14 illustrates the trend in Dom of the most relevant plant parts in each treatment in Experiment 3.Th e development of the proportion of the most di gestible part (i.e. the ear fraction) is also given. Eardigestibilit yincrease d slightlydurin gearl ystage so fgrai nfilling bu tsubse quently remained constant. The same pattern was found in Experiment 2. This agrees with results obtained by PERRY and COMPTON (1977) and AERTS et al. (1978).Temperatur e did not influence ear digestibility. Continuous shading also barely affected ear digestibility, sinceshellin gpercentag e and thuscell-wal l con-

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 83 b. c *- ao S

o C2 A es u (U *- .S o Ö o 00 > 'S o « NT CM o » C« *- '5* 10 o es •— TD

o £ C u ÎH~ D.-« *0 .S II ^o « _ Ü*°, C\oJ ."S ^ £> oo 'w '""' o 03 -ri 00 c ••6 <" 2 \ oo "Ca —^r - ctf ^ (N

E~ Ios ° "7i «8 ">« oî NT u- .H O ~ (M E O O ~ G u in S c ' D.'- » Ä o a> W) ^ i>> s* o Qg

• do o 0 „ y 1/ \ OJ I o •

it 4' Ä \ -o

o -s

84 Meded.Landbouwhogeschool Wageningen 83-3 (1983) ^om,app . wholeplan t 30/24 C/o) 80

o10 0 °/oligh t

O 5 10 15 20 25 30 35 40 45 50 55 60 time (days)

"om.app. whole plant 24/18 (•/.) 80 100"«ligh t

O 5 10 15 20 25 30 35 40 45 50 55 60 time (days)

Mom, app. wholeplan t 18/12 (%) 80 h 78 V 100°/«. light

76 i 33°/o light 74 72 i—1_ O 5 10 15 20 25 30 35 40 45 50 55 60 time (days) FIG. 15.Apparen t digestibility of thewhol e plant plotted against timedurin g period 4,fo r sixtempe rature/light combinations. Day 0 = date of initiation of treatment. tent were almost unaffected (see above). This agrees with field data obtained by STRUIK and DEINUM(1982) .Shading ,however , considerably reduced the pro portion of organic matter in the ears. The digestibility of husk + shank decreased during period 4. This decline was more rapid at higher temperatures but only slightly affected by radiation. In treatment 30/24 no consistent differences between shaded and unshaded plants could be identified. Inbot h lowertemperatur e regimes,lo wligh tintensit y initially produced lower Dom, but finally amuc h higher Dom wasfound . Alsoi n Experiment 2th edigesti bility of husk + shank in shaded crops was better: a prolonged increase in the

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 85 cell-wallconten t of thehusk san d shanks ofunshade d cropscause d thisreversal . (Thisprolonge d increasei ncell-wal lconten t probably occurred because redistri bution from thehusk s to the kernelswa snecessar y for a longer period). Stover digestibility declined during period 4 and this decline was more rapid at higher temperature and at lower light intensity. In Experiment 2som e treat ments originally showed aconsiderabl e increase in the digestibility of the stover before the decline set in. Otherwise the pattern was similar. Trends and differ ences in digestibility agree with the redistribution phenomena. Thus only the digestibility of vegetative parts and the proportion of ear parts were sensitive to temperature and light intensity during period 4.

These two effects of temperature and light intensity resulted in the patterns of whole-plant digestibility shown in Fig. 15. At 100% light, the increase in whole-plant digestibility continued for longer at lower temperatures, giving higher final digestibilities (Table 10). Similarly, Dom decreased less in shaded crops at lower temperatures. At higher temperatures, the small decline in Dcwc could not becompensate d for bya concomitan t decreasei nth ecell-wal l content. InExperiment s2 an d 3,ligh tintensit y duringgrai nfilling wa srelativel y constant and fairly high. In practice in The Netherlands, diurnal amounts of light drop sharply during grain filling, so that a standard crop merges from the conditions experienced by the unshaded crops in these experiments to those experienced by the shaded crops. The pattern of digestibility in the unshaded crops in Experi ments 2an d 3i s similar to the pattern found in Experiment 1,durin g the same period.

Differences in cell-wall digestibility had little effect on organic-matter digesti bility. Plants had reached their maximum height before the climate shift. As Fig. 6shows , an important differentiation in stover Dcwc isunlikel y beyond that stage. The Dcwc of husk + shank was not affected by light intensity either. Its rate of decline in Dcwc was affected by temperature (as was plant development) but the final extent of the Dcwc decline (thus the Dcwc at the same physiological stage) was not. Cell-wall production wasaffecte d both bytemperatur e and lightintensit y and in the same direction as was dry-matter production. This limitation of cell-wall formation was very evident in husks + shanks and in ears, but was only small in the stover. In the husk + shank and in the ear fraction, the yield of cell walls from shaded plants was only approximately 70%o f that of the unshaded plants, and plants in treatment 30/24 yielded about 30% fewer cell walls than plants in treatment 18/12.Thes e reductions in the amounts of cell wall resulted in smaller effects of the treatments on the quality ofear s and of husks + shanks than on thequalit y ofstover . Themos t relevantfacto r indeterminin g thedigesti bility of the vegetative parts was the extent of assimilate redistribution. Thus in ears, dry-matter accumulation and cell-wall formation were equally affected by climatic conditions. In stover, the amounts of cell wall and their quality werebarel y affected, sotha t thenecessit y for redistribution wasth e over-

86 Meded. Landbouwhogeschool Wageningen 83-3 (1983) ridingfacto r instove rquality . Inth ehus k + shank fraction, cell-wall formation, the rate at which the cell-wall digestibility declined, and the extent and rate of translocation of metabolites all affected quality. Since shading affected cell-wall formation in the plant organs with the best cell-wall quality, a small negative effect of shading on cell-wall digestibility of the whole plant must be expected. Table 10confirm s this supposition but also indicates that the greatest differences in cell-wall quality were found in Nicco. This hybrid showed a strong decline in Dcwc during the final part of the grain- filling period for shaded crops.Befor e thisproces sstarted , theeffect s of shading on Dcwc were certainly not greater than in Ula and Dara. It is unlikely that Nicco's greater sensitivity to shading as expressed in decreasing digestibility is genetically determined. Table 10als o presents the cell-wall contents of the whole crop at final sam pling. In Experiments 2 and 3 digestibility was mainly related to this quality criterion, as is illustrated in Fig. 16 in which the whole-crop digestibility on each sampling date is plotted against the cell-wall content on the basis of the organic matter. Physiological age, temperature and light intensity all affected quality predominantly by their effects on cell-wall content. The data from the final samplings are underlined; in Ula and Dara they were equally distributed above and below the regression line, but in Nicco they were all below that line. Although also significant in both experiments, the linear correlation coefficient between Dcwc and Dom was much lower, especially in Experiment 2.

TABLE 10. Quality parameters of all treatments in Experiments 2 and 3 at final sampling (whole plant).

Day/night 30/24 24/18 18/12 temperatures (°C) Light treatment unshaded s »haded unshaded >haded unshaded shaded

Ula 77.3 74.8 78.5 76.1 78.8 76.0 Dara 76.3 74.0 78.7 75.4 77.3 76.4 Dom (%) Nicco 76.9 73.3 77.5 72.8 78.5 75.6 Mean 76.8 74.0 78.2 74.8 78.2 76.0 75.4 76.5 77.1

Ula 68.3 6A.1 66.2 66.4 68.4 67.4 Dara 65.4 66.4 68.1 67.4 68.0 66.3 Dcwc (/o) Nicco 73.6 69.7 72.2 66.2 76.1 70.9 Mean 69.1 66.9 68.8 66.7 70.8 68.2 68.0 67.8 69.5

Ula 39.8 46.4 33.5 41.1 34.8 39.4 Dara 42.3 47.3 34.8 44.3 36.4 40.2 cwc°/ (%) 0 Nicco 43.6 51.8 38.6 47.8 37.9 46.0 Mean 41.9 48.5 35.6 44.4 36.4 41.9 45.2 40.0 39.1

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 87 unshaded shaded

pre-treatment sampling

r»0.933 (n=26) y= -0.35 1x * 90.680

701-

34 36 38 40 42 44 46 48 50 52 54 cwc "/<.(%) Dom C*.) 80 -

78 a"-<£*D ° 76

r=0868 (n= 35 ) 74 y=-0335x.91.591

34 36 38 40 42 44 46 48 50 52 54 cwc 7„(%) FIG. 16. Relation between cell-wall content of the organic matter (cwc%) of the whole plant and apparent digestibility of the organic matter (Dom) of the whole plant, in Experiment 2 (A) and Experiment 3(B) . Data from final samplings are underlined.

Résumé: Increasedtemperatures duringperiod 4 acceleratedgrain filling, there distributionof certain metabolites, Dcwc declineand plant senescence, butcurtailed the duration of grainfilling and of leaf area,final earyield, ear size and kernel activity, whole-plant yield,cell-wall yield and crop quality. In addition, lowlight intensity duringperiod 4stimulated thesenescence of the earand theredistribution of metabolites to theear, and may havestimulated cell- wallmaturation tosome extent. Poorlight conditionsreduced cell-wall formation andsometimes sloweddown leaf senescence. Both temperature and light mainly affected quality by means of their effects on theproportion of ear in thewhole plant andthe cell-wall content of the vegetative parts, resultingin astrong correlation betweencrop digestibility and cell-wall con tent of the whole crop.

88 Meded.Landbouwhogeschool Wageningen 83-3 (1983) TABLE 11. Summary of effects of temperature during different stages of development on final dry- matter and cell-wall production, and on final quality parameters. Light intensity is assumed to be constant.

Dry-matter Cell-wall Cell-wall Cell-wall Organic-matter production production content digestibility digestibility

Period 1 + + + + ± or + ± ±or- Period 2 ± Period 3 -or + + Period 4 — + + or-

Entire growing season — +

-I- (+ ) indicates that a rise in temperature produces a (strong) positive effect. ± indicates that inconsistent or small effects are expected. — (— ) indicates that a rise in temperature produces a (strong) negative effect.

Comparisons withfield data Table 11summarize s the findings of the above-described phytotron and desk research. It also presents the expected effects of temperature over the entire growingseason .Thes eexpectation sagre ewit hdat a obtained by DEINUM(1976) , although he did not present data on whole-crop quality. In the years 1977, 1978, 1979, 1980 and 1981 the hybrid LG 11 was grown in the field at the same location and following the same cultural practices. De tailed data on temperature, crop development and quality were available, ena bling the validity of the hypothesis to be tested. In Table 12som e relevant data are presented. Thenumbe ro fleave spe rplan t differed significantly overth eyears .Fo rexam ple, in 1977, LG 11 had 1.5 leaves per plant more than in 1979, although the mean air temperature during the pre-tassel initiation period was almost the same. TOLLENAAR and HUNTER (1981), however, found that leaf number was determined during a short period to the tassel initiation. In the data presented in Table 12,th e simplelinea r correlation coefficient between mean air tempera turedurin gth e four days before the6.5-lea fstag ean d thefinal numbe r ofleave s was0.9 9( P < 0.01).Th e regression coefficient was0.2 8leaves/°C ,whic h agrees with the value of 0.2 found by TOLLENAARe t al. (1979).Thi s temperature effect restricts the usefulness of maturity indexing systems that are based on the rela tionship between rate of crop development and temperature or heat unit. The number of leaves, or rather the number of stem internodes, is crucial for final cell-wall yield and final cell-wall content. A significant linear relation ship between number of leaves and cell-wall yield did indeed exist (r = 0.97; n = 4; P < 0.05). However, the cell-wall analysis of the 1978 crop was not available and most probably the cell-wall yield in that cool year was lower than expected on thebasi so f this relation.Thi s supposition issupporte d by thegoo d digestibility compared with the 1977 crop. The low height of the plant given the large number of stem internodes may beconnecte d with this deviation. Cli matic conditions during periods 2, 3 and 4 of the 1978 growing season were

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 89 TABLE 12. Crop descriptions of LG 11, grown at the same location for five years, together with themea n temperatures during different stages of growth for each year.

Year 1977 1978 1979 1980 1981

number of leavespe r plant 15.3 15.7 13.8 14.2 14.9 height of plant (cm) 261 226 214 215 235

dry-matter yield (Mg.ha~ ') 15.4 13.4 12.8 14.1 17.0

cell-wall yield (Mg.ha- ') 7.1 _ 5.2 6.1 7.0 cell-wall content (%o f organic matter) 49.3 - 42.2 44.8 42.4 digestibility (% of organic matter) 71.5 74.1') 74.8 73.6 74.3 cell-walldigestibilit y(% )afte r standardization of the true digestibility 61 - 61 61 61

Ti (°C) 12.1 12.9 12.0 11.7 12.5 T,'(°C ) 19.8 20.6 13.8 15.9 17.6 T2 (°C) 16.2 14.7 15.3 15.5 15.2 T3 (°Q 16.4 15.5 16.0 17.8 19.0 T4(°C) 13.0 12.8 13.7 14.5 14.9

Tm (°C) 14.1 13.8 14.0 14.4 14.8

Ti = mean temperature during period 1. T[ = mean temperature during 4 days prior to the 6.5-leaf stage. T2 = mean temperature during period 2. T3 = mean temperature during period 3. T4 = mean temperature during period 4. Tm = mean temperature during the entire growing season. ') Ear samples wereno t analysed in this year. Digestibility wascalculate d assuming that thedigesti bility and ash content of the ear were equal to the means of the years 1977, 1979, 1980an d 1981.

clearly unfavourable for dry-matter production and cell-wall formation. Thus, the annual variation incell-wal l yieldca n largely beexplaine d by varia tion in air temperature just prior to the 6.5-leaf stage. Extreme climatic condi tions during the post-tassel initiation period, however, may cause deviations from this general pattern. The cell-wall content also depends on the dilution of the cell walls with non structural carbohydrates after silking. During the autumn in The Netherlands, prevailing temperatures are mostly below the optimum for dry-matter produc tion. Therefore, an increase in temperature during period 4 will mostly benefit dry-matter production and thus crop quality. This means that the 1981 crop diluted its amounts of cell wall much more than the 1977 crop, although the cell-wall yields were approximately the same. The light intensity also plays an important roledurin g thisstag ean d isclosel ycorrelate d with temperature under uncontrolled conditions. Mean air temperatures during periods 2 and 3varie d considerably between years, but the mean temperatures during the period from 6.5-leaf stage until the grain-filling period ranged between 14.8-16.2°C only. This range is much too small to induce differences in cell-wall digestibility. The Dcwc of all crops

90 Meded. Landbouwhogeschool Wageningen 83-3 (1983) for which thecell-wal lanalysi swa savailable ,wa sth e same,resultin gi na signifi cant linearcorrelatio n betweencell-wal lconten t and digestibility oforgani c mat ter (r = - 0.99; n = 4; P < 0.01). High temperatures during grain filling make the crop suitable for ensiling at an earlier date or cause higher dry-matter contents at harvest if the harvest date is not advanced. This aspect of suitability for ensiling has not been taken into account in this analysis, but certainly plays an important role in areas at the limits of the range of maize.

The practical implications of the results obtained will be discussed in the au thor's doctoral thesis.

SUMMARY

The effects of temperature on the growth, development, dry-matter produc tion, dry-matter distribution and digestibility of forage maize were analysed. Higher temperatures during the period before tassel initiation stimulated whole-crop yield without affecting itsquality . During thisperiod , however, tem perature may affect the number of stem internodes and thus the plant's ability to form cell walls. High temperatures during early growth may therefore reduce crop quality, especially when the digestibility of cell walls is poor. Higher temperatures during theperiod'from tassel initiation to anthesis greatl y accelerates plant development, without affecting leaf number. Stem diameter decreased as temperature rose but the final plant height in the various tempera ture treatments was similar. The interval between anthesis and silking was dra matically lengthened byhig h temperatures during thisperiod . Initially, dry-mat ter production was more rapid at higher temperatures, but total dry matter at anthesis and productivity after anthesis decreased as temperatures xose. The digestibility of organic matter and of cell walls before anthesis declined more rapidlya thighe r temperatures,becaus etemperatur e affected therat eo fdevelop ment, the cell-wall content, the encrustation of lignin and of silica and other physical/chemical processes.Th e latter wereascertaine d byestimatin g potential cell-wall digestibility and the rate ofdigestio n ofpotentiall y digestible cellwalls . Differences disappeared during thepost-anthesi s period, during which the tem perature was the same for all treatments in this experiment. The temperature during flowering may affect production and quality by its influence on anther emergence, pollen viability, silk emergence and grain set. In addition, temperature may affect theintensit y of theongoin gcell-wal l forma tion and the quality of the cell walls. High temperatures duringgrain fill not only accelerated grain filling but also leaf senescence: they also reduced kernel viability, the duration of grain filling, and final plant yield. Crop quality was affected because temperature influenced the proportion of ear in the whole plant and the cell-wall content of the stover. Low light during this period influenced crop quality in the same way as high

Meded.Landbouwhogeschool Wageningen 83-3 (1983) 91 temperature. Leaf senescence, however, was sometimes retarded by shading. When these results were compared with field data itappeare d that in practice it ismainl y the temperature just prior totasse l initiation that is critical for crop quality.

ACKNOWLEDGMENTS

I thank MrsL . M.va n Ravenswaaij and MrsT . de Vent forthei r sharei n handling the experiments and collecting the data. Thanks aredu et oMr s E. van Heusden, MrsJ .G .M . Miechels, MrsI .A . M. Reurink and MrsC . de Wit for skilful chemical analysis. I am very indebted toProf . DrJ . Bruinsma, DrI r B. Deinum, Prof. Ir J. G. P.Dirven , Prof. DrI rA .J . H.va n Es,Prof . Ir M. L.' t Hart andProf . Ir L. J.P .Kuper s for their valuable andconstructiv e criticism. I gratefully acknowledge the 'Stichting Nederlands Graan-Centrum' for a grant permitting the employment ofa full-time assistant.

REFERENCES

ADELANA, B. O. and G.M . MILBOURN: 1972. The growth ofmaize..II . Dry-matter partition in three maize hybrids. J.agric . Sei., Camb., 78: 73-78. AERTS, J. V., B.G . COTTYN, D. L. DE BRABANDER, CH.V . BOUCQUÉ and F. X. BUYSSE: 1978. Digesti bility and feeding value of maize. Proc. European Maize Meeting, Louvain-La-Neuve (Belgium), (ed.) J.-F. LEDENT, pp. 106-128. AKIN, D.an d D. BURDICK: 1981. Relationships ofdifferen t histochemical types of lignified cell walls to forage digestibility. Crop Sei., 21: 577-581. ALLISON, J.C .S .an dT . B. DAYNARD: 1979. Effect ofa change intim e offlowering , inducedb y altering photoperiod ortemperatur e on attributes related to yield in maize. Crop Sei., 19: 1-4. ALLISON, J.C .S .an dD .J . WATSON: 1966. Theproductio n anddistributio n of dry matter in maize after flowering. Ann. Bot.N.S. , 30: 365-381. ANDRIEU, J.: 1976. Factors influencing thecompositio n and nutritive value of ensiled whole-crop maize. Animal Feed Science andTechnology , 1: 381-392. BAILEY, R. W., J. A. MONRO, S. E. PICKMERE and A. CHESSON: 1976. Herbage hemicellulose and its digestion byth e ruminant. In: Carbohydrate research inplant s and animals. Misc. Papers nr. 12, Agric. Univ. Wageningen, pp. 1-15. BEAUCHAMP, E. G., L. W. KANNENBERG and R. B. HUNTER: 1976. Nitrogen accumulation and trans location in corn genotypes following silking. Agron. J., 68: 418-422. BELOW, F. E., L. E. CHRISTENSEN, A. J. REED and R. H. HAGEMAN: 1981. Availability of reduced N andcarbohydrate s forea rdevelopmen t of maize. Plant Physiol., 68: 1186-1190. BLACKLOW, W. M.: 1972a. Mathematical description of the influence oftemperatur e and seed quali ty on imbibition by seeds ofcor n (Zea mays L.). Crop Sei., 12: 643-646. BLACKLOW, W.M. : 1972b. Influence of temperature on germination andelongatio n of the radicle and shoot ofcor n (Zea mays L.). Crop Sei., 12: 647-650. BLONDON, F.an dA . GALLAIS: 1976. Influence del atempérature , del avaleu r de l'éclairement et de la photopériode sur ledéveloppemen t floral dequatr e génotypes demaïs . Ann. Amélior. Plantes, 26: 195-213. BREUER, C. M., R. B. HUNTER and L. W. KANNENBERG: 1976. Effects of 10- and 20-hour photoperiod treatments at2 0an d 30C o nrat e ofdevelopmen t ofa single-cross maize (Zea mays) hybrid. Can. J.Plan t Sei.. 56: 795-798.

92 Meded. Landbouwhogeschool Wageningen 83-3 (1983) BROUWER, R., A. KLEINENDORST and J. TH. LOCHER: 1973. Growth responses of maize plants to temperature. In: Plant response toclimati c factors. Proc. Uppsala Symp., 1970. UNESCO, Paris, pp. 169-174. BUNTING, E. S.: 1975. Thequestio n of grain content and forage quality in maize: comparisons be tween isogenic fertile and sterile plants. J. agric. Sei., Camb., 85: 455-463. BUNTING, E. S.: 1976.Effect s of grain formation on dry matter distribution and forage quality in maize. Expl Agric, 12: 417-428. BUREN, L. L., J. J. MOCK and I. C. ANDERSON: 1974. Morphological and physiological traits in maize associated with tolerance to high plant density. Crop Sei., 14: 426-429. CHESSON, A.: 1982.Degradatio n of plant cell walls by rumen organisms. Livestock Prod. Sei. (in press). CHOWDHURY, S. I. and I. F. WARDLAW: 1978. The effect of temperature on kernel development in cereals. Aust. J. agric. Res., 29: 205-223. COLIGADO, M.C .an dD .M . BROWN: 1975a. A bio-photo-thermal model topredic t tassel-initiation time in corn (Zea mays L.).Agric . Met.,15 : 11-31. COLIGADO, M. C. and D. M. BROWN: 1975b. Response of corn (Zea mays L.) in the pre-tassel initiation period to temperature and photoperiod. Agric. Met.. 14:357-367 . CUMMINGS, D. G. and J. W. DOBSON JR.: 1973. Corn for silage as influenced by hybrid maturity, row spacing, plant population and climate. Agron. J., 65: 240-243. DAYNARD, T. B. and L. W. KANNENBERG: 1976.Relationship s between length of the actual and effective grain filling periods and thegrai n yield of corn. Can.J . Plant Sei., 56: 237-242. DAYNARD, T. B.,J . W. TANNER and D.J . HUME: 1969. Contribution of stalk soluble carbohydrates to grain yield in corn (Zea mays L.). Crop Sei., 9: 831-834. DEINUM. B.: 1974. Structural inhibitors ofqualit y in forage. Proc. Eur. Grassl. Fed.5t hGen . Meet ing, Växtodling, 1973,pp .42-52 . DEINUM, B.: 1976. Effect ofage , leaf number andtemperatur e oncel l wall anddigestibilit y of maize. In: Carbohydrate research inplant s andanimals . Misc. Papers nr. 12, Agric. Univ. Wageningen, pp. 29-41. DEINUM, B.: 1979. Invloed van uitwendige omstandigheden op produktie en celwandsamenstelling van gras. Proc. Symp. 'Ruwe celstof of voedingsvezel?', organized by Contactcommissie Cel- wand en celwandvertering, NRLO, Wageningen, pp. 27-33. DEINUM, B.: 1981. The influence of physical factors onth e nutrient content of forages. Mededelingen Landbouwhogeschool Wageningen 81-5, pp. 1-18. DEINUM, B. and J. G. P. DIRVEN: 1971. Climate, nitrogen and grass. 4. The influence of ageo n chemical composition and in vitro digestibility of maize (Zea mays L.)an d tall fescue (Festuca arundinacea Schreb.). Neth. J. agric. Sei., 19:264-272 . DEINUM, B.an d J. G. P. DIRVEN: 1975. Climate, nitrogen and grass. 6. Comparison of yield and chemical composition of some temperate andtropica l grass species grown at different tempera tures. Neth. J. agric. Sei., 23: 69-82. DEINUM, B.an dJ . G. P. DIRVEN: 1976. Climate, nitrogen and grass. 7. Comparison of production and chemical composition of Brachial ia ruziziensis and Selaria sphacelata grown at different temperatures. Neth. J. agric. Sei., 24: 67-78. DEINUM, B.an dJ . KNOPPERS: 1979.Th e growth of maize in the cool temperate climate ofth e Nether lands: Effect of grain filling on production of dry matter and on chemical composition and nutritive value. Neth. J. agric. Sei., 27: 116-130. DIRVEN, J. G. P. and B. DEINUM: 1977. The effect of temperature on the digestibility of grasses. An analysis. Forage Res., 3:1-17 . DONSELAAR, B. van and A. STEG: 1980. Voederwaardebepaling en voederwaardeberekening van mengvoer voor melkvee. Rapport no.132 , Instituut voor Veevoedings Onderzoek 'Hoorn*,Le lystad, pp.1-12 . DUNCAN, W. G.: 1975. Maize. In: Crop physiology. Some case histories, (ed.) L. T. EVANS, Cam bridge University Press, London, pp. 23-50. DUNCAN, W.G . and J. D. HESKETH: 1968. Net photosynthetic rates, relative leaf growth ratesan d leaf numbers of 22 races of maize grown at eight temperatures. Crop Sei.. 8: 670-674.

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 93 EDMEADES, G. O. andT . B.DAYNARD : 1979.Th e development of plant-to-plant variability in maize at different planting densities. Can. J. Plant Sei., 59: 561-576. FRIEND, D.J . C. and Marion E. POMEROY: 1970. Changes in cell size and number associated with the effects of light intensity and temperature on the leaf morphology of wheat. Can J.Bot. , 48: 85-90. GENTER, C. F., G. D. JONES and M. T. CARTER: 1970. Dry matter accumulation and depletion in leaves, stems, and ears of maturing maize. Agron. J., 62: 535-537. GMELIG MEYLING, H. D.: 1973. Effect of light intensity, temperature and daylength on the rate of leaf appearance of maize. Neth. J. agric. Sei., 21: 68-76. GOERING, H. K. andP .J . VAN SOEST: 1970. Forage fiber analysis; apparatus, reagents, procedures and some applications. USDA Agric. Handbook No. 359. GOODRICH, R. D. and J. C. MEISKE: 1979. Rate and extent of digestion. Aids for explaining some nutritional observations. Proc. 1979 Minnesota Nutrition Conference: 51-64. GROBBELAAR, W. P.: 1963. Responses of young maize plants to root temperatures. Mededelingen Landbouwhogeschool 63-5, Agric. Univ. Wageningen, pp. 1-71. GRZESIAK, S., S. B. ROOD, S. FREYMAN and D. J. MAJOR: 1981. Growth of corn seedlings: Effects of night temperature under optimum soil moisture or under drought conditions. Can. J. Plant Sei., 61: 871-877. HACKER, J. B. and D. J. MINSON: 1981. The digestibility of plant parts. Herbage Abstracts,51 : 459^182. HANWAY, J. J.: 1963. Growth stages of corn (Zea mays L.). Agron. J., 55: 487-492. HARTLEY, R. D.: 1981. Chemical constitution, properties and processing of lignocellulosic wastes in relation to nutritional quality for animals. Agric. Environm., 6: 91-113. HAY, R. E., E. B. EARLY and E. E. DETURK: 1953. Concentration and translocation of nitrogen compounds inth e corn plant (Zea mays) during grain development. Plant Physiol., 28: 606-621. HERRERO, M. P. and R. R. JOHNSON: 1980. High temperature stress and pollen viability of maize. Crop Sei., 20: 796-800. HUNTER, R. B., M. TOLLENAAR and C. M. BREUER: 1977. Effects of photoperiod and temperature on vegetative and reproductive growth of a maize {Zea mays) hybrid. Can.J . Plant Sei., 57: 1127-1133. INGLE, J., D. BEITZ and R. H. HAGEMAN: 1965. Changes in composition during development and maturation of maize seeds. Plant Physiol., 40: 835-839. JOANNING, S.W. ,D . E. JOHNSON andB .P . BARRY: 1981.Nutrien t digestibility depressions in corn silage-corn grain mixtures fed to steers. J. Anim. Sei., 53: 1095-1103. JOHNSON, D. R. and J. W. TANNER: 1972. Calculation of the rate and duration of grain filling in corn (Zea mays L.). Crop Sei., 12: 485-486. JONES, R.J. , B. G. GENGENBACH andV .B . CARDWELL: 1981. Temperature effects oni n vitro kernel development of maize. Crop Sei., 21: 761-766. JOVANOVIC, B. and Z. JOVANOVIC: 1963. The effect of temperature and relative air humidity on corn fertilization. Review of research work at the Faculty of Agriculture, Univ. of Belgrade, Yugoslavia. Year 11 no.355 , pp. 1-11. LUCAS, E. O.: 1981. Remobilization of stem assimilates in maize varieties grown under tropical conditions, Maydica, 26: 287-292. MERTENS, D. R.: 1977. Dietary fiber components: relationship to the rate and extent of ruminai digestion. Federation Proc, 36: 187-192. MERTENS, D. R. and P. J. VAN SOEST: 1972.Estimatio n of the maximum extent of digestion. J. Anim. Sei., 35: 286(Abstr.) . MINSON, D. J.: 1973. Effect of fertilizer nitrogen on digestibility and voluntary intake of Chloris gayana, Digataria decumbens and Pennisetum clandestinum. Austr. J. Exp.Agric . and Anim. Husbandry, 13: 153-157. MINSON, D.J. : 1976. Relation between digestibility andcompositio n of feed. Areview . In: Carbohy drate research in plants and animals. Misc. Papers nr. 12, Agric. Univ. Wageningen, pp. 101-114. MINSON, D.J . andM .N . MCLEOD: 1970. Thedigestibilit y of temperate and tropical grasses. Proc. XL Int.Grassl . Congress, Queensland, Australia, (ed.)M .J . T. NORMAN, pp. 719-722.

94 Meded. Landbouwhogeschool Wageningen 83-3 (1983) MONTGOMERY, F.G. : 1911.Correlatio n studieso fcorn . Nebr. agric. Exp.St n ann. Rep., 24:108-159. NELSON, C.J .an dK .J . TREHARNE: 1973. Temperature adaptation inFestuca arundinacea. Report Welsh Breeding Station for 1973, University College of Wales, Aberystwyth, p. 11. PAIN, B. F.: 1978. Nutritional requirements offorag e maize. In:Forag e maize, (eds) E.S . BUNTING, B. F. PAIN, R. H. PHIPPS, J. M. WILKINSON and R. E. GUNN, Agricultural Research Council, London, pp. 87-116. PERRY, L.J .JR .an dW .A .COMPTON : 1977. Serial measures ofdr y matter accumulation and forage quality ofleaves , stalks andear s ofthre e corn hybrids. Agron. J.,69 : 751-755. PHIPPS, R.H .an dR .F . WELLER: 1979. Thedevelopmen t of plant components and their effects on the composition of fresh and ensiled forage maize. 1.Th e accumulation of dry matter, chemi cal composition andnutritiv e value offres h maize.J .agric . Sei., Camb., 92: 471-483. PITMAN, W.D. ,D .M . VIETOR andE .C . HOLT: 1981. Digestibility ofkleingras s forage grown under moisture stress. Crop Sei., 21:951-953 . PRINS, R. A., W. C. CLINÉ-THEIL and A. TH.VA N' T KLOOSTER: 1981. An in vitro procedure for the estimation ofi n vivodigestibilit y ofroughag e plant cell wall components inherbivore s using mixed rumen microorganisms. Agric. Environm., 6: 183-194. RICHARDS, G. N.: 1976. Search for factors other than 'lignin-shielding' in protection of cell-wall polysaccharides from digestion inth erumen . In:Carbohydrat e research inplant s and animals. Misc. Papers nr. 12, Agric. Univ. Wageningen, pp. 129-135. SMITH, L.W. ,H . K. GOERING andC .H . GORDON: 1972. Relationships offorag e composition with rates ofcel l wall digestion andindigestibilit y of cell walls.J .Dair y Sei., 55: 1140-1147. SMITH, L. W., H. K. GOERING, D. R. WALDO and C. H. GORDON: 1971. In vitro digestion rate of forage cell wall components. J.Dair y Sei., 54: 71-76. SOFIELD, 1., L.T . EVANS and I.F .WARDLAW : 1974. Theeffec t oftemperatur e and light on grain filling in wheat. In: Mechanisms of regulation of plant growth. Bull. Royal Soc. N.Z. 12: 909-915. SPIERTZ, J. H.J. : 1974. Grain growth anddistributio n of dry matter in the wheat plant as influenced by temperature, light energy andea rsize . Neth. J.agric . Sei., 22: 207-220. SPIERTZ, J. H.J. : 1977. The influence of temperature andligh t intensity ongrai n growth in relation to the carbohydrate andnitroge n economy ofth e wheat plant. Neth. J. agric. Sei., 25: 182-197. STRUIK, P.C : 1982a. Effect of a switch inphotoperio d onth e reproductive development of temper ate hybrids ofmaize . Neth. J.agric . Sei., 30: 69-83. STRUIK, P. C: 1982b. Production pattern, chemical composition and digestibility offorag e maize (Zea mays L.). Mededeling no. 64, Vakgroep Landbouwplantenteelt enGraslandkunde , Agric. Univ. Wageningen, pp.1-28 . STRUIK, P.C .an d B. DEINUM: 1982. Effects ofligh t intensity after flowering onth e productivity and quality ofsilag e maize. Neth. J.agric . Sei., 30: 297-316. TOLLENAAR, M.an d T. B. DAYNARD: 1978. Kernel growth and development at twoposition so n the earo fmaiz e (Zea mays). Can. J.Plan t Sei., 58: 189-197. TOLLENAAR, M.,T .B .DAYNAR D and R. B. HUNTER: 1979. Effect of temperature on rate of leaf appearance andflowerin g date in maize. Crop Sei., 19: 363-366. TOLLENAAR, M. andR .B . HUNTER: 1981. Quantification of theeffect s of temperature and photoperi od onmaiz e development. Agronomy Abstracts 1981, Amer. Soc. of Agronomy, p. 14. VAN SOEST, P.J. : 1965. Comparison oftw o different equations forth epredictio n of digestibility from cell contents, cell wall constituents and the lignin content ofaci d detergent fiber. Paper 118, Ann. Meeting Amer. Dairy Sei. Ass., Lexington, Kentucky, 1965. pp.1-7 . VAN SOEST, P.J. : 1967. Development of a comprehensive system offee d analyses andit s application to forages. J.anim . Sei., 26: 119-128. VAN SOEST, P.J. : 1977. Modified procedure fordeterminin g plant cell wall byth eneutra l detergent procedure. Paper presented at the69t h Ann. Meeting Amer. Soc. of Animal Sei., Madison, Wisconsin,1977 . VAN SOEST, P.J . andL .H .P . JONES: 1968. Effect ofsilic a in forage upon digestibility. J. Dairy Sei.. 51: 1644-1648.

Meded. Landbouwhogeschool Wageningen 83-3 (1983) 95 VAN SOEST, P.J. , R. H. WINE und L.A . MOORE: 1966. Estimation ofth e true digestibility of forages by the in vitro digestion of cell walls. Proc. X Int. Grassl. Congress, Helsinki, Finland, (ed.) A.G.G. HILL, pp. 438-441. Vos, J.: 1981. Effect of temperature and nitrogen supply on post floral growth of wheat; measure ments and simulations. Centre foragricultura l Publishing and Documentation PUDOC , Wage ningen, pp. 1-164. WALDO, D.R. ,L .W .SMIT H andE .L .Cox : 1972. Model ofcellulos e disappearance from the rumen. J. Dairy Sei., 55: 125-129. WHIGHAM, D. K. and D.G . WOOLLEY: 1974. Effect of leaf orientation, leaf area and plant densities on corn production. Agron. J., 66: 482-486. WIEGAND, C. L. and J. A. CUELLAR: 1981. Duration of grain filling and kernel weight of wheat as affected by temperature. Crop Sei., 21: 95-101. WILKINS, R. J.: 1969.Th e potential digestibility of cellulose in forage and faeces. J.agric . Sei., Camb., 73: 57-64. WILSON, J.R. : 1982.Environmentalan d nutritional factors affecting herbage quality. In: Nutritional limits toanima l production from pastures, (ed.) J. B. HACKER. Farnham Royal, U.K., Common wealth Agricultural Bureaux, pp. 111-131. WILSON, J. R. andT .T . NG: 1975. Influence of water stress on parameters associated with herbage quality of Panicum maximum var.trichoglume. Austr. J. agric. Res., 26: 127-136. WILSON, J. R., A. O. TAYLOR and G. R. DOLBY: 1976. Temperature and atmospheric humidity effects on cell wall content and drymatte r digestibility of some tropical and temperate grasses. N.Z. J. agric. Res., 19: 41-46.

96 Meded. Landbouwhogeschool Wageningen 83-3 (1983) CHAPTER 3

Neth.J. agric. Sei.30 (J982) 297-316 Effect ofligh tintensit yafte r flowering onth eproductivit y and qualityo fsilag emaiz e

P.C .Strui k and B. Deinum

Department of Field Crops and Grassland Science, Agricultural University, Wageningen, Netherlands

Accepted: 14Jul y 1982

Key-words:forag e maize, digestibility, light intensity, sowing time, plant densi ty,hybrid , grain-filling period

Summary

After flowering, different shading treatments were imposed on crops that varied insowin gdate ,genotyp e and plant density. Itwa sfoun d that earyiel d wasclose ly related to the amount of irradiance received during grain filling: it increased by approximately 10k g ha-1 per MJ m 2 if density was not limiting. However, the intensity of carbohydrate redistribution from vegetative to reproductive plant parts differed greatly. Whole-crop yields were also affected by the distri bution ofirradianc e over time. The digestibility in vitro of the organic matter was affected most by shading during the lastpar t ofth egrowin gseason .Earlie r shading reduced cell-wall pro duction, thus limiting the detrimental effect of shading on whole-crop digesti bility. Shading influenced digestibility through its effects on cell-wall content. Cell wall digestibility only differed slightly between shading treatments. For all crops, shading effects on whole-crop digestibility showed the same pattern, but not thesam e magnitude. Aswel l as affecting yield and quality, shading also affected suitability for en siling,susceptibilit y tostal k rot (Fusarium spp.),lea fsenescenc e and mineral up take. A hypothesis is offered to explain the effect of shading on ear size, ear growth and longevity of leaves in terms of the prompt effects ofshadin g on root activity.

Introduction

The Dutch climate shows some unfavourable characteristics for growing maize (Zea mays L.). Firstly, in spring soil temperatures are too lowfo r a fast early de velopment. Secondly,durin g thelat epar t ofth egrain-fillin g period the intensity ofligh t isnormall y too low,s otha t thecarbohydrates , previously stored invege tative plant parts,mus t be redistributed for grain filling tocontinu e at an accep- 97 P.C .STRUI K AND B. DEINUM

table rate.Althoug h the second problem isconnecte d with the first one,cultura l practice emphasizes the disadvantages of the climatic conditions in September and October: maximum dry-matter yieldsar e obtained by sowingfairl y late hy bridsa t relatively high plant densities.I ti squestionabl e whether and towha t ex tent redistribution itself affects production and quality (Bunting, 1975, 1976; Deinum &Knoppers , 1979), buti ti sclea r that ifth e need for carbohydrate redis tribution is avoided by choosing early genotypes or changing cultural practices in response to the unfavourable climate, the quality of the forage crop will im prove, though unfortunately always at the expense of dry-matter yield. Maxi mum use of the possibilities ofth egrowin gseaso n willgiv eth e highestyield , but itnecessitate s amor e abundant, timeconsumin g vegetative growth.I n thatcase , later female flowering makes it necessary for the grains tob e filled by means of redistribution. This paper attempts to quantify the effect of irradiance during the grain- filling period on dry-matter production and quality. The consequences of peri ods of shading on crops that differed in intensity of redistribution due to differ encesi nsowin gtime ,genotyp e orplan t density,wer einvestigate d inthre etrials .

Materialsan dmethod s

In 1977, 1978 and 1979shadin g experiments were done on a light, moist sandy soil with abundant fertilization (both organic and inorganic) and with optimum weed and diseasecontrol . In 1977 and 1978,trial swer e laid out asa split-plo t de sign with shading as sub-plot treatment and with five replicates. The 1979 trial waslai d out asa completel y randomized block design with four replicates.

Treatments Light intensity wasreduce d during twodistinc t periods after silking,b y hanging tents of black plastic gauze of 8m x 4,5 m above and around the crop. These tents reduced light intensity to about 40 %. The following shading treatments were applied:

Code Treatment A TreatmentS (mid-August tomid-September ) (mid-September to final harvest) AUSU untreated untreated A.S, untreated shaded AA shaded untreated A.S, shaded shaded

These treatments were applied tocrop s grown in different years and under dif ferent cultural practice. In 1977, the hybrid LG 11wa s sown on two dates: 28 April (normal; code St,) and 25 May (late; code S^). In 1978,tw o extreme hy bridswer eused : Ula (H,)wit h aFA O index of 190an d Axia (H2)wit ha FA O in-

98 Neth.J. agric. Sei.30 (1982) EFFECTO F LIGHTINTENSIT Y ON PRODUCTIVITY ANDQUALIT Y OF MAIZE

dex of 500. In 1979, LG 11wa s again grown in three plant densities: approxi 2 mately5 (D,) , 10(D 2)an d 15(D 3)plants/m .

Culturaldetails and methods of measuring crop development In 1977an d 1979,sowin gdensitie s were 20.0an d 16.7seeds/m 2, respectively. In both years,th ecrop swer e thinned to 10plants/m 2 ort oth edesire d plant density shortly after emergence. In 1978,sowin g density was 10.7seeds/m 2 for Ula and 9.3seeds/m 2 for Axia.Th e rowswer ealway s 75c m apart and theplot swer e6 m X 10m ( 8row so f 10m) ; wideborder sseparate d theplot sfro m each other. In 1978,earl y development of the late hybrid Axia was accelerated by means of a plastic mulch applied for 33 days (i.e. from sowing until 8-leaf stage). To check the effect of the plastic mulch,on e extra plot ofUl a wastreate d withplas ticmulc h and oneextr a ploto fAxi a wasgrow nwithou t plastic mulch. Ifnecessary ,drough t wasprevente d by sprinkling. Growth and development were measured weekly by estimating plant height, number of leaves (young, full-grown and dead leaves) and the physiological stage of reproductive organs of four plants per plot. Leaf area was estimated shortly after flowering with an area meter (1978) or by the length X maximum width X 0.75 method (1979) (Montgomery, 1911). Maximum diameter in the middle of the second above-ground stem internode was measured with a mark ing gauge as an estimation of stem thickness. The degree of Fusarium present was estimated by pushing 10 plants in each plot. The number of broken (i.e.se verely infected) plantswa suse d toindicat e theseriousnes so fth e disease.

Yielddeterminations The second, fourth and sixth rows in each plot were used for subsequent sam plings.Th e seventh rowwa suse d for estimating Fusariuminfectio n at final sam pling. Plots were sampled at the start of the Aan d Speriod s and in October. At each sampling date, a row 6 m long (4.5 m2) was harvested by cutting off the plantsa t soillevel . The number of plants in each sample was counted. The samples were then temporarily stored in a cold chamber and separated into relevant fractions: in 1977 intoear san d stover (stem,leaves ,husks ,shank s and tassel)an d in 1978an d 1979 into upper ears, lower ears, husks + shanks and stems (stems, leaves and tassels). This separation was necessary to provide additional information and for adequate subsampling.Afte r estimationo ffres h weight,th e earswer e chopped in a vegetable cutter, subsampled and dried to a constant weight in forced ventilated ovens at a maximum temperature of 70°C . The vegetative parts of the plant were chopped with astationar y tractor-mounted 1-rowchoppe r (Fahr MH 70).Thi schoppe r blew themateria l directly through an exhaust onto acon veyorbel t which transported itint oa concret e mixer.Subsample s were taken af termixin gan d were subsequently treated likeea r samples.

Chemicalanalyses After drying, sampleso f the replicates were bulked per plant part and per treat- Nelh.J. agric. Sei.30 (J982) 99 P.C .STRUI K AND B. DEINUM ment and ground in hammer mills.Sample s were analysed for true digestibility in vitro of the organic matter, using the method described by Van Soest et al. (1966). These values were standardized and converted to apparent digestibility of organic matter by means of a series of standard-maize samples with known digestibility in vivo (sheep). Cell-wall constituents were estimated according to Van Soest's (1977) method. Cell-wall digestibility was calculated from true di gestibility, cell-wall content and ash content. Analysis for water-soluble carbo hydrates was done with ferricyanide on an automatic analysing device, and ex pressed inglucos e units.

Resultsan ddiscussio n

Weather Table 1 shows climatic data for 1977, 1978an d 1979.I n all three years, temper atures were below normal in May, June, July, August and September, but were above average in October. In all years precipitation was low, especially in Sep tember and October.Tota lsola rirradianc e wassomewha t belownorma l in 1977 and 1978.Damagin g night frosts at the end of the growing season only occurred in 1979.

Influence ofshading tents on climatic/actors Tents reduced light intensity to about 40 % of normal irradiance. This percent age was not constant, as the sun's altitude influenced the reduction to some ex tent. Aswel l asligh t intensity, many otherclimati cfactor s were affected by shading: day length, mean air temperature, temperature of plant organs, differences be tween air temperature and plant-tissue temperature, diurnal temperature cycles

Table 1.Climati c data for 1977, 1978an d 1979a t Wageningen, compared with the means over 30 years(1931-1960 )a tD e Bilt,N etherlands . Average temperature(°C ) Rainfall (mm ) Solarirradianc e (MJ/m2) 1977 1978 1979 mean 1977 1978 1979 mean 1977 1978 1979 mean

May 11.9 12.4 11.7 12.4 55.2 33.1* 75.7 52 543 473 516 518 June 14.6 15.1 15.0 15.5 64.3 61.6 148.4 57 425 507 493 531 July 16.7 15.3 15.8 17.0 68.0 56.7 31.4 78 484 480 461 478 August 16.2 15.1 15.3 16.8 134.4 31.0 84.8 89 388 417 409 415 September 13.5 13.3 13.2 14.3 6.1* 68.8 17.8 71 292 251 332 304 October 11.2 10.6 10.8 10.0 36.9 36.6 36.6 72 184 162 194 177

Average/ total 14.0 13.6 13.6 14.3 364.9 287.8 394.7 419 2315 2289 2405 2423 *Drough t wasprevente d bysprinkling .

100 Neth.J. agric. Sei. 30(1982) EFFECTO F LIGHTINTENSIT Y ON PRODUCTIVITY ANDQUALIT Y OF MAIZE

(e.g. the occurrence of night frosts!), relative humidity of the air, water supply (pF value of the soil), light quality (e.g. ratio direct: diffuse light), light extinc tion,win d speed, and perhaps alsoth e C02 gradient within the crop (cf. Gerakis & Papakosta-Tasopoulou, 1979). The following relevant plant processes may change in intensity asa result ofshading : photosynthesis, transpiration, respira tion, nitrate reduction and protein synthesis, mineral uptake and root growth, transport, translocation, grain filling, senescence (both in vegetative and repro ductive plant parts) and hormonal production. In addition, resistance to Fusa riumspp. may decrease. Of course, all these processes will interact. So, shading altered the entire climate and thischang e in climate induced acomple x reaction inth ecrop .

Cropdevelopment Since shading treatments started some time after flowering, there were no ef fects on vegetative development and flowering. For a description of the differ entcrops ,se eTabl e2 . In 1977,5 0 % emergence occurred about 14day s later in the late sowing than in the early sowing. However, the dates on which 50 %femal e flowering was achieved were only 11day s apart, indicating that the later sown crop developed

Table 2.Cro p descriptions. 1977 1978 1979

St, St2 H, H2 D, D2 D3 Sowingdat e 28/4 25/5 20/4 20/4 25/4 25/4 25/4 Density (plants/m2) 10.03 10.13 8.03 9.21 5.30 10.50 15.43 Numbero f leaves 15.3 15.2 13.5 17.5 13.8 13.8 13.8 Heighto fplan t (cm) 261 265 205 246 202 214 214 Maximum leafare a (m2/m2)* — — 2.20 4.70 1.91 3.52 4.84 Estimateddat eo f50 % ? flowering 8/8 19/8 28/7 4/8 2/8 3/8 5/8 Stemdiamete r (cm) - - - - 2.71 2.21 2.00

Pre-treatmentdata Starto ftreatmen tA 15/8 22/8 14/8 14/8 20/8 20/8 20/8 Dry-matteryiel da tstar to ftreatmen t A(M gha ~ ') 9.79 8.21 7.82 10.45 6.36 8.00 8.48 Digestibility atstar to ftreatmen t A(% ) 73.5 71.9 74.6 73.7 74.0 72.5 70.8 Starto ftreatmen tS 12/9 12/9 4/9 4/9 17/9 17/9 17/9

Datafrom untreatedstands at final sampling Dateo ffina l sampling 26/10 26/10 10/10 11/10 15/10 15/10 15/10 Final earyiel d (Mgha ~' ) 7.66 6.00 6.95 6.93 6.50 7.20 7.38 Finalstove ryiel d (Mgha ~' ) 7.78 8.97 4.99 8.42 4.55 5.60 7.50 Finalwhole-cro pyiel d (Mgha ~' ) 15.44 14.97 11.93 15.35 11.04 12.80 14.87 Whole-crop dry-matter content(%) 30.3 24.5 34.2 29.0 32.0 30.4 28.5 Fusariuminfectio n(%) 30 8 38 rare 20 45 40 Digestibility atfinal samplin g(% ) 71.5 69.7 72.8 71.1 75.7 74.8 73.5 Cell-wallyiel d(M g ha"1) 7.12 7.48 4.97 7.69 4.31 5.15 6.29 Ofthe main shootonly .

Neth.J. agric. Sei. 30(1982) 101 P.C .STRUI K AND B.DEINU M more rapidly,possibl y because ofth e higher temperatures during vegetative de velopment. From the unshaded plots,i tca n besee n that latesowin gresulte d ina non-significant reduction of0.4 8 Mg ha~' inth efina l yield, which was only 18 kgha -1pe r day the sowing was delayed. This was much lower than normal (Becker, 1976; Struik, 1982),becaus e ofth e low temperatures during Aprilan d May andth elat e date offina l sampling. Thedifference s were even smaller for shaded crops. Digestibility was lower in thelate r sown crop, because cell-wall production washighe ran d ended later. In 1978, emergence wasno toptimu m forth ehybri d Ula sinceUl a isver y sen sitivet ocold .A sthi shybri d wasals over yearly ,th e leafare a waslow . Flowering dateso fUl a andAxi a were very different inspit e of the development-accelerat ing effect of the plastic mulch. The very late hybrid Axia outyielded theex tremely early Ula byabou t 3.4 Mg ha-1 innorma lligh tconditions ; thesam e dif ference wasalread y found atth esecon d samplingdat e( 4September) .On e extra plot ofAxi a without plastic mulching showed that theyiel d increase resulting from themulc h was about 2M g ha-1, almost completely present inth e upper most ear.A n extra plot ofUl a with plasticmulchin g alsoshowe d ayiel d increase of2. 0 Mg ha-', of which 0.5M g ha~' wasi nth evegetativ e partsan d 1.5 Mg ha~' in theears .S oth e hybrid effect itselfwa sonl y responsible forabou t 1.4 Mg ha-1, although there were great differences in earliness andlea f area. Themea n dif ference between Axia andUl afo ral lshadin g treatments was only 2.6M g ha~' atal lsamplin gdates . At final sampling, theinteractio n hybrid X shading treatment was only sig nificant fortota l yield.Thi sinteractio n wasprobabl y caused byth edifferenc e in leafare a although nosuc h interaction wasfoun d inth e 1979trial . In 1979,rat e oflea f appearance was lower athighe r density, butrat e ofste m elongation was greater. Differences in final number ofleave s andplan t height, however,wer esmall . Dry-matter yields increased with density. This was true foral lshadin g treat ments. In neighbouring countries, higher plant densities are advocated (Bel gium: 11000 0 plants/ha, Behaeghe et al., 1981;Unite d Kingdom: 11000 0 plants/ha, National Instituteo fAgricultura l Botany, 1979).I nth e Netherlands,a final plant density of 9-10 plants/m2 is believed to be the optimum (Becker, 1976).Fo r maximum dry-matteryield sthi si sprobabl y not true.Th edecreas ei n quality was relatively small compared with the yield increase, especially for unshaded crops. Lower digestibility and lower dry-matter content may there fore bereason sfo rgrowin ga ta densit yo fles stha n 11plants/m 2 only inclimate s with unfavourable weather during autumn.

Influence ofshading on senescence and ripening Light treatment caused different patterns in leaf senescence, partly connected with differences indiseas e infection. Patterns were similar in the threeyears ; ex amples aregive n in Fig. 1 andTabl e 3,respectively . Fusarium infection waso f minor importance for dry-matter yield and quality, but showed a connection with the carbohydrate content of thestove r (Table 3).Difference s insenescenc e

102 Neth.J. agric. Sei.30(1982) EFFECT OF LIGHT INTENSITY ON PRODUCTIVITY AND QUALITY OF MAIZE

number of green leaves 1977, St, 12 r

40 50 60 70 days after o flowering

Fig. 1.Leaf-senescenc e pattern for four light treatments of early sowing in 1977.

were also visible in the ears. With continuous shading, the duration of grain filling increased from the tip to the base of the ear. Tip kernels shrivelled very soon, mid-kernels were half-filled and basal kernels showed almost normal ha bitus. In the control, hardly any kernel 'abortion' occurred. \SS and A^,, were intermediate. This reaction in number of active kernels started very soon after the onset of shading and long before the amounts of carbohydrate in the stem could be limiting. 'Abortion' even occurred in crops that had increasing carbo hydrate contents in their vegetative parts! Light treatment alsocause d different patterns in drying of stover, ear and whole crop (Table 3).Th e dry-matter con tento fstove r wasclosel yrelate d toFusarium infectio n (1977:r 2 = 0.976; n = 8).

Table 3. Proportion of plants that lodged when pushed, indicating infection by Fusarium spp.; con tent of water-soluble carbohydrates in stover; number of green leaves; ears as proportion of total fresh material; and dry-matter contents at final registration (197 7 data).

St, St2

Auau AUSS AjSu As^*s ÛÛ Û^S Asû AsSs

Fallen plants(% ) 30 74 10 40 8 18 0 6 wscconten t (%) 5.5 5.1 11.6 6.8 9.5 8.7 13.7 9.1 Number of green leaves 4.6 1.7 5.1 2.6 6.6 5.3 6.1 4.8

Ears, as portion of total fresh material (%) 29.3 28.3 17.9 16.9 23.3 21.6 13.0 12.3 Dry-matter content of stover{%) 21.6 25.1 20.3 22.6 19.1 20.5 18.6 19.8 Dry-matter content of ear(% ) 51.4 48.9 43.2 42.1 42.0 38.1 35.6 32.3 Dry-matter content of whole crop (%) 30.3 31.8 24.4 25.9 24.5 24.3 20.9 21.3

Neth.J.agric. Sei. 30(1982) 103 P.C .STRUI K AND B. DEINUM

However, the effects ofshadin go n eardry-matte r content and on the proportion of ears in the fresh material were much greater and better correlated with dry- matter content in the whole crop. Shading A greatly reduced these ear parame ters, while shading Scause d a small additional decline. Effects were similar for all crops. The dry-matter contents of the whole crop at final sampling were not always significantly different for Suan d Sstreatments . IfFusarium infectio n was insignificant, the dry-matter contents of AUSS were slightly lower than those of \SU, but when the Ss cropsshowe d severe stalk rot, then thedry-matte r contents of\S U were lower than those of A„SS.Ther e were large differences between the A„crop s and the\ crops,bu t these differences alsodepende d on thecro p struc ture. The means over all years and cultural practices were 29.8, 30.2, 26.0 and 25.6 % for AUSU, AUSS,\S U and A.S, respectively. So, a good ear development stimulated the drying of the crop, even if yields were similar (cf. AUSSan d ASSU),resultin gi n lessseepag e during ensiling. On the other hand, the contents of readily fermentable carbohydrates were very low in theA„S Streatments , sincealmos t allth e non-structural carbohydrates werepres ent in the ear as starch (as a result of redistribution) and these contents were very high in the \Sa treatments, where ear sink was weak. Ear parts are practi cally inert in good maize silages: starch does not play apar t in fermentation and the ear parts are normally too dry to produce effluent. However, even when the dry-matter content of the whole crop is3 0 %, seepage may occur if the stover is still too wet. So, the content of insoluble dry-matter such as cell walls, proteins etc. (on the basis of fresh weight) in vegetative parts iscrucial . For example for \SU, AUSS, A.SU and \SS this content in 1977 (early sowing) was about 16 %, 19%, 13.5 % and 16 %,respectively . Therefore Aßu was the most likely to seep and ifseepag e had occurred, thelosse so fdigestibl e dry-matter would have been highest for that treatment. On the other hand, the intensity of the fermentation process would have been best and the pH would probably have been lowest for A,SU.

Influence ofshading on dry-matter production Ear. Ear yields were strongly affected by light treatments. In Fig. 2, ear yields are plotted against the cumulative irradiance. In all years the linear correlation coefficients were highly significant. Ear yieldsa t first sampling or calculated ear yields at cumulative solar irradiance zero indicate the physiological age of the different crops at first treatment. Stj wastreate d before the linear dry-matter ac cumulation in the ears had begun: the calculated intercept appeared to be neg ative. The regression coefficient was 7.85 kgha-'/MJ m 2 for D, and ranged from 9.33 to 10.87k g ha'/MJ nr2 (i.e. 1 gpe r megajoule incoming irradiance) for all other stands. It isstrikin g that in 1979th e ear yields (upper + lower ears) ofth e threedensitie sdi d notdiffe r significantly on any samplingdate ,excep t for the first date. Statistical analysis of the regression equations, however, showed 2 that the regression coefficients (7.85, 9.50 and 9.66 kg ha '/MJ nr for D,, D2 and D3, respectively) were significantly different (P = 0.018). Yields of top ears considered separately did show significant density effects at all sampling dates.

104 Neth.J. agric. Sei.30 (1982) EFFECT OF LIGHT INTENSITY ON PRODUCTIVITY AND QUALITY OF MAIZE

ear yield (Mg ha"') 8|-

o = St, r2=0921 2 . = St2 r = 087 7

2 - , 6 1977

1c OL 1t_ O 10 20 30 40 50 60 70 ear yield cumulative solar irradiancelkJ.cm"2) (Mg.ha"') 8r -2=0.953 s,„=0.45 %. 2 r =0960 sy.x=047 4 § 5 O o

1978

1o 1' 0 10 20 30 40 50 60 70 ear yield cumulative solar irradiance (kJ.cm'') (Mg.ha-1) 8 ; Fig. 2. Ear yields in relation to cu- o=D, 1-2=0.969 syx=036 x 0 mulative solar irradiance after start 2 4 ..D2 r =o.953 s„=0.54 % ofA treatment . 2 l = x.D, r =0985 s„.Q3s 0 ' pre-treatment sampling, thus y.x" ö sampling atsola r irradiance0 . 2 = Au: secon d sampling; unshad- ç S eddurin gA . 7 3 = Agi second sampling; shaded 2L 3 1979 duringA . 4 = AySu . final samplings; L 5 = Ai,Ss ( treatments as indicat- 0 i- 10 20 30 40 50 60 70 6 = A^ f ed in 'Materials and cumulative solar irradiancetkj cm" ) 7 = AJSJ ' methods'.

In thiscase ,regressio n coefficients alsoshowe d greater differences (P = 0.001). Crop reactions to variations in light intensity were more marked in the lower ears than in top ears,becaus e lower ears flower later and are not as competitive. The consequences of these marked effects on total ear yields, however, were very small, except for the lowest density in 1979, where lower ear yields were 19% , 17% , 11% and 8 % of total earyield s for AUSU,A USS, AA and A^, respec tively.

Nelh. J. agric. Sei. 30 (1982) 105 P.C .STRUI K AND B.DEINU M

Table 4. Stoveryield s(stem s + leaves + tassels + husks + shanks)a tfinal samplin gdate s(M g ha-1). 1977 1978 1979 Mean

St, St2 H, H2 D, D2 D3

Au^u 7.78 8.97 4.99 8.42 4.55 5.60 7.50 6.83 AuSj 7.14 8.08 4.53 8.21 4.47 6.33 6.95 6.53 AsSj , 7.76 8.99 4.72 7.85 4.03 5.68 7.99 6.72 AsSj 7.28 8.53 5.17 7.45 3.82 5.13 6.62 6.29

Mean 7.49 8.64 4.85 7.98 4.22 5.69 7.27

Mean AUSUs 6.68;mea n AsSus 6.50;mea nA uS SU6.77 ; mean AuS SS6.4 1

Almost allshadin g treatmentsfitte d theregressio n lines.Apparently , low irradiance during the A period reduced the sink strength of the kernels,bu t did not affect thegrai n filling duringth e S period, except in 1977.I n thatyear ,A.S Ugav e much lower ear yields than expected, given the received irradiance at both sow ing dates. Probably the S period lasted so long that the storage capacity in the earswit h many aborted kernelsbecam e limiting.

Stover. Yields of stover (i.e. stem + leaf parts + tassel + husks + shanks) in creased during the A period for unshaded crops, except for the very early H, in 1978, but decreased for the shaded crops except for St2As (1977) and D^\ (1979),wher e a small increase wasstil lpossible ,becaus e of the latenesso f these crops.Afte r theA period , allstove ryield sdeclined .Rate so fdeclin edurin gth eS period showed clear differences, ranging from about 0t o about 100k gdr y mat ter ha-1 day-1, and were always greater ifcrop s were unshaded during theA pe riod and were also higher when shaded during the S period itself. However, in 1979 night-frost damage disturbed this ranking order, since the shading tents prevented damage in Sstreatments . Table 4 presents stover yields at final sam pling. Effects of sowing time, hybrid and density were highly significant. Light- treatment effects on stover yields were significant at the end of the A period in allyears .I n 1977,shadin g effects on stover yield at final sampling were not sig nificant, but the pattern was consistent and logical. In 1978 and 1979,yield s of husks + shankswer ever ysignificantl y negatively affected by S shading,bu t the effects onyield so fste m + leaves + tasselswer eonl ysignifican t (atP < 0.10)i n 1979.

Wholeplant. Whole-plant yieldsa tfina l samplingar e recorded inTabl e 5. Table 6 shows the linear correlation coefficients, the standard deviations from regres sion,an d the regression coefficients ofth e relations between cumulative solar ir radiance and total dry-matter yield. In all seven cases the r2 for whole-plant yieldswa slowe rtha n the r2fo r earyields .Th e distribution ofth eirradianc e over timewa sals orelevant , especially incrop swher e there wasa stron gdeclin ei n the efficiency of the green area at the end of the growing season.I n thesecrop s (St,,

106 Neth.J. agric. Sei.30(1982) EFFECTO F LIGHTINTENSIT Y ONPRODUCTIVIT Y ANDQUALIT YO FMAIZ E

Table 5.Whole-cro p dry-matteryield sa tfinal samplin gdate s(M gha -' ) . 1977 1978 1979 Mean

St, St2 H, H2 D, Dj D3

^ni^u 15.44 14.97 11.93 15.35 11.04 12.80 14.87 13.77 Ay^s 12.65 12.21 9.81 13.23 10.61 13.42 13.41 12.19 As^u 11.36 11.55 10.09 12.33 8.20 9.76 12.44 10.82 A$^s 10.03 10.50 9.46 10.63 7.32 8.70 9.77 9.49

Mean 12.37 12.31 10.32 12.89 9.29 11.17 12.62

MeanAuSus 12.98;mea n AsSus 10.15;mea nA USSU 12.30;mea nA USSS10.84 .

H2,D 2),A ,treatment s weremor edetrimenta l than Sstreatments . Moreover, the same stands produced hardly any dry-matter during shading, while other stands (S^, H,, D,, D3) were able to produce dry matter if shaded. Although the r2 values inTabl e 6d ono t differ significantly, these physiological 2 lyyounge r (S^, D3)o r open (H,,D, ) stands showed the highest r values. Ignor ing the frost damage in 1979,bot h types of reaction are illustrated schematical lyi n Fig. 3. The regression coefficients do not vary strongly. They were not even signifi cantly different in 1979 although they correlated closely with the plant density (r2 = 1.000;n = 3).

Influence ofshading on quality of the organic matter Sowing date, genotype, year and plant density all affected the apparent digesti bility of the whole crop (Dcrop), asha s already been demonstrated in Table 2.I n control stands, considerable production of cell walls — both in vegetative parts and inear s — took placedurin g theA period , while the quality ofth epartl y indi gestible cell walls continued to decrease after flowering. However, ear devel opment ensured thatcell-wal lproductio n ended.

2 Table 6.r ,S yx and bfo r the linear relations between cumulative solar irradiance and total dry-mat teryiel d( n = 7). 2 1 - 2 r Sy.x (Mg ha" ) b(k g ha VMJm- ) 1977 St, 0.688* 1.30 7.85 St2 0.860** 0.90 9.99

1978 H, 0.852** 0.54 6.27 H2 0.753** 1.00 8.21

1979 D, 0.864** 0.72 7.13 Da 0.742** 1.28 8.45 D3 0.908** 0.79 9.68

Neth.J. agric. Sei. 30(1982) 107 P.C .STRUI K AND B. DEINUM

dm applies toSt,,H2,D2 dm applies to St2 ,H,,D, ,D3 yield yield

AuSu ——o

Au,-' s'' AU,-1AUSS ,o' oAufs

s .

O-'^-'A, ""O o -^ ASSS r. amount of irradiance amount of irradiance Fig. 3.Relatio n between dry-matter yield and amount of irradiance received (schematic). (- regression line,— = control;.... = continuously shaded crops).

The most relevant process in relation to changes in digestibility after grain set isth e dilution of the then present cell-wallmateria l with new products of photo synthesis. The newly synthesized sugars are completely digestible and may be stored in grains (asstarch )o ri n vegetative parts (asshor t carbohydrates).Th e fi nalcro pqualit y isdetermine d by: — content, amount and qualityo fcel lwall spresen t atgrai n set. —increas ei ncell-wal lyiel d after grain set. —rat e ofdeclin e incell-wal ldigestibilit y after grain set. —yiel d increaseo fnon-structura l carbohydrates. These properties varied according to sowing date, genotype and plant density. Moreover, the pattern varied from year to year. For example, in 1977, LG 11 showed an abundant vegetative development, resulting in a retarded ear devel opment (and thus a delay in the dilution process), a high cell-wall production (more than 7 Mg ha-1 for both sowing times), and rather small ears; it received low amounts of irradiance during grain filling and was harvested late. In 1979, conditions for thesam e hybrid werequit e different. D for all treatments at final sampling is reported in Table 7. As may be clear from the above-mentioned quality determinants, the effects ofshadin g on Dcrop depended on crop structure: the early sown crop reacted more severely than the later sown one, the early hybrid showed a more pronounced reaction than the late one and the densest crop showed a much greater effect of A shad ingtha n theothe r two. Shading effects can partly be explained by non-structural carbohydrate pro duction during the treatment (see also Fig. 1).I n addition, cell-wall production almost stopped with low light intensity: shading A caused a final reduction in -1 the cell-wall yield of vegetative parts of 440- 66 0k g ha for St,, S^, H2,D, and -1 D2; the reduction ofcell-wal lyiel d in ear partswa s 540- 97 0k g ha . Asa result, digestibility was only slightly reduced by shading A, although ear yield was greatly reduced. The effect ofshadin g So n digestibility waspracticall y confined

108 Neth. J.agric. Sei.30(1982) EFFECTO F LIGHT INTENSITY ON PRODUCTIVITY ANDQUALIT Y OF MAIZE

Table 7. Apparent digestibility ofth e wholecro p atfinal samplin g in % ofth eorgani c matter (calcu lated from data on thedifferen t fractions). 1977 1978 1979 Mean

St, St2 H, H2 D, D2 D3

Aubu 71.5 69.7 72.8 71.1 75.7 74.8 73.5 72.7 Au^s 68.6 68.9 69.7 69.4 73.8 73.3 71.9 70.8 AsSu 70.0 69.2 72.4 71.1 74.5 74.1 71.9 71.9 As^s 67.5 68.0 69.1 68.4 73.5 72.8 70.1 69.9

Mean 69.4 69.0 71.0 70.0 74.4 73.8 71.9

MeanA USUS71.8 ;mea n AsSus 70.9;meanA usSu 72.3; mean AUSSS70. 4 to a reduction of cell-wall dilution and therefore greater, especially in 1978 when the A period was short. H, and D3 reacted in different ways. H, only showed minor reductions in cell-wallyields .Also ,dry-matte r production was less affected by shading than it was in other stands, because Ula was an early and open crop. Ascell-wal l digestibility and dry-matter yield were low, these small reductions still had consequences of at least the same magnitude and direction as in the other crops. For D3, the cell-wall yield of A^ was intermediate be tween \SUS and A^: some additional cell-wall production could occur in the stover during the Su period for this treatment as compensation for 'neglected' earlier cell-wall formation, while for other light treatments the cell-wall yield decreased because of leaf senescence. This compensation caused a stronger de cline in Dcrop than was expected. Final reduction in cell-wall yield was 670 kg ha-' for A,S„an d 1510kg ha"1 for A.S.. The decline in cell-wall digestibility was unaffected by shading. The mean val ues of cell-wall digestibility for \Sa, K%, A^ and A.S, were 65.0 %, 64.9%, 65.4 % and 65.5 %, respectively. Cell-wall digestibility did show differences be tween cropso fdifferen t density, genotype and year. The apparent digestibility ofth ewhol ecro pca n beexpresse d by:

Dcrop = (earcontent x Dear + (100-earcontent) x Dslover)/100 (1)

The ear content (organic-matter yield in ears as a percentage of organic- matter yield in the whole crop)showe d a wide range in these trials (20.3 -63.1%). Variationi n eardigestibilit y(D ear)wa sfairl y small(range :80. 6- 86. 1 %). Ear diges tibilitywa salway slowes tfo r A„SS.Thi s treatment made a normal early ear devel opment possible, but hampered late grain filling, thus causing a low shelling percentage. As the digestibility of the cob is much lower than of the kernels (Struik, 1982)a reduction in qualityoccurred . Among theothe r three light treat ments,difference s were smallan d inconsistent, asA jtreatmen t limited both cob and kernel development. Overall means were 83.6 %, 82.5 %, 84.5 % and 84.4 % for AUSU, \SS, \SU and A^, respectively. Quality differences in vegetative

Neth.J. agric. Sei.30 (1982) 109 P.C .STRUI K AND B.DEINU M

Table 8.Apparen t digestibility ofth eorgani c matter in thevegetativ e parts(% )a tfinal sampling .

St, St2 H, H2 D, D2 D3 Mean

Auou 59.0 59.9 58.4 61.1 61.8 60.5 61.7 60.3 AUSS 56.6 60.9 56.2 61.2 61.9 59.4 61.0 59.6

As!>u 62.8 64.5 59.5 63.3 63.4 65.4 63.4 63.2 AsS, 60.6 63.6 57.5 61.7 62.6 62.5 61.6 61.4

Mean 59.8 62.2 57.9 61.8 62.4 62.0 61.9

Mean AUSU560.0 ;mea n AsSus 62.3;A USSU 61.8;mea n AUSSS 60.5.

parts were greater (range 56.2 - 65.4). Stover digestibility for all treatments is given in Table 8.Cell-wal l production invegetativ e parts,physiologica l age,rel ative source size (and thus measure of storage or redistribution), year and geno type all affected the quality of the vegetative parts. Since cell-wall production was reduced in the \ period and redistribution was unnecessary because of poor ear development, stover digestibility was always highest in the \Sa treat ment. In these experiments, the different variables of Eq. 1 are not all mutually in dependent. In Table 9 their linear correlation coefficients are presented. The most conspicuous findings were theabsenc e ofa significant correlation between Dslover and Dcrop (because of theambivalen t character ofth e influence ofsuccess ful ear development) and the significance of the relation between ear content and Dcrop, which was usually absent within years. Certain other significant rela tionsals obecam e lessimportan t ifonl y thedat a from oneyea rwer e pooled. It is clear that the effects on crop quality are more complex than can be de scribed by effects on proportion of plant parts or on the quality of plant parts. The Dcropca n alsob eexpresse d by:

Dcrop = (cwc% x Dcwc + (100- cwc%) X DJ/100 - b (2)

inwhich :

Table9 .Matri xo flinea rcorrelatio n coefficients ofvariable si nEquatio n 1 (n = 28). 100-earconten t 1 ^ Dear ^stover L'crop

Earconten t -0.306ns -1.000** -0.441* 0.751** s ns Dear 0.306n 0.665** 0.286 100-earconten t 0.441* -0.751** s ^stover 0.230" ns = not significant * P<0.05 \ , ... > two-sided. ** P<0.01

11o Neth.J. agric. Sei.30 (1982) EFFECTO F LIGHT INTENSITY ON PRODUCTIVITY ANDQUALIT Y OF MAIZE

J i_ _i i i i_ 40 42 44 46 48 50 52 54 56 58 60 62 64 cell-wall content (%) Fig.4 .Th eapparen t digestibility ofth ewhole-cro porgani cmatte r inrelatio n toth ecell-wal lconten t ofth ewhol ecro p(als oa s% ofth eorgani cmatter )a tfina l sampling. cwc% = percentageo fcell-wal l constituents

D,.„,cwc, = truecell-wal l digestibility 100-cwc% = percentage ofcellula r contents Dec = truedigestibilit y ofcellula r contents b •• difference between true digestibility and apparent digestibili ty.Thi s difference includesundigeste d rumen microflora and endogenous excretion. As stated earlier, cell-wall digestibility was hardly affected by shading treat ment. The digestibility of the cellcontent s isalway s almost complete.Th e most variable components of Eq. 2ar e thus cwc% and 100— cwc%. Fig.4 shows the relation between cwc% and Dcrop.Th e cell-wallconten t of the whole crop iscal culated from the cell-wall contents of the fractions. The correlation, although depressed by differences in cell-wall quality among the different crops, was high. The calculated regression coefficient was almost equal to the difference between Dccan d the mean Dcwc. Résumé: ear yield, whole-crop yield and cell-wall yield of normal crops were mainly affected by shading during the Aperiod . Because of itseffec t on ear de velopment, shading A also determined the rate of crop drying. Digestibility, content of cell-wall constituents and of water-soluble carbohydrates, leaf area duration and Fusarium infection were mainly influenced by shading during the Speriod . Neither cell-wall content nor digestibility correlated well with the amount of irradiance received after flowering, sincecell-wal l content wasdetermine d both by cell-wall production before and during the A period and by carbohydrate production during theA an d Speriods . Insubsequen t papers more detailswil lb epresente d about the effects of shad-

Neth.J. agric. Sei.30(1982) 111 P.C .STRUI K AND B. DEINUM ingo n thereductio n ofcell-wal lproductio n and itsconsequence s for cropdiges tibility. The effects of temperature during the grain filling willals ob e discussed infutur e papers.

Implications

The effects of shading treatments were not confined to areductio n in photosyn thesis.Th e mostnoticeabl e side-effects were: —Ea r size was severely affected, especially by shading during the A period, even at lowerdensities . —Ea r yields were closely related to amounts of irradiance, suggesting a direct connection between light and eargrowt h apart from photosynthesis. —Cell-wal l production after flowering, which normally occurs in stems, husks and ears, was more hampered by shading than was dry-matter production. Therefore, the differences in cell-wall content between unshaded and A, treat mentswer esmalle r than expected (cf. Table 5 and Table7) . —Longevit y ofleave san d diseaseresistanc ewer eaffecte d byshading , especial lydurin g the S periods. Shadingha sth e following repercussions on the ears: —Abortio n of the younger tip and mid-kernels; actually this is an accelerated senescence of kernels, including a very early Black Layer Formation and early cessation of dry-matter accumulation. This abortion occurred too soon after the beginning of the shading to have been caused by exhaustion of carbohydrates. Abortion even occurred in crops that had increasing carbohydrate levelsi n their vegetative parts, and in crops with very low plant densities. So even if devel oping kernels are verywea k sinks,i t isunlikel y that abortion iscause d by carbo hydrate shortage alone. —Th e rate of dry-matter accumulation in the ear ismodifie d without a notice able time-lag, just as occurs after complete defoliation (Jenner, 1979; Major, 1980;Struik , unpublished data).

Physiologicalimplications Hormones. Thus, the sink strength and sink sizewer e limited before there was a shortage of carbohydrates. This limitation may be caused by plant hormones (e.g.auxins ,cytokinins , gibberellins, abscisic acid),eithe r being produced in the kernelsthemselves ,o ri nothe r plant partssuc h asroots .Th e lattersuppositio n is most likely. Roots play a leading part in the longevity and vitality of above- ground plant parts, since root tips produce cytokinins necessary for kernel de velopment, sink activity and delay of senescence. For this production root growth isnecessar y (Vaadia &Itai , 1968;Boote , 1977).Th e roots themselves are weak sinks for carbohydrates after flowering (Noodén & Leopold, 1978) and they can only be provided with carbohydrates by the lower leaves (Lupton, 1966; Tripathy et al., 1972; Palmer et al., 1973; Fairey & Daynard, 1978). For several reasons lower leaves are in unfavourable position for photosynthesis,es pecially in shaded crops. After silking there is hardly any net increase in root

112 Neth.J. agric. Sei.30 (1982) EFFECT OF LIGHT INTENSITY ON PRODUCTIVITY ANDQUALIT Y OF MAIZE

weight,althoug h at least part of the normal degeneration iscompensate d for by renewal (Koedjikov, 1967; Mengel &Barbe r 1974;Andr é et al., 1978).Renewa l is hampered and degeneration is stimulated by shading (Pendleton & Weibel, 1965; Brouwer &D e Wit, 1968;Hess , 1968; Boote, 1977; Crapo & Ketellapper, 1981). Root activity declines particularly strongly as a result of low irradiance, because of low carbohydrate levels in the roots (Crapo & Ketellapper, 1981; Massimino et al., 1981). Therefore, it is possible that certain prompt effects of shading are caused bya decrease in root activity and hence in cytokinin produc tion. If shading occurs shortly after grain set, a new balance between root activ ity, leaf activity and ear activity may be achieved after a certain number of ker nels have aborted, as partial sterility promotes the translocation of carbohy drates to the roots (Palmer etal. , 1973).I f shading treatment starts later or isap plied to older crops, the effects will be more detrimental, because of a loss of compensating abilitieso fth ecrop .

N metabolism. Another possible explanation of kernel abortion due to shading may be the shortage ofcertai n newly synthesized nitrogen compounds, because of a lack of nitrate reductase activity (Knipmeyer et al., 1962; Early et al., 1966; Early etal. , 1967).Grai n development requiresspecia l proteins.Sinc enitrat e re duction and nitrogen metabolism areexpensiv e in energy use,thei r assimilation may be hampered more than dry-matter production. As stated earlier, this ex planation can also be used for cell-wall production; it isknow n that lignin pro duction is also energy consuming (Penning de Vries, 1974). Both possibilities may be combined. Trewavas (1981a, b) postulated that although growth sub stances perform an essential function in plant organization, the controlling fac tor may be sensitivity to growth substances rather than a particular growth sub stance itself. The only way of varying this sensitivity is by changing the amount and/or characteristics of specific proteins that form the hormonal binding sites in the cells. Trewavas (1981a, b) and Bogers & Libbenga (1981) suggested that there might be a correlation between developmental stage and binder concen tration. So protein and hormone synthesis may both be necessary for hormonal effect.

If the above-mentioned prompt reaction of root activity to shading is accepted, thefas t reaction ofkerne l development and ofea r growth could beexplained . In analogy, hormonal activity might also explain the close relation between irra diance and ear yield. Finally, a part of the differences in leaf senescing pattern (especially in earlier stages) might be caused by differences in root activity (see Table 3an d Fig. 1),sinc e root cytokinins are required for leaves tofunctio n and toinhibi t senescence. The above-developed hypothesis wasteste d by analysing the accumulation in the above-ground plant parts ofcertai n minerals such ascalciu m and phospho rustha t are difficult totak e up.Estimatin g Ca uptake could beespeciall y useful, since Ca is transported in the same way as cytokinin (Michael et al., 1970), Ca uptake requires energy and Ca is only slightly redistributed in the plant. How-

Neth.J. agric. Sei.30(1982) 113 P.C .STRUI K AND B.DEINU M

ever, mineral uptake decreases sofas t after flowering that differences were only obtained for theA period.

Agricultural implications In regions with low light intensity during grain filling, the ripening of forage maize isaccompanie d bya declin ei ncro pquality .Yet ,majo r falls inyiel d caused by a period with low irradiance do not automatically involve declines in di gestibility, if this period occurs during a stage of crop growth in which cell-wall production istakin g place.O n the other hand, an overcast period shortly before harvesting willgiv ea smaller yield loss,bu t willgreatl y depressdigestibilit y and willstimulat e Fusarium infection. Suitability for ensiling ismainl y determined by dry-matter content and con tent of readily fermentable carbohydrates. Shading shortly after flowering will cause a strong decline in thefirst paramete r and will increase the latter.Th e op posite is true for shading after mid-September. Considerable losses during the ensiling process are most likely if shading occurs during the first part of the grain-filling period. It isno t possible to avoid the effects of an overcast autumn by simple modifi cations to cultural practice, although later sowing shows relatively smaller re ductions in both dry-matter yield and crop quality. Later sowing, however, is not advisable, because in normal years yield and quality will decline consider ably. Even the digestibility of a very early hybrid reacted sharply to shading if shadingoccurre d inlate r stageso fth egrowin g season. The effects ofirradianc e after grain seto ndigestibilit y willb eminimize d if —littl ecel lwal l ispresen t at grain set —th e quality ofth ecel lwall i shig han d remains high —cell-wal l production after grainse ti slimite d —lea factivit y ismaintaine d for alon gtime .

Conclusions

1. Ear development is strongly hampered by shading during and shortly after grainse tan dea rgrowt hi sclosel yrelate d toamount s ofirradianc e after grain set. 2. Final yields ofvegetativ e plant parts are fairly independent of amounts of ir radiance (except yields of husks + shanks), but the quality is affected by light reduction. 3. Whole-plant yields are determined by amounts of irradiance, but also to someexten t bydistributio n ofirradianc e overtime . 4. Whole-crop digestibility is only slightly reduced by shading during the first part of the grain-filling period, because cell-wall production islimite d by shad ing during this phase. Shading after mid-September causes a more severe de cline incro pquality , except indens estands . 5. Infirmities ofol d age,suc h asth e Fusariumdisease ,ar e promoted by shading during the final part ofth e growing season. 6. The above-mentioned effects are modified, but not altered bycro p structure. 1 H Neth.J. agric. Sei.30(1982) EFFECTO FLIGH TINTENSIT Y ONPRODUCTIVIT Y ANDQUALIT Y OF MAIZE

References

André, M.,D .Massimin o& A .Daguenet , 1978.Dail y patterns under thelif e cycleo f a maizecrop . II.Minera l nutrition,roo t respiration and rootexcretion .Physiologia PL 44: 197-204. Becker, W.R. , 1976.Ee nhandleidin g voor de teelt vankorrel - ensnijmais . P.A.Publicati e No 21, pp. 1-84. Behaeghe, T., E.Va n Bockstaele &A .D e Baets, 1981. Maïs als ruwvoederteelt. 4. Belang vand e plantdichtheid, dezaaidatum , deoogstdatu m eneventuel e rijenbemesting bij maïsteelt. Samen vattingva n recenteproefresultaten. Landbouwtijdschrift34 :573-587 . Bogers,R .J .& K .R .Libbenga , 1981.Molecula ractio nmechanism s ofplan t growth regulators.In :B . Jeffcoat (Ed.),Aspect s and prospects ofplan t growth regulators. Monograph No6 , British Plant Growth RegulatorGroup ,Wantage ,pp .177-185 . Boote,K .J. , 1977.Root : shoot relationships.Proc. SoilCrop Sei.Soc. Florida 36 : 15-23. Brouwer, R.& C .T .D eWit , 1968.A simulatio n model ofplan t growth with specialattentio n toroo t growth andit sconsequences .In : W.J .Whittingto n (Ed.),Roo tgrowth .Butterworth , London,pp . 224-244. Bunting, E.S. , 1975.Th equestio no fgrai n contentan d forage qualityi nmaize :compariso n between isogenicfertil e andsteril eplants./ , agric. Sei.,Camb. 85: 455-463. Bunting, E.S. , 1976.Effect s ofgrai n formation ondr y matter distribution andforag e quality inmaize . ExplAgric. 12:417-428. Crapo, N.L .& H .J . Ketellapper, 1981.Metaboli c priorities with respect togrowt h andminera lup takei nroot so fHordeum, Triticum an d Lycopersicon. Am. J.Bot. 68 : 10-16. Deinum, B.& J .Knoppers , 1979. Thegrowt h ofmaiz ei nth e cool temperate climate of the Nether lands: Effects ofgrai n filling on production ofdr y matter and onchemica l composition and nutri tivevalue .Neth. J. agric. Set.27 : 116-130. Early.E .B. ,W .O .Mcllrath ,R .D .Sei f& R .H .Hageman , 1967.Effect s ofshad eapplie d at different stageso fdevelopmen t oncor n (Zeamays L.)production . Crop. Sei.7 : 151-156. Early, E.B. ,R .J . Miller, G.L . Reichert, R.H .Hagema n &R .D .Seif , 1966. Effects ofshad eo n maize production underfield conditions .Crop Sei. 6 :1-7 . Fairey, N. A.& T .B .Daynard , 1978. Assimilate distribution andutilizatio n inmaize .Can. J.Plant. Sei.58:719-730 . Gerakis, P.A .& D . Papakosta-Tasopoulou, 1979.Growt h dynamicso fZea mays L .population s dif fering ingenotyp e and density and grown under illuminance stress.Oecol. Plant.14 : 13-26. Hess,C .E. ,1968 .Interna l andexterna l factors regulatingroo t initiation. In:W .J .Whittingto n (Ed.), Rootgrowth . Butterworth, London,pp . 42-53. Jenner, C.F. , 1979.Grain-fillin g inwhea t plants shaded forbrie f periods after anthesis.Aust. J. PI. Physiol. 6:629-641. Knipmeyer,J .W. , R.H .Hageman , E.B .Earl y &R .D .Seif , 1962. Effect ofligh t intensity on certain metabolites ofth ecor n plant (Zeamays L.) .Crop Sei. 2 :1-5 . Koedjikov, H., 1967. Theroo t system ofmaize . Bulgarian Academy of Sciences Press,Sofia , pp.1 - 154. Lupton, F.G .H. , 1966.Translocationofphotosyntheti c assimilates.Ann. appl. Biol. 57: 355-364. Major, D.J. , 1980. Effect ofsimulate d frost injury induced byparaqua t onkerne lgrowt h and devel opment incorn . Can.J. Plant. Sei.60.419-426 . Massimino, D., M.André , C.Richaud , A.Daguenet ,J .Massimin o & J.Vivoli , 1981.Th e effect ofa day at lowirràdianc e ofa maize crop.I .Roo t respiration and uptake ofN , Pan d K. Physiologia />/.51 : 150-155. Mengel, D.B . &S .A . Barber, 1974.Developmen t and distribution of the corn root system under field conditions.Agron. J. 66 :341-344 . Michael, G., P. Allinger & E. Wilberg, 1970. Einige Aspekte zur hormonalen Regulation der Korngrösse beiGetreide .Z. PßErnähr. Bodenkd. 125 : 24-35. Montgomery, F.G. , 1911.Correlatio n studieso fcorn .Nebr. agric. Exp. StnAnn. Rep.24 : 108-159. National Institute ofAgricultura l Botany, 1979. Recommended varieties offorag e maize. Farmers leaflet No7 ,pp .1-5 .

Neth.J. agric. Sei.30 (1982) 115 P.C .STRUI K AND B.DEINU M

Noodén, L.D .& A.C . Leopold, 1978. Phytohormones and the endogenous regulation ofsenescenc e and abscission. In: D.S . Letham, P.B .Goodwi n &T .J .V .Higgin s (Ed.),Phytohormone s and re lated compounds.A comprehensiv e treatise,Vol .2 .Elsevier/North-Holland ,pp .329-361 . Palmer, A. F. E., G. H. Heichel &R . B.Musgrave , 1973.Pattern s of translocation, respiratory loss and redistribution ofl4 C inmaiz e labeled after flowering. Crop Sei. 13:371-376 . Pendleton,J .W .& R .O .Weibel , 1965. Shading studieso nwinte rwheat .Agron. J. 57: 292-293. Penning de Vries, F. W. T., 1974. Substrate utilization and respiration in relation to growth and maintenance in higher plants.Neth. J. agric. Sei.22 : 40-44. Struik, P.C , 1982.Productio n pattern, chemical composition and digestibility of forage maize (Zea mays L.). Mededeling No 64, Department of Field Crops and Grassland Science, Agricultural University,Wageningen , 28pp . Trewavas, A., 1981a. What is the function of growth substances in the intact growing plant? In: B. Jeffcoat (Ed.),Aspect s and prospects of plant growth regulators. Monograph No 6,Bristis h Plant Growth Regulator Group,Wantage , pp. 197-208. Trewavas,A. , 198lb .Ho wd oplan t growth substanceswork ?Plant, Cell& Environment 4 :203-228 . Tripathy, P.C , J. A.Easti n &L . E.Schrader , 1972.A compariso n of l4C-labeled photosynthate ex port from twolea fposition s ina cor n(Zea mays L.)canopy .Crop Sei. 12: 495-497. Vaadia, Y.& C . Itai, 1968.Interrelationship s of growth with reference to the distribution of growth substances. In: W.J .Whittingto n (Ed.),Roo t growth. Butterworth, London,pp . 65-79. Van Soest, P.J. , 1977. Modified procedure for determining plant cell wall by the neutral detergent procedure.Pape r presented atth eAnnua l Meetingo fth eAmerica n Societyo fAnima lScience . Van Soest, P.J. , R. H. Wine & L.A . Moore, 1966.Estimatio n of the true digestibility of forages by thei nvitr odigestio n ofcel lwalls .Proc. 10th int. GrassldCongr. (Helsinki)438-441 .

116 Neth.J. agric. Sei.30 (1982) CHAPTER 4 Netn. J. agric. Sei. 31 (1983) 101-124

Theeffect s of short and longshading , applied duringdifferen t stages ofgrowth , onth e development, productivity and qualityo f forage maize (Zeamays L.)

P. C. Struik

Department of Field Crops and Grassland Science,Agricultura l University, Wage ningen, Netherlands

Received 11 November 1982; accepted 22Novembe r 1982

Key-words: forage maize,ligh t intensity, development, productivity, digestibility

Summary

In two field experiments, shading was applied to normal stands of forage maize. Theshadin gtreatment s differed induratio n and date of initiation. Short shading during vegetative development affected leaf area, plant height, stem thickness and reproductive development. Final effects on dry-matter yield and quality, however, were small. Short shading during silking drastically reduced ear size and final ear yield. Although the deleterious effect on ear yield was partly compensated for by the higher stover yield, productivity waslo w after the shading tents were removed. Digestibility was also greatly reduced because the production of total dry matter was hampered more than the production of partly indigestible cell walls. Short shading soon after silking curtailed cell-wall formation more than dry-matter production and asa result , cropdigestibilit y wasno t adversely affected. Thereductio n in dry-matter production, however, remained large,especiall y inth e ear, because there wasextensiv e abortion of kernels. Shading after grain set stimu lated the depletion of short carbohydrates in the stover and slowed down the de creasei nth ecell-wal lconten t ofth ewhol ecrop . Crops shaded for long periods yielded more than expected on the basis of the short treatments. The long shading treatments lasted until final sampling. There fore, the earlier a long treatment was initiated, the greater the reduction in yield. The same wastru e for whole-crop digestibility, except in the earliest shading treat ment inwhic hpoo r vegetative development accompanied poor ear development. Shading affected digestibility mainlyb yaffectin g thecell-wal l content.

Introduction

Longperiod s of low light intensity are common in northwest Europe. Such periods affect the development, physiology, production pattern and quality of forage

117 P.C .STRUI K maize. In a previous report (Struik & Deinum, 1982) the effects of reduced amounts of radiation during the post-silking period were described. One of the striking results reported in that paper was that shading had a major effect on cell- wall formation. Shading during certain periods of intense production of structural material might reduce cell-wall production more than dry-matter production, thereby improving crop quality. It was also observed in these earlier experiments that maizema yadap t toadvers e climaticconditions ,becaus e duringlon gperiod so f low light intensity maize produced more than had been expected on the basis of short shadingtreatments . Shadingdurin gan d aroundflowerin g isknow nt olimi tre productive development dramatically (e.g. Early et al., 1967, 1974), thus inducing adifferen t pattern of dry-matter distribution. To study these effects of shading more closely, two trials were set up in which long and short periods of shading were applied to standard crops of forage maize duringdifferen t stageso fearl yan d late development.

Materialsan dmethod s

In 1980e n 1981 thehybri d LG 11 wassow no na light ,sand ysoi lwit hoptimu m ferti lization, weed and disease control. LG 11 isi ncurren t usei nth eNetherland s andi s knownt ob etoleran t todensit y (and thusshading) .Th esowin gdat ewa s2 4Apri li n bothyears . Seeddensit ywa shig henoug ht oensur e afina l plant densityo f 10nr 2. If necessary, the crop was thinned shortly after emergence. In the 1981 experiment drought wasprevente d bysprinkling . The trials were laid out ascompletel y randomized block designs with four repli cates. In the 1981experimen t the continuously unshaded and continuously shaded treatments had twoplot si neac h block toenabl e these treatments tob e sampled on eachsamplin gdate .

Treatments Light intensity wasreduce d to4 0 %o f natural light intensity asdescribe d byStrui k & Deinum (1982). The timing, duration and code of each shading treatment are schematically recorded in Fig. 1,togethe r with the sampling dates, the main physi ologicalprocesse soccurrin gi nth econtro lcro pi ntha t period and the average natu ralligh tintensit y duringth eperio d involved, asrecorde d at Wageningen. The 1980 experiment (henceforth called Experiment 1) contained five short treatments each about twoweek slong ,an d five longer treatments. Each longtreat ment terminated at final harvest, and therefore the later the treatment was ini tiated, the shorter its duration. Treatment S2wa s of intermediate duration. It will beconsidere d asth efina l longtreatment ; the treatment alsoprove d tob eusefu l be causei tenable d theprobabl e effect ofshor t treatments initiated duringth efina l de velopment ofth ecro pt ob e estimated. The 1981 experiment (henceforth called Experiment 2) contained four shading treatments,eac h lastingfou r weeks,an d one continuously shaded treatment. The controls (i.e. unshaded treatments) of both experiments are regarded as shadingtreatment sinitiate d onth edat e offina l harvest.

118 Neth. J.agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELDAN DQUALIT Y OFMAIZ E

1980 physiological av natural light infen- timetable of shading treatments uration (days) code characterization SI y during treatment 2 1 *) 1+) l+l U) M (J cm' day" ) 0 control 1254

leaf appearance ; 1195 « Ji s stem elongation

15 -M stem elongation ; 1595 tassel emergence Tîr-ï '.v.v . 16 J3S anthesis; silking ; K79 fertilization 'llll ns 17 A s grain set* start 1261 of grain filling f) [•) (+) (•0 H -I 15 S, s grain filling 1207

M M M .».•_•.• grain filling and 921. 22 s2 mm maturation -I- (+) + + 100 J i l from late vegetative per lod 1254 '•'•'•'*'»'•'-"•'"'''''*'''**''*'''*'''•'•'•' until harvest 1+) + + 85 hi from tassel emergence 1264 until harvest TTTT'lVl I I I H i i . . u . •. • .. . * 1193 70 J3I flowermg^rain set and grain filling (+) M M 54 A 1 grain set and grain 1109 filling M M M 37 V gram-filling period 1039

30/6 15/7 30/7 15/8 1/9 16/9 1/10 8/10 —» date

1981

av.natural light inten- timetable of shading treatments duration (days) code physiological s during treatment characterization ".5cm- z day1) 0 control 1225

,v.v.;. 28 J, s vegetative growth; 1304 development of inflores

15/6 10/8 7/9 5/10 —- date dotted- shaded undotted =unshade d + indicates sampling date of treatment involved. I+) indicaressampling date ofanothe r treatment projected to the treatment in question. Fig. 1. Timetable ofth etreatment s in 1980 and1981 .

Seth. J.agric. Sei. 31 (1983) 119 P.C . STRUIK

Crop measurementsand yield estimates Vegetative development wasanalyse d asdescribe d byStrui k & Deinum (1982).Es timates of flowering and desynchronization were done as described by Struik (1983a). Ear length and number of 'active' (i.e. dry-matter accumulating) kernels were recorded at final sampling. 10 top ears were analysed per plot. Each short treatment wassample d at thestar t ofth etreatment , atth een do fth etreatmen t and atfina l harvest. Each longtreatmen t (excluding treatment J,li n Experiment 2)wa s sampled atth e start of the treatment, at final sampling and once inbetween . Treat ment Jjl (the long shading treatment, initiated in June) in Experiment 2wa s sam pledo neac h date that ane wshor t treatment wasinitiated , and atfina l harvest. Pre- treatment samplingswer e used for estimating theproductio n of thecontro lcrop . In addition, control cropswer e sampled on 16/9,1/10an d 8/10i nExperimen t 1 ando n 13/7 (4plots) , 10/8( 4plots) , 7/9 (4plots ) and 5/10 (8plots ) in Experiment 2. Thus control samplingsalway sinvolve d twoplot spe rbloc k except for the final twosam plingdate si nExperimen t 1.Th eestimat e ofyiel dmad ewhe n ashor t shading treat ment was terminated also gives an estimate of the yield of the ongoing long treat menttha t had been initiated onth esam edate . The final sampling in 1980 had to be advanced by one week because of bad weather. In Fig. 1 the dates on which treatments were sampled are marked by a + sign. (+) marks a sampling of another treatment that was projected to the treat ment in question. The methods of sampling, separation into fractions and subsampling used in these trials have been described in earlier papers (Struik & Deinum, 1982;Struik , 1983a).

Chemicalanalyses Subsamples were analysed for digestibility invitr o of the organic matter (expressed as apparent digestibility), cell-wall content and cell-wall digestibility. Subsamples ofExperimen t 1 were alsoanalyse dfo r concentrations ofN , P04, Caan dnon-struc tural carbohydrates. The methods used have been described in a previous paper (Struik, 1983b).

Resultsan ddiscussio n

Climaticconditions

The weather in 1980wa s not favourable for growing maize. During May, tempera tures were below normal and precipitation was insufficient. The first part of July wascold ,extremel y wet and overcast (cf. Fig.1) . 1981wa s a very good year for growing maize, mainly because of the favourable conditions in May, when temperatures were high and rainfall was sufficient. In 1981,however , therewer e longovercas tperiod si nth e second half ofJun e (seeFig . 1). Thus in both years shading treatment JjSwa sprobabl y more effective than nor mal.

120 Neth.J. agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD AND QUALITY OFMAIZ E

Vegetativedevelopment

Rateof leaf appearance and number of leaves. Leaf appearance wasslowe d downb y shading in both years. This effect of light on the rate of early vegetative devel opment hasals obee n reported byGmeli gMeylin g (1973).Shadin gprobabl y lowers the temperature of the growing point, which isth e main factor in determining the rateo flea f appearance. The final number of leaves was unaffected by shading. Averages were 14.2 leaves/plant in 1980an d 14.9leaves/plan t in 1981.

Leaf area and leaf-area duration. Maximum leaf area was measured shortly after midsilk. At that time, only a limited number of treatments was in progress: the re sults from these treatments are presented in Table 1. Only the size of the upper leaveswa saffected . Shading duringintensiv e leaf synthesisreduce d leaf area byre ducinglea f length and leaf width. Leavesgrow ni nhig hligh t intensitiesusuall ycon tain more and larger cells than those grown in lowligh t (Dale, 1982). However, fi nal leaf expansion washardl y affected by shading during period J2, suggesting that theeffec t wasmainl yobtained bya reductio n inth enumbe r ofcells . Shadingals oaffecte d the longevity of theleaves .Tabl e 2illustrate sthi sphenom enon with the number of green leaves at final sampling as a criterion of longevity. However, itmus tb eremembere d that thefac t that alea f isgree n doesno t necessar ilymea ni ti sactive . The effects of the shading treatments depended on when they were initiated and onthei r duration. 1) Short shading initiated before flowering stimulated the longevity of the leaves. Longshadin gha d asimila r effect, butonl yi fshadin gwa sinitiate d longbefor e flow ering. 2) Shading initiated at flowering hastened leaf senescence, especially when the shadingwa sprolonged . 3) Shortshadin ginitiate d duringgrai nse tha d asmal lpositiv e effect onth elea fIon -

Table 1. Mean leaf area per plant (in dm2) shortly after silking for all treatments initiated before silk ing.1

Treatment code Experiment1 Experiment2

J,s 35.7ab 32.6* J2s 38.1" 38.5" ab J3s= J31 37.6

J,l 33.6" 32.7a ab J21 36.9

Control 38.3" 39.6b 1 Means without a letter in common are significantly different at P < 0.05 according to Tukey's stu- dentizedrang e test.

Neth.J. agric. Sei. 31(1983) 121 P.C . STRUIK

Table 2. Number of green leaves per plant at final sampling (A leaf was classified as green if less than 50 %o fit sare awa syello wo rdead) .

Experiment1 Experiment2 treatment code numbero f green leaves treatment code numbenun r ofgree nleave s

J^ 6.6 J[S 8.1 J2s 6.4 J2s 5.9 J3s 5.1 As 6.5 As 5.9 Ss 1.3 Sts 4.3

J,l 6.6 J,l 6.4 J21 4.1 Jjl 3.5 Al 1.7 Sil 0.7 s. 2.3 Control 5.2 Control 6.1

gevity. Longshadin g initiated atthi sstag egreatl y reduced the longevityo fleaves . 4) Shading during grain filling greatly accelerated leaf senescence, especially when shadingwa sprolonge d andwhe nshadin gwa sinitiate d ata lat estag eo fgrai n filling. Leavesforme d under the lowligh t conditions of early shading mayb e able totol erate low light intensities during autumn: this would account for the positive effect ofearl y shading. Another possible explanation isth efac t that inshadin g treatments initiated early in the crop's development, the relative sink size of the ear is better adapted to the poor light conditions during ear filling. (The latter hypothesis might alsoexplai n thesmall ,positiv e effect ofth eA s treatments.) Shading initiated at flowering affected leaf senescence because the ear sink was greatly reduced by such treatments. When astron g ear sink was absent, the leaves soon turned purplish red and leaf senescence started earlier (cf. Allison & Wein- mann, 1970). The occurrence of the red colour and the earlier onset of leaf senes cence were also observed when the effect on thefinal number of green leaves was only small (e.g.J 3s).Th e effects were most pronounced for treatment J21 of Experi ment 1. Shadingdurin ggrai n set also reduced the sink strength of the ear but to asmalle r extenttha n shading duringflowering . Asstate d earlier, asmal lreductio n inth esin k size might affect the longevity of the leaves but only when shading isno t long. For treatment Al the source was limited so much that even the considerable reduction ofth e sinkcoul d not prevent senescence beingaccelerate d asi ntreatment s that had been initiated later. When initiated at later stageso f grain development, both short and long shading affected leaf senescence dramatically: the effects of shading ap peared more rapidly if shading was applied later, although the repercussions of the treatment stilldepende d onit sduration . Theexistenc e ofa nea rsin kwhos esiz ean d

122 Neth. J.agric. Sei. 31 (1983) EFFECTS OFSHADIN G ONDEVELOPMENT , YIELD AND QUALITY OFMAIZ E

relative leaf area duration ("tà o— =shor t shading , _ . . HO |- -_.--= long shading 1 Experiment 1 K = short shading , _ . _ • •continuousshading I ExPer.ment 2 100

80 leaf development earaborhon Fusariuminfectio n Fig. 2. Effect of date of initiation of short _1_ _1_ and long shading treatments on the relative -60 -40 -20 0 .20 .40 .60 duration of leaf area. Leaf-area duration of initiation date of shading treatment {days after midsilk of the control ) thecontrol s = 100 %.

strength can no longer be substantially reduced by shading apparently causes the plant todi eprematurel y ifth e sourcei slimited . The effects of shade on leaf senescence after grain set were strongly connected with the severity of Fusarium infection (cf. Struik &Deinum , 1982). It isno t clear whether the Fusarium infection isth e actual cause of the premature senescence or just aconcomitan t side-effect ofshading . Leaf-area duration illustratesth e combined effects of shading on leaf sizean d on leaf senescence. Leaf-area duration after silking was calculated from the weekly data onth enumbe r ofgree n leaves,an dth earea so fth eleave sshortl y after silking. The resulting patterns, shown in Fig. 2, are essentially similar if the duration of the treatments istake n into account. Thethre e factors that affect leaf-area duration are clearlydiscernabl e inth epatter n for Experiment 1.

Plantheight andstem diameter. Table 3illustrate s that early shading reduced plant height considerably. The later ashadin g treatment wasinitiated , the taller the final plant height. Prolonged shadinginitiate d just before flowering even tended tostim ulateth elongitudina l growth ofth estem .Difference s between short and longtreat mentsinitiate d onth esam edat ewer esignifican t butinconsistent . Probably bothdi -

Table3 . Effect ofshadin gtreatment s onplan t height andste mdiamete r (means ± standard erroro f the mean).

Experiment 1 Experiment 2 code plant height (cm) stem diameter (cm) code plant height (cm)

J[S 189 ± 4.8 2.11+0.06 J,s 189 ±6.1 J2s 197 ± 3.7 2.26 + 0.08 J2s 241 ± 4.9 J3s 206 ± 4.2 2.23 + 0.09

J,l 178 ±3.1 2.03 + 0.04 J,l 210 ±4.1 J21 198 ± 3.6 2.35 + 0.05 J31 220 ± 2.7 2.23 + 0.05

Control 215 + 1.4 2.33 ± 0.03 Control 235 ± 2.2

Neth.J. agrlc. Sei. 31 (1983) 123 P. C. STRUIK vision and elongation of stem cells were sensitive to shading. The number of cells alongth e longitudinal axisma yhav e declined asa resul t ofshading :i ntha t case,th e duration and date of initiation of the shading would haveplaye d arole . Short shad ing treatments probably reduced cell number less than long shading; early shading probably resulted infewe r cellsbein gforme d than lateshading . But shading normally stimulates cell elongation in stems (etiolation!). This stim ulation would have been more effective ifmor e cellswer e inth e processo f elongat ingdurin g the shading treatments. Acombinatio n of the effects of shadingo n num ber and sizeo f the cellscoul d explain theobserve d effects onplan t height. The pat tern of radial cell growth (see stem diameter, Table 3)wa ssimila r to the pattern of longitudinal growth, except thatJ 3san dJ 31 had lowervalue stha n expected. Data onste m development mayb erelevan t todigestibility , sinceth enumbe r and thesiz eo fth este mcell saffec t theplant' sabilit yt ofor m cellwall so fpoo rdigestibil ity(cf . section 'Quality').

Reproductivedevelopment

Anthesis, silking, anthesis-to-silking interval andlower-ear development. The flow ering dates for treatments initiated before flowering are listed in Table 4. Treat mentsJ 3san d J31 of Experiment 1 can be regarded asth e same treatment for allob servations mentioned in this table, except for the number of lower ears. These treatments received the same amount of radiation until the end of flowering. Be-

Table 4. Flowering dates, desynchronization, degree of total sterility, and development of lower ears for all treatments initiated before flowering.

Anthesis (cf) Silking (Ç) Desynchroni- Percentage Percentage Number of date (days date (days zation($-cf; of sterile of sterile lower ears after sowing) after sowing) days) tassels top ears per plant

1980 J,s 103 101 —2 5 0 1.1

J2S 103 101 —2 2 5 0.9 J^s 101 99 —2 0 9 1.3

J,l 106 103 —3 12-13 12-13 0.6 J,l 105 104 —1 4 15 0.3 J3I 101 99 —2 0 9 1.0

Control 102 99 —3 1.2

1981 J|S 97 96 —1 5 3 1.1 J2S 94 95 +1 0 42 1.0

J,l 99 98 —1 4 5-6 0.2

Control 94 91 —3 0 0 1.0

124 Neth. J. agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT ,YIEL DAN DQUALIT YO FMAIZ E cause the shading of J3swa sstoppe d before the end of lower-ear development, the effects oftreatment sJ 3san dJ 31 onth enumbe r oflowe r ears differed. Shading before flowering retarded both anthesis and silking, especially when shading was prolonged. Silking, however, was delayed more than pollen shed, es pecially in Experiment 2. This resulted in the female inflorescence having asmalle r lead (see desynchronization values in Table 4). Desynchronization was always small,therefor e pollination wasno thampere d bythi sshadin geffect . Shading,how ever, not only retarded but also reduced flowering by inducing complete or partial sterilityi ntassel san d ears.Onl yth eproportion so fcomplet esteril etassel san dear s are given in Table 4, but the fecundity of the fertile inflorescences in treatments with a high percentage of sterile inflorescences was also low. Sterility in the tassel wasmainl y induced by early shading an increased concomitantly with the duration of shading. Sterility in the ear, however, was mainly induced by shading during silking. If long shading was initiated long before flowering, however, the crop adapted sufficiently tomaintai n itsabilit yt osil k(cf . Jtl,Experimen t 2),thoug h silk ingwa sno tprolific . Fortreatment sJj San d J^ inExperimen t 1 the relation between the proportion of flowering plants and time was not sigmoid but double sigmoid. This indicates that early shading divided the crop into two separate populations. Development of lower ears (i.e. all ears below the top ear that protrude from the axils of the leaves) was inhibited by early, long shading and - to some extent - by short shading that ended before silking. The lower ears can only develop if conditions permit several ears to develop per plant atabou t thesam e (fast orslow )rate ,o ri fcondition sar eadvers e for thedevel opment ofth eto pea r but are lessunfavourabl e for the lowerears .

Earsize. Fig.3 illustrate s the successo f development of theto pear . Ear length and thenumbe r of active kernels at final sampling are plotted against the date onwhic h shading was initiated. All three curves of Fig. 3a clearly show that shading had a pronounced effect on the size of the top ear when it was applied during silking. In the long treatments, the effects of shading were just as large if the shading wasini tiated before silking. Short shading that had been terminated before silking had little effect on ear length. The effects of long and short shading after silking on ear length decreased, concomitantly withth eprogres so fth eea r development. The effects of shading on the number of active kernelswer e similar to the effects onea r length (Fig.3b) . However, sinceshadin g induced kernelst oabor t after grain set, theeffect s remained considerable during earlygrai n fill. Theresult sfro m treatment JjSi n Experiment 1 were atypical. Thelo wnumbe ro f active kernelsresulte d from areductio n inpollination . Pollen wasscarc e during the silking period of the tip kernels of J^ plants. The partial or complete sterility of many tassels in this treatment might have been responsible for this. The pollinated basal kernels, however, were larger than normal. In addition, the rachides of the topear so fthi streatmen t were alsothicke r than normal. The length of the top ear is a more accurate and more objective characteristic than the number of active kernels. The number of active kernels, however, ismor e significant, sincei ti smor e closely related toth e actual sink strength of the ear.

Neth. J. agric. Sei. 31 (1983) 125 P.C . STRUIK

length of ear (cm) 17h

/ o =shor t shad ng , .- „ ,„ t , •* ' irtn^ c*«^ «S Experiment i v y • long shading ' ^.^ « =shor t shading i c ^„ör,to » »continuousshading'ExPenment2 <• l~'t 15 30 1315 30 10 15 1 7 16 158 . June July August September October actiwkernels initiation date of shading treatment 350

/// '/" ' ƒ '/ / . o = short shading , ^ J = long shading I Experiment 1 S ' ""'*Vc'ont™ous shadingl Experiment 2 Fig. 3. Effect of date of initiation of shading (a) on length of the top ear and 15june3° 'juTy 3° Sgust September œfober (b) on number of active kernels on the initiation date of shading treatment top ear.

Dry-matterproduction

Production ofcontrol s ando f continuously shaded treatments

Since the controls and the Jjl treatments serve as references in these trials, their production patterns inbot h experiments arepresente d inFig .4 .Th eproductivit yo f J[ldurin gth eentir e experimental period was35. 4 %o fth econtro l inExperimen t 1 and 35.0 %o fth econtro li n Experiment 2,i.e . productivity wasreduce d more than illuminance. Because of the responses of photosynthesis, respiration, dry-matter distribution and leaf development (andthu sligh tinterception) tosuc hdrasti creduc tionsi nligh tthi si sno t unrealistic. Inbot h yearsther ewa sa characteristi c declinei n stover yield and husk + shank yield duringth e later part of thegrain-fillin g period. Natural light conditions in the Netherlands during September are so poor that the growth rates of the ear are much higher than growth rates of the whole crop. This necessitates the redistribution of water-soluble carbohydrates and other com-

126 Neth. J.agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD ANDQUALIT Y OFMAIZ E

dry-matter yield (Mg ha"1) 16h

control Experiment 1

dry-matter yield (Mgha"1) 10 (- Ji" Experiment 1

top ear

husk*shank 2 / •/ © ...«.rrr —* -I'iB—«,-••!-& a" i ..„ J.-—yiowereafrs huslysnahk* , 50 75 100 125 150 175 50 75 100 125 150 175 days after sowing days after sowing

dry-matter yield (Mg ha"1) 16

125 150 175 50 100 125 150 175 days after sowing days after sowing Fig. 4. Production pattern of unshaded and continuously shaded crops in both experiments. (— o - = whole crop; - - - • = stover; ... + ... = husk + shank; — x — = top ear; .— A .— ; lowerears ;number sindicat eproductio n ratesi nk gha -1day -1fo r theperiod sinvolved) .

Neth.J. agric. Sei. 31 (1983) 127 P.C . STRUIK poundsfro m vegetativepart s to the growing grains.Th e intensity of the redistribu tion depends onth esin ksiz eo fth eea r and onth eproductivit y ofth eleaves .

Finaldry-matte r yields

Fig. 5illustrate s the relation between the final dry-matter yields of stover, husk + shank, top ear + lower ears and of the whole crop and the date of initiation of the shading treatment. Stover yields were comparatively little affected by shading. A very significant yield increase, however, was obtained when shading wasinitiate d just prior to silk ing, especially for short treatments. The absence of an ear sink in these treatments resulted in a marked accumulation of water-soluble carbohydrates in the stover in stead ofi nth eredistributio n mentioned earlier. Theeffect s weresimila rt othos ere sultingfro m the prevention of pollination (e.g. reported byBunting , 1975;Deinu m & Knoppers, 1979). The productivity of such grainless crops probably depends on thestorag e capacity ofth estems ,cobs ,husk s andshanks . Stover yield was greatly reduced when long shading was initiated during vegeta tive development. The earlier the prolonged shading was initiated, the larger the reduction in stover yield. Shadingdurin g grain filling caused small (non-significant) reductions in stover yield because redistribution was more intense (cf. Struik & Deinum, 1982). The yields of husks and shanks declined if long shading was ini tiated at an early date. In contrast, short shading treatments JjStende d to stimulate theyiel do f thisfractio n inbot hyears . The effects of shading on the dry-matter yields of the ears were substantial and were very similar to the effects of shading on number of active kernels. Simplelin ear correlation coefficients of the relation between number of active kernels of the top ear and dry-matter yield of the ears were 0.968 for Experiment 1(P < 0.01; n = 12) and 0.977 for Experiment 2 (P < 0.01;n = 6). In Experiment 1, Jxsde viated from the regression line. This deviation was very significant (P < 0.001) and resulted from the large size of the kernels and the thick cobs, mentioned ear lier. The linear correlation coefficient calculated without this deviation was 0.995 (P<0.01;n = ll). The effects of shading on the yields of the various fractions resulted in large dif ferences in whole-plant yield between treatments. These differences were similar todifference s inea r yield,wit hth efollowin g exceptions: — in all cases, shading during flowering affected whole-crop yield less than ear yield; — for long shading treatments initiated well before anthesis, the effects on whole cropwer eeve n greater than theeffect s onears . Whole-crop yields depended both on the amounts of radiation and on the devel opmental stageo f thecro pwhe n theligh twa sreduced .

128 Neth.J. agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD AND QUALITY OFMAIZ E stover yield or husk+shank yield (Mg ha"1) 11 h

.jT^x»Q i••••TT^4i-* : * • 15 30 1315 30 1015 1 7 16 1 58 June July August September October initiation date of shading treatment ear yield ( Mg ha-1) 10r -

0 L-\, 15 30 1315 30 1015 1 7 16 1 58 June July August September October initiation date of shading treatment whole-crop yield (Mg ha'1) 17h ,x

Fig. 5. Effects of shading on the yields of the various fractions and on whole- crop yield. (— o — = short shading, Experiment 1; — • - - = long shad i ' i 1 i i ing, Experiment 1; ----x = 15 30 1315 30 1015 1 7 16 158 June July August SeptemberOctober shortshading ,Experimen t 2;* = contin initiation date of shading treatment uousshading ,Experimen t2) .

Neth. J.agric. Sei. 31 (1983) 129 P.C . STRUIK

Production rates

Shortshading treatments. Fig. 4illustrate d the production rates of the controls and ofth eJj l treatments. As expected, shading reduced production rate. (The method of calculating this reduction inrat eo f dry-matter production isgive ni nTabl e5 ,wit hJ\ san dJ :lo fEx periment 1 asa nexample. ) Onewoul dexpec t thisreductio n tob edependen t on the productivity of the control. In Experiment 2thi swa scertainl y true (see Fig. 6). In Experiment 1,however , the effects of short shading also strongly depended on the physiological stageo f thecro pwhe n thetreatmen t wasinitiated . Short shading dur ing early grain growth affected dry-matter production much more than was ex pected on the basis of the production rate of the control (Fig. 6). The discrepancy between the two experiments wasprobabl y caused by the difference in duration of theshading . After the shading tents were removed, the crops in Experiment 1tha t had re-

Table 5. Calculation of reduction in rate of dry-matter production for treatments J[San d J(l of Experi ment1 .

Sampling date Dry-matter yields (kg ha-')

control J[S J,l

30 June 942 942 942 15Jul y 3204 1844 1844 1 September 11711 6165 8 October 14112 14676 5602

Reduction inrat eo fdry-matte r production duringshor t treatment (i.e.ope n circlei nFig .6 )(1 5 days): (3204-942)-(1844-942) = ^ fcg^ ^ 15

Reduction inrat eo fdry-matte r production after shortshadin g (i.e.close dcircl ei nFig .6 )(8 5days) : (14112-3204)-(14676-1844) _ „ „ „. ^„ = —23tk gfcha' 1 dayI -1I 85

Reduction inrat eo f dry-matter production during longshadin g (o o inFig .7) : period 30Jun et o 15Jul y (15 days): (3204-942)-(1844-942) = ^ kg^^, 15 period 15 Julyt o 1 September (48days) : (11711 —3204)—(616 5—1844 ) „, , , _ : . = 807k g ha-u 1 dar J 1 48 period 1 September to8 Octobe r (37 days): (14112—11711 )—(560 2—6165 ) 80k g ha-1 dar1 37

130 Neth. J.agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD AND QUALITY OFMAIZ E

reduction mrat e of dry-matter production {kg ha"1day" 1) •240 —o during shading ,,_ . , Expenment 1 a,ter shading ' ._a-_ durlng shadmg, , 2 --• after shading

Fig. 6. Effect of date of initiation of short shading on the reduction in rate of dry-matter production -40 -20 0 «20 «40 «60 during and after the treatment (including S2 treat- initiation dote of shading treatment (days after midsilk of the control) ment) ceived theshor t treatments produced more than the control crop (i.e.th e reduction in production rate wasnegative) , with the exception of J3s.Thus , in Experiment 1, the yield pattern shown in Fig. 5 was determined by the productivity during the shading period itself and duringth epost-shadin gperiod . Notetha t themor eth eini tiation of the short treatment was delayed, the shorter the period after removal of thetents , and the lessreliabl e thecalculate d reductions inproductio n rates. In Experiment 2, the reduction in productivity after shading was affected by the date of initiation of the treatment in the same way as the reduction in productivity duringshadin g (Fig.6) .

Long shadingtreatments. The reduction in yield caused by prolonged shading was always less than expected on the basis of the cumulative effects of the short shad ings. This was especially true for treatments initiated after silking (see Fig. 7). In Fig. 7 the reductions in productivity during different periods of the long shadings are plotted against time. For treatments initiated before silking (J,l,J 21 and J31)th e reduction in rate of dry-matter production eventually increased or remained con stant. A small upward trend in the reduction of production rate was followed bya larger downturn during the final part of thegrowin gseason . The decrease waslarg er the later the shading was initiated. For treatments initiated during early grain filling (Al and S,l)th e initial reduction wasextremel y large but alsodecline d sharp ly.A considerabl e decline wasals ofoun d for treatmentS 2. The pattern illustrated in Fig. 7indicate s that when prolonged shading starts af ter silking, the main effect is achieved during the first part of the treatment. This

Neth. J.agric. Sei. 31(1983) 131 P. C. STRUIK

o—o ^ Ji I 1 .—. = Jj I izrr=Ai'|Expenmenti +—*=S, I • D =S2 J reduction m rate of *—*=J, I Experiment 2 dry-matter production (kg ha"1 day"1) .200

• X i • • 8 o a a x x o

D—D Fig. 7. Development over time ofth e reduction in rate of dry-matter production caused by long 15 30 1315 30 1015 1 7 16 158 shading treatments initiated at different stages September October June July August ofgrowth . shockeffec t ismor esever ei fshadin gi s appliedlate r anddoe sno toccu ri fshadin gi s applied before silking. After theshock , however, theproductio n capacity^f ashad ed crop ismuc h higher (orth e yield losses are much lower) than circumstances would suggest. This phenomenon cannot solely be explained in terms of the devel opment overtim eo fth erat e of dry-matter production ofth econtrol .

Dry-mattercontent

Datao nth efina l dry-matter content of the wholecro par eliste di nTabl e 6. Shading influenced thedry-matte r content byth efollowin g mechanisms. — The drying ofth e stover and ofth e husk + shank fraction was stimulated by shading when shading enhanced Fusarium infection. Fusarium mainly occurred whenth econcentratio n ofsuga r inth estove rwa slow . — The dry-matter content in vegetative parts wasals ohig hwhe n earsfaile d tode velop. Inthes e cases high levels of water-soluble carbohydrates were responsible for the high dry-matter content. The concentrations of sugar-free dry matter in the vegetative partswer emainl y determined byth eFusarium infection. — Ear dry-down wasinhibite d byshadin gwhe n itinduce d ear abortion or reduced thenumbe r of activekernels . — Aswel la sdeceleratin g thedryin go f theear , shadingconcomitantl y reduced the proportion of ear inth efres h matter. Thesedat a clearlyillustrat e howimportan t successful ear development and grain fill are to ensure high dry-matter content and thus the crop's suitability for ensiling

132 Neth. J.agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD AND QUALITY OFMAIZ E

Table6 . Dry-matter content of thewhol ecro pfro m each treatment atfina l sampling.1

Experiment 1 Experiment 2

treatment code dry-matter content (%) treatment code dry-mattedry-m r content(% )

J^ 33.0de J[S 33.3cd cde 1 J2s 31.7 J2s 30.6 * abc J3s 28.0 As 29.3" As 31.1cdc Ss 35.7d S,s 34.4e

J,l 25.0ab J,l 25. ¥ a J21 23.6 ab J31 26.4 Al 29.4bcd e Sil 35.8 \ s. 34.7= Control 31.6cde Control 33.8d 1 Numberswithou t alette ri ncommo n aresignificantl y different accordingt oTukey' sstudentize d range test (P< 0.05). andfo r ensuringa hig hintak eo fdr ymatte rb yth eruminant . Theyals oindicat e that shading determined the chemical composition of the non-structural carbohydrates by affecting ear development. The ratio of starch to total non-structural carbohy drates varied greatly. The composition of the non-structural carbohydrates may af fect the processes in the silage, the digestibility and the feed efficiency (Wilkinson, 1976;Phipps ,1980) . Thedat a on dry-matter content of thepost-silkin g treatments agreewit hdat aob tained earlier (Struik &Deinum , 1982).

Quality

Developmentof quality parameters of thecontrols and of theJ tl treatments. Fig. 8 presents the development over time of the proportion of ear in the organic matter, thecell-wal l yield, theproportio n of cellwal li nth eorgani cmatter , thecell-wal ldi gestibility andth e apparent digestibility ofth eorgani c matter. Ear proportion might affect whole-crop digestibility, because ears are more di gestible than vegetative parts. In the unshaded crops the proportion of ear in creased rapidly from 0 %t o about 55 %i n approximately 80 days. Cell-wallproductio n wasintens e during theperio d from 70t o 125 daysafte r sow ing,bu t ceased thereafter. Therefore thecell-wal lconten t increased prior tosilkin g andwa sa tit smaximu m at silking. Grain filling wasaccompanie d bya declin ei nth e cell-wall content of the crop. The cell-wall content is extremely important for whole-crop digestibility. The cellwal l isth e only organelle of the plant that cannot bedigeste d completely byruminants . In addition toth econten t ofth ecel lwalls ,th e extent towhic hth ecel lwall sca nb edigeste d inth erume n affects thedigestibilit yo f

Neth.J. agric. Sei. 31 (1983) 133 proportion, proportion, content or digestibility content or digestibility

90 r + 90 + >Nceil-wall digestibility s. cell-wall digestibility

80 organic cell-wall yield cell-wall yield matter 1 digestibility .. —-. (Mgha' ) (Mg ha"') ^;=:;; 7 70

60 6 60

50 5 50 cell-walS"l content

4 40 J1 ' Experiment 1 30 3 30

20 2 20

10 - 1 10

0 OL I a—1—a- 100 125 150 175 50 100 125 150 175 days after sowing days after sowing proportion, proportion, content or digestibility content or digestibility (•>/.) 90 90 r

80 cell-wall yield

100 125 150 175 125 150 175 days after sowing days after sowing Fig. 8. Development over time of certain quality parameters in the control and J,l treatments of both experiments. Numbersindicat e rates ofcell-wal l production ink gha- 1day-' . Arrowsindicat e5 0 %silk ing.

134 Neth. J.agric. Sei. 31 (1983) EFFECTS OFSHADIN G ONDEVELOPMENT , YIELDAN D QUALITY OFMAIZ E

thecrop .Th edigestibilit y ofth ecel lwall si nth ewhol ecro pdecline dsteadil y during cropgrowt h but thisdeclin ewa smos t pronounced before silking. Digestibility invitr oonl y dependso n the cell-wallconten t and onth e digestibility ofth ecel lwall san dtherefor e thedigestibilit y ofth eorgani cmatte r declined rapidly during the pre-silkingperiod . After silking the decline sometimes reverses and be comes a small increase, as cell-wall content falls and the decline in the digestibility of the cell walls is decelerated. If climatic conditions limit the decline in cell-wall content (aswa sth e casefo r Jtl, Experiment 1)th e decline indigestibilit y of the or ganic matter may continue. Cell-wall digestibility was little affected by continuous shading. Patterns were similar in both years. Differences in cell-wall digestibility between years were caused by differences between in vitro runs. These differences disappear after standardization.

Effectsof shading treatment on in vitro digestibility. Theeffect s ofshadin g onwhole - crop digestibility are illustrated in Fig. 9. The differences observed mainly devel oped during thefina l part of thegrowin gseason . At intermediate samplings, differ encesneve rexceede d 3 units. Digestibility was poor when ear development was poor. Ear proportion corre lated significantly withwhole-cro p digestibility. In Experiment 1 the linear correla tion coefficient was 0.856 (P < 0.01) and in Experiment 2 it was 0.826 (P < 0.05). The digestibility of the treatments initiated before grain set was particularly well predicted by the linear regression equation. The good digestibility of treat mentsJjl , for example, arose because lowstove r yieldsaccompanie d lowea ryields , whereasi ntreatment s J21,J 3s,J 31 (Experiment 1)an dJ 2s(Experimen t 2)simila r ear yieldswer eaccompanie d bymuc h higher stoveryields . The digestibility of the treatments initiated after grain set did not fit the regres sion equation very well. The effects of longshadin g treatments were mostly greatly overestimated and those of short treatments were sometimes underestimated. An explanation willb eoffere d below. in vitro digestibility of organic matter (•fc) 76-

* \ s \X N ; / / / v.\* / y o short shading \' • long shading Exp.1 Exp.2 -J*- long shading i i ,i ii iii i Fig. 9. Effect of date of initiation of long and short 15 30 1315 30 1015 1 7 16 158 June July August September October shadingtreatment so nth edigestibilit y invitr oo f or initiation date of shading tredtment ganicmatte r atfina l sampling.

Neth. J.agric. Sei, 31 (1983) 135 P. C. STRUIK

Relationbetween cell-wallformation and crop quality.Th e way newly synthesized sugars are used varies during the growing season. In Fig. 8 it has already been shown that the synthesis of cell-wall constituents ceases before that of dry matter. Reducing productivity during the final part of the growing season only reduces the yield of the completely digestible cellsoluble s (predominantly starch and short car bohydrates): shading at the end of the growing season willthu s affect quality more than earlier shading. Incontrast , cell-wallproductio n isintens e from midJul yunti lSeptember . During thisperio d about4 0 %o fth e drymatte r produced consistso fcell-wal lconstituents . During the first half of August this proportion may even exceed 50 %. Reducing the light intensity during this period will reduce the amounts of cell-wall constitu ents more than final dry-matter yields if shading affects the cell-wall production of thewhol eplan t toth esam eexten t asdry-matte r production. However, in both years continuous shading reduced cell-wall formation much less than dry-matter production (see Fig. 8). The short shading treatments of both experiments showed that this was only true for the pre-silking period. But during the final period of cell-wall formation (i.e. during treatments As in 1980 and in 1981)productio n of cell-wall constituents wasreduce d twicea smuc h as dry-matter production. In Fig. 10a the effects of shading treatments on final cell-wall yield are illus trated. The reduction in the cell-wall yield caused by long shading was smaller the later shadingwa sinitiated , upunti lth een d ofth eperio d ofcell-wal lformation . The cell-wall yield ofJ 31 wasremarkabl y high because of the large amount of cellwal li n the stover: this was in turn connected with the increased plant height (Table 3). Short shading in Experiment 1affecte d the cell-wall yield of the whole crop most when applied during and just after grain setting. InFig . 10bth eamount so f cellwal l inth efraction s are plotted against thedate so n whichth eshor t treatmentswer eini tiated. The final amounts of cell wall in the stover of short treatments of Experi -1 ment 1 were always45 0k gha lesstha n thecontrol ,excep t intreatmen t J3s.I n that treatment some additional cell-wall constituents were produced after the shading tents were removed, resulting in exactly the same amount of cell-wall constituents asfo r the control. The high levelo f non-structural carbohydrates that resulted from thefailur e of ear development enabled this 'luxuriant' cell-wallformatio n to occur. This additional cell-wall production wasals oobserve d for the husk + shank frac tion, though less clearly, because early short shading also stimulated cell-wall pro duction inthi sfractio n (cf. Fig.5) . The amounts of cell wall in the ears reflected the success of ear development. Early short shading, however, resulted in a comparatively high cell-wall content in the ear because of a low shelling percentage. As mentioned earlier, JjS had thick cobs. The pattern was similar in Experiment 2. However, the longer duration of the treatments, the smaller number of treatments and thefaste r development made the pattern less pronounced. However, in this trial the cell-wall yield of As was also comparatively low. Because of these effects of shading on the amount of cell wall in the different

136 Neth. J.agric. Sei. 31 (1983) EFFECTSO FSHADIN G ONDEVELOPMENT , YIELD ANDQUALIT Y OFMAIZ E all yield 1 ,a- ) cell-wall yield (Mg ha'1) cell-wall content 5.5h in organic matter (%) —o— = short treatments, Exp. 1 60 - 5.0 --x-- = short treatments,Exp. 2 [•) = S2treatmentof Exp.1 58 4.5 / \ —o—=short shading] Exp 1 56 ...._= long shading) - -—x-—=shor t shading] \ 4.0 •Exp.2 stover 54 long shading -V 3.5 V --' A, / 52 3.0 X o—o \> o 50 2.5 48 2.0 .„„,.= 46 1.5 ' —o— =sh.sh. l husk» 44 .<^.T_--_* ' , u EXP-1 1.0 shank ,. —... * i. sh. \^x 42 Exp. 2 \ * » l.sh. 0.5- 40 0 5 30 1315 30 1015 1 7 16 158 15 301315 30 1015 1 7 16 158 15 301315 30 1015 17 16 158 June July August Sept. Oct June July August Sept. Oct. June July August Sept. Oct. litiation date of shading treatment initiation date of shading treatment initiation date of shading treatment Fig. 10. The effects of shading (a) on the cell-wall yield of the whole crop, (b) on the cell-wall yieldo f the fractions (short shading only),an d (c)o n the content of cellwall si nth e organic matter atfina l sam pling. InFig . 10bth e S2treatmen t hasbee n added tosho wtha t the period during whichcell-wal l forma tioncoul db eaffecte d byshadin g had ended before final harvest.

plant fractions, the pattern of cell-wall yield differed from the pattern of the dry- matter yield of the whole crop, shown in Fig. 6. The consequences of this for the content ofcel lwall si nth eorgani cmatte r areshow ni nFig . 10c.Thes ecell-wal lcon tents correlated significantly with organic-matter digestibility (Experiment 1: r = —0.961 ,P < 0.01;Experimen t 2:r = —0.935 ,P < 0.01) .

Cell-walldigestibility. Th e high linear correlation coefficients between cell-wall content and whole-crop digestibility suggest that the cell-wall digestibility waslittl e affected by shading (cf. Fig. 8). Indeed, the cell-wall digestibility of the shaded cropshardl y differed from the cell-wall digestibility of the control crops,excep t for J21 of Experiment 1 and J2so f Experiment 2. These treatments both induced anex tremely high proportion of cell wallso f the whole crop to be present in the stover. Because stover cell walls are less digestible than the cell walls in the ear shoot this resulted in a considerable decrease in the cell-wall digestibility of the whole crop. Other treatments e.g. J31 and Jxl also showed high proportions of stover cell walls but in these cases these high proportions were compensated for by the better cell- wall digestibility of some of the plant fractions, for the cell-wall digestibility of the plantfractions wa s much more variable than the cell-wall digestibility of thewhole

Neth.J. agric. Sei. 31 (1983) 137 P. C.STRUI K mineral accumulation (kg ha"1) 220

160

100

1_ _L_ _J 1_ 30 15 30 15 1 16 1 8 June July August September October initiation date of shading treatment

Fig. 11. Effectsof shadeo naccumulatio no fCa ,N and P04.

crop. For example,poo r ear development wasofte n accompanied bya bette rdiges tibility of the cellwall so f thewhol e ear shoot. However, it mustb e concluded that the effects ofshadin go n cell-walldigestibilit y onlyplaye d amino r rolei ndetermin ing differences in whole-crop digestibility. Thus, the effects of shading on cell-wall formation and onproductio n ratewer eresponsibl efo r thevariatio n in digestibility.

Mineraluptake

Fig. 11 showsho wth e accumulation of Ca, P04 and Ni nth e above-ground partso f the plant at final sampling was affected by the date on which long or short shading wasinitiate d inExperimen t 1. Calcium, the uptake of which isactiv e (i.e. requires energy),i smainl y present in vegetative parts. Ca accumulation was reduced by long shading if the shading was initiated during vegetative growth. Short shading before silking also reduced the uptake of Ca during the shading but uptake was probably faster after the shading tentswer e removed.

138 Neth. J.agric. Sei. 31 (1983) The accumulation of N and P04 was affected in the same way ascell-wal l forma tion. Nitrogen and phosphorus uptake and cell-wall formation show the same de velopment over time and also seemed to be very sensitive to shading during the same stage of crop development. After pollination has occurred, reproductive de velopment might befavoure d aboveal lothe r plant processes. However, for both N and P04 accumulation, the curves of the long shadings in tersected thecurve so fth eshor t shadings.I ntreatment s Al, Sjlan d S2hig hlevel so f these minerals were found in all plant fractions. These treatments also showed the most severe Fusariuminfection . Long shading during grain filling may have re duced root activityt osuc ha nexten t that selectivityi nth euptak eo fion stha t canb e takenu ppassivel ywa sfinall y lost. Mineral uptake thusillustrate stha t shading effects are not confined toth e above- ground parts of the plant. Root growth and root activity were affected in the same manner as certain other plant processes (e.g. cell-wall formation). Part of the ob served effects of shading might therefore be connected with mineral or protein de pletion or shortage. Root functions other than water and mineral uptake may also haveplaye d arol e (cf. Struik &Deinum ,1982) .

Conclusion

The primary effect of reducing light intensity is to reduce photosynthesis. But the distribution of photosynthates over the plant is determined by the developmental stageo fth eplant , thegrowt h rateso fdifferen t tissueso rorgans ,prevailin gan dpre viousweathe r conditions, and many other factors. In turn, this distribution affects theproductio n capacity and the development ofth ecro pi nlate rperiods . Light also influences growth directly by means of its photomorphogenetic effects on vegeta tive development. Moreover, maize has a short critical period in its development duringwhic h adverse factors such aslo wligh t intensity cause dramatic, irreversible damaget oth ereproductiv e organs. The stage at which shading is applied and the duration of the shading thus affect productivity during and after shading, dry-matter distribution and quality. During shading, productivity is always reduced: after short shading, productivity may be higher, depending on the date of initiation and the duration of the short treatment. Long shading is accompanied by an adaptation to the adverse conditions, but also bya nincrease d susceptibility todisease san d adecreas e inreproductiv e capacity. Shadingaffecte d quality mainly byit seffect s oncell-wal lcontent . During vegeta tive growth, cell-wallproductio n wasaffecte d lesstha n dry-matter production. The opposite occurred during reproductive development. Sincecell-wal lformatio n con tinuesunti lth eearl ypar t ofth egrain-fillin g period, thecell-wal lconten t washighe r in shaded crops than in the control, except when short shading occurred during grain set. Later shadingmerel y curtails theformatio n of cellsoluble s and therefore delaysth efavourabl e declineo f thecell-wal l content.

Neth. J.agric. Sei. 31(1983) 139 References

Allison, J. C. S. &H . Weinmann, 1970.Effec t of absence of developing grain oncarbohydrat e content andsenescenc e ofmaiz eleaves .Plant Physiol. 46: 435-436. Bunting, E. S., 1975.Th e question of grain content and forage quality in maize: comparison between isogenicfertil e andsteril eplants .J. agric. Sei., Camb. 85: 455-463. Dale,J . E., 1982.Th egrowt ho f leaves. Studiesi nBiolog yN o 137.Edwar d Arnold Publishers,London , pp. 1-60. Deinum,B . &J . Knoppers, 1979.Th egrowt ho fmaiz ei nth ecoo ltemperat eclimat eo fth eNetherlands : Effect of grain filling on production of dry matter and on chemical composition and nutritive value. Neth.J. agric. Sei. 27:116-130 . Early, E. B.,W . O. Mcllrath, R. D. Seif &R . H. Hageman, 1967.Effect s of shadeapplie d at different stageso fplan tdevelopmen t oncor n (Zeamays L.)production . Crop Sei. 7:151-156 . Early,E .B. ,J . C.Lyons ,E . Inselberg,R . H. Maier& E . R. Leng, 1974. Earshootdevelopmen t ofMid westden tcor n (Zeamays L.) .Bull. III. Agric.Exp. Stn747 ,pp . 1-44. GmeligMeyling ,H . D., 1973.Effec t of light intensity, temperature anddaylengt ho nth erat eo f leafap pearance ofmaize .Neth. J. agric. Sei. 21:68-76 . Phipps,R . H., 1980.A revie wo f thecarbohydrat e content anddigestibilit yvalu eo fforag e maizegrow n inth ecoo lclimati ccondition s of the UKan d their relevance toanima lproduction . In: W.G . Pollmer & R. H. Phipps (Eds), Improvement of quality traits of maize for grain and silage use. MartinusNij - hoff, TheHague/Boston/London , pp. 291-317. Struik,P.C. , 1983a.Effect s ofswitche si nphotoperio do ncro pmorphology , production pattern andqual ity of forage maize (Zea mays L.) under field conditions. Meded.Landbouwhogesch. Wageningen 83-2:1-27. Struik, P. C, 1983b.Effec t of temperature on development, dry-matter production, dry-matter distribu tion and quality of forage maize (Zeamays L.). An analysis.Meded. Landbouwhogesch. Wageningen 83-3:1-41. Struik, P.C . &B .Deinum , 1982.Effec t of light intensity after flowering onth e productivity andqualit y ofsilag emaize .Neth. J. agric. Sei. 30: 297-316. Wilkinson, J. M., 1976.Voluntar y intake and efficiency ofutilisatio n of whole-crop maize silage. Anim. FeedSci.Technol. 1:441-454.

140 Neth. J.agric. Sei. 31 (1983) CHAPTER 5

Neth. J. agric. Sei.30 (1982) 69-83

Effect ofa switc h inphotoperio d on the reproductive development oftemperat e hybrids of maize

P.C . Struik

Department of Field Crops and Grassland Science, Agricultural University, Wageningen, Netherlands

Accepted: 24Septembe r 1981

Key-words: maize, photoperiod, day length, temperature, reproductive development, flowering, hybrid

Summary

In three phytotron experiments, the reaction of maize (Zea mays L.) to a switch in light phase was investigated. Number of leaves was increased by a long-day phase (20 h) before tassel initiation but was not affected thereafter. Repro ductive development was delayed by long days before tassel initiation and sloweddow n bylon gday safte r tasselinitiation ,bu t eardevelopmen t was affect ed more than tassel development. So the time lag between anthesis and silking increased when short days (12h ) were followed by long days.Th e opposite was true when long days were followed by short days. Direct responses to photope riod, such as number of leaves and tassel branches, occurred over a rather short time.Indirec t effects, such asare a ofleaves ,heigh t of plant and length ofth e ear shoot, however, were maximum when day length did not affect the number of leaves any more. One can therefore control vegetative and reproductive de velopment separately to some extent by a day-length treatment and can desyn- chronize development of the male and female inflorescences, especially at higher temperature.Th ephotoperiodi c response ofmaiz ei sclearl y complex.

Introduction

Maize (Zea mays L.) is a monoecious plant with the staminate inflorescence on top (the tassel) and the pistillate ones in the axils of several lower leaves (the ears). The tassel terminates the main shoot and the ears terminate lateral branches, called shanks.Ther e are mostly ten internodes on ashank , which nor mally dono t elongate. Maize is known as a (sub)tropical quantitative short-day plant, although qualitative short-day, day-neutral and long-day genotypes have been reported (Niopek, 1960; Francis et al., 1969; Francis et al., 1970; Hunter et al., 1974;

141 P.C . STRUIK

Teschemacher, 1974; Coligado & Brown, 1975; Blondon & Gallais, 1976; Ait- ken, 1980; Rood & Major, 1980). According to many authors (Francis et al., 1969; Rood &Major , 1980),th e floral differentiation ofmaiz e can be evaluated by examining the developing tassel. In this view, the effects of photoperiod on plant development end with tassel differentiation. Because maize isdeterminat e ingrowth ,th e rateo fdevelopmen t isshow n byth e final number ofleaves . Under natural conditions, the ear isalway s initiated at acertai n stageo f tassel development, about two days after tassel initiation. The ear can only complete development ifi tdoe sno t lagto ofa r behind thetasse l(Fuchs , 1968). However the female inflorescence has greater requirements for induction than the tassel (Niopek, 1960; Messiaen, 1963; Blondon & Gallais, 1976) and the gap between male and female flowering widens with a longer photoperiod (Messiaen, 1963;Mos s& Heslop-Harrison , 1968;Faungfupong , 1975; Blondon & Gallais, 1976; Aitken, 1980). Because of a longer period to initiation, the number of leaves increases with longer days. The time of initiation is also longer; therefore the number ofmal e and female florets can alsob elarge r (Rag- land et al, 1966; Moss & Heslop-Harrison, 1968; Hunter et al., 1977; Hunter, 1980). Only a few people have worked on the effects of temporary changes in photo period. Faungfupong (1975) shortened the dark period after completion of tas sel initiation and hardly found any effects on tassel development but a pro nounced delay in silking. Scheffer (1978)accelerate d reproductive development by shortening the photoperiod for some days. The moment of treatment was crucial: from the 1-leaf stage until the 9-leaf stage, there was a continuous in crease in efficiency of the treatment. The effects also increased when the num ber of short days increased. Niopek (1960) and Kim et al. (1976) also found an acceleration of development when the photoperiod was shortened for a few days,an d greater effects ifth enumbe r ofshor t photoperiods increased. So one can influence vegetative development and the size of reproductive organs by photoperiod. However the ear and tassel differ in photoperiodic re quirement for induction; they differ also in moment of initiation; the ear may develop poorly if it develops much slower than the tassel. These three aspects provide a way of uncoupling vegetative development, tassel development and ear development. Such an uncoupling byphotoperio d could be useful inphysio logical and agricultural studies, for example on seed production or on the relevance of the ear for production pattern, productivity and quality of forage maize. The purpose of the study was to find a method of changing the production pattern ofmaiz ewithou t changing therat e ofdevelopmen t ofth emai n shoot. Three trials were designed to influence initiation and development of the ear independently of the tassel by a different photoperiod at certain stages of growth. I used two hybrids from temperate regions (both described by Bundes sortenamt, 1980),becaus e they are almost day neutral. If these hybrids respond, photoperiod-sensitive strainswil lreac t in thesam ewa yo rmor e sharply. This article will be followed by a report on two trials in which some of the

142 Neth. J.agric. Sei.30 (1982) SWITCH IN PHOTOPERIOD AND REPRODUCTIVE DEVELOPMENT OF MAIZE main treatments were imposed on anorma l maizecrop .Specia l attention will be paid then toth econsequence s for yield and quality.

Materialsan dmethod s

Maize was grown in 6-litre pots (Trial 1) or 10-litre pots (Trial 2 and 3). Four seeds were sown in each pot. After emergence, the number of seedlings was re duced totwo .Fina l plant density wasabou t 6m~ 2. The potscontaine d a mixture ofsand y soil and peat in equal volumes.Nutrien t solution, adjusted to soil type, wasprovide d adequately. Plants were watered once or twicea day . Relative hu midity waskep t at about 75 %. When the plants grew taller, the volume fraction 6 of C02 in air waskep t at 450 X 10~ . The pots were placed on carts,whic h were moved around in each growth chamber three times per week until the plants were tootal lan d had tob epu to n the floor. Photosynthetically active irradiance in the waveband 400-700 nm was 100 W/m2 1.20 m above the floor for 12 h. Long-day treatment of2 0h wa s achieved byfou r incandescent bulbs(10 0W )ove r 10 m2,whic h burnt for4 h befor e and 4 h after the basic light period. Minimum illuminance during the supplementary photoperiod was 100l xcorrespondin g toa n irradiance in thewaveban d 400-700 nm of0. 4 W/m2, which ismor e than the saturation point of the photosensitivity of maize (Francis et al., 1970; Francis, 1973; Teschemacher, 1974; Faungfu- pong, 1975). InTria l 1,th e plants that showed anther or silk extrusion were counted daily. In the other two trials, the dates of first visible extrusion of anthers and of silks were noted for each plant separately. The plants were checked daily at the same timeo fday . Maximum leaf area wascalculate d atanthesi s by the equation length X max imum width X 0.75 (Montgomery, 1911). The maximum diameter in the middle of the second internode above the soil was estimated with a marking gauge as a measure of stem thickness. Final plant height, tassel length (meas ured from the axil of the top leaf) and number of leaves were measured some timeafte r theen d offlowering . Earswer emeasure d duringgrai n filling. Total number ofvisibl ekernel so rfloret s wasestimate d for theto pea ran d for all the lower ears that arose from the axils.Th e area of the husk laminae (nor mally rudimentary, but for given treatments sometimes large) was estimated with an area meter. Dry-matter yields were of little relevance in these trials. They werecorrelate d withlea farea ,s ofa r as estimated. The treatmentsi neac h trialar etabulate d and described withth eresults .

Results

Trial 1: effect ofphotoperiod and temperatureafter tassel initiation ondevelop ment ofhybrid Blizzard Before treatment, all plants received a light phase of 12h a t 20° Cwit h an equal dark phasea t 15 °C.

Neth.J. agric. Sei.30(1982) 143 P. C.STRUI K

Table 1. Growth conditions after switch in photoperiod inTrial s 1 and2 .

Temperature (°C) Photoperiod (h) day(1 2 h) night(12h)

18 12 12 18 12 20 30 24 12 30 24 20

Treatments with 60 plants each as in Table 1bega n at the 6.5-leaf stage (i.e. 6.5 visible leaves). Because the rate of leaf appearance isconstan t with a certain temperature regime, time and plant age are described linearly by means of a linear scale of visible leaves. In 16 dissected plants the shoot apex showed diffe rentiation ofth e tasselbranche s and sometimes elongation ofth ebasa l branches (i.e. Stage D-E in Fig. 2o f Bonnett, 1966). Photoperiod after tassel initiation influenced development rate. Male flower ing was retarded by only about two days for both temperature regimes, when plants were exposed to long days. Female flowering, however, was retarded more,resultin g ingreate r desynchronization. Variation indat e offemal e flower ing increased. Effects were greater at the high temperature; at the low tempera ture,protogyn y wasfoun d with continuance ofth e 12-hphotoperio d (Table2) .

Table 2. Some plant characteristics indicating vegetative and reproductive development in Trial 1 for hybrid Blizzard.

Temperature after 6.5-leafstag e(°C ) day 18/night 12 day 30/night 24 Photoperiod regime(h ) -> 12-.12 12^20 I2-.I2 12^20

Desynchronization offlowering (60plants) 50 % 9 - 50% a (days) -2 1 0 4. 75 %Ç - 75% C? (days) -2 3 2 7 95 %9 - 95% Cj (days) -2 4 7 10

Reproductivedevelopment (24plants) length ofto pea r(cm ) 16.5 18.1 15.1 18.6 number ofkernels i nto pea r 410 492 489 514 proportion ofbisexua l tassels (%) 15 V/i 0 0

Vegetativedevelopment (24plants) number ofleave s 13.2 13.3 13.2 13.1 heighto fplan t (cm) 234.9 243.0 231.7 250.7 heighto fplant/numbe r ofleave s(cm ) 17.8 18.3 17.6 19.1 av.lea fare a ofa plan t (dm2)1 35.1 37.8 34.5 39.1 area ofhus k laminae (cm2) 0.6 6.1 0.9 22.5 proportion oftillere d plants(% ) 54 29 0 0 1Especiall y theleave sabov e thetop-ea r nodewer elarge r for 12 —> 20h .

144 Neth.J. agric. Sei. 30(1982) SWITCH IN PHOTOPERIOD ANDREPRODUCTIV E DEVELOPMENT OF MAIZE

Differences in ear size reflect differences in duration of floret initiation and more pronounced elongation of the cob. Sex expression in the male inflores cencewa sinfluence d bytemperatur e and photoperiod. As treatment started when the number of leaf primordia was already fixed, there was no difference in final number of leaves. But there were some differ ences in vegetative development (Table 2),indicatin g that long day stimulated vegetative growth. Longday safte r tasselinitiatio n apparently caused anincreas e inapica l domi nance of the tassel and depressed development of the ear-shoot buds and the proportion of tillered plants.Th e main shoot showed a more pronounced vege tative growth.Althoug h high temperatures normally cause alos so fsensitivit y to photoperiod (Hunter et al., 1974; Coligado &Brown , 1975),ther e was a greater effect ofphotoperio d on thevegetativ e growth with acycl eo f3 0an d 24°C .

Trial2: effect ofphotoperiod beforeand aftertassel initiation and oftemperature ondevelopment of hybrid Nicco The trial included 8 X 30plants , in two photoperiod treatments of 12 and 20h in early growth and the four combinations of temperature and photoperiod shown inTabl e 1 from the5.2-lea fstage . Double ridges could not yet be seen in most growing tips but the apex had started to elongate, indicating the real start of the reproductive phase (Niopek, 1960).Bonnet t (1953)calle d thisth e'transitiona l stage'. Asexpected , earlier treatment (5.2-leaf stage)gav e greater effects with photoperiods 12 —» 20h than in Trial 1,althoug h the hybrid used in this trial also ap peared to be more sensitive than Blizzard. Again effects of photoperiod were greater atth ehighe r temperature (Table3) . The photoperiod treatment 20— » 12 h, absent in Trial 1, acted in the opposite way to the treatment 12 —» 20 h. For example, desynchronization was less than with the treatment 12 —> 12 h and the plants had shorter internodes (plant height divided by number of leaves in Table 3). With the treatment 20— > 20 h, anthesis wasmuc h later than for 12 —> 20h ,bu t silkingdat e wasabou t thesame , with smaller standard deviations. Soanthesi s date was more influenced by pho toperiod after thechang e than inTria l 1. Low temperature after the photoperiod switch improved synchronization in all photoperiod treatments but especially with long photoperiod after tassel ini tiation. Reproductive development was also less affected by photoperiod at lower temperature. Some abnormalities occurred. Shanks were enormous for 12 —> 20 h treat ment (compare length ofth e top-ear shoot with length of the top ear), especially with the cycle of3 0an d 24° Cbecaus e of excessive elongation ofth e internodes. Sex expression of the ear shoots wassometime s disturbed, again especially with the temperature cycle of 30 and 24°C , and the photoperiods 12 —*• 20 h. Once there was a plume 13.5c m long on an ear. Such aberrations caused a severe re duction inth enumbe r ofkernels .Th ehybri d Nicco tendst ofor m more than one (flowering) ear per lateral branch, ashappene d in the trial,bu t itsexten t was not

Neth.J. agric. Sei.30 (1982) 145 P.C. STRUIK

12-» 20h 20—• 12 h Ç-o flowering Ç-a flowering (days) number of leaves (days

12 days 17 - i

16 number of leaves

1- L\ J I I I I l_ -L ^V J J L A,J J 5 5 5 : 20/ 3 4 4 5 5 6 6 5 71 75 12/ T 20 '20 'i: 20 leaf stage leaf sfage Fig. 1. Number of leaves ( % ) and desynchronization of silking and anthesis ( O )i n relation to leaf stage at time of photoperiodic switch. Vertical bars in all figures indicate the least-significant difference for 19 treatments, according to Tukey's range test (P < 0.10).

number of tassel branches number of kernels,to p ear number of tassel branches number of kernels,to p ei

20 —» 12h - 6

- 61

- 51

- 5i

- 5J number of tassel branches - 5; o - 5( -« - 4 - U number of »..,»' kernels - 4:

_i i 1_ 5 5 5 12/ 3 4 4 5 5 6 7 76 20, 20 leaf stage leaf stage Fig. 2. Number of tassel branches ( O ) and number of kernels in the top ear( % ) in relation to leaf stage at time of photoperiodic switch.

Neth.J.agric. Sei. 30(1982) 148 SWITCH IN PHOTOPERIOD AND REPRODUCTIVE DEVELOPMENT OF MAIZE av.lea f area/plant (dm2 ) av. leaf arec /plar \ (dm2) 12 -*• 20 h 20 - -»-12 h 63 63 -

61 61 • y • 59 59 57 57 - • / 55 55 - 53 53 - /y=4.21x +29.26 51 51 / r2=0.81;n= 8 49 49 47 47 • / • y=-3.30x +69.43 45 r2=0.61 ,n=9 45 • • 43 43 41 41 _• * 39 39

! i I • ii i i » i 20, 5 5 5 6 U 3 12/. 12 3 4 4 5 5 6 7 7 20/ /20 leaf stage 12 /12 leaf stage 720 Fig. 3. Average leaf area per plant in relation to leaf stage at time of photoperiodic switch.

leaf number upper leaves i 4

3 4|- 5 6

12 o = 12-»12 h .= 20-4.12 h(lea f stage 6.0) 13 x= 12-»20 h(lea f stage 6.0) lower leaves + = 20* 20 h 14 - 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 leaf area (cm2) Fig. 4. Leaf area in relation tolea f number for four treatments.

Neth. J. agric. Sei. 30(1982) 149 P.C. STRUIK

Average leaf area per plant showed a linear relation with the moment of switch until the latest treatments (Fig. 3).Thi s relation is hardly influenced by thenumbe r ofleaves ,bu t mainlyb yth eare a ofth e upper leaves. In Fig.4 th e leaf areas for four treatments are given as an example. 12 —> 20h had larger upper leaves than 12 -» 12h , while 20— » 12h had smaller ones than 20— » 20h .Th e effect of alon gphotoperio d on leaf enlargement was dependent on thenumbe r oflon gday sdurin g theearl y development ofth eleaf . In Fig. 5th e length of the tassel and of the complete top-ear shoot are related to the time of photoperiodic switch. These curves look like the desynchroniza- tioncurves ,bu t the minima or maxima are shifted tolate r stages.Simila r curves can be drawn for stem thickness,lengt h of the top ear, area of the husk laminae, height of the plant divided by number of leaves and individual leaf area if the leaves are counted form above; if leaves are counted from below, the relations are linear like for the total leaf area. For the ear shoot the correlation is not as high as for the tassel length, connected with the differences in number of kernels(compar e Fig.2 an d 5). Length of the top ear ranged from 16.4c m for the 12 —> 12 h control till 22.2 cm for 12 —» 20h , 6.5-leaf stage.Th e areas of the husk laminae were very small for 20- » 12h (less than 20cmVplant) , but very large for 12 -+ 20 h (till almost 200cmVplant) ,a si nTria l2 . From Trial 3, it is clear that different plant characteristics show different patterns of photoperiod response. With regard to number of leaves, for example, plants were only photosensitive during a short time but tassel length, among other things, was influenced during a long period and reached its extreme, when number of leaves was not changeable any more. Because of the

tassel length 12-»-20h length top-ear shoot tassel length 20-»-12 h length top-ear shoot (cm) (cm) (cm) (cm) o 50 46 5( 48 44 4I 46 42 4< 44 40 4- 42 38 4;

40 36 • 4i

•38 34 •31

- 36 32 • 3<

-3 4 30 • 3.

•f _ V-1 J 71 75 12/ 76 20/ leaf stage 12 leaf stage 20 Fig.5 . Tassel length ( 0 )an d length of the top-ear shoot ( -) in relation to leaf stagea ttim eo fphotoperiodi c switch.

150 Neth.J. agric. Sei.30 (1982) SWITCH IN PHOTOPERIOD ANDREPRODUCTIV E DEVELOPMENT OF MAIZE complexity ofth eprocesse sinvolved , evencurve swit h more than one maximum or minimum can be obtained. In these trials,i t hasbee n demonstrated that photoperiod sensitivity inmaiz e isno t confined toth e time from emergence to tassel initiation. The results of the three trials are in agreement with each other, although therei sa n interaction with temperature and hybrid.Th e sexual abnormalities in Trial 2,however ,cause d some disturbance.

Discussion

Flowering. Rate of development of the reproductive organs of maize was re tarded with longday sbu t in thefemal e inflorescence more than in themal eone . Together with the time of initiation, this effect determined the course of desynchronization with a maximum for photoperiods 12 —» 20h and a minimum for 20—> 12h (Fig. 6).Th e distance between the male and the female curve is in fluenced by temperature. At lower temperatures, protandry can even be re versed to protogyny.

Tasseldevelopment. Lon g days increased the number of leaf and tassel-branch primordia but only during the relatively short period before tassel initiation. The production of leaf primordia already stopped before the transition to the double-ridge stage. The tassel branches are the first parts of the tassel to dif ferentiate (Bonnett, 1966). The effects of photoperiod and temperature on the

time time after emergence after emergence

20 h 20- -12 h

date of photoperiodic switch date of photoperiodic switch Fig. 6. Effects of photoperiodic switch on time to extrusion of anthers ($) orsilk s (Ç>)(model) . A gives the maximum desynchronization for 12 - • 20h . B gives the minimum desynchronization for 20-» 12 h.

Neth.J. agric. Sei.30(1982) 151 P.C .STRUI K number of tasselbranche s confirm those ofMos s& Heslop-Harriso n (1968) and Blondon & Gallais (1976).Th e development of the apex is very fast with short days: the larger the number of short days aplan t undergoes during the sensitive stage, the fewer branches it will have. The minimum (number for treatment 12 —» 12 h)wa sver y soonreached . Development ofth e apexwit h longday s took more time, so the maximum number of branches (number for 20— » 20 h) was reached much later.

Sex expression.Photoperio d caused mixing of ears and tassels in Trials 1 and 2. Allflower s ofa maiz e plant are originally bisexual and differentiation ofth epri - mordia proceeds acropetally (Bonnett, 1953). Sex reversal in the inflorescences would only be possible in the top of the ear or at the end ofth e tassel branchesi f it were caused by treatments after the 5.2-leaf stage. Moss & Heslop-Harrison (1968) found sex reversal in the tasselwit h very short days, and Galinat &Nay - lor (1951) even found proliferation of the tassel with short days. In Trial 2, female flowers reverted to male with high temperatures and a photoperiodic treatment of 12 —> 20 h. In Trial 1,som e sex reversal was found in the tassel at lower temperatures, especially for the photoperiods 12—> 12 h. These photoperiod and temperature effects on sexexpressio n ofa maiz e plant correspond to effects found in numerous other monoecious short-day plants (e.g. Heslop-Har rison, 1957).

Indirect responses. The effects on sexversatility , flowering dates and desynchronization, and number of leaf primordia and of tassel branches are the only spe cific reactions to the photoperiod stimulus, found in these trials (contrast Moss & Heslop-Harrison, 1968). Maximum reactions coincided with the period be fore and during the transition stage. These direct responses are 'qualitative' reactions to photoperiod, as they require a certain number of short days. Most other unspecific reactions are completely different, since they are consequences of effects on elongation of vegetative organs. They reached their maximum or minimum later, namely at about the first stage at which photoperiod no longer affected tassel-branch initiation. A later change in photoperiod changed no longer the rate ofdevelopmen t ofth e main shoot, but reduced oraugmente d the number of long days during cell division or cell enlargement. So, most of the vegetative cells experienced the extreme number of long days available for growth at this point. These indirect responses are due to 'quantitative' reactions to photoperiod: the effects depend on the number of long days after a certain stage, since the measure and duration of depression of the dominance of given reproductive organs isaffecte d bythi s number.

Indirect responses witha different pattern. Two curves deviated from the general pattern. The relation for total leaf area was linear (Fig. 3), because the area of the individual leaves increased linearly with leaf stage. Under natural condi tions, the transformation of the apex is responsible for a progressive decline in

!5 2 Neth.J. agric. Sei. 30(1982) SWITCH IN PHOTOPERIOD AND REPRODUCTIVE DEVELOPMENT OF MAIZE initial fractional growth rate of thesuccessiv e leaf primordia (Williams, 1966). If the initiation or development is retarded, the decline may be retarded or re duced, respectively. Effects of day length on rate of development or initiation were recorded for the entire range oftime ,a twhic h the switch wasmad e inTria l 3.A furthe r extension ofth e rangewoul d have provided sigmoid curves. Number ofkernel s in the top ear showed twoclea r peaks for 12 —» 20h ,on e at the beginning of the stage at which the plant issensitiv e tophotoperio d and one almost coinciding with the peak in elongation. Itmigh t be expected that number of kernels would give curves like the desynchronization curves, as they reflect the time available for initiation of floret primordia and asi t isunlikel y that rates of initiation differ (Allison &Daynard , 1979).Th e number of kernels, however, was much lower than expected when the change occurred at stages with 4.5,5.0 , 5.5 and 6.0 leaves,whic h probably form the trasition stage.Th e initiation rateo f female florets could decline when the intensity of the flowering stimulus is drastically reduced during that stage, in which the ear apices are susceptible be causeo fthei r backwardness.

Concluding remarks. Photoperiod treatments of maize should last until the female flowering; on no account should they be stopped after tassel initiation as requirements for induction, initiation and development are not the same for the two inflorescences. The sensitive stage for some direct effects isshorte r than for theindirec t effects. Since conditions like temperature, radiation during the basicligh t period and drought influence the apical dominance ofth e tasselan d the measure of protandry,ther e isa n interaction with photoperiod. The genotypic variation in photoperiodic sensitivity is enormous. But even accepted 'day-neutral' hybrids showed a large effect of switch in photoperiod. The induction, initiation and development offemal e organs are possibly still too photosensitive for West Europe.Th e developmental rate ofth e main-shoot apex is the main determinant of the vegetative growth; the rate of ear development influences the maturing process. Selection for a greater sensitivity to photo period of the main-shoot apex relative to ear-shoot apices and a smaller sensiti vity ofth e lateral branches would provide plants with larger leaf area and better synchronization; if so, genotypes are created, in which the early-maturing characteristics of the treatment with photoperiods 20— > 12h ar e combined with some of the positive effects on vegetative development of 20—> 20h . So the po sitiveeffect s ofearl y and lategenotype s are united. Growing maize under unfavourable conditions (poor light, dense planting) often leads to a poor grain-set, partly by desynchronization of inflorescences. The trials suggest that this decrease in fertility can be partly overcome by long day before tassel initiation. The methods used offer a new line for plant physiol ogy,sinc e sink-source relation can be affected in an unusual way and asprocess esi nmal e and female flowering can be separated.

Neth../. agric. Sei.30 (1982) 153 CHAPTER 6 THE EFFECTS OF SWITCHES IN PHOTOPERIOD ON CROP MORPHOLOGY, PRODUCTION PATTERN AND QUALITY OF FORAGE MAIZE (ZEA MA YS L.) UNDER FIELD CONDITIONS INTRODUCTION

Like all plants, maize consists of a variety of differentiated structures, each with itsspecia l form and function. These specialized organs and tissues are close ly related via the distribution of photosynthates, nitrogenous compounds, nu trients and growth regulators. It is on these relations that the organization of the plant as a growing, developing and producing entity is based. The breeder and the grower, however, value certain plant parts more than others and will try to maximize their yield, even in the case of forage maize, where the whole plant is harvested. The morphology of a forage-maize crop affects its quality as a roughage for ruminants. The digestibility of the plant parts varies greatly within a plant, be cause of differences in cell-wall content and in cell-wall digestibility (STRUIK, 1982a). The proportions of the various plant parts in the final crop can be af fected by harvest date, cultural practice, genotype and climate, or can be artifi cially manipulated. Effects stimulating the proportions of the most digestible parts of the plant in the organic matter will increase digestibility of the organic matter of the whole crop unless these stimulative effects simultaneously cause a decline in digestibil ity in other parts of the plant. The most digestible part of the forage-maize plant is the kernel (BARNES et al., 1971; AERTS et al., 1978; WEAVER et al., 1978; HACKER and MINSON, 1981; STRUIK, 1982a).Numerou s authors have reported that an increase in the propor tion of grains or ears (grain + rachis) is accompanied by a decline in the digesti bility of the non-ear parts (e.g. DEINUM and DIRVEN, 1971; DAYNARD and HUNTER, 1975; GALLAIS et al., 1976; PERRY and COMPTON, 1977; AERTS et al., 1978; WEAVER et al., 1978; PHIPPS and WELLER, 1979; GROSS and PESCHKE, 1980; HUNTER, 1981; STRUIK, 1982b). Continuous ageing of cell walls is one of the causes of this decline (STRUIK, 1982a). More important, however, is the fact that in most maize-growing regions part of the dry-matter accumulation in the grains is realized by the translocation of completely digestible cell solubles from vegetative parts to the ear. This material translocated includes minerals, nitro genous compounds and carbohydrates (HANWAY, 1963; DAYNARD et al., 1969; BEAUCHAMP et al., 1976; STRUIK, 1982a, b); the intensity of the translocation greatly affects the final digestibility of the vegetative plant parts (STRUIK, 1982b; STRUIK and DEINUM, 1982). The combined effects of cell-wall maturation, an increase in the proportion of ear in the crop and a decrease in stover quality mostly result in the whole-crop digestibility after grain set being approximately constant. The continuous de-

156 Meded.Landbouwhogeschool Wageningen 83-2 (1983) cline in quality that precedes flowering ishalte d in the case of maize. Because of the negative effect ofgrai n filling on stover quality, iti squestionabl e whether a high proportion ofgrai n isneede d to obtain a forage maize ofgoo d quality. Artificially preventing grain filling usually only induces slight decreases in whole-plant digestibility (CUMMINS and MCCULLOUGH, 1971; MARTEN and WES- TERBERG, 1972; BUNTING, 1975, 1976; DEINUM and KNOPPERS, 1979), although STRUIK (1982b) hasreporte d larger decreases. PHIPPSe t al. (1982) even reported a considerable increase in whole-plant digestibility, caused byth e improbably low digestibility of the ear fraction (grains + rachis + husks) of the fertile crops. Complete removal ofea r shoots before pollination causes considerable declines in crop digestibility (STRUIK, unpublished data). Since plant organs aremutuall y interdependent, therat e ofpost-silkin g pro duction may depend onth e success ofgrai n set. Barrenness, artificial sterility and ear removal reduce photosynthesis (Moss, 1962; RODE etal. , 1979). BUNTING (1975, 1976), DEINUM and KNOPPERS (1979) and PHIPPSe tal . (1982), however, reported that sterility hardly affected dry-matter yield in North-West Europe. In contrast, KIESSELBACH (1948) in Nebraska (U.S.A.), CAMPBELL (1964; Mis sissippi, U.S.A.), MARTEN and WESTERBERG (1972; Minnesota, U.S.A.) and STRUIK (1982b;Netherlands ) found that the yield of sterile crops was considera blydepressed . Removing the ears completely before pollination can depress yield by up to50-60 % (IREMIREN and MILBOURN, 1978; LESHEM and WERMKE, 1981; STRUIK, unpublished data). Therepercussion s ofea r removal seem tob e much greater than the repercussions ofpreventin g grain set.I nsteril e plants that still bear intact husks, shanks andcobs , the storage capacity-though greatly re duced- islimite d less than inplant s whose ear shoots have been removed. The difference between therepercussion s of removing theear s ando fea r sterility is equivalent toth estorag e capacity ofhusks , shanks andcobs . Only when stor age capacity inth estems , husks, shanks andcob s is insufficient (e.g. because of climate orweathe r conditions) grain filling isapparentl y required to maintain high productivity. As well asth e above-mentioned effects ondigestibility , photosynthesis, pro duction and storage capacity, grain filling hascertai n side effects: - anincreas e instarc h content. Thestarc h content isimportan t because starch tends tob einer t during fermentation in thesilage , in contrast with soluble carbohydrates, which areconverte d toorgani c acids (McALLAN and PHIPPS, 1977). - according to DEINUM and KNOPPERS (1979) more cell-wall material will be produced in thestove r if grain filling isinhibited . The data obtained by KING et al. (1972), however, dono t accord with this. - the dry-matter content ofa normal crop increases much faster than that of a grainless crop or that of a crop with a low proportion of the dry matter present in the ear. This effect ofgrai n filling has been reported by BUNTING (1976), DEINUM and KNOPPERS (1979), PHIPPSe tal . (1982), STRUIK and DEI NUM (1982) and STRUIK (1983). - leaf senescence mayb e affected byea rdevelopment ; both delayed senescence

Meded. Landbouwhogeschool Wageningen 83-2 (1983J 157 (Moss, 1962) and advanced senescence (ALLISON and WEINMANN, 1970; CHRISTENSEN et al., 1981; THIAGARAJAH et al., 1981; STRUIK, unpublished data) may occur in sterile or earless crops. WILSON and ALLISON (1978) stated that an exceptionally large grain sink may cause the plant to die prematurely.

Removal of ears and prevention of pollination are rather drastic measures to take when investigating the effects of grain filling: these treatments are im posed at a physiological stage at which the plant is already fixed and 'pro grammed'. MCALLAN and PHIPPS (1977) and LESHEM and WERMKE (1981) used different plant densities to trace effects of grain filling and concluded that grain filling is not important for quality of the fresh crop. Other researchers (BEERE- POOT, 1981; DEINUM and BAKKER, 1981) have used genotypic variation to show that the proportion of ear in a crop isver y positively correlated with crop digesti bility, though it is not necessarily the most important factor. Earlier phytotron experiments done by the present author revealed that switches in photoperiod may alter vegetative and reproductive development after the duration of the vegetative phase has been fixed (STRUIK, 1982c). If these effects could be induced under field conditions, an elegant method would be available to measure the effects of crop structure on productivity, senescence, dry-matter content and digestibility. This report describes attempts to use this method.

MATERIALS AND METHODS

Background to the method The method is based on the following physiological facts: 1. Initiation of the tassel (the terminal, staminate inflorescence) stops the initia tion of leaf primordia. 2. Initiation of the ears (pistillate inflorescences) occurs some time after tassel initiation. 3. The photoperiodic requirements for the induction of the female inflorescence are greater than those of the male inflorescence. Ear development isals o more sensitive to photoperiod than tassel development. 4. If the ear is made to lag behind the tassel more than normal during its early development, the gap between male and female flowering can widen greatly. 5. The rate at which the inflorescences develop partly determines the vegetative growth (e.g. stem elongation, leaf size) and the size of the reproductive or gans. Lengthening the photoperiod shortly after tassel initiation, but before the photoperiodic requirements of the ears have been completely fulfilled will induce the following reactions: 1. A short delay in anthesis but a pronounced delay in silking. 2. A considerable desynchronization of male and female flowering. 3. A larger leaf area. It is possible to produce these effects without affecting the number of leaves

158 Meded. Landbouwhogeschool Wageningen 83-2 f1983) numbero f numbero f leaves tassel branches

desynchroni zation (o-o*)

leaf area per plant

physiological stage FIG. 1.Schemati c representation of theeffect s ofa photoperio d switcho n number ofleaves ,numbe r of tassel branches,desynchronizatio n and leaf area as afunctio n ofth ephysiologica l stagea t which the switch occurs. A, B and C indicate the stagesa twhic h 4.5, 5.5 and 6.5 leaves are visible. SD = short day; LD = longday ; (based on STRUIK, 1982C).

(and thus the number of stem internodes) (Fig. 1).A s well as the characteristics shown in Fig. 1, plant height, size ofth e reproductive organs and numbero f tillers may also be affected. Shortening thephotoperio d after tasselinitiatio n willaccelerat e the fulfilment of the photoperiodic requirements ofth e ears and will therefore reduce the gap between silkingan d anthesis and willreduc e thesiz eo fvegetativ e and reproduc tive organs. The longer the lengthened photoperiod, the larger the effects will be.

Meded. Landbouwhogeschool Wageningen 83-2 (1983) 159 Method of lengtheningphotoperiod underfield conditions and treatments In 1980an d 1981,field experiment swer edon e in which thephotoperio d was lengthened by suspending strings of incandescent bulbs (60 W) about 2.25 m above the soil level.Th e incandescent bulbs were distributed equally over each netplo tan dwer ecappe dwit haluminiu mt oincreas eilluminanc ean dt odecreas e light dispersal to neighbouring plots. The equipment was checked daily. Net plots were separated by large borders both between and within blocks. Theaverag eilluminanc ea t soilleve lo fplot sreceivin ga lengthene dphotoperio d was 75.1 lx in 1980 and 77.0 lx in 1981; 95%o f the measurements were above 50lx ,correspondin gt oa nirradianc ei nth ewaveban d400-70 0n mo f0. 2W. m" 2. The average illuminance at soil level of plots without photoperiod supplement was0. 2(1980 )an d 0.4(1981 )lx ;illuminanc ei nthes eplot sneve rexceede dvalue s of 2.5 lx (0.01 W.m 2), not even with considerable wind force. Saturation of thephotosensitivit y of maizei sobtaine d at illuminances above43-6 5l x (FRAN CIS et al., 1970; TESCHEMACHER, 1974; FAUNGFUPONG, 1975), while no photo period effects are observed with illuminance below 3l x (FAUNGFUPONG, 1975). In 1980th ephotoperiod swer eswitche d at the 5.5-leafstage ;th e photoperiod treatmentswere :

code photoperiod before photoperiod from 5.5-leafstag e 5.5-leafstag e untilen d of$ flowering n — n natural natural n -20 natural 20h n -24 natural 24h 20-n 20h natural 20-20 20h 20h 24-n 24h natural 24-24 24h 24h

The 20 h treatment was obtained by lengthening the photoperiod both before and after the basic light period (night phase from 23.45 h to 3.45 h). In this paper the emphasis will be on the results of treatments n -*• n, n ->• 24, 24- vn and 24-> 24. In the 1981 trial the photoperiods were switched at the 4.5-leaf stage and the 6.5-leaf stage. The following treatments were applied: code photoperiod before photoperiod from4.5-lea f photoperiod from6.5-lea f 4.5-leafstag e stageunti l6.5-lea fstag e stageunti len dof ? flower ing n — n natural natural natural n — 24a natural 24h 24h n -24b natural natural 24h 24-n 24h 24h natural 24-24 24h 24h 24h

160 Meded. Landbouwhogeschool Wageningen83-2 (1983) Culturalpractice and technical details The soils were amply fertilized. Rows were 75 cm wide. Herbicide had to be applied before emergence becauseo f the installation of theequipmen t to length en the photoperiod. For optimum weed control an extra mechanical treatment was necessary in both years. If necessary, drought was prevented by sprinkling. In 1981 emergence was disappointing. To obtain uniform stands the density was therefore reduced to 4.4 plants per m2. The two experiments differed in year, treatments, location, choice of hybrid and density. Table 1 presents some general information about the methods.

Measurements ofplant growth anddevelopment

Vegetative development The data recorded weekly included number of visibleleaves ,numbe r of green leavesan d height ofth eplant . Duringearl y development thesecro p descriptions weredon emuc h more frequently (sometimes twicedaily ) to determine the exact date for the switch in photoperiod. At silking, the leaf area of the main shoot of 16 (1980) or 20 (1981) plants per treatment was estimated by multiplying the maximum length ofeac h leaf byit smaximu m width by 0.75 (MONTGOMERY, 1911). Shortly after flowering the number of leaves above the top ear was recorded for 16(1980 ) or 20(1981 )plant s per treatment. The stem thickness of the main shoot was measured by estimating the maxi mum diameter in the centre of the second internode above the soil level. These observations weredon eafte r stemgrowt h had ended and alsoinvolve d 16(1980) or 20(1981 ) plants per treatment. On each sampling date in 1981, the number of tillers per row harvested was also recorded.

Reproductive development In 1980,th epercentag eo fplant sshowin g anther or silkextrusio n wasestimat ed every second day by observing 80 plants per treatment (i.e. 20 plants per plot). In 1981, 25 plants per plot (i.e. 100 per treatment) were screened daily

TABLE 1.Cultura l practice and date of application of first photoperiod extension in 1980an d 1981.

Year 1980 1981

Location Wageningen Achterberg Soil type fine-textured clay light and moist sand Hybrid LG 11(FA O 260) Nicco (FAO 300) Final plant density (pl.nr2) 10.05 4.36 Sowing date 24Apri l 24 April Date of 50%emergenc e 16Ma y 12 May First date of long-day treatment 14Ma y 7 May

Meded. LandbouwhogeschoolWageningen 83-2 (1983) 161 during the main period and every second day at the start or at the end of the flowering period. The number of tassel branches per plant wasestimate d on 20plant s per treat ment in the 1981 experiment. The length and number of kernels of the top ear were measured on 40 plants per treatment at the final sampling of both experiments. In 1981maximu m ear thickness was also measured. The number of lower ears (i.e. all ears emerging from the axils of the leaves below the ear leaf of the main shoot) was measured on each sampling date. In 1981 the number of axillary ears (i.e. small ear shoots developed from the reproductive axillary buds in the axils of the husks of the top ear and large enough to extrude from the husks) was also recorded.

Plot size andsampling technique The plots occupied an area of 10 x 9 m2 (1980) or 10 x 7.5 m2 (1981) with two border rows on either side of the plot and one row separating the rows intended for sampling. One extra net row was available for possible additional observationsa tfinal sampling .Bot hexperiment swer elai ddow n asa completel y randomized block design with four replicates. The plots were sampled 23 days after midsilk of the control (approximately at the onset of the rapid dry-matter accumulation in the kernels) and twice thereafter. In 1980th e dry-matter yields at the 5.5-leaf stage were estimated as well. One row 6 m long (4.5 m2) was harvested. The plants were cut off at soil level,counte dan dstore di na col dchambe r duringfurthe r processing.Th e plants were separated into stover (stem + leaves + tassel), husk + •shank , top ear and lowerears . In 1981,tiller s weretreate d asth e fifth fraction. After recording the fresh weight, the fractions were chopped. Husk + shank and stover were chopped with astationar y 1-rowFAH R MH 70chopper . Thechoppe d material was transported directly into an operating concrete mixer by means of a jet of air and a conveyor belt. Subsamples were taken from the stream of material while emptying the mixer. Top ears, lower ears and tillers were chopped with a vegetable cutter. Subsampleswer edrie dt oconstan tweigh ti nforce d ventilated ovensa ta maxi mum temperature of 70°C . After dry weighing, samples were bulked per plant part and per treatment, ground in hammer millswit h sieves of 1 mm and subsampled again.

Chemicalanalyses Although an extensive chemical analysis was carried out, only the results of the in vitro digestibility and cell-wall analysis will be presented, since these two criteria adequately describe quality dynamics. True digestibility in vitro of or ganic matter (DtrUe) was estimated according to the method of VAN SOEST et al. (1966). A series of standard maize samples of known in vivo digestibility for sheep,analyse d ineac h run, made itpossibl e toconver t thedat a to apparent digestibility (Dom). The cell-wall content of dry matter (after dissolving the

162 Meded. Landbouwhogeschool Wageningen 83-2 (1983) starch)wa sestimate d usingth emetho d describedb yVA N SOEST( 1977) . Cell-wall digestibility(D cwc)wa scalculate dfro m truedigestibilit y(D truc),cell-wal lconten t (cwc%)an d ash content (ash%) by means of the formula (100-D, ue) x (100-ash(%) Dcwc= 100 r cwc

RESULTS AND DISCUSSION

1. Climaticdata Table 2show sth emea n temperature,amount s of radiation and precipitation for 1980 and 1981 at Wageningen. The most relevant differences in weather between these two yearswere : a. May 1980 was cold, but sunny and dry; in contrast May 1981 was much warmer, with sufficient precipitation but lessirradiance . b. July wascool and extremely wet in 1980, especially in the first threeweeks . c. The period between 10%an d 90%silkin g was much warmer in 1980 (mean temperature 19.6°C) than in 1981 (mean temperature 15.4°C). These climatic patterns affected the way that the physiological effects induced

TABLE 2.Climati c data for Wageningen for 1980an d 1981.

Month Average temperature ( C) Solar irradiance (MJ.m 2) Rainfall (mm)

Year 1980 1981 1980 1981 1980 1981

May 12.0 13.4 649 496 9.3 64.3 June 14.8 14.4 488 419 66.5 64.3 July 15.6 16.3 425 441 145.7 49.4 August 16.9 16.5 422 406 46.4 19.8') September 15.2 14.7 333 311 27.4 57.9') October 8.7 8.8 7 144 67.4 137.2

') Drought prevented by sprinkling.

TABLE 3.Tim e required to reach specific developmental stages, expressed in days after sowing (24 April in 1980an d 1981).

1980 1981

50% emergence 22 19 4.5-leaf stage 38 31 5.5-leaf stage 43* 35 6.5-leaf stage 48 39 50% £ flowering1) 102 91 50%? flowering1) 100 92

') of the control. *tim e of change in photoperiod in some treatments.

Meded. Landbouwhogeschool Wageningen 83-2 (1983) 163 bymanipulatin g thephotoperio d weremanifested . Thecoo lweathe r during ear lygrowt h in 1980delaye d development and consequently the timeo f the photoperiod switch was later (Table 3). Therefore in 1980 the switch was done at a timewhe nnatura l daylengthwa ssomewha t longertha n in 1981.A swell ,dens e cloudcove raroun d thetim eo fsunris ean d sunsetma yshorte n natural daylength considerably (FRANCIS, 1970).I n 1980th eamount s ofirradianc e andth e relative duration of sunshine during May and June weremuc h higher than in 1981. The data on hourly recorded light intensity also suggest that photoperiods were longer in 1980.I tmus t therefore beconclude d that lengthening the photoperiod was lesseffectiv e in 1980.Coo l weather during the pre-silking period decreases apical dominance and will thus limit the effects of photoperiod on desynchronization (STRUIK, 1982c).Lo wtemperature s alsocaus eprotandr y to revert topro - togyny (Table 3; cf. STRUIK, 1982c). High temperatures during the flowering period shorten the anthesis-to-silking interval of each individual plant and will therefore reduce the effects of photoperiod treatments.

2. Vegetative development

2.1. Leaf appearance The rate of leaf appearance was not affected by photoperiod. This agrees with data presented by BROUWER et al. (1973), GMELIG MEYLING (1973) and HUNTER et al. (1977). Because of differences in the duration of leaf initiation, the numbers of leaves ultimately produced per plant differed (Table 4). The data fitted inth eexpecte d pattern shown inFig . 1. Only thephotoperiod s before the photoperiod switch influenced the number of leaves, except in the case of treatment n -*• 24a, where the switch took place at the 4.5-leaf stage. However, the differences between the number of leaves in the different treat ments were small in both years.

2.2. Plant height and stem diameter Photoperiod affects plant height by affecting the number of internodes and internode length (AITKEN, 1980; STRUIK, 1982c). Differences in plant height arose when differences in leaf number became apparent. Final plant heights areliste di nTabl e4 togethe r with themea n internode length (estimated bydivid ing final plant height by final number of leaves) and stem diameter. In 1980, the photoperiod before the switch affected plant height by means of its effect on the number of phytomeres. The photoperiod after the 5.5-leaf stage affected plant height through its effect on internode length, sometimes at theexpens e of the radial growth of the stem. Internod e elongation correlated significantly with the anthesis-to-silking interval (simple linear correlation coef ficient r = 0.899, P<0.01) mentioned below. In 1981,difference s were smaller than in 1980, and the internodes of plants grown under long days elongated less than in 1980. The linear correlation between desynchronization and internode elongation wasagai n significant (r = 0.936, P< 0.05) . Stem thickness was not affected in this experiment. Since the correlation between elongation and

164 Meded. LandbouwhogeschoolWageningen 83-2 (1983) desynchronization was significant in both years and since photoperiod itself is not the only factor determining internode elongation, these two correlated phenomena might have a common physiological basis. Perhaps the size of the tassel influences its production of auxins and gibberellins; these growth regula tors are necessary for the suppression of axillary buds, cell elongation and cell division (cf. MESSIAEN, 1963; STRUIK, 1982C). The production of these growth regulators is probably not only affected by the duration of the light phase but also by the quality and intensity of the light during the extension of the photope riod.

2.3. Leaf area and leaf senescence Leaf area increases with longer photoperiods, not only because more leaves are produced but also because the individual leaves are larger (AITKEN, 1980; HUNTER, 1980; STRUIK, 1982C; see also Fig. 1). Leaf areas at silking are listed in Table 4. Data of individual plants suggest that 20->20 and 24->24 (1980) were somewhat underestimated. Otherwise the data agree with the trends antic ipated in Fig. 1.Difference s in light interception were not large enough to induce significant differences in dry-matter production. The number of dead leaves in all photoperiod treatments showed a similar development over time. In 1980, however, 24 -+n tended to senesce faster.

2.4. Other data on vegetative development The number of above-ear leaves in 1980 was independent of photoperiod treatment. Thus, differences in final number of leaves were caused by differences in the number of leaves below the top ear. The ratio of leaf area above the ear to total leaf area was therefore smaller in treatments receiving longer photoperi ods before the switch, especially when a long-day treatment was followed by a short-day treatment. In the 1981 experiment, both the number of leaves below the ear and the number of leaves above the ear differed between treatments, resulting in relative ly more leaf area above the ear in n ->24a and n -*24 b than in the other treat ments. These differences in distribution of leaf area might induce differences in dry-matter distribution. The number of tillers will be discussed in section 3.2, together with other phe nomena related to apical dominance.

Résumé: The data on vegetative development agreed with those presented in an earlier paper (STRUIK, 1982C). Differences between the treatments in these field experi ments, however, were small. The main differences were in leaf area per plant and inplant height.

Meded.Landbouwhogeschool Wageningen 83-2 (1983) 165 TABLE 4. Data on vegetative development of all treatments in both experiments.

Treatment Mean Mean Mean Mean Mean number of plantheigh t internode stemdiamete r leafarea/pl leaves/pl (cm) length(cm) t (cm) (dm2)

1980 n — n 14.1 a§ 195 a 13.8 2.43 b 35.7 ab n - 20 14.0 a 207 ab 14.8 2.22 ab 38.9 ab n -24 14.2 a 221b c 15.5 2.02 a 41.6b

20-n 14.5a b 207 ab 14.3 2.21 ab 36.5 ab 20-20 14.5a b 204 ab 14.0 2.12 ab 35.2a

24-n 15.1 b 213 abc 14.1 2.10 ab 38.3 ab 24-24 15.2b 231c 15.2 2.32 ab 39.9 ab

1981 n — n 15.1 ab 212a 14.0 3.21 65.3a n — 24a 15.6 bc 224b 14.3 3.43 70.1 ab n -24b 14.9 a 222 b 14.9 3.30 71.0ab c

24-n 16.3 d 219 ab 13.4 3.31 71.7 bc 24-24 16.2 cd 226 b 13.9 3.31 76.2 c t Statistical analysis isnot possible for this parameter. § Means with a letter in common are not significantly different at the 0.05 probability level, ac cording toTukey' s studentized range test.

3. Reproductive development

3.1. Flowering dates and desynchronization Fig. 2illustrate s the development over time of the proportion ofplant s show ingpolle n shed and silk extrusion for the n -*• ntreatment s ofbot h experiments. The way ofestimatin g desynchronization (i.e.numbe r of days required to reach 50% silking minus number of days required to reach 50% pollen shed) is also illustrated. Estimates of 50%flowerin g dates and desynchronization valuesar e presented in Table 5. To simplify the discussion, the desynchronization data have been modified by subtracting the desynchronization value of the control. In this way the direct effect of temperature on desynchronization is neutralized. The flowering dates differed in the same way in 1980 and in 1981. However, in 1981 the differences were much more pronounced. Long days before and after the photoperiod switch retarded both pollen shed and silking. However, the photoperiod before tassel initiation affected anthesis more than silking, whereasth eopposit e wastru e for photoperiod after tasselinitiation . Each treat ment therefore showed a characteristic desynchronization value. Long photoperiods during the entire growing season increase the desynchro nization because silking is delayed more than anthesis. This has already been 166 Meded. Landbouwhogeschool Wageningen 83-2 (1983) proportion of flowering plants (°/o) 100 90 80 - 1980 70 -o— .

98 102 106 110 days after sowing FIG. 2.Cours e of proportion of flowering plants in untreated plots of both experiments, a indicates the desynchronization (Ç-cî).

reported by FAUNGFUPONG (1975), BLONDON and GALLAIS (1976), AITKEN (1980), STRUIK (1982C) and other researchers (see also Fig. 1). Although the difference between n -»• n and 24 ->2 4 was similar in both years, Nicco seems to react more sharply to photoperiod switches than LG 11, certainly if the later stage of the switch is taken into account. Again, the differences between treatments were rather small but agreed with expectations based on phytotron experiments. Similar effects resulting from photoperiod switches were also obtained by FAUNGFUPONG (1975). Inal lcase sdesynchronizatio n wasto o short toaffec t theexten t of pollination.

Meded.Landbouwhogeschool Wageningen 83-2 (1983J 167 5. Dry-matter content The proportions of dry matter in fresh material ('dry-matter content') are listed in Table 8fo r certain fractions at final sampling. The dry-matter content of top ear, husk + shank and of the whole crop was significantly different at all samplings in both experiments. In all cases trends were similar: dry-matter content was approximately the same for n -»n and 24- »n and much higher than for n- +2 4an d 24 ->24 . There were no clear differences in the dry-matter content of stover, or lower ears, or tillers, although the trends were often the same as those in the top ear, husk + shank and wholecro p in 1981(Tabl e 8).Whol e cropdry-matte r content wascalculate d from thedry-matte r content of theindividua l fractions and their proportions of fresh matter. During the grain-filling period the dry-matter con tent and the ear proportion both increase very rapidly; the proportion of husk + shank issmal l and thedry-matte r content in the stover increases only slightly before complete senescence or frost damage. In these trials therefore, the dry- matter content of the whole crop was mainly determined by the proportion of ear in the fresh material and its dry-matter content (see Fig. 4).An y differences between treatments in the proportion of ears decreased during grain filling, whereas differences inth edry-matte r content ofth eear sdi d not alter very much. Differences in the dry-matter content of the whole crop increased during the post-silking period because the fraction that exhibited the greatest differences

TABLE 8. Whole-crop yield and dry-matter content of stover, husk + shank, top ear and whole crop at final sampling.

Dry-matter yield Proportion ofdr y matter in fresh material (%) (Mg.ha"1)

wholecro p stover husk + shank topea r wholeplan t (incl.tillers )

1980 n — n 14.36 18.5 24.7 51.3 29.3 n — 24 14.79 18.7 23.0 47.9 27.3 24 — n 15.03 19.3 24.7 51.4 29.6 24 — 24 14.47 18.5 21.9 47.0 26.7

0.051 0.011 0.005

1981 n -» n 15.29 20.2 27.1 55.9 31.3 n — 24a 15.21 18.2 24.5 53.7 28.7 n -24b 15.93 18.3 23.4 53.8 28.8 24-n 15.45 19.5 27.9 55.5 30.6 24-24 15.39 18.9 24.2 53.6 29.1

P ns ns 0.013 0.004 0.039

' ns = not significant.

174 Meded. Landbouwhogeschool Wageningen 83-2 (1983) dry-matter content dry- matter content whole crop (%) top ear (%) 30 60 26 ear as a 50 proportion of whole c fresh matter -)22 40 32 18 30 - topear^O' ::.- ,4 28 14 20 s*'' .--•••" .-.^ 24 Ï*' ...'•- .•;•••" 1980 o = n-»n 10 : • = n• »2 4 20 .:::-' 'proportion x=24-«-n of ear +=24-»2 4 O»- *'•' 16 -*i 20 30 40 50 60 70 80 days after midsilko f control dry-matter content dry-matter content whole crop(% ) top ear (%) 30

60 ear as a whole proportiono f 50 fresh matter C/o) 30 40

26 30 22 20 A• « n-»n * n-»24a 18 10 • • n-*24b ,~* proportion • =24 -»n ^fi- of ear + =24— 24 14 0 »J-, JL. "20 30 40 50 60 70 80 days after midsilk of control FIG. 4. Development over time of dry-matter content of the whole crop ( ) and of the top ear ( )togethe r with the proportion of whole crop fresh material that is accounted for by the ears (....). between treatments (i.e. the ear) became increasingly important. Sinceea rdry - matter content correlated withsilkin gdate , thedry-matte r content ofth e whole crop also closely correlated with silkingdate .Th e linear correlation coefficients at final sampling were -0.943 (P<0.01; n = 7)an d -0.998 (P<0.01; n *= 5)fo r 1980an d 1981, respectively. Thus the rate ofth eea r development andno tth e rate ofdevelopmen t ofth e main shoot determined the course ofth e dry-matter content ofth e whole crop. At final sampling the dry-matter content ofth e whole crop decreased by 1.1% (1980)o r0.5 %(1981 )fo rever y day the silking was delayed. These high regres sioncoefficient s emphasize therelevanc e ofgoo d ear development forth e matu ration ofmaiz e asa forage crop.

Meded. Landbouwhogeschool Wageningen 83-2 (1983) 175 Résumé: Thedry-matter content of thewhole cropwas mainly affected by thedry-matter content of theear and the proportion of earin the fresh material. Dry-matter con tent was closelycorrelated with silking date.

6. Cell-wall content and invitro digestibility A plant is composed of cell walls and cell contents. Cell contents are almost completelydigestibl efo r ruminantsbu tcel lwall sar eonl ydigestibl et oa certain - variable-extent. The digestibility of a forage-maize crop as roughage for rumi nants is therefore determined by the cell-wall content and the digestibility of the cell walls. Vegetative parts contain a considerable amount of poorly diges tible cell-wall constituents. By contrast, ear parts are mainly composed of cell contents and highly digestible cell walls.

Sincewhole-cro p yieldswer e fairly constant and dry-matter distribution was variable, the cell-wall content, cell-wall yield, cell-wall digestibility and in vitro digestibility of organic matter may vary. Table 9 presents the data from the most relevant treatments and fractions at final sampling. The cell-wall yield at first post-anthesis sampling (23 days after midsilk of the control) showed only a small variation between treatments. The amounts of cell wall in the stover, however, were much greater if long days were applied after tassel initiation. In both years these differences were still present at final sampling (Table 9), although in 1980 the 20 h treatments did not conform to the pattern very well:a t first the smaller amounts of cell wall in the stover were compensated for by larger amounts of cell wall present in the ear parts. At the first sampling after silking the ears in treatments n -»n and 24 -»n were more developed. Final ear sizewa sstimulate d by aphotoperiod-induce d deceleration of ear development, resulting in considerably high cell-wall production during September and high yields of cellwal l in the ear (Table 9).N o important differ ences were induced in cell-wall formation in husks + shanks. The combined effects of photoperiod treatment on cell-wall formation in different plant frac tionsresulte d infinal cell-wal lyield so fth ewhol ecro p shown inTabl e9 .Whole - cropdat a ofth e 1981 experimentwer esomewha t distorted bytille r development. Therefore data for the crops without tillers are given. Total cell-wall yield was affected by theexten t ofvegetativ e development, delay ofreproductiv e develop ment and ear size. Theeffect s ofphotoperio d switches on thecell-wal l content in the stover were much greater in 1981tha n in 1980,bu t cell-wall content in the ear differed con siderably in both experiments because of differences in physiological stage and shelling percentage. In the 1981 experiment the cell-wall content of the top ear of 24- >2 4wa s lower than expected on the basis of data from other treatments and earlier samplings. Because of these effects on cell-wall content of the top earan d becauseo fth eeffect s ofphotoperio d mentioned aboveo nth e proportion of the ear, the cell-wall content of the whole crop showed clear differences be tween treatments, especially in the 1980experiment . In thisexperiment , thecell -

176 Meded. Landbouwhogeschool Wageningen83-2 (1983) wall content of the whole crop correlated significantly with silking date (P<0.05). Estimates of cell-wall digestibility are more inaccurate than estimates of cell- wall content or organic-matter digestibility, especially in ear samples where the cell-wall residue after in vitro digestion is only small. Differences in cell-wall digestibilitywer esmal lan d inconsistent;whol ecro pcell-wal ldigestibilit ya t final samplingshoul d therefore beregarde d asbein gunaffecte d byphotoperio d treat ments. Thus the continuous decrease in cell-wall digestibility was similarly not affected by the physiological stage of the crop. Photoperiod treatments seemed tohav edisturbe d thesynchronizatio n betweencro pmaturit y and cell-wall matu ration. In vitro digestibility of the fractions differed only slightly in both experiments (Table 9). Differences in whole-crop digestibility therefore depended mainly on differences in the proportions of the different fractions in the organic matter. Only in the 1980experimen t did these proportions still differ at final sampling. Résumé: Long days before and after tassel initiation stimulated cell-wallformation in vegetative parts. Long days after tassel initiation stimulated cell-wellformation in the ears. Both cell-wall yield and cell-wallcontent were therefore affected by photoperiod treatment. The consequences of thison whole-crop digestibilitywere small.

OVERVIEW

Thereactio n ofth eplant st ophotoperio d switches,a sexpresse d in the number of leaves, number of tassel branches, desynchronization and leaf area was as postulated in Fig. 1.

VBLE 9.Cell-wal l yield (cwc yield),cell-wal l content (cwc%),cell-wal l digestibility (Dcwc)an d in vitro digestibility organic matter (Dom) of stover, top ear and whole crop, excluding tillers, at final sampling.

Stover Topea r Wholec ;ro p

cwcyiel d cwc% i-'cwc J-'om cwcyiel d cwc% L'cwc L^om cwcyiel d cwc% Ucwc i-'om 1 -1 (Mg.ruT ) (%) (%) (%) (Mg.ha ') (%) (%) (%) (Mg.ha ) {%) (%) (%)

1980 — n 3.19 60.5 62.0 61.2 1.18 15.4 73.1 83.6 5.33 37.1 65.6 74.0 -24 3.70 61.1 62.1 61.3 1.40 19.3 80.4 84.0 6.04 40.8 67.2 73.3 — n 3.51 62.1 62.3 61.1 1.38 17.4 78.3 84.0 5.88 39.1 67.0 74.0 -24 3.70 61.3 62.5 61.7 1.52 21.6 76.4 82.5 6.16 42.6 67.1 72.7

1981 — n 2.58 58.2 57.1 62.9 1.12 16.1 75.0 86.8 5.17 37.7 63.8 76.2 -24a 2.82 60.5 58.8 62.8 1.33 19.5 75.4 86.1 5.66 40.1 65.8 76.2 -24b 2.95 60.6 58.3 62.3 1.40 19.2 72.1 85.5 5.79 39.9 64.0 75.5 — n 2.61 57.0 58.1 63.9 1.23 18.2 78.3 86.9 5.43 38.8 65.3 76.5 -24 2.91 59.7 58.6 63.0 1.29 18.1 74.6 85.6 5.61 39.1 64.1 75.9

Meded.Landbouwhogeschool Wageningen 83-2 (1983) 177 CAMPBELL, C. M.: 1964.Influenc e of seed formation ofcor n on accumulation of vegetative dry matter and stalk strength. Crop Sei., 4: 31-34. CHRISTENSEN, L. E., F. E. BELOW and R. H. HAGEMAN: 1981. The effects of ear removal on senescence and metabolism of maize. Plant Physiol., 68: 1180-1185. CUMMINS, D.G .an dM .E . MCCULLOUGH: 1971.Compariso n ofmal e sterile and male fertile corn for silage. Agron. J., 63: 46-47. DAYNARD, T. B.an dR . B. HUNTER: 1975. Relationships among whole-plant moisture, grain mois ture, drymatte r yield andqualit y ofwhole-plan t corn silage. Can.J .Plan t Sei., 55: 77-84. DAYNARD, T. B.,J .W . TANNER andD .J . HUME: 1969. Contribution of stalk soluble carbohydrates to grain yield incor n (Zea mays L.). Crop Sei., 9: 831-834. DEINUM, B. and J. J. BAKKER: 1981. Genetic differences in digestibility of forage maize hybrids. Neth. J.agric . Sei., 29: 93-98. DEINUM, B. and J. G.P . DIRVEN: 1971. Climate, nitrogen and grass. 4.Th e influence ofag e on chemical composition andi nvitr o digestibility ofmaiz e (Zea mays L.)an d tall fescue (Festuca arundinacea Schreb.). Neth. J.agric . Sei., 19: 264-272. DEINUM, B.an d J. KNOPPERS: 1979.Th e growth of maize inth e cool temperate climate of the Nether lands: Effect of grain filling on production ofdr y matter and on chemical compositionan d nutritive value. Neth. J.agric . Sei., 27: 116-130. FAUNGFUPONG, S.: 1975. Effects ofprolonge d low light intensity and photoperiod ongrai n yield and some other agronomic characteristics of corn (Zea mays L.). Ph.D. thesis, Iowa State Univ., Ames, pp. 1-171. FRANCIS, C.A. : 1970. Effective day lengths for the study of photoperiod sensitive reactions in plants. Agron. J., 62: 790-792. FRANCIS, C. A., D. SARRIA V., D. D. HARPSTEAD and C. CASSALETT D.: 1970. Identification of photoperiod insensitive strains of maize (Zea mays L.). II.Fiel d testsi nth etropic s with artificial lights. Crop Sei., 10: 465-468. GALLAIS, A., M.POLLACSE K and L. HUGUET: 1976.Possibilité s desélectio n dumaï s entan t que plante fourragère. Ann. Amélior. Plantes, 26: 591-605. GMELIG MEYLING, H.D. : 1973. Effect of light intensity, temperature and daylength onth e rate of leaf appearance of maize. Neth. J.agric . Sei., 21: 68-76. GROSS, F.an d W. PESCHKE: 1980. Nährstoffgehalt und Verdaulichkeit von Mais. 2. Mitteilung: Nährstoffgehalt und Verdaulichkeit von Maisstroh (Maispflanze ohne Kolben). Z.Da s wirt schaftseigene Futter, 26: 104-117. HACKER, J. B.an d D.J . MINSON: 1981. The digestibility of plant parts. Herbage Abstracts,51 : 459-482. HANWAY, J.J. : 1963. Growth stages of corn (Zea mays L.). Agron. J.55 : 487^192. HUNTER, R.B. : 1980. Increased leaf area (source) and yield ofmaiz e inshort-seaso n areas. Crop. Sei. 20:571-574. HUNTER, R.B. : 1981. Silage -increasin g grain content is notth e answer. Highlights ofagric . Res., 4: 19-20. HUNTER, R. B., M. TOLLENAAR andC . M. BREUER: 1977. Effects of photoperiod and temperature on vegetative and reproductive growth ofa maize (Zeamays) hybrid. Can.J . Plant Sei., 57: 1127-1133. IREMIREN, G.O . andG .M . MILBOURN: 1978. The growth of maize. IVDry-matte r yields and quality components for silage. J.agric . Sei., Camb., 90: 569-577. KIESSELBACH, T.A. : 1948. Endosperm type as a physiological factor incor n yields. J. Amer. Soc. Agron., 40: 216-236. KIM, G. S., S. E. PARK, G. B. SUNG, S. G. HAN, M. H. HEU and Y. H. JUN: 1976. Effects of short-day length upon growth and tasseling incorn . Res. Rep. Off. rur.Dev . (Suwon), 18: 193-198. KING, C.C . JR,D .L .THOMPSO N andJ .C . BURNS: 1972. Plant component yield and cell contents of an adapted anda tropical corn, Zea mays L. Crop Sei., 12: 446-449. LESHEM, Y. and M. WERMKE: 1981. Effect of plant density and removal ofear s on thequalit y and quantity of forage maize ina temperate climate. Grass and Forage Sei., 36: 147-153. MARTEN, G. C. andP . M. WESTERBERG: 1972. Maize fodder -influenc e ofbarrennes s on yield and quality. Crop Sei., 12:367-369 .

180 Meded. Landbouwhogeschool Wageningen 83-2 (1983) MCALLAN, A. B.and R. H.PHIPPS: 1977.Th e effect of sampledat e and plant density onth e carbohy drate content of forage maize andth e changes that occur on ensiling. J. agric. Sei., Camb., 89: 589-597. MESSIAEN, C.-M.: 1963.Physiologi e du développement chez Zea mays. Annales des Epiphyties, 14, no.Hors-séri e II, pp. 1-90. MONTGOMERY, F.G. : 1911.Correlatio n studies of corn. Nebr. agric. Exp. StnAnn . Rep., 24: 108-159. Moss, D. N.: 1962. Photosynthesis and barrenness. Crop Sei., 2: 366-367. PERRY, L.J .J Ran d W.A . COMPTON: 1977. Serial measures of dry matter accumulation and forage quality ofleaves , stalks andear s of three corn hybrids. Agron. J., 69: 751-755. PHIPPS, R.H .an dR .F . WELLER: 1979. The development of plant components and their effects on the composition offres h andensile d forage maize. 1.Th e accumulation of dry matter, chemi cal composition and nutritive value offres h maize. J.agric . Sei., Camb., 92: 471-483. PHIPPS, R. H., R. F. WELLER and A. COOPER: 1982. A comparison between the accumulation of dry matter, chemical composition andnutritiv e value ofisogeni c sterile andfertil e forage maize. Maydica, 27: 27-40. RAGLAND, J. L., A. L. HATFIELD and G. R. BENOIT: 1966. Photoperiod effects on the ear components of corn, Zeamays L. Agron. J., 58: 455-456. RODE, J.C ,O . BERTHENOD andP . CHARTIER: 1979. Influence dudegr é de fécondation sur l'assimila tion de la feuille de l'épi dans leca s du maïs. In: Inventaire desopération s de recherches 1973-1978. Département de bioclimatologie, INRA, p. 53. SCHEFFER, K.: 1978. Kurzfassungen der Vorträge. 22.Jahrestagun g der Gesellschaft für Pflanzen bauwissenschaften, Berlin, p. 12. SCHEFFER, K.: 1982a. Pflanzversuche mit Mais. I. Ertrag und Wachstumsverlauf von mittelspätem Mais auf einem klimatischen Grenzstandort inAbhängigkei t vom Aussaattermin. Kali-Briefe (BüntehoO, 16(2) : 111-122. SCHEFFER, K.: 1982b. Pflanzversuche mit Mais. ILDe rAnba u von späten Sorten unter dem Einfluss einer künstlich verlängerten Photoperiode. Kali-Briefe (Büntehof), 16(3) : 123-138. STRUIK, P.C : 1982a. Production pattern, chemical composition and digestibility offorag e maize (Zea mays L.). Mededeling no. 64,Vakgroe p Landbouwplantenteelt enGraslandkunde , Agric. Univ., Wageningen, pp.1-28 . STRUIK, P.C : 1982b. Effect of temperature ondevelopment , dry-matter production, dry-matter distribution andqualit y of forage maize (Zea mays L.). An analysis. Mededelingen Landbouw hogeschool Wageningen, (in press). STRUIK, P.C.: 1982c. Effect of a switch in photoperiod onth e reproductive development of temperate hybrids of maize. Neth. J.agric . Sei., 30: 69-83. STRUIK, P.C : 1983.Th e effects of short andlon g shading, applied during different stages of growth, on the development, productivity and quality of forage maize (Zeamays L.). Neth. J. agric. Sei., 31 (2), (in press). STRUIK, P.C .an d B. DEINUM: 1982. Effects of light intensity after flowering onth e productivity and quality ofsilag e maize. Neth. J.agric . Sei., 30: 297-316. TESCHEMACHER, H. R.: 1974. Untersuchungen zur quantitativen Bedeutung der photoperiodischen Abhängigkeit der Infloreszenzentwicklung verschiedener Maissorten. Inaugural Dissertation, Christian-Albrechts-Universität, Kiel, pp. 1-87. THIAGARAJAH, M. R., L. A. HUNT and J. D. MAHON: 1981. Effects of position and age on leaf photosynthesis incor n (Zea mays L.). Can.J . Bot., 59: 28-33. VAN SOEST, P.J. : 1977. Modified procedure for determining plant cell wall byth eneutra l detergent procedure. Paper presented at the69t h Ann. Meeting Amer. Soc. of Animal Sei., Madison, Wisconsin,1977 . VAN SOEST, P.J. ,R . H. WINE andL .A . MOORE: 1966. Estimation of the true digestibility of forage by thei nvitr o digestion ofcel l walls. Proc. X.Int . Grassl. Congress, Helsinki, Finland, (ed.) A. G.G. HILL, pp. 438-441. WEAVER, D. E., C. E. COPPOCK, G. B. LAKE and R. W. EVERETT: 1978. Effects of maturation on composition andi nvitr o dry matter digestibility of corn plant parts.J .Dair y Sei., 61:1782-1788.

Meded. Landbouwhogeschool Wageningen 83-2 (1983) 181 WILSON,J . H.an d J. C.S .ALLISON : 1978. Production and distribution ofdr ymatte r inmaiz e follow ing changes in plant population after flowering. Ann. appl. Biol., 90: 121-126.

182 Meded. Landbouwhogeschool Wageningen 83-2 (1983) GENERAL DISCUSSION

The generaldiscussio n falls intotw oparts .First ,th eeffect so f climatean dweathe ro nyiel dan dqualit yar ediscussed :thi slead so nint o adescriptio no fth eidea lweathe rcondition sfo rgrowin gforag emaiz e inNorth-Wes tEurope .Th esecon d sectiondescribe sa nideotyp eo fmaiz efo r theproductio no fforag eunde rth econdition snorma li nNorth-Wes tEurope .

1.INFLUENC EO FCLIMAT EAN DWEATHE RO NTH EYIEL DAN DQUALIT YO FFORAG EMAIZ E INTH ENETHERLAND S

Theinfluenc eo fclimat ean dweathe ro nth eyiel dan dqualit yo fforag e maizei sver ycomple xan di scomplicate db yth evariatio ni nproductio n environment. Asizeabl eamoun to fliteratur eo nth esubjec to fth erelationship s betweenth emaiz ecro pan dweathe rha saccumulate ddurin grecen tdecades . Mosto fthes estudies ,however ,ar eonl y concernedwit hdry-matte ryiel do f thewhol ecro po ro fth egrains .I nth epreviou schapter sth eeffect so f climatic conditionso nth ephysiology ,development ,productivity ,dry-matte r allocation,an dqualit yo fforag emaiz ewer e describedan ddiscussed .Thi s parto fth egenera ldiscussio n - assessesth esuitabilit yo fth eDutc hclimat efo rgrowin g foragemaiz e - summarizesth eeffect so fshor tperiod so fadvers eo rfavourabl eweathe r conditionsdurin gdifferen tstage so fgrowt h - describesth eidea lweathe rfo rgrowin g foragemaiz ewit hth ecultivatio n techniquescurren ti nTh eNetherlands .

1.1. Evaluation of the suitability of the Dutch climate for growing forage maize Maizeoriginate s fromsubtropica lregion san dhenc eth emaiz eplan ti s endowedwit hth efollowin gecophysiologica l characteristics: -it sminimu m temperature forgerminatio nan dgrowt hi shig h -it soptimu mtemperatur e forgermination ,photosynthesis ,growt han ddevelopme i ishig h -i ti sabl et oproduc eCH_ 0vi ath eC .pathwa yo fphotosynthesi san dthu si t showsa hig hrat eo fne tphotosynthesi sa thig htemperatur ean dhig hligh t

183 intensity - itrequire sshor tday s forth einitiatio no fmal e and female inflorescences - itmake seconomica l useo favailabl ewater ;however ,maiz e isver ysensitiv e todrought ,especiall y duringreproductiv e development. Thissuggest s thatth eDutc h climate isno tver y suitable forgrowin gmaize . Indeed,Th eNetherland sar eo nth enorther nmargin so fth erang eo fmaize . InTabl e 1,averag eclimati c conditionsa tD eBil t (thecentra lmeteoro logicalstation )durin g theperio d 1931-1960ar ecompare dwit h therang eo f thesecondition sa tWageninge n (approx.4 0k meas to fD eBilt )durin gth e period 1977-1981.I twa sthi slatte rperio d thatth e fieldexperiment s reported inthi sthesi swer e carriedout .Compare dwit hnorma lvalues ,thes e fiveyear swer ecoole r (especially duringearl y springan ddurin g summer), drier,an dcloudie rdurin gJune .Dat ao nphotoperio d areno tpresented :th e patterno fthi sclimati c factorhardl y differsbetwee nyear salthoug hsom e variation exists (Chapter 6).A tth e6-lea fstag eo f field-grownmaize ,th e naturalphotoperio d is 17-18h .Breedin gha ssatisfactoril y overcome the constraint ofsensitivit y tophotoperiod . Theprevailin gweathe rcondition s inTh eNetherland sdeviat emarkedl y fromth eoptimu m conditions forman yprocesse si nth eplant ,particularl y becauseo fth ethermophili cnatur e ofmaize .Tabl e 2illustrate s thisnatur e by showing theoptimu m temperature ortemperatur e ranges forplan tprocesse s occurring duringearl yplan tgrowt han d forplan tparameter s determinedi n thesam egrowt hphase .Th e thermophilicnatur e isals oa nimportan t constraint on theplant' sproductivit y anddevelopmen tdurin g latesumme ran dautumn . Theminimu m temperatures required forprocesse s sucha simbibition , germination,earl y seedlinggrowt h andphotosynthesi s range from6-1 0 C (e.g. Blacklow, 1972a,b;Miedema , 1982).Th eminimu m temperaturesfo r pollination,silkin gan dfertilizatio n aremuc hhigher .Fo rexample ,durin g a certainnumbe ro fconsecutiv e daysth emaximu mdail y temperaturemus t exceed 15-20 C,dependin go ngenotype ,t oenabl esilking . Theoptimu m temperatures foral lprocesse s aremuc hhighe r thanth e normal temperatures inTh eNetherlands .Yield ,however ,i sdetermine db y both ratean dduratio no fdry-matte rproduction .Th eoptimu mtemperatur e for finalyiel d thereforedepend so nth eduratio no fth eperio d duringwhic h active leavesca nb epresent .Th eduratio no fthi sperio dis ,fo rexample , affectedb y genotype andth eoccurrenc eo f frost,pest san ddiseases .Th e numbero fday savailabl e forth egrowt ho fa forage-maiz e cropi slarg ei n TheNetherland s (160-180days) .T eVeld e (1983)ha sstate d thatyear swit h

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185 % of maximum dry /T % of maximum matter in the plant \£j dry matter inth e plant 100( - 00 90 V Netherlands (1980),c v LG11 90 Netherlands(1981) CVLG11 / Based on Chapter4,Fig.4 / Q0 - Based on Chapter 4,Fig . 4 80 1 1 100% = ISMg.ha' 100°/«= 17M g ha" A/ grain« co b 6/ 60 *y l^ •^^huskS'Shanks'*^^

/ stalk, tassel* leaves 20 46 days / 66 days 33 days 10 . _•—-r-^i , .9 , . , , I . 4 , . , 100 120 140 160 days after emergence

80 100 120 140 days after emergence

Fig.1 .Productio n and allocation ofdr ymatte r in amaiz e crop,grow nunde r variousconditions .Th egrowin gperio d isdivide d intoth eperio d from emergence until 10%o fmaximu m drymatter ,th eperio d from 10%unti l90 %o f maximum drymatter ,an dth eperio d after90 %o f themaximu m drymatte rha s beenreached .Th e duration ofthes eperiod s isindicated ,a swel l asth erat e of increase inrelativ ewhole-plan t yield during theperio d from10 %unti l 90%o fmaximu m drymatter . o signsindicat emid-silking . Vertical arrows indicate 30%dr ymatte r inth e freshcrop .

188 - above-normal lightintensit y duringJul y- Septembe r -norma lprecipitation ,equall ydistribute dove rth eentir egrowin gseaso n - absenceo fstresse ssuc ha s frostso rperiod so fdrought .

InTh eNetherland s digestibility ishig h andvarie s Utile between locationsan dyear s (Chapter2 ;B .Deinum ,persona l communication;se eTabl e3) .

Table 3.Apparen t digestibility (D ) +_standar d deviationo fsevera l groups ofsample sobtaine d from farmer'slots .Dat ao nth eensile dcrop s are from arando m testo fsample soffere d toth eroutin e laboratory forfee devaluation .Dat ao n the freshcrop s are from the factor analyses,carrie dou tb yth eResearc hStatio n forArabl eFarmin gan d FieldProductio no fVegetable s (Lelystad), fora selecte d regiono f TheNetherlands . year 1981 1982 n D (%) n D (%) om om ensiled 25 73.5+ 1.26 ensiled 50 73.5+ 1.21 fresh 54 72.8+ 1.39 fresh 54 73.3+ 1.69

Thevariatio ni nwhole-cro pdigestibilit y shownabov ei smainl ycause db y genotype,samplin gerror ,proportio no fea ri nth edr ymatte ran dcell-wal l content.However ,i nth efacto ranalysi so f 1982,considerabl e variation indigestibilit y of thecel lwall so fth estove rwa sobserve dbetwee n locations (range55. 1- 65.8%) .Thi svariatio n contributed considerably toth edifference s inorganic-matte r digestibility ofth ewhol e cropbu tcoul dno tb e ascribed too rexplaine db yan yo fth eove r20 0plan tan d location characteristics measured (J.Boer ,pers . comm.).Thi si ssurprising ,sinc eonl y temperature treatments duringlon gperiod so fgrowt h areknow n toaffec tcell-wal l digestibility ofth estove rt othi sexten twhe nharvestin gdat ean dgenotyp e areno tvarie d (Chapter 2).Thus ,som eunknow n factoro rfactor sno tinclude d inth eresearc h reported inthi sthesi si so rar eals orelevan tfo rcro p quality. Aftergrai nset ,bot h cell-wall digestibility and cell-wall content decline (Chapters 1an d 4).Th erat eo fdecreas e incell-wal l content,however , stronglydepend so nligh tintensit y (Chapters2 ,3 an d 4).Sinc e light intensitybecome s solo wdurin gOctobe rtha tne tproductio nbecome snegative , digestibilitypeak sa tth ebeginnin go fOctobe r (seeFig .2 ;cf .Kilkenny , 1978). Theoptimu mi smos tpronounce d forhybrid sshowin ga lo wcell-wal l

189 digestibility. For these hybrids the year-to-year variation also will be greater.

76 h Hybrid LG11 + =1979,Achterberg o »1980, Achterberg A- 1981, Achterberg x =1979,Bennekom O=1980 , Wageningen O 75

73 recommended harvest date

.^-L. 10 15 20 25 30 35 40 45 50 55 dm *h top ear Fig. 2. Relation between ear maturity (dm% top ear) and organic-matter digestibility (D ). om

Variationbetwee nyear si scause db y therati oo fproductio no fcel l wallst oproductio no fcellula r contents.Thi srati odepend so nth eweathe r conditions duringspecifi cgrowt h stagesan dth ephysiologica lreaction so f theplan ttha tthes e conditions induce.Drough tdurin gsilking ,fo rexample , hasbee non eo fth emos timportan t constraintso ndigestibilit y duringrecen t years.Th eeffect so fweathe r conditionso nspecifi cphysiologica lprocesse s andthei rconsequence s foryiel dan ddigestibilit y aredescribe di nsectio n 1.2.

Dry-matterconten to fth ewhol ecro pmainl y correlateswit h therat e ofth ecrop' sdevelopmen t andthu swit h temperature:th eproportio no fea r inth e freshmatter ,th ematurit yo fth eea ran dth eredistributio no f solubledr ymatte r fromth estove rt oth eea rmainl ydetermin e thedry-matte r contento fth ewhol ecro p (cf.Ideotyp e description).Th erat eo fdevelopmen t ofa certai ngenotyp e canb ewel lpredicte d fromth ecumulativ e temperature

190 totals.Thi si sespeciall y true forth eperio d aftersilkin g (e.g.Blo ce tal. , 1983a). However,i ti smor e difficult tous e cumulativetemperatur e totalst o predictth eduratio n ofth eperio d fromsowin gunti lsilking ,becaus eo fth e variationi nnumbe ro fleave s (Bloce tal. , 1983b)an dth eeffect so n developmento fpre-emergenc e soilcondition s (e.g.Coligad o &Brown , 1975b). Fusarium infectionmigh tals opla ya rol e (Chapters 3an d 4),wherea s frost maycontribut et oa rapi ddeclin eo fth ewate rcontent .

Theweathe r conditionsmentione dearlie ra sbein gnecessar y tooptimiz e thedry-matte ryiel di nTh eNetherland sals oincreas edry-matte r contentbu t have littleeffec to ndigestibility .

1.2. Evaluation of the effects of weather on the development, productivity and quality of forage maize Inadditio n toth emor egenera leffect so fclimati ccondition so nyield , dry-matter contentan ddigestibilit y offorag emaize ,weathe rcondition shav e specificeffect so nphysiolog y anddevelopmen tdurin gcertai nstage so fth e crop'sdevelopment .Thes eeffect shav e repercussions onth esubsequen t productivity anddry-matte rdistributio n ofth ecro pan dthu so nyield ,dry - matterconten tan ddigestibility .Thes eeffect san d theirrepercussion swil l bedescribe d indetai li nthi ssection .

Sowingt oemergenc e Soiltemperature sar eseldo minjuriou s toimbibe d seedso ryoun gseedling s ifmaiz e issow na tth een do fApri l (Miedema, 1982).Soi l temperaturesan d soilmoistur ed oaffec tth e rateo fimbibitio n andgerminatio n andthu s influence theinterceptio no firradianc edurin gth eperiod swit hhig h light intensity.Thes e influencesmainl yaffec tyield .Becaus e soiltemperatur e affectsth erat eo fextensio no fth emesocoty lmor etha nth erat eo fshoo t extension,hig h temperaturesdurin g thisphas emigh tstimulat e lodgingdurin g later stageso fgrowt h (cf.Ideotyp e description).Soi lcondition sdurin gger minationar eextremel yimportan tfo rsubsequen tgrowt han ddevelopmen t (Coligado & Brown, 1975b;Miedema , 1982).Thi swil lb eeviden tfro mth ediscussio nbelow . Thisphenomeno nstresse sth eimportanc e ofprope r tillagei nspring .

Emergence totasse linitiatio n Duringthi sphas e thegrowin gpoin to fa plan t ofon eo fth epopula r genotypesi sstil lbelo wth esurface ,bu tth eleave sar epartl yabov esoi l

191 level.Th emai n factorsaffectin g growthdurin gthi sstag ear esoi ltemperature , soilmoistur e (directlyo rb y itsinfluenc eo nsoi l temperature),ai rtempera turean dsola rirradianc e (directlyo rb yit sinfluenc eo ntemperatur eo f leaves,shoo tape xan d soil).Thes e factorsaffec tth erate so f the following processes: - leafinitiation ,i.e .th eproductio no f leafprimordi a - leafappearanc e - leafextensio n - growthan dactivit y ofroot s - photosynthesis - tasselinitiatio n Since temperatureha sa greate r effecto n leafinitiatio ntha no ntasse l initiation,mor e leavesar einitiate da thighe r temperatures.Th e finalnumbe r ofleave sals odepend so ngenotyp ean dphotoperio d andi sdetermine d duringa shortperio dprio r totasse linitiatio n (Tollenaar &Hunter ,1981 ;Bonhomme ,1983 ; Derieux, 1983;Chapter s 2,5 an d 6); leafnumbe r increasesb y 0.1 -0.3 5 leaves per Cincreas e intemperatur e (e.g.Dunca n &Hesketh , 1968;Coligad o &Brown , 1975a;Tollenaa re tal. , 1979;Derieux , 1983)bu tthi sincreas ema yvar y according togenotype ,photoperio d anddiurna l temperature range.Th eai ran d soiltemperature s justprio r totasse linitiatio n showconsiderabl e variation bothbetwee nyear san dbetwee n locationswithi nyears .Thi s short-termweathe r factorstrongl y influences thesubsequen tgrowt h anddevelopmen to fth ecro p and thereforerestrict s thevalu eo fmaturity-indexin g systemsbase do n temperature orhea tunit s (Chapter 2;cf .Bloc ,e tal. , 1983b). Under field conditions,photoperio d ismuc h lessimportan ttha nsoi lan d airtemperatures . Theeffect so fsowin gdat eo n leafnumber ,fo rexample ,ar eprobabl y entirely causedb ydifference s intemperature .A nincreas e innumbe ro f leaveswil l positively influenceproductivit ybecaus e (cf.Ideotyp e description): - totallea fare ai sslightl ylarger ; - leaf-areaduratio n islonger ; - thepresenc eo fyoun g (thusver yactiv ean dmor e frostresistant ) leaves inth eto po fth ecanop y isprolonged ; - theemergenc eo fth etassel ,whic h shadesth e leaves,i sdelayed . However,a nincreas ei nnumbe ro fleave s (orphytomeres )als oprolong scell-wal l formation,raise sth epotentia l cell-wallyield ,prolong sth epre-silkin gperiod , andboost s thewate raccumulatio n (seeChapte r 2). Delayedmaturit y andreduce d digestibility (especiallywhe ncell-wal ldigestibilit y ofth estove ri spoor )ar e thusadvers e side-effects ofa large rnumbe ro fleaves .

192 Thetemperatur eo fth eshoo tape xi sth eprimar y factorinfluencin grat e oflea fappearanc e (e.g.Brouwe re tal. , 1973;Gmeli gMeyling , 1973;Tollenaa r etal. , 1979;Thiagaraja h &Hunt ,1982 ;Bonhomme ,1983 ;Chapte r 2).A nincrease d rateo flea fappearance ,irrespectiv eo flea fnumber ,i sfavourable ,sinc ei t acceleratesvegetativ e developmentan dthereb y advances theformatio no fa closedcanop y (seesectio n 1.1),reproductiv edevelopmen tan dmaturity .Becaus e ofthi sacceleration ,th eclimati c conditionsdurin gal lsubsequen tstage so f growthar emor e favourable forproductio nan ddevelopment ,i.e . thecro pi s moreabl e toprofi t fromth e favourableperiod so fth egrowin gseaso n (cf. Fig. 1).Th eeffect so fthes efavourabl e conditionso ndigestibility ,however , aresmal lan dinconsistent ,sinc ebot h theproductio no fcel lwal lan do f cellsoluble sar e favoured (Chapter2) . Leafextensio ngreatl ydepend so ntemperature ,ligh tintensity ,wate r availability andphotoperiod .Temperatur e isth emai n limiting factordurin g earlyseedlin ggrowt ha slea fextensio n ismainl yaffecte db y thetemperatur e ofth emeristemati c regiono fth eshoot .Temperatur eals oaffect sth eultimat e sizean dshap eo fth eleaves .Hig h temperatures induce amor e linearshape , thusincreasin g theproportio no fth emidrib .Fo rsmal lleave s thisinfluenc e iso fmino rimportance . Thever yyoun gseedlin gi sals oextremel ysensitiv et owate rshortag e (Barloy, 1983).Wate rstres slimit s leafextensio nparticularly .Accordin g toMiedem a (1982), lowtemperature s per se dono tinduc ewate rstress , although leaftemperatur e androo ttemperatur ema y differgreatly .Ther ei s analmos tlinea rrelationshi pbetwee n thegrowt ho f theprimar y rootan d temperature inth erang eo f 10-25 C (Blacklow, 1972b). Because therat eo f growtho froot sa tlo wsoi ltemperature s isslow ,th eavailabilit y ofphosphat e maybecom e limiting,resultin gi nanthocyani npigmentatio no fth eleaves . According toMiedem a (1982)minera l deficiencies areno tcause db yreduce droo t activity atlowe rtemperatures . Photosynthesis isver y sensitive totemperatur e inth erang eprevailin g duringearl ygrowth .Blondo nan dco-workers ,however ,foun dtha tth eoptimu m temperature forphotosynthesi s shifted towardsa lowe rvalu ewhe na col d treatmentwa sgive ndurin gearl y growth (Blondone tal. , 1981,1983) .Thi s shifto fth eoptimu m isa nimportan tadaptatio no fth eplan tt oth ecoo l conditionso ftemperate ,maritim e climatesan di smos tpronounce d incold - resistantgenotype s (Blondone tal. , 1981,1983) . Theduratio no fth epre-tasse linitiatio nperio d isles ssensitiv et o temperature thanmos tothe rprocesses .Thu sth erat eo fdifferentiatio no f

193 1981, 1983),hig h temperature (Chapter2 )an dlo wligh tintensit y (Chapter4) : theyma yb ever y important,a sthe yinfluenc e the late-seasonvigou ro fth e maize crop.A coldspell ,suc ha sfrequentl y occursi nJune ,migh tcaus e temporary chlorosis. Fromth e limitednumbe ro fobservation sobtaine d during thepresen tresearch , itappeare d thatmaximu m leafare ao f thecontro l crops (reacheda to r shortlyafte rsilking )closel y correlatedwit h thesoi ltemperatur e at- 5c m duringth e first 10day so fMay ,i.e .durin g germination. Thisobservatio n agreeswit hth e resultso fMiedem ae tal . (1982)wh o found thatearl yvigou r ofth eseedlin gi saffecte db ycondition sdurin ggermination .Coligad o& Brown (1975b)eve nincorporate d adevelopmen tpotentia l factori nthei r bio-photo-thermalmodel :thi sfacto rdepende do nth enumbe ro fday sfro m sowing toemergence .Thi s factorexplain swh y the leafare ao fth ecrop s growni nglasshouse si smuc hhighe r thanth e leafare ao ffield-grow nplant s (seeFig . 3).I tals oexplain s the largepositiv eeffect so fplasti cmulche s inspring ,an d theeffect so fsowin gdat eo nlea fare aan drat eo fdevelopmen t (seee.g .Chapter s 1an d2) . Yet, climatic factorsafte rtasse linitiatio nals oaffec tlea fdimensions . Prolonged differences intemperatur e levelsdurin gth eperio d fromtasse l initiation toanthesi sar eo fmino r importance forlea fare a (Chapter2) . Low lightintensit y reduceslea fare aconsiderabl ywhe nplant sar eexpose d tosuc hcondition sdurin gth eearl y growtho f the leaves (i.e.befor emid - July). Photoperio donl yaffecte dlea fare adurin gth e 3-8 leafstag e (Chapter 5).Lo wtemperature shav e alarg enegativ eeffec to nth erat e oflea fextension ,wherea sdrough tals ogreatl yreduce slea fextension . Undercondition sprevailin gi nTh eNetherlands ,variatio ni nlea fare a withinon egenotyp e fromyea rt oyea r isprobabl ymainl y causedb yvariatio n insoi ltemperature sbefor eemergence ,provide d thatal lothe r conditions areoptimum .Thi sagree swit h the findingtha tdelayin g the sowingtim e resultsi na n increasei n leafare a (seee.g .Fig .3) .Th e conclusiontha t soiltemperature sdurin gearl ygrowt h areth emai ndeterminan tfo rlea f area,however ,need s further confirmation.Longevit y ofleave san dlea f activity aremuc hmor evariabl ean dmor eaffecte db y conditionsdurin g laterstage so fgrowth .

b.Th erat eo f floretinitiatio ni sconstan tunde rdefine dconditions ,bu t affectedb y temperature (Allison &Daynard , 1979).Th efina lnumbe ro f floretprimordi ao nth eto pea ri saffecte db ytemperatur ean dphotoperiod ,

196 butonl yt osom eexten t (e.g.Hunte re tal. , 1977;Alliso n &Daynard ,1979 ; Hunter, 1980;Chapter s 2,5 an d 6). Theoptimu m temperature fornumbe ro f floretsi slo w (Brooking, 1979)wherea s theoptimu mphotoperio d islong . Thus thetemperat emaritim e conditionso fNorth-Wes tEurop ear e favourable forea rdevelopment .Becaus eo flo wtemperatures ,th erate so f floret initiation,grai nse tan dgrai n filling are tooslo w forhigh - yieldinghybrid s toreac hmaturit ybefor ekillin g frostsoccur ;therefor e thepotentiall y largeea ryield sar eno trealized . Shadingdramaticall y limits the fecundity and fertilitybot hi nth etasse l andi nth eear s (Chapter 4). Other stressessuc ha sdrough tar eals o extremelyharmfu ldurin gthi sphase .Th e criticalphas e forsuccessfu l pollendevelopmen ti ssomewha tearlie r than forsuccessfu lovul e development andsil kemergence .I nTh eNetherlands ,thes esensitiv ephase sar ei nJul y andearl yAugust .Sola rirradianc edurin gJul yi stherefor e themai nclimati c factordeterminin gpotentia lea r sizeo fth ecommerciall y grownforage - maize cropi nTh eNetherlands . Factorsaffectin g thesiz eo fth e topea rinfluenc e thedevelopmen to f lowerears .Thes e lowerears ,however ,ar eusuall yaborted .

Stemheigh ti sdetermine db y thenumbe ro fste minternode s (i.e.numbe r ofleaves )an d themea ninternod e length.Th enumbe ro fste minternode s isdetermine db yphotoperio dan d temperatureprio r totasse linitiatio n (seeabove) .Th e lengtho f theinternode s isaffecte db yphotoperio d (see e.g.Blondo n &Gallais ,1976 ;Aitken , 1980;Chapter s 5an d 6), temperature (seee.g .Blondo n &Gallais ,"1976 ;Aitken , 1980;Chapter s 2an d 5), water availability (unpublisheddata )an dligh tintensit y (seeBlondo n &Gallais , 1976;Chapte r4 )bot hbefor ean dafte rtasse linitiation .Soi lcondition s duringearl y seedlinggrowt hma yals oaffec tstem-internod e length. Photoperiod isa fairl yconstan tclimati cphenomenon .Temperatur edi d notprov e toaffec tinternod e length toa grea texten tbu tha d adramati c effecto nste mdiamete r (e.g.Chapte r 2). Droughtgreatl y reducesste m growthbot h longitudinally andradiall y (unpublished data). InTh eNetherlands , water availability ismostl y sufficient foroptimu mste melongation .Plant s growni nglasshouse s (withregula rwatering) ,however ,ar ealway stalle r thanfield-grow nplants .Thes edifference s cannotb eattribute d merelyt o wateraccumulation .Th e favourablecondition sbefor e tassel initiation mayals oboos tplan theight .Ligh tintensit yaffect splan theigh tbu tth e effectsdepen do n thegrowt h stage.Shadin ggreatl y reducesplan theigh t

197 Résumé: Weather conditions during the period from tassel initiation until anthesis affect productivity, the rates of development and the dimensions of the leaves and the stem, the development of the inflorescences, and the amounts of poorly digestible cell-wall components and of water in the plant. Since these processes and parameters are partly independently affected, weather conditions during this phase influence yield, digestibility and dry-matter content.

Anthesisunti lgrai nse t Thisperio di scrucia lbecause : -th estem ,roots ,tasse lan dea rshoot sar egrowin gsimultaneously ;durin gthi s stagebot h rootsan dea rshoot sar ewea k competitorsan dthu sreac tsharpl yt o slightchange si nweathe r conditions -th ereproductiv epotentia lo fth eplan tmus tbecom eoperational ;th edevelopmen t fromunfertilize dovul et odry-matte r accumulatingkerne li sa crucia lbu t critical stepi nth eplant' s development -th ebalanc ebetwee nsin kan dsourc ei sse tdurin g thisperiod ,althoug hrapi d adjustmentt oreduce d source sizeremain spossibl e duringearl ygrai nfilling . Productivity duringgrai n fillingdepend so nth esucces so fea rdevelopmen t (e.g.Tollenaa r& Daynard , 1982). Root sprobabl ypla ya nimportan trol edurin g grainse t(Chapte r3) . -I nadditio nt othei reffec to nproductivity ,ea rdevelopmen tan dsubsequen t grain fillingaffec tsenescence ,dry-matte rcontent ,digestibility ,fee dintak e and feedefficiency ,processe si nth esilo ,etc .Thes eeffect swil lb e discussedwhe ndescribin gth eideotyp efo rNorth-Wes tEurope .Th eidea l proportiono fea ri nth edr ymatte ra tharves ti sapprox .50 %fo rconcomitan t hybrids.

Toenabl eth etassel ,th eea rshoot san dth eroot st odevelo pan dgro wa tthei r optimumrates ,th ene tphotosynthesi s ratemus tb emaximal ,wherea s temperature mustb emoderate .Hig h lightintensit yan dmaximu m daily temperatureso f 20-25C ,(combine dwit ha nabsenc eo fdrough to rlo wai rhumidity )ar efavourabl e forgrai nse tan droo tgrowth .Th eoptimu m sizeo fth eto pea ractuall y depends onth eweathe r conditionsdurin ggrai nfilling .

Grain filling,maturatio nan dsenescenc e Thisdevelopmenta lphas eo fth eforage-maiz e cropi scharacterize db yth e starto rcontinuatio no fth efollowin gprocesses :

200 -productio no fphotosynthate s - grain filling -maturatio n - senescence Iflarg eamount so fhighl y digestible organicmatte r thatar eeas y toharves t andt opreserv ear et ob eobtaine d iti svita ltha tthes eprocesse soccu ri n harmonyan da trate s thatar eno tdetrimenta l forth e continuationo fth eothe r processes (seeals oIdeotyp e description).A prerequisit e istha tth elea f apparatus remainsmaximall y active aslon ga spossible .Thi srequire sabsenc eo f drought,fros tan dinfirmitie so fol dage .I nphytotro nexperiment si tha softe n beenobserve d thatprolonge d lowligh tintensit y initiated duringgrai nse ti s favourable forth elongevit y of leaves,especiall y atlowe r temperatures (Chapter 2).I nfiel dexperiments ,shor tshadin g treatments applied atgrai nse t alsoretarde d leafsenescenc e tosom eexten t (Chapter4) . Longshadin g treatments initiateddurin go rafte rgrai nse tan dshor tshadin g treatments initiated duringgrai nfillin gbooste d leafsenescenc e underfiel d conditions (Chapter 4).A ris ei ntemperatur e duringSeptembe r andOctobe rno t onlyaccelerate s leafsenescenc ebu tals orat eo fphotosynthesis .Becaus eth e durationo fth egrowin gseaso ni slimite db y thelo wligh tintensit y during Octoberan dth eoccurrenc eo f frost,above-norma l temperatures duringautum nar e beneficial inNorth-Wes tEurope .Th eproductio no fphotosynthate s duringgrai n fillingdepend so nth eweathe rdurin gthi sphas e andals oo ncondition sdurin g previousphase s (see above). Photosynthatesproduce d.durin ggrai n fillingar emainl y used forth e synthesiso fstarc hi nth ekernels .Th eproductivit y duringgrai n filling greatly affects therat eo fredistribution ,wherea s itha ssmalle r -thoug h certainly relevant- effect so nth erat eo fgrai n filling.Thi sdiscrepanc yan d itsconsequence shav ebee ndiscusse dextensively ,e.g .b yDeinu m &Knopper s (1979),an di nChapter s 2,3 an d4 . Rateo fgrai n fillingi smainl y determinedb y temperatureprovide dth e carbohydrate supplyi sadequate .Th edry-matte r contento fth egrain san dth e 1000-kernelweigh t cantherefor eeasil yb epredicte db y cumulative temperature totalsafte rsilkin go rafte rgrai nse t (e.g.Blo ce tal. , 1983). Rateo fdry-matte rproduction ,however ,i smor edependen to nligh t intensity,althoug h temperaturesdurin gSeptembe r areofte n too lowfo rhig h photosynthetic rates.I naddition ,th emaiz e cropprove d tob ever y sensitive totemporar y reductions inligh tintensit y inth emiddl eo fit sgrain-fillin g

201 of increased light intensity on the yield of digestible organic matter increases after tassel initiation and is maximum during pollination, grain set and grain filling. The consequences of changes in climate during a certain period, however, affect the efficiency of the effects of changes in climate during earlier or later stages of growth.

1.4. Implications Onth ebasi so fthes ean dearlie r considerations thedigestibilit yo f foragemaiz e canb epredicte dwit h anaccurac y thati ssimila r toth eon e obtainedb y chemical analysis.A roug hpredictio nmode li sdescribe d inTabl e5 . Thismode l isbase do ncontemporar y hybrids.I nth eperio d frommid-Septembe r to mid-October thedigestibilit y ofa forage-maiz e crophardl y changes (Fig.2) . Innorma lyear sth eorganic-matte r digestibility ofensile dmaiz egrow na sa standard farmer's crop,usin gcontemporar yhybrid s andharveste d duringthi s period isapproximatel y 73.5% (cf.Tabl e 3).I fth ecro pi sharveste dbefor eo r afterthi speriod ,th edigestibilit y willb eapprox . 1%lowe rfo rever y 10day s theharves t isdelaye do r advanced.Th edigestibilit ywil l certainlyb elowe ri f thegrai n seti spoo rbecaus eo fextremel y lowligh tintensit y ordrough tdurin g silkingo rbecaus epollinatio nha sbee nprevente d artificially (Chapters 2an d 4). Reductions indigestibilit y aresmal lwhe nth eproportio no fea ri nth e finaldr ymatte rexceed s 30-40%.Belo wthi svalue ,digestibilit y declinesa t approx. 1%uni tpe r 10%uni tdecreas e inea rproportion .Abundan tvegetativ e development,cause db y favourable conditionsbefor e tasselinitiatio nan d estimated fromste mheigh tan dste mdiameter ,increase sdry-matte ryiel dbu t may reducedigestibility ,sinc e structuralmateria li sproduce d fasteran dfo r longeran d thusmor e cell solublesmus tb eproduce d toachiev e acertai ndeclin e incell-wal l content.Moreover ,th eproductio no fthes e cellsoluble smus toccu r lateri nth egrowin gseaso nan dthu sunde rles sfavourabl econditions . Digestibility mightb e 1%lowe ri nyear swit h extensivevegetativ e growthan d 1%highe ri nyear si nwhic hvegetativ e developmenti spoo rbu treproductiv e developmenti snormal .Unfavourabl eweathe rcondition s duringgrai n filling (especiallypoo r lightintensity )wil lals olowe rdigestibilit y byapprox .1% . Incontrast ,th edigestibilit y ofcrop sgrow ni nyear swit h favourableweathe r duringSeptembe rwil lb e about 1%higher .Th eadvers eeffect so fabundan t vegetative developmentan dpoo r lightintensit ydurin ggrai nfillin gwil lno t be foundwhe nea rproportio n islo wbecaus eo fpreviou s conditions.I ntha tcase , thedeclin e incell-wal l contenti slimite db yphysiologica l reasons.Thi s

204 Table4 .Id#a ltemperatur ean dligh tcondition sdurin gsevera lstage so fcro pdevelopmen t foryiel dan dqualit yo fforag emaiz e underDutc hconditions .

pre-em ergenc e emergence periodjus t taBsel silking\ grainse t totasse l priort otas initiation \to to initiation selinitiatio n tosilkin g grainse t maturity weatherfacto r plantparamete r

highdry-matte ryiel d ++ + +o r- + ±° r+ highdry-matte rconten t + - ++ + +++ lowcell-wal lconten t + - +o r+ + +o r+ high cell-wall digestibility highorganic-matte r digestibility high yield of digestible organicmatte r

lightintensit y highdry-matte ryiel d highdry-matte rconten t ^o r+ lowcell-wal lconten t •o r- +++ highcell-wal ldigestibilit y +o r+ highorganic-matte r digestibility highyiel do fdigestibl e organicmatte r

- s=idea ltemperatur eo rligh tintensit ylowe rtha nnorma lcondition s +s =idea ltemperatur eo rligh tintensit yequivalen tt onorma lconditions ,o rchange si nweathe rfacto rcaus einconsisten teffect s +,++ ,++ +- idea ltemperatur eo rligh tintensit y somewhat,muc ho rver ymuc hhighe rtha nnorma lconditions . restriction istherefor eno tvali dwhe nhybrid sar euse d showingextremel y low earproportio nwhe n growni nTh eNetherlands .Th erang eo fdigestibilit ybetwee n yearswil lb eapprox .69-76% .B .Deinu m (personalcommunication ) foundrange si n digestibility withinyear so f 70.6-76.1%fo r 1981an d68.3-77.0 %fo r 1982.Th e rangei ndigestibilit y ofth e forage-maizehybrid sdescribe d inth elates tDutc h nationalvariet y listsi sonl yapprox .4 unit swid e (Deinum& Bakker ,1981 ; RIVRO, 1983). Asbot hth erelativ edigestibilit y ofth ehybri d andth eweathe r conditions duringdifferen tstage so fgrowt har eknown ,th efina ldigestibilit y canb e roughlyestimated .Thi sestimat ei sgoo denoug h togiv e the farmera ninklin go f thedigestibilit y relative toth edigestibilit y informe ryears . Furtherresearch ,however ,i srequire d toidentif y theeffect so fsit eo n digestibilitywithi non eyear .I naddition ,mor eprecis e andextensiv e research onth eeffect so fcultivatio n techniques,weathe ran dthei rinteraction so n digestibility ofth eensile dproduc ti srequired .Wit h this additional information themode lcoul db e refined tosuc ha nexten ttha tdigestibilit y couldb epredicte d soaccuratel y thati twoul ddispens ewit h thenee d forth e farmert ohav eth e forage-maize silageanalysed .

205 Table 5.Tentativ emode l fordeterminin g thedigestibilit y of foragemaize , grown under the cultivation techniques recommended inTh eNetherland s andusin g concomitant hybrids.Estimate d normalvalue :73.5% .

Correction factor

Cultivation hybrid seerelativ evalue si nvariet y list harvestdat e -1% per 10day sdela yo radvanc eo f harvestdate ;norma ldat e mid-September tomid-October ,dependin go nyea r

Cropcharacteristic s poorgrai nse t -1%pe r 10%declin ei nea rproportio n below 30-40%ea ri nth efina ldr y drymatter .I fthi scorrectio n is appliedn ocorrectio nshoul db emad e forweathe rconditions . abundantvegetativ e development -1% poorvegetativ e developmentbu tnorma l reproductive development +1%

Weather overcastperiod sdurin gSeptembe r -1% high lightintensit y duringSeptembe r +1%

206 2.A NIDEOTYP EO FFORAG EMAIZ EFO RNORTH-WES TEUROP E

Anideotyp ema yb edefine da sth eidea lgenotype ,i nwhic h thecapacitie s necessary tomaximiz eproductivit y andqualit yunde rth eprevailin g climatic conditionsan dunde rrecommende d culturalpractic ear ecombine d (contrast Donald, 1968;Moc k &Pearce ,1975 ;Gunn ,1978) .Thi simplie stha tth eideotyp e thusdescribe d isonl yvali d fora define dproductio nenvironment ,i nthi scas e forth eclimat edescribe d inth eprecedin gchapte ran d forth e cultivation techniquescurren ti nTh eNetherlands .I tals oimplie stha tth eideotyp eshoul d berealistic ;a descriptio no fa nideotyp emigh tb euseful ,bu ta descriptio n ofa nUtopia ntyp e (oreve nidiotype )woul d certainlyno tbe . Theideotyp eo fforag emaiz eshould : - yield amaximu man dstabl eamoun to fdigestibl eorgani cmatte r -b eeas yt oharves tan dt opreserv e -b etasty ,nutritiou san dallo wa hig hdry-matte rintak e - beefficientl y utilizedb yth eanimal . Thesedemand sca nb etranslate d intoth efollowin gmode lcharacteristics , whichwil lb e discussedbelow : 1. highan dstabl edry-matte ryiel d 2. optimumcompositio no fcellula rcontent s 3. lowamoun to fpoorl y digestible cell-wall constituents 4. highpotentia lcell-wal ldigestibilit y anda fas trat eo fcell-wal ldigestio n 5. highdry-matte rintak eb yruminant s 6. sufficientlyhig hdry-matte rcontent ,especiall yi nth estove r 7. moderate levelo fwater-solubl e carbohydrates inth estove r 8. acertai nproportio no fea ri nth edr ymatte r 9. alo wsusceptibilit y topest san ddisease s 10. astock y steman da superio rroo tsystem . Itwil lals ob enote d thatsom echaracteristic s canb eimprove db ymodifyin g culturalpractice .Som erelevan tdat ao nth eeffect so fweathe rcondition shav e alsobee nadded .

1. High and stable dry-matter yield Theproductivit yo fa cro pdepend so nth epresenc eo fenoug hefficien t leafare adurin gperiod swit hhig hirradianc e ando nth eplant' s capacityt o store thedr ymatte rproduced .Maiz e isthermophilic ;thu si tmus tb e sownlat e andi tusuall yfinishe sdevelopin git slea fapparatu si nAugust .Therefor eth e leafare ai sinsufficien tt ointercep tal lth eincomin g lightdurin gth emonth s

207 with thehighes tirradiance .Genotype swit h amaximu mearly-seaso nvigou rar e thereforeadvantageous .Th eearl yvigou r ismainl ydetermine db y thegenotype' s cold tolerance,i.e .toleratin g alo wminimu m temperature forgerminatio nan d growth,an dhavin ga hig h rateo fphotosynthesis ,vegetativ e growth (including rootgrowth )an dvegetativ e developmenta tlo wtemperatures .Earl yvigou rshow s a considerable geneticvariatio nan dth erespons e toselectio nprove st ob e high (e.g.Dunca n &Hesketh , 1968;Moc k &Eberhart , 1972;Gunn , 1975;Moc k& Bakri, 1976;Moc k &Skrdla , 1978;Eagle s &Hardacre , 1979;Miedema ,1979a,b ; Mock &McNeill ,1979 ;Stamp , 1980;Eagle s aBrooking , 1981;Fakored e &Ojo , 1981; Semuguruka etal. , 1981;Land i &Crosbie ,1982 ;Miedema , 1982;0 .Dolstr a pers. connu.) . A slowearl ydevelopmen t requiresplan tdensit y tob ehigh .Therefor e the ideotypemus tb ea wea k intraspecific competitor.Mutua lshadin gdurin g laterstage so fth ecrop' sdevelopmen tmus tb eminimized ,wherea s lightinter ceptionmus tb emaximized .Thi s canb erealize db y selectionfor : - aprostrat e leaforientation ,especiall yo fth e longmid-leaves .Numerou s authorshav e indicated theadvantage s ofverticall yoriented ,stif fleave s aboveth eto pea runde rhig hplan tdensitie so rwit hnarro wro wspacing s (e.g. Pendleton etal. , 1968;Duncan , 1971;Hick s &Strucker , 1972;Winte r &Ohlrogge ,1973 ;Ariyanayaga me tal. , 1974;Vidovic ,1974 ;Whigha m &Woolley , 1974; Mock &Pearce ,1975 ;Fakored e &Mock , 1977;Frölic he tal. ,1977 ; Peppere tal. , 1977;Frölic h &Pollmer , 1978;Lamber t &Johnson , 1978).I t hasbee nsuggeste d thatthi serec tlea fhabi tma yb eeve nmor e importantfo r foragemaiz e thanfo rth egrai n crop (Gunn,1975 ). However ,thi scanop y structurei sno tadvantageou s forwhole-cro pyiel di nNorth-Wes tEurope .Th e minimum leaf-areainde x toprofi t fromth e lowerlight-extinctio n coefficient inth euppe rcanop y layersi sseldo mrealize d (seeMonteith , 1965;Duncan , 1971; Winter &Ohlrogge ,1973 ;Vidovic , 1974;Fakored e &Mock , 1977).O nth e contrary,th erigidit yo fleave si sa nadvers e characteristic sincei ti s associatedwit h amuc h lowerdigestibilit y ofth e cellwall so fth elea fan d probably ofth ewhol e crop.Fro m theresult sreporte d inStrui k (1982a)i t appeared thatgenotypicall y determined differences incell-wal l digestibility areexpresse d inal lplan tpart s (seebelow) . Inaddition ,lodging ,transpira tion,an dwin d andhai ldamag eals odepen do nth estructur eo fth elea f canopy. Leafangl ei nitsel fprobabl y doesno taffec tdigestibility . - amor epronounce d oblongshap eo fth eleave s - smaller tassels (Mock &Schuetz ,1974 ;Moc k SPearce ,1975 ;Paterniani , 1981).

208 Tasselsma yreduc eyiel db y reducingth eradian tflu xt oth euppe rcanop y layers,especiall ya thig hplan tdensitie s (Grogan,1956 ;Dunca ne tal. , 1967; Huntere tal. , 1969)an dals ob y competingwit hdevelopin gear sfo r nutrientso rphotosynthate s (Grogan, 1956;Dunca ne tal. , 1967). Small tasselsiz ei sals oassociate dwit h tolerance tohig hplan tdensit y (Mock &Buren , 1972;Bure ne tal. , 1974).Th esucces so fpollinatio n isprobabl y notgreatl yaffecte db y areductio n intasse lsiz e (cf.Daynard , 1983). Maximum lightinterceptio nwit hminima lmutua lshadin g canals ob erealize d bycultura lpractice : -b y anotherplan tarrangement :narrowe r inter-row spacingsan dmor espac e betweenplant swithi n thero w (Hoff& Mederski , I960;Woolle ye tal. ,1962 ; Hepting &Zscheischler , 1975;Parks ,1977 ;Prine ,1977 ;Pomme re tal. , 1981) -b ynorth-sout horientatio no fth erow s -b yoriente dpositionin go fth esee di nth erow ,causin gth eplan eo f thetw o leaforthostiche s tob eperpendicula r toth edirectio no fth eplan tro w (see Peters &Woolley , 1959;Prine ,1977 ) - byunifor mdistributio no fplant swithi na ro w (Hoff& Mederski ,I960 ;Kral l etal. , 1977;Johnso n &Mulvaney , 1980). Theeffect so fmutua l shadingo n thereproductiv e developmentca nb e minimizedb yth eus eo fdensity-toleran t (oftenprolific )hybrid s (StinsonS Moss, 1960;Mos s &Stinson ,1961 ;Collin se tal. , 1965;Knlpmeye re tal. ,1962 ; Earlye tal. , 1966,1967 ;Rüssel , 1968;Bure ne tal. , 1974;Berti ne tal. , 1976; Phipps &Weller , 1979;Wilkinso n &Phipps ,1979 ;Phipps , 1980).Thes e hybridsar eals oles sstress-sensitiv e andsho wmor establ eyields .Prolificac y anddensit y tolerancear evariabl ean dheritabl e traits (e.g.Moc k &Buren , 1972; Harrise tal. , 1976;Sorrell se tal. , 1979).Hybrid s showingthes e characteristics show lesspronounce d dominanceo fth etasse love rth eear san d ofth euppermos tea rove rlowe rear s (e.g.Bauman ,1960 ;Bure ne tal. ,1974 ; Bertine tal. , 1976). Struik (1982b)suggeste d thatselectin g forth eear-shoo tapexe st ob e lesssensitiv e tophotoperio d thanth emain-shoo t apexwoul dprovid eplant swit h largerlea farea ,bette rsynchronizatio no f theinflorescence san d therefore with agreate rresistanc e tostress ,especiall ydurin gan dprio r tosilking . Genotypes thatar ecompletel yda yneutra lmigh tals osho wthes e favourable characteristicsbecaus e synchronizationi sassociate dwit hphotoperiodi c sensitivityan dphotoperio d (Struik,1982b , 1983a). Selectionfo rinsensitivit y tophotoperio d ispossibl e (Mock &Pearce , 1975;Roo d &Major , 1981a), although heritability islo w (Rood &Major , 1981a).

209 Thelea fare apresen ti nth eideotyp eshoul dhav e anoptimu mefficiency . Thisincludes : -maximu mrat eo fphotosynthesis ,fo rwhic h geneticvariatio n andrespons et o selection exist (Duncan& Hesketh , 1968;Heiche l& Musgrave , 1969;Crosbi e etal. , 1977,1978a,b ;Crosbi e &Mock , 1980;Crosbi ee tal. , 1981a,b). - longevity (slowlea fsenescence ,late-seaso nvigour )wit hmaintenanc eo fa high activity.Th erat eo f theapparen tphotosynthesi so feac h leafdecline s duringageing ,bu tth erat eo fdeclin edepend so ngenotyp e (e.g.Vieto re t al., 1977).Th erat eo fsenescenc e (relativet oth erat eo fdry-dow no fth e ear)als ovarie sconsiderabl y amonghybrid s (Tollenaar &Daynard ,1978 ; Daynard etal. , 1979;RIVRO , 1983).Th e 'stay-greenindex 'i sa nimportan t selectioncriterio ni nbreedin gprogrammes . -resistanc e tofros t -minimu mdeman do fresource spe runi to fphotosynthate sproduced . Amaximu mrat eo fphotosynthesi s throughoutth egrowin g seasonnecessitate s theus eo freasonabl y latehybrid s (cf.Daynar de tal. , 1979;Fairey ,1980 ) becauseof : - theirlarg elea fare a (seee.g .Hunter ,1980 ) - theprolonge dpresenc e atth eto po fth ecanop yo fne wleaves ,whic hhav e higherrate so fphotosynthesi san dwhic htolerat elowe rtemperature stha n olderleaves . - thedelaye demergenc eo fth e tassel,whic hshade sth euppe rleaves . Latehybrid sma yals ob edesirabl ebecaus eo fth e largestorag ecapacit yo f theirvegetativ eparts .'Late 'her emean s latei nflowering ,lat ei nmaturatio n and latei nsenescence . Furthermore,respirator y lossesmus tb eminimize d andphotosynthate s shouldb euse da sefficientl y aspossibl eb yreducing : - thephotosynthate swastefull yemploye d forth eformatio no fnon-harvestabl e orundesire dplan tparts ,suc ha stassel san dsmal ltiller s - maintenance costs,especiall yo fstorag eorgan s - energyneed s forth etranspor to fsucros e tostorag eorgan s (thusa minimu m oftranspor tagains tconcentratio n gradients). The lattertw oitem sindicat e thatth estorag eo fnon-structura l carbohydrates ismos tefficien ti nth egrains .

2.Optimu m composition of cellular contents -Mineral s Maize silagei sdeficien ti nman yminera lelement ssuc ha sCa ,Co ,Cu ,I ,

210 Mg, Mn,Na ,P an dZ n (Demarquillye tal. ,1971 ;Malterre , 1976;Kilkenny , 1978; Leaver, 1978;Phipps , 1978;Phipp s s, Weller, 1979).Geneti c variation inth econten to ruptak eo fthes eminerals ,irrespectiv eo fmaturit ystage , issmal l (Phipps,1978),bu tbot h genotypicvariatio nan dinheritanc ehav e beenreporte d forC a (Gorslinee tal. , 1961;Naismit he tal. , 1974;Bruetsc h &Estes ,1976) ,C u (Gorslinee tal. ,1964) ,M g (Gorsline etal. ,1961 ,1964 ; Bruetsch &Estes , 1976),M n (Gorslinee tal. ,1964) ,P (Gorslinee tal. , 1964; Bakere tal. , 1970;Naismit he tal. ,1974 ;Bruetsc h &Estes ,1976 ; Kovacevic, 1982)an dZ n (Gorslinee tal. ,1964 ;Bruetsc h &Estes , 1976). Sinceminera l supplements aregiven ,thes edeficiencie s areno timportant .

Crude-protein content (CPcontent ) CPconten ti sinsufficien tt omee tth eprotei nrequirement so fyoun gcattle , finishingbee fcattl ean dlactatin gcow s (e.g.Demarquill y etal. ,1971 ; Gunn, 1975;Kilkenny , 1978;Leaver ,1978 ;Phipps ,1978 ;Vérité , 1979). Considerable geneticvariatio ni nC Pconten texist s (Dudley &Lambert ,1969 ; Rothe tal. , 1970;Gallai se tal. , 1976;Dudle ye tal. , 1977;Derieu x & Montalant,1978 ;Maggior e etal. , 1980;Mott oe tal. , 1980),wherea s heritabilityprove d tob ehig h (Manne tal. , 1980;Mott oe tal. , 1980;Schmidt , 1980). Increases inth eprotei n contento fth emaiz eplant ,however ,canno t be achievedwithou tlowerin gth etota lyiel do fdr ymatte rpe rhectar e (e.g. Wilkinson &Osbourn ,1975 ;Dudle ye tal. , 1977;Derieu x& Montalant ,1978 ; Gallais& Vincourt ,1983 ;Landry , 1983).

Qualityo fcrud eprotei n (CPquality ) Innorma lmaiz ehybrids ,th eprotei no fth ekernel s (predominantly zein)i s deficienti nth eessentia lamin oacid slysin ean d tryptophan.Th e introduction ofopaque- 2an dothe rmutan tstrain so fmaiz ewit h ahighe rC P contentan da higherconten to flysin ean d tryptophantha ni nnorma lhybrid s significantly improvesth enutritiona lvalu ean dprotei nqualit y formonogastri canimal s (e.g. Mertze tal. , 1965;Pollme re tal. , 1974;Thoma se tal. , 1976;Barbos a & Glover,1978 ;Ros ae tal. , 1977a,b). Inth erume nsubstantia l degradation ofprotei nan dresynthesi so fmicrobia lprotei nb y themicro-organism soccur ; therefore,high-lysin emaiz eha sno tbee nprove d tohav ea nutritiona l advantagewhe n fedt oruminant s (e.g.Wilkinso n SOsbourn , 1975;Andre we t al., 1979).Th eintroductio no fthes emutan tstrain sals oreduce sth e agronomicvalu eo fth ecro p (cf.b mmutan tstrains ;e.g .Klei ne tal. , 1980). Lysineconten ti nnorma lstrains ,however ,i sals ovariabl e (Zubere tal. ,

211 1975)an dth erespons e toselectio nca nb econsiderabl e (Choee tal. , 1973). The apparentdigestibilit y ofC Pdepend so nit sconten t (e.g.Demarquilly , 1969).Durin g fermentation inth esilo ,a proportio no fth eC P isreadil y degraded tonon-protei nN (Bergene tal. , 1974;Wilkinson , 1976, 1979).Th e utilizationo fprotei n can thereforeb eincrease db yreducin g the fermentation inth esil o (Wilkinson, 1976, 1979), e.g.b yreducin g themas s fractiono f water-soluble carbohydrates.Sinc e themicro-organism s ofth erume nar eth e mainprotei n source forth eruminant ,i ti smuc hmor eimportan ttha t sufficient substrate isavailabl e forthei rgrowth .

Vitamins Vitamin supplementsmus talway sb egiven ,becaus emaiz e isdeficien ti n vitaminse.g .vitami nA ,D an dE (Demarquillye tal. , 1971,-Phipps , 1978). Vitaminso f theB comple xar eprovide db y themicrobe s inth eforestomachs . Nothing isknow n aboutth egeneti cvariatio ni nvitami nconten to fforag e maize.

Non-structural carbohydrates (NSC) Theimportanc eo fth emas s fractiono fwater-solubl e carbohydrates (WSC)i s discussedbelow .Hig hcontent so fWS C+ starc h (i.e.NSC )increas eth e efficiencyo futilizatio no fth e feed (seebelow )bu treduc ecell-wal l digestibility (D ),especiall y athig h levelso fintake ,b y - lowering thep Han dincreasin g theosmoti cpressur eo fth erume nliquo r (e.g. deVisser ,1980 ) - increasing thetim e lagbetwee n ingestion anddigestio no fcel lwall san d decreasing thepotentia l extento fcell-wal ldigestio n (Mertens& Loften , 1980),possibl ybecaus eo fcompetitio n fornutrient sbetwee n cellulolytic andamylolyti cgroup so frume nbacteri a (El-Shalzye tal. , 1961;d e Visser,1980 ) - shortening theretentio ntime . Toeliminat e theadvers eeffect so fhig hNS Cconten ti n foragemaize ,th e rationmus tb e supplementedwit h someroughage .Thes eeffect so fNS Cconten t alsoconcea lgeneti cdifference s inD at ad libitum intake (seebelow ) cwc butreinforc e theeffec to fNS Cconten to nintake .I npractice ,geneti c differences incell-wal l contento rconten to fNS Cmigh tb emor e important forth efeedin gvalu e thangeneti cvariabilit y inD Endospermmutant s (seeIntroduction )whic h change thesusceptibilit y of starch granules toattac kb y amylases,hav e nonutritiona l advantagefo r

212 ruminants (e.g.Thoma se tal. , 1976).

Foragemaiz ei sprimaril y useda sa nenerg y source forruminants .I n addition,th enutritiona lqualit yo fth ecellula r contents (e.g.C P content) correlatesnegativel ywit h dry-matteryield .Wherea s theenerg yconten ti s essential,th ecompositio no fth enon-structura lmateria l should therefore beo fmino rimportanc e asa breedin gobjective .

3. Low amount of poorly digestible cell-wall constituents The indigestible fractiono fth emaiz eplan ti slocate d inth ecel l walls.Thu s theamoun to fcertai n cell-wall constituents shouldb eminimize d toenabl eextensiv e dilutiono fpoorl y digestible cellwall swit h completely digestiblecellula r contents.Sinc e thedigestibilit yo fth ecel lwall si s lowesti nste mparts ,th eproductio no fthes ecel lwall sshoul db e limited. A lowcell-wal l contenti sals oadvantageou s fordry-matte r intake:th econten t oftota lcel lwal lo ro findigestibl e cellwall ,th eshort-ter m digestibility ofcel lwal lan d thebul k volumeo fcel lwall si nth e feedar eth ebes t predictorso fvoluntar yintak e (e.g.Va nSoest ,1967 ;Mertens , 1973;Marte n etal. , 1976;Va nSoest , 1976;Merten s &Ely , 1979;Collin se tal. , 1980;va n derAa re tal. , 1981;Wald o &Jorgensen , 1981).Th econten to f total cellwal l shouldno tb e toolow :optimu m functioningo f therume nnecessitate sa certai n levelo fstructura lmaterial .Thi sstructura lmaterial ,however ,shoul dsho w a fastrat eo fdigestio nan da hig hpotentia ldigestibilit y (seebelow) . Cell-wallproductio n inth e stoverstop sshortl y afterth eonse to f grain filling,bu tonl yi fpollinatio nha sbee n sufficiently successful.Thi s meanstha tselectio n fora lo wamoun to fcel lwall si nth estove rwil lyiel d veryearl yhybrid swit h ahig hproportio no fear .Th edemand s forresistanc e tolodgin g (see10 )an d thenecessit yo fconstructin ga ver yproductiv ean d large leafapparatu s limitth epossibilitie s ofselectin gagains tamoun to f cellwal li nth estover .Th e ideotype should thus: - showa reasonabl yearl yanthesi s (i.e.shoul dhav ea limite dnumbe ro fshor t phytomeres) - showa hig h leaf:ste mrati o - showa slo wdecreas e inth e rateo fcarbo nassimilatio n aftereac h individual leafha s fullyexpande d - have alarg eea rt oprovid ea storag e capacity largeenoug h tocompensat e forth esmalle rste man dt osto pcell-wal l formation inth estover .Grai n filling,however ,shoul db eslo w (seesectio n8) .

213 Maximumdry-matte rproductio n andminimu m cell-wallproductio ni nth estove r arecontradictor y demands andthu sth eearlines so f floweringmus tb ea compromisebetwee n them.Fortunately ,othe rcharacteristic so flatenes s (slow senescencean dmaturation ) arepartl y independento fflowerin gdate .

4. High potential cell-wall digestibility and a fast rate of cell-wall digestion Geneticvariatio n incell-wal ldigestibilit y existsan dheritabilit y proved tob ehig h (Beerepoot,1981 ;Deinu m& Bakker , 1981;Deinu m &Struik , 1982). Incontras twit h theamoun to fcel lwal lan dmos tothe rqualit y characteristics,selectio n fora hig hdigestibilit y ofcel lwall s (D )i s possiblewithou taffectin ggrai nyiel do rwhole-plan tyiel d (Gallaise tal. , 1976; Deinum &Bakker , 1981). Selection fora hig hpotentia lexten tan drat e ofcell-wal ldigestio nwil l resulti na reductio n inth eproportio no fligni n andsilic ai nth ecel lwalls ,ma ychang eth ecellulose :hemicellulos eratio , butwil lals oinclud eselectio n forcertai nphysical-chemica l characteristics ofcellulos e andhemicellulos e and forth ebondin go fan dlinkage sbetwee n allcell-wal l components.Selectio n forhig hD maytherefor ehav e repercussionso nresistanc e tolodging .Undersande r etal . (1977),however , foundtha tlodgin gresistanc emigh tb eincrease dwithou tgreatl y affecting cell-wallcomposition ,wherea sGallai se tal . (1980)suggeste dtha tth elowe r lodgingresistanc e ofbrown-midri bhybrid smigh tb eovercom eb ymodifyin g the geneticbackgroun d andwithou taffectin g digestibility. Selection forimprove dcell-wal ldigestibilit ywil lb eeasie rtha n selection forincrease dorganic-matte rdigestibility .Ther e isa hig h correlationbetwee nth eD ofdifferen tplan tparts ,an dth eorde ri nwhic h cwc hybridsar eranke daccordin g tothei rD doesno tchang e intim ei frat eo f cwc development issufficientl y uniform.Therefor e selectioni spossibl eb y analysingan yplan tpar ta tan ystag eo fdevelopment ,providin g allgenotype s aresample d atth esam etime .I ti sprobabl ymos tconvenien tt oanalys eth e complete stoverharveste dprio r toanthesis ,becaus e thisavoid ssamplin g problems. Someprogres sca nb emad eb yreducin g theproportio no fcertai nplan t partswit hhig hcell-wal lcontent san dpoorl ydigestibl ecel lwalls ,e.g . rindan dmidrib .Rin d thicknesse.g . showsgrea tgeneti cvariatio nan d selection canb esuccessfu l (Chang& Loesch ,1972 ;Thompson , 1972;Undersande r etal. , 1977;Zube re tal. , 1980;Twusami-Afriyi e &Hunter , 1982). Muchha sbee nwritte no n theeffect so ndigestibility ,intak e andfee d

214 efficiencyo fth e foragecro po fincorporatin gbrown-midri bmutan tallele s (mostlyb m )int oth emos tpromisin ghybrid s (e.g.Barne se tal. ,1971 ; Lechtenberge t al., 1972;Mulle re tal. , 1972;Colenbrande r etal. ,1973 ; Colenbrandere tal. ,1975 ;Roo ke tal. ,1977 ;Keit he tal. ,1979 ;Sheldrick , 1979;Gallai se tal. ,1980 ;Bloc k etal. ,1982 ;Daccor d &Vogel ,1982 ; Stallingse tal. ,1982 ;Struik , 1982a).Advers eeffect so fthes emutant so n otheragronomi c characteristics sucha sgrai nyield ,whole-plan tyield , earliness,dry-matte rconten tan dlodgin gresistanc e (Zubere t al.,1977 ; Sheldrick, 1979;Gallai se tal. , 1980;Daccor d &Vogel ,1982 )an d susceptibility towater-stres s (V.L.Lechtenberg ,persona l communication)hav e sofa r prevented thecommercia lus eo fb m hybrids.However ,th eresearc h citedha s stressedth epossibilit yan dnecessit yo fbreedin gspecia lhybrid sintende d forforag eproduction . Geneticvariatio ni nnorma lmateria li slarg eenoug h tocreat ehybrid s thatar ea sdigestibl e asth eb mmutant sbu twhic hhav enon eo fth elatter' s disadvantages (Gallaise tal. , 1980).Accurat e laboratorytechnique sfo r determiningth e foragequalit yo fcrosses ,however ,ar eexpensiv ean d complicated.Laborator y testsshoul dtherefor eb erestricte d togenotype s thatar ea ta nadvance d stage inth eselectio nprocess ,an d toinbreds .Rapid , simplean d cheapmethod s foraccuratel yestimatin g foragequalit ymus tb e developed (seeIntroduction) .

5. High dry-matter intake by ruminants Dry-matter intake (dmintake )i simportan ti fmaiz e isvoluntaril y fed asth emai n feedi nth eratio n andals owhe n therat eo fsubstitutio n for other forageso r feedsi simportant .Voluntar yd mintak e isaffecte dby : - cell-wall content (e.g.Va nSoest ,1976 ;Wald o &Jorgensen , 1981)o rcell - wallvolum e (vande rAa re tal. , 1981) - ratean dexten to forganic-matte r digestion (e.g.Donefe re tal. ,1960 ; VanSoest ,1976 ;Va nSoes te tal. , 1978;Wald o& Jorgensen ,1981 ) - dry-matterconten t (Daynard &Hunter , 1975;Malterre , 1976;Wilkinson ,1976 ; seeals obelow ) - changesi nth ecompositio no fth ecel l solublesoccurrin gdurin gensiling : conversiono fWS Ct oshort-chai norgani c acids (increasing theleve lo f freeacidit y andth eleve lo faceti cacid )an dth econversio no fprotei n tonon-protei n nitrogenous compounds (increasing theconten to fammoni aN ) (Wilkinson,1976 ;Phipps ,1980 ;Gallasz ,1982 ) - NSC%,throug hit seffect so np Hi nth esilag ean di nth erumen ,protei n

215 degradation andretentio n timei nth erume n -palatabilit y oracceptability ,partl y influencedb y the factorsmentione d above. Athig h levelso fintake ,th eavailabl e energy isuse d lessefficiently . Thecompositio n ofth eideotyp emus tminimiz e thisdecline .Th edepressio n ofdigestio n isgrea tfo rcell-wal l constituents andalmos tabsen t forcel l solubles (Waldo& Jorgensen , 1981). Cell-wallconten tshoul d thereforeb elow , thecell-wal l components shouldhav e alarg eproportio no fpotentiall y digestible cell-wall components andth erat eo fdigestio no f thepotentiall y digestible cellwal lshoul db erapi d (seeabove) .O nth eothe rhand ,a hig h contento fNS C (parto f thecel lsolubles )ma y increase thedepressio nb y reducing therat eo fcell-wal ldigestion . Thecel lwall :NS C ratioi nth edie tshoul dno tb eto olow :plan tfibr e feda slon gmateria l (overapprox - 0.5 - 1.0cm )stimulate srume nmotilit yan d rumination (e.g.va nVuuren , 1979).Rume nmotilit y stimulatesdigestio nb y intensifying thecontac tbetwee nmicro-organism s and feedparticles .Ruminatio n resultsi na reductio n ofparticl e sizean di scouple dwit h thesecretio no f saliva.Saliv aneutralize s thevolatil e fattyacid sproduce db y therumina i micro-organisms,thu sbufferin g the rumenflui dagains ta lo wpH .A hig h contento freadil y available carbohydrates,however ,migh tresul ti na lo w ruminaip H (seeabove) .A hig h digestibilityo fcel lwall sma ylimi tth epositiv e effecto flon groughage .Th erisk so f feedingdisturbance s canb eminimize d by feedinga balance d ration:a tleas ton ethir do f thedail yd mintak eshoul d consisto f longroughag e (vanVuuren , 1979). Genotypeswit hhig hproportion so fgrai nwil lhav ea ver yhig hnutritiv e valueprovide d thecondition s foroptimu m rumenfermentatio n aremaintained ; genotypically determined differences inpotentia lcell-wal l digestibility are ofmino rimportanc e forthes egenotypes . Theplan tcharacteristic s affecting dmintak ehav ea larg egeneti c variation.Selectio n forsom eo fthes e factors,however ,i sver ydifficult . Someplan tmeasurement sma yb euse da sindicator so fpotentia ld mintake . Forexample ,Gallai se t al. (1976)reporte d thatste mdiamete r correlated positivelywit hintak eo fdigestibl eorgani cmatter .

6. Sufficiently high dry-matter content, especially in the stover Thedry-matte rconten t (dm%)i srelevan ta sa qualit y factor,becaus e itaffects : - thesuitabilit y forensilin gwhic h isseverel y limiteda tdm % <30-35 %fo r

216 towersilo san da tdm % <25 %fo rlo wclam psilo s - theconcentratio n ofnutrient si nth efres hmateria l - thedry-matte r intake;dry-matte rintak e isconsistentl y and largely limitedb ydm %i fdm %i slowe rtha n30 % (e.g.Fishe re tal. , 1968;Daynar d &Hunter , 1975;Malterre , 1976;Daynard , 1978;Fishe r &Fairey , 1979).Th e positiveeffec to fa nincreas e indm %o ndry-matte r intakei ssmal lo r absenti nth erang eo f 30-35%.Abov e 35-40%a sligh tdecreas e inintak ei s observedwit h increasing dm% (e.g.Malterre , 1976).Thi s decrease inintak e mayb ecause db yheatin g resulting from thelo wbul k densityo fdr y forage inth esil oo rb y secondary fermentation. Thedm %i sinfluence dby : a.th eproductio n environment (e.g.plan tdensity ,temperature ) b. theduratio no fth evegetativ eperio d (orearlines si nflowering ) c.th esiz eo fth eear ,th erat eo fgrai n fillingan d therat eo fgrai n dry-down (i.e.earlines so fgrai nmaturatio nan dproportio no fgrain si n thedr ymatter ) d.rat eo ftissu e senescence,affecte db ygenotype ,disease s andpests ,o r otherwise (i.e.earlines so fsenescenc e ofvegetativ e parts). a.Environmenta l factorstha treduc eo rlimi tth eproportio n ofea rals olimi t therat ea twhic h thedm %o fth ewhol e cropincreases .However ,i tshoul d benote d thatth erelationship sbetwee nea ran dstove rar eals orelevan t forth edevelopmen to fdm% . Overa wid erang eo fdm %o fth eear ,th edm %o fth estove ri sfairl y constant (e.g.Hunter ,1978 ;Gros s &Peschke , 1980a).Extensiv e remobilizationo fcel lsoluble s fromth estove rt oth eea rcause db y adverse conditions,ma ycaus e thedm %o fth estove rt odecline .Thi s declinei srarel yvisible ,sinc ei ti scompensate d forb y thecontemporar y senescence andobscure db yweathe rconditions .Dat a froma glasshous e experimentwit h threetemperature san d twoligh tintensitie s aftergrai n set (Struik,unpublishe d data)clearl y revealed theeffec to fredistributio n ondm % (Fig. 2). Atlo wligh tintensity ,grai n fillingan dincreas e inea rdm %ar eslowe d down.Bu teve na ta give ndm %i nth eear ,th edm %o fth estove ran do fth e wholeplan ti slowe rbecaus e thegrain sfil lwit hdr ymatte rtha tha sbee n temporarily storedi nth estover .Th edm %o fth estove ri stherefor e affectedb yth emas sfractio no fredistributabl e cellsoluble sstil l presenti nth e stover.Thi smas s fractionstrongl y dependso nth eproductio n

217 7. Moderatelevel of water-soluble carbohydrates in the stover Themas s fractiono fWS Ci nth edr ymatte ro fth estove r shouldno tb e toolo wbecaus e: -WS Car enecessar yt oobtai na goo dan d stable silage,sinc eWS Car eth e substrate forth emicrobe sdurin g fermentation -a certai n levelo fWS Creduce sth eplant' svulnerabilit yt oinfirmitie so f oldag e sucha sFusarium infection (Blanco& Blanco , I960;Mortimor e& Ward , 1964;Molot , 1969a,b,c;Cook , 1978a;Strui k& Deinum , 1982) -WS Cincreas e thenutritiv evalu eo fth e feeda tvoluntar y intake,althoug h thecell-wal ldigestio n canb ereduce d (seeabove) .

Themas s fractiono fWS Ci nth edr ymatte ro fth estove rshoul dno tb e toohig heither ,because : -WS Car econverte dt oshort-chai norgani c acidsan dma y thusreduc evoluntar y intake andprotei nutilizatio n (seeabove ;Wilkinson , 1976;Phipps ,1980 ; Gallasz, 1982) - theproportio no fvolatil e acidsmigh tbecom e large (Gallasz, 1982) -i fahig hproportio no fth eNS Ci swater-soluble ,losse so fdigestibl e organicmatte rar eproportionall y largewhe n seepageoccur s - gaseouslosse sdurin g fermentationi nth esil omigh tbecom elarg e (Wilkinson &Phipps ,1979 ;Phipps ,1980 ;Gallasz , 1982) - lossesar eals olarg ewhe n theensile dmateria li sexpose dt oth eair , if theWS Cconten ti nth e freshcro pwa shig h - ensiling cropswit hhig hWS Ccontent smigh treduc edigestibility ,bu t digestibilityi sno taltere db yensilin gwhe nWS Chav eprimaril ybee n convertedt ostarc h (McAllan& Phipps ,1977 ;Phipp se tal. , 1979;Phipps , 1980).Thi sdifferenc ei scause db yadifferenc ei nth eexten to fth e lossesmentione d above.Analytica lerror sma yals opla ya part .

Thismean stha tth econversio no fWS Ct ostarc hi sfavourabl efo r preservation and fornutritiv e valuea slon ga si tdoe sno taffec tth elate - seasonvigou ro fth eplant .Thi svigour ,however ,i softe naffecte di n North-WestEurop eb yprolonge dperiod so flo wligh tintensit yi nlat esumme r andautumn .A WS C contento f5 %o nth ebasi so fth edr ymatte ro fth estove r mightb eenoug ht opreven tth enegativ eeffect so flo wlevel so fWSC .

8. A certain proportion of ear in the dry matter Numerousreport shav ediscusse d therelevanc eo fgrai n filling forth e

220 nutritivevalue ,crop-growt h ratean dsuitabilit y forensilin go fforag e maize.A revie wi sgive nb yStrui k (1983a) (seeChapte r 6). Below,thi srevie w willb esummarize d andsom eothe raspect san dth emos trecen tliterature , notcite di nChapte r6 wil lb ediscussed . Earformatio nan dgrai n fillingar eimportan tbecause : - theyaffec tth erat eo fcro pgrowt h duringth epost-silkin gperio d (recentlyreporte db yTollenaa r& Daynard , 1982)b yaffectin g therat eo f photosynthesis.Th eeffect so falteration s insource :sin k ratioo ncrop - growthrat edepen do ngenotyp e (Tollenaar &Daynard , 1982). - thegrain sprovid ecapacit y tostor ephotosynthates .Thi sstorag e capacity isalway snecessar ybu ti sespeciall yimportan ti nyear swhe nplant sar e smallan d theweathe rdurin gautum ni s favourable (e.g.198 0i nTh e Netherlands). - ahig hproportio no fea ri nth edr ymatte rmigh tb ebeneficia l forwhole - plantquality ,althoug h thiseffec ti sver ylimite di nmargina l growing regions (e.g.Fishe r &Fairey , 1979;Fairey , 1982).Th ecob :grai nrati o mustb elow ,sinc eth eco bi sles sdigestibl e thanth egrain s (Struik, 1982a). Shellingpercentag e isa variabl e andheritabl e trait (e.g.Loesc he tal. , 1976). - ear formation inhibitsth eongoin go fth eproductio no fpoorl y digestible cell-wallmateria l inth estove r (Struik, 1983a). - grain filling limitsth e fermentationprocesse si nth esilo ,an dpositivel y influences voluntary intake,apparen tdigestibilit y afterensilin gan d feedefficienc yb yinducin gwater-solubl e carbohydrates tob econverte dt o starch (seeabove ;Wilkinson, "1976 ;McAlla n& Phipps , 1977;Phipp se tal. , 1979;Phipps ,1980 ;Gallasz , 1982). - thedry-matte rconten to fa norma lcro pincrease smuc h fastertha n thato f agrainles s cropo rtha to fa cro pwit h alo wproportio no fth edr ymatte r presenti nth eea r (e.g.Deinum , 1982,unpublishe d data;Fairey ,1982 ; Phippse tal. , 1982;Strui k &Deinum , 1982;Struik , 1983a,b). - grainfillin gincrease s theproportio no finsolubl ematte ri nth efractio n thati scompletel y digestible,thu sreducin g losseso fdigestibl eorgani c matterwhe n seepageoccurs . - thesink :sourc e ratioaffect s thelongevit y ofleave s (Tollenaar &Daynard , 1982;Struik , 1983b);literatur eo nthi stopi c isno tconsistent ,partl y becauseth eeffect sdepen do ngenotyp e (Tollenaar &Daynard , 1982).I n general,i fth eea rmonopolize s thecarbohydrates ,nitrogenou scompounds ,

221 hormonesan dothe r substances thismigh tb edeleteriou sunde r conditions thatcaus e largedifference sbetwee n crop-growth ratean dear-growt h rate (e.g. defoliation,shadin getc. ;se eals oStrui k &Deinum , 1982;Struik , 1983c).A drasti c reductioni nth enumbe ro factiv ekernel smigh tals o reducecrop-growt h rate,becaus ehig h levelso fcarbohydrate s inth e leaveso rchange si nth eproductio no fhormone saccelerat e ageingprocesse s andreduc ephotosyntheti c activity.Th egenotypicall y determinedbalanc e betweensin kan d sourcedoe sno tinfluenc e leafsenescenc e asdelicatel ya s Tollenaar &Daynar d (1982)hav esuggested ;i npractic e thetoleranc e for smallchange si nsource :sin k ratioi sgrea t (e.g.Struik , 1983a;se eals o Fig.3) . number of green leaves/plant

90 100 110 ear yield (g/pl)

Fig.5 .Relatio nbetwee nea ryiel d (asmeasur eo f relative sinksize )an d numbero fgree nleave sa t finalharvest . Earyiel dwa svarie db y removingear so rb y artificially preventing pollination.(Plan t density 8.9 m ;location :Wageningen ; year1980 ; harvest date:1 3October ; Struik,unpublishe d data;se eals oStruik ,1983c , Fig.8) .

- rapidgrai n fillingmigh taffec tlate-seaso nvigou rb y stimulatingth e susceptibility toFusariu m infection (seee.g .Barrièr ee tal. ,1981 ; Barrière &Gay , 1983),especiall yi nyear swit hrelativel yhig hnigh t temperatures andlo wligh tintensitie sdurin gSeptembe ran dOctober . Susceptibility to Fusarium, however,i sno tnecessaril y relatedt oearl y maturity (e.g.Cook , 1978a;Barrièr ee tal. , 1981).

222 -hig hdm %i nth egrain scause db yhig hrate so fgrai n fillingma yinduc e insufficientutilizatio no fth ekernels .T oensur e thatstarc hdigestio n isno treduced ,kernel sshoul dno thav epasse d thehard-doug h stagea t maximumorganic-matte ryiel d (e.g.Honi g &Rohr , 1982a,b;se eals o above).

Onth ebasi so fthes e considerations itma yb econclude d thatth e forage-maize ideotype shouldhav e anearl ysilkin gdat ean dshoul dhav ea largeear ,wit h aslo wrat eo fgrai n filling.Selectio n forincrease dear - sizecomponent s reducesgrain-fillin g rate (Ottaviano &Camussi , 1981),thu s themonopolizin geffec to fth eea rwil lno tb eincrease d (cf.Struik , 1982a). Inthi swa yth epositiv eeffect so fgrai n formationan dgrai nfillin gar e ensured,wherea sth enegativ eeffect sar eminimized .However ,earl ysilkin g ismostl yassociate dwit h asmal l leafare a (seeabove )an d thuswit hreduce d productivity,unles sth eare aan dare aduratio no fth eindividua l leavesar e verylarge .Thi sassociatio nmigh tb eovercom eb yselectin g forimprove drat e oflea fdevelopmen t (seeRoo dS Major , 1981b;Bonhomme , 1983;Vincour te tal. , 1983).Rat eo flea fappearanc e alsocorrelate swit h finalnumbe ro fleaves , earlinessan dearl yvigou r (Vincourte tal. , 1983).Th enecessar y variation andselectio nrespons eo fear-siz eparameter s (earlengt han ddiameter ,numbe r ofovule san dkernels ,kerne lsiz eo rdepth ,co blengt h anddiamete ran d shellingpercentage )ar econsiderabl e (e.g.Loesc he tal. , 1976;Crosbi ee t al., 1978b;Cortez-Mendoz a& Hallauer , 1979;Crosbi e &Mock , 1980;Ponelei t etal. ,1980 ;Ottavian o &Camussi ,1981 ;Derieu xe tal. , 1983).

9. A low susceptibility to pests and diseases Climatic conditionsi nNorth-Wes tEurop ear eunfavourabl e forth e developmento fmos to fth eimportan tmaiz epest san ddisease s (Cook, 1978a). Thosepest san ddisease s thatar eadapte d tocoo lweathe rcondition sar e oftenles simportan tfo rforag emaiz e than theyar efo rgrai nmaiz eo rCC M maize.Thus ,t odate ,forag emaiz eha sbee n ahealth y cropan ddamag eo f economicimportanc e isinfrequent .Ye ti ti seviden ttha tth e forage-maize ideotypeshoul dhav eth eminimu msusceptibilit y toal lpest san ddisease s thatmigh toccu ri nNorth-Wes tEurope .

Themos twidesprea d diseasesi nN.W .Europ ear eroot ,ea ran dstal k rots, causedby ,amon gothers , Fusarium spp.suc ha sF . graminearum Schw. (syn. Gibberella zeae (Schw.)Petch ), F. culmorum (W.G.Sm. )Sacc , F. moniliforme Sheld, F. avenaceum (Fr.)Sacc .an dman yothe rspecie s (seee.g .Mensa h&

223 Zwatz, 1975;Cook , 1977,1978a,b ;Barrière , 1979).Damag edu et oFusariu m infectiondepend so nth egenotyp eo fth emaiz eplant ,o ncultura lpractice , stageo fmaturity ,climati c conditionsan dsink-sourc e relationsdurin g grain filling (e.g.Ott o &Everett , 1956;Fole y &Wernham , 1957;Michaelson , 1957;Mortimor e& Wall , 1965;Krüger ,1970a,b ;Krüge r &Reiner ,1974 ; Krügere tal. , 1975;Mensa h& Zwatz , 1975a,b;Cook , 1977,1978b ;Krüger , 1978;Barrière , 1979;Krüge r &Rogdaki-Papadaki , 1980;Barrièr e etal. ,1981 ; Ebskamp, 1981). Fusarium infectionmigh tcaus ea smal lreductio n inbiologica l dry-matteryiel do fabove-groun dplan tpart san di ndigestibility ;i t stimulates thedry-dow no fth ecro pbu treduce s lodgingresistance .Th e relevanceo f lodgingresistanc e isdiscusse dbelow .Sinc e themos tproductiv e hybrids showprolonge d longevity and activityo fleave sand/o r flowerlate , selection forhigh-yieldin g abilitywil lgenerall y concomitantly limit Fusarium infection.Th esusceptibilit y to Fusarium irrespective ofstag eo f maturity,however ,als ovarie sconsiderabl y (seee.g .Andrew , 1954;Krüge r etal. , 1975;Mensa h &Zwatz , 1975a,b;Barrière ,1979 ;Barrièr ee tal. ,1981 ; Ebskamp,1981 ;RIVRO , 1983). Ifth edamag e ist ob ekep ta ta lo wlevel , theremus tb ea certai nmas s fractiono fWS C inth epit h (seeabove) .Th e ideotypeshoul db e fairly latean dhav e anactiv e resistance inturgescen t tissue (including roots),resistanc e insenescen to rsemi-senescen t tissue,resistanc e tostresse s (e.g.chilling ,drought) ,a balance dsink : sourceratio ,a nexcellen tstay-gree ninde xan da slo wdeclin eo fphotosynthesi s afteranthesi s (Barrière,1979 ;Barrièr ee tal. , 1981;Barrièr e SGay , 1983). Afterreachin gmaximu m dry-matteryiel d ofth ewhol eplant ,th edry-dow n shouldb ever yfast .

Common smut (Ustilago maydis (DC)Corda )i smor e spectaculartha n Fusarium infection and isobserve dearlie ri nth eseason .Th econdition s thatgiv eris et osever e infection arestil llargel y unknown.Genotypi c differences inrespons e tosmut ,however ,ar elarg e (Ebskamp, 1981).Sinc e thehybrid s thatar emos tpopula ri nTh eNetherlands ,ar e relatively resistant,n oextensiv ebuil d upo fspore si nth esoi lha soccurred ,eve n whenmaiz eha sbee n growncontinuously .Th e latest,high-yieldin ghybrid s (e.g.Splenda ), however ,d osho wa greate r susceptibility tosmu tinfectio n (RIVRO,1983 ;A.G .Ebskamp ,persona l communication) andthi sma y leadt o abuil d upo fa damagin gpopulatio n density of Ustilago maydis spores (A.G. Ebskamp,persona lcommunication) .Therefore ,th erotatio no fhybrid sma y have tob erecommende d inth efuture .

224 High levelso fsmu tinfectio n arestil lrar ei nTh eNetherland s (Ebskamp,1981 )bu tthe ymigh tb etoxi ct oanimal sunles sth eforag emaiz e isensile d (e.g.va nde rBeek , 1977;Burgstalle re tal. , 1977;Cook ,1978a ; RIVRO, 1983).Fermentatio nprocesse s inth esil odestro y thespores .Th e qualityo fth eensile dproduct ,however ,i slower ,a si sth edry-matte r yield,an dth e fermentation lossesar ehighe rwhe nsever einfectio noccur s (e.g. Burgstallere tal. , 1977;Gross ,1977 ;Ebskamp , 1981).

Fritfl y (Oscinella frit L.) andwireworm s (Agriotes spp.) areth e mostimportan tpest so fmaiz ei nNorth-Wes tEurope .Genotype swit hgrea t earlyvigou rmigh tb eles ssensitive .I ti sfeare d thatth eEuropea ncor n borer (Ostrinia nubilalis Hbn.)ma yestablis h itselfi nNorth-Wes tEurope .

Sincebreeder sar ewel lawar eo fth erelevanc eo fresistanc et o diseases andpests ,thi site mdoe sno tnee d furtheremphasis .

10. A stocky stem and a superior root system Lodging isa seriou sproble mbot h ingrai nmaiz e and foragemaize .I t causesa reductio ni ndry-matte ryield ,greate rharvestin glosses ,a reductio n inharvestin g capacity and thecontaminatio n ofth eforag ewit h soil. Resistance tolodgin gi stherefor ea nimportan t characteristic ofgenotypes , andselectio n fordecrease d lodgingha sbee na nimportan t concerno fal l breeders. Resistance tolodgin gi saffecte db yo rcorrelate dwith : - susceptibility topathogen s (mainly Fusarium spp.se eabove ) - stemcharacteristic s sucha sste mheight ,ste man drin dthickness ,rind : pithratio ,rin dan dpit h strength (breakingforce,-crushin gstrength , resistance topuncture) ,stalk-sectio nweigh tan dstalk-ligni nconten t (cf. Zubere tal. , 1980;Twusami-Afriyi e &Hunter ,1982 ) - root-system characteristics,suc ha sroo tnumber ,roo tvolume ,roo t (clump) weight,amoun to f fibrous roots,roo tdistributio n through thesoi l profile,pattern so fchang ei nth eroot :shoo trati othroug h thegrowin g season,an dtimin gan dexten to fbrace-roo tdevelopmen t (cf.Gunn ,1978 ; Jenisone tal. , 1981;Arihar a& Crosbie ,1982 ) - leafcharacteristic s (leaforientation ,lea fangle ,stiffness ,siz ean d shape) - earcharacteristic s (earheight ,ea rweight ) - otherplan tcharacteristics ,suc ha searly-seaso n andlate-seaso nvigour ,

225 cell-wall digestibility andearlines s - cultivationtechnique s (e.g.plan tdensity ,fertilization) .

Stemcharacteristic s arefairl yeas yt oassess .I nadditio n toplan t heightan dste m thickness,numerou sothe rscreenin g techniqueshav ebee n assessed forthei rusefulnes s asindicator so fresistanc e tostal klodging . Stemheigh t (regardlesso fnumbe ro f leaves) (Giesbrecht,1961 ;Acost a &Crane , 1972; Josephson &Kincer , 1977),ste mdiamete r (Twusami-Afriyie &Hunter , 1982),rin dthicknes s (Chang& Loesch ,1972 ;Thompson ,1972 ;Twusami-Afriyi e &Hunter , 1982),stem ,rin dan dpit h strength (Chang& Loesch ,1972 ;Thompson , 1972; Change tal. , 1976;Zube re tal. , 1980;Twusami-Afriyi e &Hunter , 1982), rindcompositio n (Change tal. , 1976;Undersande re tal. , 1977;Zube re tal. , 1980),stalk-ligni nconten t (Undersandere tal. , 1977;Twusami-Afriyi e& Hunter, 1982), andstalk-sectio nweigh t (Chang& Loesch ,1972 ;Thompson ,1972 ; Change tal. ,1976 ;Twusami-Afriyi e &Hunter ,1982 )al lsho wconsiderabl e geneticvariatio nan dinheritance .Ste m diameteri sprobabl y themos tinterestin g plantcharacteristi c correlatedwit h stalk strength.Diamete r isfairl yeas y tomeasur ean dcorrelate spositivel ywit hdry-matte ryiel d (A.Gallais ,persona l communication),lodgin gresistanc e (Twusami-Afriyie &Hunter , 1982),earl y vigour (Beerepoot,1981 )an dintak eo fdigestibl eorgani cmatte r (Gallaise t al., 1976).However ,i tcorrelate snegativel ywit hdry-matte rconten t (Beerepoot, 1981)an ddigestibilit y (Gallaise tal. , 1976;Beerepoot , 1981). Improvemento fresistanc e tostal k lodgingseem spossible ,withou tgrea t repercussionso ngrai nyiel d (Thompson,1982 ;Twusami-Afriyi e &Hunter ,1982 ) andprobabl y alsowithou trepercussion so nwhole-plan tyield .Stal k firmness often correlatesnegativel ywit hdigestibilit y orothe rqualit y factors (Change tal. , 1976;Undersande r etal. , 1977;Twusami-Afriyi e &Hunter , 1982), sinceth emorpholog y andanatom yo frin dan dpit h changea sa consequenc eo f selectionagains tth etendenc y forstal klodgin g (Chang& Loesch , 1972;Chan g etal. , 1976).Th enegativ e correlationbetwee nresistanc e toste mlodgin g anddigestibility ,however ,i shighl y significantbu tfa rfro mstrict ,wherea s relativedifference s inlodgin gar eofte nmuc h greater thanrelativ e differences indigestibilit y (Undersandere tal. , 1977;Gallai se tal. , 1980;Beerepoot , 1981; Twusami-Afriyie &Hunter , 1982). Zubere tal . (1980)foun dtha ta nimportan tpar to fth evariatio ni n stalk strengthca nb eattribute dt opit hcharacteristics .Th enumbe ro f vascularbundle s (witha hig hproportio no f lignin)i nth epit h isno to f

226 greatimportanc e forstal k strength (Chang &Loesch , 1972).Thu si twoul d seem tob epossibl e toselec tfo rimprove dstal k strengthb yimprovin gpit hstrength , withoutgreatl y increasing ligninconten ti nth epith .Sinc e thepit h ismuc h moredigestibl e thanth erin d (Struik, 1982a)an da sth epit h strengthca nb e improvedwithou tgreatl y reducingpit h digestibility,improvin go fpit h strength (measureda sdescribe db y Zubere tal. , 1980)mus tb eadvocated .Improve d pith strengthmigh tals oreduc epit hdegradatio nb y Fusarium. A stocky stemwit h alo wrind :pit h ratioan da stron gpit hbenefit s intake,yield ,an dlodgin gresistance ,an dminimize s theadvers eeffect so f thickstems .

Severaleffective ,empirica lmethod s forassessin g genotypic differences inroo tanchorag ehav ebee n developed.Thes e techniquesenabl e selectionfo r superiorroo ttype san dthi sreduce sth eris ko froo tlodgin gcause db yroo t weaknesso rroo tpests .Genotype sdiffe rver ysignificantl y insevera lroo t characteristics (Thompson,1972 ;Jeniso n et al., 1981;Penny , 1981;Arihar a & Crosbie,1982 ;Peter se tal. , 1982)an droo tlodgin gi sa heritabl e trait thatca nb eimprove d throughbreedin g (Thompson, 1972;Roger se tal. ,1976 ; Penny,1981 ;Arihar a &Crosbie , 1982).Susceptibilit y toroo tlodgin g correlatespositivel y withearl yvigou r (Gunn,1977 , 1978),bu tselectio n for rootcharacteristic s ispossibl ewithou treducin ggrain-yiel dpotentia l (Peterse tal. , 1982). Insom ecase sther emigh tb ea correlatio nbetwee n root:shoo trati oan dkernel-growt h rate (A.Gallais ,persona lcommunication) . Selecting forsuperio rroo tsystem smigh tresul ti na reductio n inth ewhole - plantyield .Ye ti tseem swort hpayin gattentio nt oroot-lodgin g tolerance inmaiz ehybrid sbre d forforag eproductio n inNorth-Wes tEurope . Genotypesals odiffe ri nroo t activity understres scondition s (Derieux, 1983).

Rootlodgin gi smos tlikel yt ooccu r fromtw oweek sbefor e silkingt o fourweek sthereafte r (Gunn,1978 ). Win d andheav yrain s fosterbot hroo t andstal k lodging.Lea fcharacteristics ,suc ha slea forientation ,lea f rigidity,lea fsiz ean dlea fshap eaffec tth emagnitud e ofth e forcesexerte d onth eplant ,especiall y aroundsilking . Thisi sanothe rreaso nwh yth eerec tlea fhabi ti sundesirabl e inTh e Netherlands (seeals osectio n1) . The (physical)momen to fth eforce sexerte do nth eplan tals ogreatl y dependso nth eea rweigh tan d theea rheight .Effectiv e selection forlowe r earheigh ti spossibl e (Giesbrecht,1961 ;Ver a &Crane ,1970 ;Acost a &Crane ,

227 1972;Thompson , 1972;Josephso n &Kincer , 1977;Harvill e etal. r 1978; Paterniani,1981 )bu t fora balance ddistributio no fassimilate sbetwee n above-ground plantpart san droots ,a shor tdistanc ebetwee n themonopolizin g earan d thewea k rootsink si sno tdesirabl e (cf.Strui k &Deinum , 1982). Vera &Cran e (1970)an dJosephso n &Kince r (1977)hav eactuall y reported lowerea ryield sresultin g from loweringth eplacemen to fth eear . Ofth eothe rplan tcharacteristics ,vigou r andcell-wal l digestibility have alreadybee n discussed.Finally ,lodgin gmigh tb ereduce db y growing earlierhybrid so ralterin g culturalpractice .Th econsequence so fthes e measureso nyield ,however ,ar es ofar-reachin g thatthei rapplicatio nt o minimizeintermitten t andunpredictabl y occurring lodgingi sno tjustifiable .

Conclusions Theabove-describe dpictur eo fa nideotyp eo fforag emaiz efo r cultivation inth emargina l regionso fNorth-Wes tEurop e isno tfinal .Th e qualificationso fa forage-maiz e ideotype ares odivers e andofte neve n contradictory thati ti sno tpossibl e tocombin e themal li non egenotype .Th e search fora forage-maize ideotype istherefor ea searc h forth ebes tcompromise . Inth eopinio no fth eauthor ,thi scompromis e resultsi na genotyp e thathas : - goodcol dtoleranc ean dearl yvigou r - early floweringcombine dwit ha fas trat eo flea fdevelopment ,approximatel y 15leave spe rplant ,larg ean dprostrat e leaves,an da maximu m longevityo f leaves -maximu mrat eo fphotosynthesi s - asmal ltasse l - tolerance tohig hplan tdensitie s - alarg eea rwit ha slo w rateo fgrai n fillingan dplace di nth eaxi lo fth e sixthlea ffro mabov e - astock y stemwit h ahig h leaf:stal k ratio,a hig hpith :rin drati oan d aver y strongpit h - lowsusceptibilit y topest san ddisease s - ahig hpotentia l extentan da fas trat eo fcell-wal ldigestio n - amoderat e formationo fbrac eroots .

Ifa hybri dwit hth eabov echaracteristic s isproduced ,th eresultin g ideotypewil lhave : - anabilit y togiv ehig hyield s - agoo dtoleranc e tostres s

228 - anexcellen tresistanc e tolodgin gan ddisease s andwil lbe : - verysuitabl e forensilin g - verydigestible ,wil lallo wa hig hd mintak ean dwil lhav ea nexcellen t feedefficiency .

Noneo fthes equalities ,however ,wil lb emaximized .

229 REFERENCES

Aar,P.J . vander ,H .Boer ,B .Deinu m& G .Hof ,1981 .Bul kvolume :a paramete r formeasurin g foragequalit y and itsinfluenc e onvoluntar y intake.In : J.A.Smit h& V.W .Hay s (eds.), Proc.XlVt hInt .Grassl dCongr. , Lexington,Ky ,pp .502-505 . Acosta,A.E .& P.L .Crane ,1972 .Furthe rselectio n forlowe rea rheigh ti n maize.Cro pSei . 12:165-167 . Aitken,Y. , 1980.Th eearl ymaturin g character inmaiz e (2eamay sL. )i n relation totemperatur e andphotoperiod .Z .Acker -u .PflBa u149 :89-106 . Aldrich,S.R. , W.O.Scot t& E.R .Leng ,1975 .Moder n cornproductio n (2nd edition),A & L Publications ,Champaign ,Illinois ,U.S.A . Allison,J.C.S .& T.B .Daynard ,1979 .Effec to fa chang ei ntim eo fflowering , inducedb y alteringphotoperio d ortemperatur eo nattribute srelate dt o yield inmaize .Cro pSei . 19:1-4 . Andrew,R.H. ,1954 .Breedin g forstalk-ro t resistance inmaize .Euphytic a3 : 43-48. Andrew,S.M. ,J.H .Clar k& C.L .Davis ,1979 .Feedin gvalu eo fopaque- 2cor n grainan dcor nsilag e forlactatin g cows.J . DairySei .62 :1619-1625 . Arihara,J .& T.M . Crosbie,1982 .Relationship s amongseedlin g andmatur e root systemtrait so fmaize .Cro pSei .22 :1197-1202 . Ariyanayagam,R.P. ,C.L .Moor e& V.R .Carangal , 1974.Selectio n forlea fangl e inmaiz e and itseffect so ngrai nyiel d andothe r characters.Cro pSei . 14:551-556 . Baker,D.E. ,A.E .Jarrell ,L.E .Marshal l &W.I. Thomas,1970 .Phosphoru s uptake fromsoil sb y cornhybrid s selected forhig h and lowphosphoru s accumulation.Agron .J .62 :103-106 . Barbosa,H.M . &D.V . Glover,1978 .Gene san d gene interactions affecting protein and lysine content inth eendosper m ofmaize .Braz .J . Genetics 1:29-39 . Barloy,J. , 1983.Phas egerminatio n- levé ee timplantation .Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Barnes,R.F. ,L.D .Muller ,L.F .Bauma n& V.F .Colenbrander ,1971 .I nvitr o drymatte rdisappearanc e ofbrow nmidri bmutant so fmaize .J .Anim . Sei. 33:881-884 . Baron,V.S .& T.B .Daynard , 1980.Compariso no fEuropea n andCanadia ncor n hybrids forfactor saffectin g fielddryin g andharvestibility .Agron . Abstr., 1980Ann .Meeting ,Amer .Soc .Agron. ,Detroit ,Michigan ,p .96 . Barrière,Y. ,1979 .Sélectio nd umaï spou r larésistanc e àl apourritur ed e tiges.Etud ed egénotype sprécoces .Ann .Amélior .Plante s29 :289-304 . Barrière,Y .& J.-P . Gay,1983 .Approch ephysiologiqu e del asénescenc ed u maïs.Colloqu e"Physiologi ed umaïs" ,Roya n 15-17Mar s1983 . Barrière,Y. ,A .Panouill é& R .Cassini ,1981 .Relation s source-puitse t sélection dumaï spou r larésistanc e àl apourritur e destiges . Agronomie 1(8) :707-711 . Bauman,L.F. , 1960.Relativ eyield so f first (apical)an d second earso f semi-prolific southern cornhybrids .Agron .J . 52:220-222 . Beek,D .va nder ,1977 .Builenbran d inmais .Bedrijfsontwikkelin g8 :253-256 . Beerepoot,L.J. , 1981.D e genetische variatie inverteerbaarhei d bij snij- mais.LH ,Vakgroe pLandbouwplantenteel t enGraslandkunde ,Doctoraal verslag,pp .1-43 . Bergen,W.G. ,E.H .Cas h& H.E .Henderson ,1974 .Change s innitrogenou s compoundso fth ewhol ecor nplan tdurin gensilin g andsubsequen teffect s ondr ymatte r intakeb y sheep.J .Anim .Sei . 39:629-637 .

230 Bertin,Ch ., A .Panouill é& S .Rautou ,1976 .Obtentio nd evariété sd emaï s "prolifiquese népis "productive se ngrai ne t àlarg e adaptation écologique.Ann .Amélior .Plante s26 :387-418 . Blacklow,W.M. ,1972a .Mathematica l descriptiono f theinfluenc eo ftemperatur e andsee dqualit y on imbibitionb y seedso fcor n (Zea mays L.). CropSei . 12:643-646 . Blacklow,W.M. , 1972b.Influenc eo f temperatureo ngerminatio n andelongatio n ofth e radicle and shooto fcor n (Zea mays L.). CropSei . 12:647-650 . Blanco,M .& J.L .Blanco ,1960 .Breedin g forhig hsuga ri nth estal ka t maturity andrelate d subjects.Proc .Eucarpi a 1stmeetin go fth eMaiz e & SorghumSection ,Rome ,23-2 6February ,pp .25-28 . Bloc,D. ,J.P .Ga y& J.P .Gouet ,1983a .Evolutio n del ateneu re nea ue td u poidsd e 1000grain spendan t lamaturatio n dumaïs .Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Bloc,D. , J.P. Gay& J.P . Gouet,1983b .Duré ede sphase svégétative se t reproductives chezl emaïs : influenced el atempérature .Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Block,E. ,L.D .Mulle r& L.H .Kilmer , 1982.Brow nmidrib- 3versu snorma lcor n plants (Zea mays L.)harveste d aswhol eplan t orstove ran d frozenfres h orpreserve d assilag e forsheep .Can .J .Anim .Sei .62 :487-498 . Blondon,F. , G.Clabaul t& M .Rainguez ,1981 .Déplacemen t de l'optimum thermiqued el'activit é photosynthétique,sou s l'action d'un traitement à temperature fraîche (10°C)che zl emaïs :différenciatio n dedeu x variétés.CR . Acad.Sei. , série III,t .292 :149-152 . Blondon,F. ,G .Clabaul t& M .Rainguez ,1983 .Adaptatio n aufroi de tactivit é photosynthétique chezl emaïs .Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Blondon,F. , &A .Gallais ,1976 .Influenc ed el atempérature ,d el avaleu rd e 1'éclairemente td el aphotopériod e sur ledéveloppemen t florald e quatregénotype sd emaïs .Ann .Amélior .Plante s26 :195-213 . Bonhomme,R. , 1983.Mis e enplac e desappareil s foliairee tracinair e chezl e maïs.Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Brooking,I.R. , 1979.Temperatur eeffect so ninflorescenc e development and grain fillingo fcereals .Proc .Agron .Soc .N .Zealan d 9:65-69 . Brouwer,R. ,A .Kleinendors t &J.Th .Locher ,1973 .Growt h responseso fmaiz e plantst otemperature . In:Plan t response toclimati c factors.Proc . UppsalaSymp. ,1970 .UNESCO ,Paris ,pp .169-174 . Bruetsch,T.F . &G.O .Estes ,1976 .Genotyp evariatio n innutrien t uptake efficiency incorn .Agron .J .68 :521-523 . Buren,L.L. ,J.J . Mock& I.C .Anderson ,1974 .Morphologica l andphysiologica l traitsi nmaiz e associatedwit h tolerance tohig hplan t density.Cro p Sei. 14:426-429 . Burgstaller,G. ,B .Gedek ,W .Gedek ,D .Günzler ,R .Hoffmann ,W .Hollwich , W.Kle e& P .Plank , 1977.Maisbeulenbran d (ustilago zeae) -Einfluss aufFutterwer tde r Silageun dTiergesundheit .Z .Da swirtschaftseigen e Futter23 :60-76 . Campling,R.C. ,1977 .Th e feedingvalu eo fmaize :a review .Ann .appl .Biol . 87:284-290 . Carter,M.W .& C.G .Poneleit ,1973 .Blac k layermaturit y and fillingperio d variation amonginbre d lineso fcor n (Zea mays L.). CropSei . 13:436 - 439. Chang,H.S .& P.J . Loesch,jr. ,1972 .Geneti c variationo f fouranatomica l traitsan d theirassociatio nwit h stalkqualit y traits inmaiz e (Zea mays L.). CropSei .12 :271-274 . Chang,H.S. ,P.J . Loesch,jr .& M.S .Zuber ,1976 .Effect so frecurren t selection forcrushin g strengtho nmorphologica l and anatomicalstal k traits incorn .Cro pSei . 16:621-625 .

231 Choe,B.-H. ,M.S .Zuber ,G.F .Kraus e &E.S. Hildebrand, 1976.Inheritanc e ofhig h lysine inmaize .Cro pSei . 16:34-38 . Colenbrander,V.F. ,L.F .Bauma n& V.L .Lechtenberg ,1973 .Effec t ofbrow n midribmutan t geneso nth enutritiona l quality of corn.Proc .28t h ann.Cor n& Sorghu mRes .Conf. ,Chicago ,1973 .Amer .See dTrad eAss . Publ. 28:92-97 . Colenbrander,V.F. ,V.L .Lechtenber g& L.F .Bauman ,1975 .Feedin gvalu eo f lowligni ncor nsilage .J .Anim .Sei . 41:332-33 3 (Abstr.). Coligado,M.C .& D.M . Brown,1975a .Respons eo fcor n (Zea mays L.) inth e pre-tasselinitiatio nperio d totemperatur e andphotoperiod .Agric . Meteorol. 14:357-367 . Coligado,M.C .& D.M . Brown,1975b .A bio-photo-therma lmode l topredic t tassel-initiation timei ncor n (Zea mays L.). Agric.Meteorol .15 : 11-31. Collins,M ., A.M .Ferreira ,D.A . Rohweder& N.A .Jorgensen ,1980 .Laborator y analyses forpredictin g digestibility and intakeo fcor nsilage .Agron . J. 72:889-892 . Collins,W.K. ,W.A .Rüsse l& S.A . Eberhart,1965 .Performanc e oftwo-ea r typeo fCor nBel tmaize .Cro pSei . 15:113-116 . Cook,R.J. , 1977.Th e importanceo f stalk rot andsmu ti nBritis hmaize .Ann . appl.Biol .87 :266-270 . Cook,R.J. , 1978a.Disease s andpest so fmaize .In :E.S .Bunting ,B.F .Pain , R.H.Phipps ,J.M . Wilkinson &R.E .Gun n (eds.),Forag emaize ,Agric . Res.Council ,London ,pp .117-132 . Cook,R.J. , 1978b.Th eincidenc eo f stalk rot (Fusarium spp.)o nmaiz e hybrids andit seffect so nyiel d ofmaiz ei nBritain .Ann .appl .Biol . 88: 23-30. Cortez-Mendoza,H .& A.R .Hallauer ,1979 .Divergen tmas sselectio n forea r length inmaize .Cro pSei . 19:175-178 . Cottyn,B.G. ,Ch.V .Boucqué ,J.V . Aerts& F.X .Buysse ,1978 .Verteerbaarhei d envoederwaard e vandroo go fvochti gmalsgraa nonde r verschillende structuurvormen.Landbouwtijdschrif t 31:281-289 . Crosbie,T.M . &J.J . Mock,1980 .Effect so frecurren t selection forgrai n yieldo nplan t andea r traitso f fivemaiz epopulations .Euphytie a 29: 57-64. Crosbie,T.M. , J.J. Mock& R.B .Pearce ,1977 .Variabilit y andselectio n advance forphotosynthesi s inIow aStif fStal kSyntheti cmaiz e population.Cro pSei . 17:511-514 . Crosbie,T.M. , J.J.Moc k& R.B .Pearce ,1978a .Inheritanc eo fphotosynthesi s ina dialle l amongeigh tmaiz e inbred lines from IowaStif fStal k Synthetic.Euphytie a27 :657-664 . Crosbie,T.M. , R.B.Pearc e& J.J . Mock, 1978b.Relationship s amongC O-exchang e rate andplan t traits in IowaStif fStal kSyntheti cmaiz epopulation . CropSei . 18:87-90 . Crosbie,T.M. , R.B.Pearc e &J.J . Mock,1981a .Selectio n forhig hC0 2-exchange rateamon g inbred lineso fmaize .Cro pSei .21 :629-631 . Crosbie,T.M. , R.B.Pearc e &J.J . Mock, 1981b.Recurren t phenotypic selection forhig h and lowphotosynthesi s intw omaiz epopulations .Cro pSei .21 : 736-740. Cross,H.Z. ,1975 .Dialle l analysiso fduratio n andrat eo fgrai n filling ofseve n inbred lineso fcorn .Cro pSei .15 :532-535 . Daccord,R . &R .Vogel ,1982 .Feedin g valueo fLG-1 1maiz e ando fit sbrow n midribmutant .In :H.J .Oslag e& R .Daccor d (eds.),Proc .Semina ro n COST-PROJECT 82"Maiz e asbasi c feed forbee fproduction" ,Grangeneuve , Switzerland,pp .17-29 . Daynard,T.B. , 1978.Practice s affecting quality andpreservatio n ofwhole - plantcor nsilage .Can .J .Plan tSei .58 :651-659 .

232 Daynard,T.B. , 1983.Possibilité s d'amélioration del aproductivit é desmaï s précoces.Colloqu e "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Daynard,T.B. ,V .Baron ,B .Andrew s& P .Verdier ,1980 .Evaluatio n ofshort - seasonCanadia n andEuropea n cornhybrid sgrow ni nOntario ,Manitob a andFrance .Agron .Abstr. ,198 0Ann .Meeting ,Amer .Soc .Agron. , Detroit,Michigan ,p .98 . Daynard,T.B. ,V.S .Baro n &M .Tollenaar ,1979 .Point so fcurren t interest instudie so f thephysiolog y of themaiz eplant .Pape rpresente da t Euromais Congress,Cambridge ,1979 . Daynard,T.B .& R.B .Hunter ,1975 .Relationship s amongwhole-plan tmoisture , grainmoisture ,dr ymatte ryiel d andqualit y ofwhole-plan t corn silage.Can .J .Plan t Sei. 55:77-84 . Deinum,B. ,1976 .Effec t ofage ,lea fnumbe r and temperature oncel lwal l anddigestibilit y ofmaize . In:Carbohydrat e research inplant san d animals.Misc .Paper snr .12 ,Agric .Univ .Wageningen ,pp .29-41 . Deinum,B .& J.J . Bakker,1981 .Geneti c differences indigestibilit y of foragemaiz ehybrids .Neth .J . agric.Sei .29 :93-98 . Deinum,B .& J .Knoppers ,1979 .Th egrowt ho fmaiz e inth ecoo l temperate climateo f theNetherlands :Effec to fgrai n fillingo nproductio no f drymatte r ando nchemica l composition andnutritiv e value.Neth .J . agric.Sei . 27:116-130 . Deinum,B. ,A .Ste g& G .Hof ,1983 .Measuremen t andpredictio no fdigesti bilityo f foragemaiz e inth eNetherlands .Anim . FeedSei .Technol . 8 (inpress) . Deinum,B .& P.C . Struik, 1982.Productivit y andnutritiv e valueo f forage maize. In:H.J . Oslage& R .Daccor d (eds.),Proc .Semina ro nCOST - PROJECT8 2"Maiz e asbasi c feed forbee fproduction" ,Grangeneuve , Switzerland,pp .8-16 . Demarquilly,C , 1969.Valeu r alimentaire dumaï s fourrage.Ann .Zootechni e 18: 17-32. Demarquilly,C. ,Ph .Haurez ,M .Journet ,C .Lelon g& C .Malterre ,1971 .L e maïsplant eentière :composition ,valeu ralimentaire ,utilisatio npa r lesbovins .Bulleti nTechniqu e d'Information 264-265:1-18 . Derieux,M. , 1983.Sélectio n etadaptation .Colloqu e "Physiologie dumaïs" , Royan 15-17Mar s1983 . Derieux,M. ,R .Bonhomme ,F .-Ruge t& J.-B . Duburcq, 1983.Influenc ed u génotypee td umilie u sur lenombr ed'ovule s présents àl afloraison . Colloque"Physiologi e dumaïs" ,Roya n15-1 7Mar s1983 . Derieux,M .& Y .Montalant ,1978 .Résultat s d'un cycled esélectio ngénéalo giquepou rl ateneu re nprotéine s dugrai nd emaïs .Ann .Amélior . Plantes28 :463-474 . Donald,CM. , 1968.Th ebreedin g ofcro p ideotypes.Euphytic a 17:385-403 . Donefer,E. ,E.W .Crampto n& L.E .Lloyd , 1960.Predictio no f thenutritiv e valueinde xo fa forag e fromi nvitr orume nfermentatio n data.J .Anim . Sei. 19:545-552 . Dudley,J.W . &R.J .Lambert ,1969 .Geneti cvariabilit y after6 5generation s ofselectio n inIllinoi shig hoil ,lo woil ,hig hprotei n andlo w protein straino f Zea mays L.Cro pSei . 9:179-181 . Dudley,J.W. , R.J.Lamber t & I.A. del aRoche ,1977 .Geneti c analysiso f crossesamon gcor nstrain sdivergentl y selected forpercen toi lan d protein.Cro pSei . 17:111-116 . Duncan,W.G. ,1971 .Lea f angles,lea fare aan dcanop yphotosynthesis .Cro p Sei. 11:482-485 . Duncan,W.G. ,1975 .Maize .In :L.T .Evan s (ed.), Cropphysiology .Som ecas e studies.Cambridg e UniversityPress ,London ,pp .23-50 .

233 Duncan,W.G .& J.D .Hesketh ,1968 .Ne tphotosynthesi s rates,relativ e growth rates,an d leafnumber so f2 2race so fmaiz egrow na teigh ttemperatures . CropSei . 8:670-674 . Duncan,W.G. ,W.A .William s& R.S .Loomis ,1967 .Tassel san d theproductivit y ofmaize .Cro pSei . 7:37-39 . Eagles,H.A . &I.R .Brooking , 1981.Population so fmaiz ewit hmor erapi dan d reliable seedlingemergenc e thanCornbel tdent sa tlo wtemperatures . Euphytica30 :755-763 . Eagles,H.A . &A.K .Hardacre , 1979.Geneti cvariatio n inmaiz e (Zeamay sL. ) forgerminatio n andemergenc e at10°C .Euphytic a28 :287-295 . Early,E.B. ,W.O .Mcllrath ,R.D .Sei f &R.H .Hageman ,1967 .Effect so fshad e applied atdifferen t stageso fplan t development oncor n (Zeamay sL. ) production.Cro pSei .7 :151-156 . Early,E.B. ,R.J .Miller ,G.L .Reichert ,R.H .Hagema n& R.D .Seif ,1966 . Effectso f shadeo nmaiz eproductio n underfiel dconditions .Cro pSei . 6: 1-7. Ebskamp,A.G. ,1981 .He tcultuurwaardeonderzoe kva nsnijmaisrasse ni nNeder land (II).Criteri abi jd ebeoordelin g vansnijmaisrassen .Bedrijfs ontwikkeling 12:269-275 . El-Shalzy,K. ,B.A .Dehorit y &R.R . Johnson,1961 .Effec to fstarc ho nth e digestiono fcellulos e invitr oan d inviv ob y rumenmicroorganisms . J.Anim .Sei .20 :268-273 . Fairey,N.A. ,1980 .Hybri dmaturit y and therelativ eimportanc e ofgrai nan d stover forth eassessmen t of theforag epotentia lo fmaiz e genotypes growni nmargina l andnon-margina l environments.Can .J .Plan t Sei.60 : 539-545. Fairey,N.A. , 1982.Influenc eo fpopulatio ndensit y andhybri dmaturit yo n productivity andqualit y offorag emaize .Can .J .Plan tSei .62 :427 - 434. Fakorede,M.A.B .& J.J . Mock,1977 .Lea forientatio n andefficien t utilization ofsola renerg yb ymaiz e (Zea mays L.). In:Agrometeorolog y ofth e maize (corn)plant .Worl dMeteorologica l Organization,no .481 ,Geneva , pp.207-230 . Fakorede,M.A.B .& D.K . Ojo,1981 .Variabilit y forseedlin gvigou r inmaize . ExplAgric .17 :195-201 . Fisher,L.J . &N.A .Fairey ,1979 .Factor s influencing theutilizatio nb y ruminantso fcor nsilag e inmargina l growingareas .Can .J .Anim .Sei . 59:427-439 . Fisher,L.J. , V.S.Logan ,L.S .Donova n& R.B .Carson ,1968 .Factor s influencing drymatte r intake andutilizatio no f cornsilag eb y lactating cows.Can . J.Anim .Sei .48 :207-214 . Foley,D.C .& C.C .Wernham ,1957 .Th eeffec to ffertilizer so nstal k roto f corn inPennsylvania .Phytopatholog y 47:11-12 . Frölich,W.G .& W.G .Pollmer ,1978 .Di eBlatthaltun gbe iMai s (Zea mays L.) alsertragsbeeinflussende r Faktor.Kali-Brief e (Büntehof)14 :345-354 . Frölich,W.G. ,W.G .Pollme r& D .Klein ,1977 .Performanc e ofisogeni c liguleless-2maiz ehybrid sa sinfluence db y irrigation,ro wwidth , plant density andnitroge n fertilizer.Z .Acker -u .PflBa u145 : 207-223. Gallais,A. ,L .Huguet ,H .Berthet ,G .Bertin ,B .Broqua ,A .Mourgue t & R.Traineau ,1980 .Preliminar y evaluationo fbrow nmidri bmaiz ehybrid s forthei r feedingan d agronomicvalu e inFrance .In :W.G .Pollme r& R.H.Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai n and silageuse .Martinu sNijhoff ,Th eHague ,pp .319-339 . Gallais,A. ,M .Pollacse k &L .Huguet ,1976 .Possibilité s desélectio nd u maïse ntan tqu eplant e fourragère.Ann .Amélior .Plante s26 :591-605 .

234 Gallais,A .& P . Vincourt,1983 .Possibilité s d'amélioration durendemen te n matière sèched umaï s ensilage.Colloqu e "Physiologie dumaïs" , Royan 15-17Mar s1983 . Gallasz,E. ,1982 .Silierversuc h von6 verschiedene nhigh-sugar-maiz eHybride n imVergleic h zuzwe ibekannte nMaissorte n (ohneun dmi t ausgebildeten Kolben).Versuchsberich t Eidgenössische Forschungsanstalt fürviehwirt schaftlicheProduktion ,Grangeneuve ,Switzerland ,pp .1-5 . Giesbrecht,J. , 1961.Th einheritanc eo fea rheigh ti n Zea mays. Can.J . Genet.Cytol . 3:26-33 . GmeligMeyling ,H.D. , 1973.Effec to fligh t intensity,temperatur e andday - lengtho n therat eo flea fappearanc e ofmaize .Neth .J . agric.Sei . 21:68-76 . Gorsline,G.W. , J.L.Raglan d &W.I .Thomas ,1961 .Evidenc e forinheritanc e ofdifferentia l accumulation ofcalcium ,magnesiu m andpotassiu mb y maize.Cro pSei . 1:155-156 . Gorsline,G.W. ,W.I .Thoma s& D.E .Baker ,1964 .Inheritanc eo fP ,K ,Mg ,Cu , B,Zn ,Mn ,A lan dF econcentration sb y corn (Zea mays L.) leavesan d grain.Cro pSei .4 :207-210 . Grogan,CO. , 1956.Detasselin g responsesi ncorn .Agron .J . 48:247-249 . Gross,F. , 1977.Einflus s vonMaisbeulenbran d (Ustilago zeae) aufdi e Silagegärung.Z .Da swirtschaftseigen e Futter23 :77-82 . Gross,F. , 1979.Nährstoffgehal t undVerdaulichkei t vonSilomais .1 .Mitteilung : Bewertung vonSilomais .Z .Da swirtschaftseigen e Futter25 :215-225 . Gross,F .& W .Peschke ,1980a .Nährstoffgehal t undVerdaulichkei t vonSilomais . 2.Mitteilung :Nährstoffgehal t undVerdaulichkei t vonMaisstro h(Mais pflanzeohn eKolben) .Z .Da swirtschaftseigen e Futter26 :104-117 . Gross,F .& W .Peschke ,1980b .Nährstoffgehal tun dVerdaulichkei t vonSilomais . 4.Mitteilung :Einflus sde rKolbenbildun g aufNährstoffgehal t und Verdaulichkeit vonSilomais .Z .Da swirtschaftseigen e Futter26 :193 - 206. Gunn,R.E. ,1975 .Breedin gmaiz e forforag eproduction .Compt e renduintégra l de8m eCongrè sinternationa l del asectio nMaïs-Sorgho ,Eucarpia , Paris-Versailles,pp .563-575 . Gunn,RE. , 1977.Breedin g foragemaiz evarietie s forBritain .Ann .appl . Biol. 87:254-258 . Gunn,R.E. ,1978 .Forag ebreedin g andsee dproduction .In :E.S .Bunting , B.F.Pain ,R.H .Phipps ,J.M .Wilkinso n& R.E .Gun n (eds.),Forag e maize.Agric .Res .Council ,London ,pp .133-151 . Hall,A.J .,H.D .Ginzo ,J.H . Lemcoff& A .Soriano ,1980 .Influenc eo fdrough t duringpollen-sheddin g on flowering,growt h andyiel do fmaize .Z . Acker-u .PflBa u149 :287-298 . Hall,A.J. ,J.H . Lemcoff& N .Trapani ,1981 .Wate rstres sbefor e anddurin g flowering inmaiz ean d itseffect so nyield ,it scomponents ,an dthei r determinants.Maydic a26 :19-38 . Hanway,J.J. , 1963.Growt hstage so fcor n (Zea mays L.). Agron.J . 55:487 - 492. Hanway,J.J. , 1966.Ho w acor nplan t develops.Specia l reportno .48 ,Iow a StateUniv. ,Ames , Iowa,U.S.A. , pp.1-18 . Harris,R.E. ,R.H .Mol l& C.W . Stuber,1976 .Contro lan dinheritanc eo f prolificacy inmaize .Cro pSei .16:843-850 . Harville,B.G. ,L.M . Josephson& H.C .Kincer ,1978 .Dialle l analysiso fea r height andassociate d characters incorn .Cro pSei . 18:273-275 . Heichel,G.H .& R.B .Musgrave ,1969 .Varieta ldifference s inne tphoto synthesiso f Zea mays L.Cro pSei .9 :483-486 . Hepting,L .& J . Zscheischler,1975 .Th eeffec to fbetween-ro w spacingan d plant densityo ngrai nyiel d and dry-matter content ingrai nmaize . Z.Acker -u .PflBa u141 :178-186 .

235 Hicks,D.B .& R.E .Strucker ,1972 .Plan t density effecto ngrai nyiel do f cornhybrid sdivers e inlea forientation .Agron .J .64 :484-486 . Hoff,D.J . &H.J . Mederski,1960 .Effec to fequidistan t cornplan t spacing onyield .Agron .J .52 :295-297 . Honig,H .& K .Rohr ,1982a .Th e influenceo fchoppin go n lossesb yundigeste d kernelsan dkerne l fragmentso fmaize ,whe n feedingruminants .In :H.J . Oslage& R .Daccor d (eds.),Proc .Semina ro nCOST-PROJEC T8 2"Maiz ea s basic feed forbee fproduction" ,Grangeneuve ,Switzerland ,pp .32-41 . Honig,H .& K .Rohr ,1982b .Zu rBedeutun g desZerkleinerungsgrade s von Silomais. 1.Mitteilung :Einflus sde sZerkleinerungsgrade s aufdi e Verlustedurc hunverdau t ausgeschiedeneKörner .Z .Da swirtschafts eigeneFutte r28 :183-192 . Hunter,R.B. ,1978 .Selectio nan devaluatio nprocedure s forwhole-plan t corn silage.Can .J .Plan t Sei. 58:661-678 . Hunter,R.B. ,1980 .Increase d leaf area (source)an dyiel do fmaiz ei n short-season areas.Cro pSei . 20:571-574 . Hunter,R.B. ,T.B .Daynard ,D.J .Hume ,J.W . Tanner,J.D .Curti s& L.W . Kannenberg, 1969.Effec t oftasse l removalo ngrai nyiel do fcor n (Zea maysL.) .Cro pSei . 9:405-406 . Hunter,R.B. ,M .Tollenaa r& CM . Breuer,1977 .Effect so fphotoperio d and temperature onvegetativ e andreproductiv e growtho fa maiz e (Zeamays ) hybrid.Can .J .Plan tSei.57 :1127-1133 . Jenison,J.R. , D.B.Shan k& L.H .Penny , 1981.Roo t characteristics of4 4 maize inbredsevaluate d infou renvironments .Cro p Sei. 21:233-237 . Johnson,R.R . &D.L .Mulvaney ,1980 .Developmen t of amode l forus ei n maize replant decisions.Agron .J . 72:459-464 . Johnson,D.R . &J.W .Tanner ,1972 .Calculatio n ofth erat e andduratio no f grain filling incor n (Zea mays L.). CropSei . 12:485-486 . Josephson,L.M . &H.C .Kincer ,1977 .Selectio n forlowe rea rplacemen t in twosyntheti cpopulation s ofmaize .Cro pSei . 17:499-502 . Keith,E.A. ,V.F .Colenbrander ,T.V . Perry &L.F .Bauman ,1979 .Nutritiona l valueo fbrow nmidri b cornsilag e forlactatin gcows .J .Dair ySei .62 : 788-792. Kilkenny,J.B. , 1978.Utilisatio n ofmaiz e silage forbee fproduction .In : E.S. Bunting,B.F .Pain ,R.H .Phipps ,J.M . Wilkinson& R.E .Gun n (eds.), Foragemaize .Agric .Res .Council ,London ,pp .239-261 . Klein,D. ,W.G .Frölich ,W.G .Pollme r& D .Eberhard , 1980.Performanc eo f high-lysinemaiz ehybrid sunde rwester nEuropea n conditions.In :W.G . Pollmer& R.H .Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai n and silageuse .Martinu sNijhoff ,Th eHague ,pp .75-90 . Knipmeyer,J.W. , R.H.Hageman ,E.B .Earl y& R.D .Seif ,1962 .Effec to fligh t intensity oncertai nmetabolite so f thecor nplan t (Zea mays L.).Cro p Sei. 2:1-5 . KovaSevié,V. ,1982 .Th eear-lea fpercentag e ofnitrogen ,phosphoru san d potassium inth ecor n (Zeamay sL. ) inbred linesan dthei rdialle l progeny.Proc .1s tint .Symp .o nGeneti c specificity ofminera l nutrition ofplants ,Belgrade ,Yugoslavia ,3 0VII I- 4 I X1982 ,pp .371-375 . Krall,J.M. , H.A.Eseschie ,R.J .Raney ,S .Clark ,G .TenEyck ,M .Lundquist , N.E. Humburg,L.S .Axthelm ,A.D .Dayto n& R.L .Vanderlip ,1977 .Influenc e ofwithin-ro wvariabilit y inplan t spacingo ncor ngrai nyield .Agron . J.69 :797-799 . Krüger,W. , 1970a.Wurzel -un dStammfäul ebe iMai s III.Di eWirkun gvo n Bodenbearbeitungsmassnahmen aufStammfäule .Phytopath .Z .68 :1-8 . Krüger,W. , 1970b.Wurzel -un dStammfäul ebe iMai s IV.Di eWirkun gvo n Dünger aufda sAuftrete n derWurzel -un dStammfäule .Phytopath .Z . 68:334-345 .

236 Krüger,W. , 1978.Einflus s vonDüngun gun dBestandesdicht e aufStengelfäule , Stengelbruch undErtra gde sMaises .Z .Acker -u .PflBa u147 :190-203 . Krüger,W . &L .Reiner ,1974 .Einflus s vonSaattermin ,Bestandesdicht eun d Sorten aufdi eStengelfäul e desMaises .Z .Acker -u .PflBa u 139:172 - 185. Krüger,W. ,L .Reine r& H .Hoffmann ,1975 .Zu mAuftrete n derStengelfäul e des Maises inAbhängigkei t vonReihenabstan d undAnfälligkei t derHybriden . Z.Acker -u .PflBa u141 :160-164 . Krüger,W .& C .Rogdaki-Papadaki , 1980.übe rdi eWirkun g vonTemperatur , Bodenart,Bodenverdichtun g undDüngun g aufdi eWurzelfäul e undda s Pilzspektrum desMaises .Z .PflKrankh. ,PflSchut z87 :298-316 . Lambert,R.J . &R.R . Johnson, 1978.Lea f angle,tasse lmorphology ,an dth e performance ofmaiz ehybrids .Cro pSei . 18:499-502 . Landi,P .& T.M . Crosbie,1982 .Respons eo fmaiz et ocol dstres sdurin g vegetative growth.Agron .J . 74:765-768 . Landry,J. , 1983.Accumulatio n desprotéine s dans legrai n demaïs .Colloqu e "Physiologied umaïs" ,Roya n15-1 7Mar s1983 . Leaver,J.D. , 1978.Utilisatio no fmaiz e silageb y dairyher dreplacement . In: E.S.Bunting ,B.F .Pain ,R.H .Phipps ,J.M . Wilkinson& R.E .Gun n (eds.), Foragemaize .Agric .Res .Council ,London ,pp .297-307 . Lechtenberg,V.L. ,L.D .Muller ,L.F .Bauman ,CL . Rhykerd& R.F .Barnes ,1972 . Laboratory and invitr oevaluatio no finbre d andF 2population so fbrow n midribmutant so f Zea mays L.Agron .J . 64:657-660 . Loesch,P.J. , jr.,CF . Stark &M.S .Zuber ,1976 .Effec t ofplan t densityo n thequalit y ofcob suse d forcor n cobpipes .Cro pSei . 16:706-709 . Maggiore,T. ,E .Gentinetta ,M .Motto ,M .Perenzin ,F .Salamin i &C .Lorenzoni , 1980. Variability forprotei n and fibreconten t inthre ediallel so f maize forsilag eproduction .In :W.G .Pollme r& R.H .Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai nan dsilag euse .Martinu s Nijhoff,Th eHague ,pp .135-153 . Malterre,C , 1976.Differen t wayso futilisin gth emaiz e crop forbee f production.In :J. C Tayler& J.M . Wilkinson (eds.), Improvingth e nutritional efficiency ofbee fproduction .Publ .EU R 5488e,Commissio n ofth eEur .Committees ,Brussels ,pp .104-164 . Mann,Ch.E. ,W.G .Pollme r& D .Klein ,1980 .Parent-offsprin gcorrelation s inmaiz ematerial sdivers e forprotei ncontent .In :W.G .Pollme r& R.H . Phipps (eds.), Improvement ofqualit y traitso fmaiz e forgrai nan d silageuse .Martinu sNijhoff ,Th eHague ,pp .155-170 . Marten,G.C , R.D.Goodrich ,R.M .Jordan ,A.R .Schmi d& J.C .Meiske ,1976 . Evaluationo f laboratorymethod s fordeterminin gqualit y ofcor nan d sorghum silages:III .Biologica l andchemica lmethod s forpredictin g animal intake.Agron .J .68 :289-291 . McAllan,A.B .8 1R.H .Phipps ,1977 .Th eeffec to fsampl e date andplan t density onth ecarbohydrat e contento f foragemaiz e and thechange s thatoccu ro nensiling .J . agric.Sei .Camb . 89:589-597 . Mensah,R.A .& B.G .Zwatz ,1975a .Studi eübe rdi eStengelbruchkrankhei t des Maises (Zea mays L.),Krankheitskomple xmi tbesondere r Berücksichtigung derMöglichkeite n einerkünstliche n Infektion.Pflanzenschutz-Bericht e XLIV:161-194 . Mensah,R.A . &B.G .Zwatz ,1975b .Studi eübe rdi eStengelbruchkrankhei t des Maises (Zea mays L.)mi tbesondere rBerücksichtigun g derErtragsbeein flussungsowi e derAnfälligkei t derSorten .Di eBodenkultu r 26:175 - 197. Mertens,D.R. , 1973.Applicatio n oftheoretica lmathematica lmodel s tocel l walldigestio n and forage intake inruminants .Ph.D .Thesi sCornel l Univ.,Ithaca ,NY .

237 Mertens,D.R .& L.O .Ely ,1979 .A dynami cmode lo ffibe rdigestio nan d passagei nth eruminan tfo revaluatin g foragequality .J .Anim .Sei . 49:1085-1095 . Mertens,D.R .8 tJ.R .Loften ,1980 .Th eeffect so fstarc ho nforag e fiber digestionkinetic si nvitro .J .Dair ySei .63 :1437-1446 . Mertz,E.T. ,L.S .Bate s8 iO.E .Nelson ,1965 .Growt ho frat sfe do nopaque- 2 maize.Scienc e148 :1741-1742 . Michaelson,M.E. ,1957 .Factor saffectin g developmento fstal kro to fcor n causedb y Diplodia zeae and Gibberella zeae.Phytopatholog y 47: 499- 503. Miedema,P. ,1979a .Veredelin go pkoudetoleranti ebi jwarmteminnend eveld - gewassen.Zaadbelange n33 :198-200 . Miedema,P. ,1979b .Potentia lus eo fCIMMY Tgen epoo lmateria l forimprovin g low-temperature adaptationi n Zea mays. Euphytica28 :661-664 . Miedema,P. ,1982 .Th eeffect so flo wtemperatur eo n Zea mays. Advancesi n Agronomy35 :93-128 . Miedema,P. ,J .Pos tS iP.J .Groot ,1982 .Th eeffect so flo wtemperatur eo n seedling growtho fmaiz egenotypes .PUDOC ,Wageningen . Mock,J.J .& A.A .Bakri ,1976 .Recurren t selectionfo rcol d tolerancei n maize.Cro pSei .16 :230-233 . Mock,J.J .S tL.L .Buren ,1972 .Classificatio no fmaiz e (Zea mays L.)inbred s forpopulatio n toleranceb ygenera lcombinin g ability.Iow aStat eJ . Sei.46 :395-404 . Mock,J.J .S tS.A .Eberhart ,1972 .Col d tolerancei nadapte dmaiz epopulations . CropSei .12 :466-469 . Mock,J.J .& M.J .McNeill ,1979 .Col d toleranceo fmaiz e inbred lines adaptedt ovariou slatitude si nNort hAmerica .Cro pSei .19 :239-242 . Mock,J.J .& R.B .Pearce ,1975 .A nideotyp eo fmaize .Euphytic a24 :613-623 . Mock,J.J .& S.H .Schuetz ,1974 .Inheritanc eo ftasse lbranc hnumbe ri n maize.Cro pSei .14 :885-888 . Mock,J.J .S iW.H .Skrdla ,1978 .Evaluatio no fmaiz eplan t introductionsfo r cold tolerance.Euphytic a27 :27-32 . Molot,P.-M. ,1969a .Recherche ssu rl arésistanc ed umaï sà l'Helminthosporiose etau xFusarioses .I .Rôl ed el acompositio n chimiqued el aplante . Annalesd ePhytopathologi e1 :55-74 . Molot,P.-M. ,1969b .Recherche s surl arésistanc ed umai sà l'Helminthosporiose etau xFusarioses .II .Facteur sd erésistance .Annale sd ePhytopathologi e 1:353-366 . Molot,P.-M. ,1969c .Recherche ssu rl arésistanc ed umaï sà l'Helminthosporiose etau xFusarioses .III .Mod ed'actio n descomposé sphénologiques .Annale s dePhytopathologi e 1:367-383 . Monteith,J.L. ,1965 .Ligh tdistributio nan dphotosynthesi si nfiel dcrops . Ann.Bot .29 :17-37 . Morizet,J. ,M .Pollacse kS tD .Togola ,1983 .Toléranc eà l asécheress ed e4 variétésd emaïs .Essa id emis ee nevidenc ede smécanisme simpliqués . Colloque "Physiologied umaïs" ,Roya n15-1 7Mar s1983 . Mortimore,CG . StR.E .Wall ,1965 .Stal kro to fcor ni nrelatio nt oplan t populationan dgrai nyield .Can .J .Plan tSei .45 :487-492 . Mortimore,CG . 8tG.M .Ward ,1964 .Roo tan dstal kro to fcor ni nsouthwester n Ontario.III .Suga r levelsa sa measur eo fplan tvigo ran dresistance . Can.J .Plan tSei .44 :451-457 . Moss,G.I .& L.A .Downey ,1971 .Influenc eo fdrough t stresso nfemal e gametophytedevelopmen ti ncor nan dsubsequen t grainyield .Cro pSei . 11:368-372 . Moss,D.N .S tH.T .Stinson ,1961 .Differentia l responseo fcor nhybrid st o shade.Cro pSei .1 :416-418 .

238 Motto,M. ,N .Difanzo ,M .Perenzin ,E .Gentinetta ,T .Maggiore ,F .Salamin i & C.Lorenzoni ,1980 .Geneti c controlo fprotei npercentag e ina dialle l involvinghigh-protei n inbreds.In :W.G .Pollme r& R.H .Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai n and silageuse , MartinusNijhoff ,Th eHague ,pp .117-134 . Muller,L.D. ,V.L .Lechtenberg ,L.F .Bauman ,R.F .Barne s& C.L .Rhykerd ,1972 . Inviv oevaluatio no fa brow nmidri bmutan to f Zea mays L.J .Anim . Sei. 35:883-889 . Naismith,R.W. ,M.W .Johnso n& W.I .Thomas ,1974 .Geneti c controlo f relative calcium,phosphoru s andmanganes eaccumulatio no nchromosom e 9i nmaize . Crop Sei. 14:845-849 . Ottaviano,E .& A .Camussi ,1981 .Phenotypi c andgeneti crelationship sbetwee n yieldcomponent s inmaize .Euphytic a 30:601-609 . Otto,H.J .& H.L .Everett ,1956 .Influenc eo fnitroge n andpotassiu mfertili zationo nth e incidenceo fstal k roto fcorn .Agron .J .48 :301-305 . Parks,W.L. ,1977 .Ro wspacin g affectscor nyield .Bette rCrop swit hPlan t Food61 :24-27 . Paterniani,E. ,1981 .Influenc eo f tasselsiz eo nea rplacemen t inmaiz e (Zea mays L.). Maydica26 :85-91 . Pendleton,J.W. , G.E.Smith ,S.R . Winter& T.J . Johnston,1968 .Fiel d investigations ofth erelationship s oflea fangl ei ncor n (Zea mays L.) tograi nyiel d and apparentphotosynthesis .Agron .J .60 :422-424 . Penny,L.H. , 1981.Vertical-pul l resistanceo fmaiz e inbreds andthei r testcrosses.Cro pSei .21 :237-240 . Pepper,G.E. ,R.B .Pearc e& J.J . Mock,1977 .Lea forientatio n andyiel do fmaize . CropSei .17 :883-886 . Peters,D.W. , D.B.Shan k &W.E .Nyquist ,1982 .Root-pullin g resistancean d itsrelationshi p tograi nyiel d inF hybridso fmaize .Cro pSei .22 : 1112-1114. Peters& Woolley ,1959 .New sReleas eU.S.D.A. ,Washington ,Feb .25 ,1959 , citedb yHof f& Medersk i (1960). Phipps,R.H. ,1978 .Utilisatio no fmaiz esilag e formil kproduction . In:E.S . Bunting,B.F .Pain ,R.H .Phipps ,J.M . Wilkinson& R.E .Gun n (eds.), Foragemaize .Agric .Res .Council ,London ,pp .263-295 . Phipps,R.H. , 1980.A revie wo fth ecarbohydrat e content and digestibility valueo fforag emaiz egrow ni nth ecoo lclimati c conditionso fth eU K andthei rrelevanc e toanima lproduction .In :W.G .Pollme r& R.H .Phipp s (eds.), Improvement ofqualit y traitso fmaiz e forgrai n andsilag euse . MartinusNijhoff ,Th eHague ,pp .291-317 . Phipps,R.H .& R.F .Weiler ,1979 .Th edevelopmen t ofplan t componentsan d theireffect so nth ecompositio no ffres han densile d foragemaize .1 . Theaccumulatio no fdr ymatter ,chemica lcompositio n andnutritiv e valueo ffres hmaize .J . agric.Sei .Camb .92 :471-483 . Phipps,R.H. ,R.F .Weile r& A .Cooper ,1982 .A compariso nbetwee nth e accumulationo fdr ymatter ,chemica l composition andnutritiv evalu e ofisogeni c sterilean d fertile foragemaize .Maydic a 27:27-40 . Phipps,R.H. ,R.F .Weile r& R.J .Fulford ,1979 .Th edevelopmen t ofplan t componentsan dthei reffect so nth ecompositio no ffres han densile d foragemaize .3 .Th eeffec to fgrai nconten t onmil kproduction .J .agric . Sei.Camb .92 :493-498 . Pollmer,W.G. ,D .Klein ,M .Bjarnaso n& D .Eberhard , 1974.Di eVerbesserun g derProteinqualitä t undProteinquantitä tbe iMai sal sZüchtungsaufgabe . Z.Acker -u .PflBa u140 :241-257 . Pommer,G. ,W .Sanche z& H .Häckel ,1981 .Auswirkunge n verschiedenerReihen weitenun dBestandesdichte n aufde nErtra gvo nMaissorte nmi twaag rechterun d aufrechterBlatthaltung .Z .Acker -u .PflBa u 150:113-128 .

239 Poneleit,CG . &D.B .Egli , 1979.Kerne l growth rate andduratio n Inmaiz ea s affectedb yplan t density andgenotype .Cro pSei . 19:385-388 . Poneleit,CG. , D.B.Egli ,P.L . Cornelius& D.A . Reicosky,1980 .Variatio n and associationso fkerne lgrowt h characteristics inmaiz epopulations . Crop Sei. 20:766-770 . Prine,G.M. , 1977.Plan t population,ro wwidt h andkerne l orientation effectso ngrai n yieldo fearl y andmedium-maturin g corn.Proc .Soi l Crop Sei.Soc .Flor .36 :157-160 . Purdy,J.L .& P.L .Crane ,1967 .Inheritanc e ofdryin grat ei n 'mature'cor n (Zeamay s L.). Crop Sei. 7:294-297 . Rijksinstituutvoo rhe tRassenonderzoe k vanCultuurgewasse n (RIVRO),1983 . 58eBeschrijvend e rassenlijst voorlandbouwgewasse n 1983,Leiter - Nypels,Maastricht . Robelin,M. , 1983.Fonctionnemen t hydrique etadaptatio n àl asécheresse . Colloque "Physiologie dumaïs" ,Roya n 15-17Mar s1983 . Rogers,R.R. ,W.A .Russel l& J.C .Owens ,1976 .Evaluatio n ofa vertical-pul l technique inpopulatio n improvement ofmaiz e forcor nrootwor m tolerance.Cro p Sei. 16:591-594 . Rohr,K. ,H .Honi g& R .Daenicke ,1982 .Effec to falterin gth ephysica lfor m ofmaiz e silageo nrumination ,rume n fermentation anddigestibilit y of nutrients.In :H.J .Oslag e &R .Daccor d (eds.),Proc .Semina ro n COST-PROJECT 82 'Maizea sbasi c feed forbee fproduction' ,Grangeneuve , Switzerland,pp .42-52 . Rohr,K. ,H .Honi g &R .Daenicke ,1983 .Zu rBedeutun g des Zerkleinerungsgrades vonSilomais .2 .Mitteilung :Einflus s desZerkleinerungsgrade s aufdi e Wiederkauaktivität,di ePansenfermentatio n unddi eVerdaulichkei t der Rohnährstoffe.Z .Da swirtschaftseigen e Futter 29 (inpress) . Rood,S.B . &D.J . Major, 1981a.Dialle l analysiso f thephotoperiodi c response ofmaize .Cro p Sei.21 :875-878 . Rood,S.B . &D.J . Major,1981b .Dialle l analysiso flea fnumber ,lea f development rate,an dplan theigh to fearl ymaturin gmaize .Cro pSei . 21:867-873 . Rook,J.A. ,L.D .Mulle r& D.B . Shank,1977 .Intak e anddigestibilit y ofbrow n midrib corn silageb y lactating dairycows .J .Dair y Sei.60 :1894-1904 . Rosa,J.G. , D.M. Forsyth,D.V . Glover& T.R . Cline,1977a .Normal ,opaque-2 , waxy,wax yopaque-2 ,sugary- 2 andsugary- 2opaque- 2 corn (Zeamay sL. ) endosperm types forrat san dpigs .Studie so nenerg yutilizatio n J. Anim.Sei . 44:1004-1010 . Rosa,J.G. , D.M. Forsyth,D.V . Glover& T.R . Cline,1977b .Normal ,opaque-2 , waxy,wax yopaque-2 ,sugary- 2an d sugary-2opaque- 2cor n (Zea mays L.) endosperm types forrat s andpigs .Studie so nprotei nquality .J .Anim . Sei. 44:1011-1020 . Roth,L.S. ,G.C .Marten ,W.A .Compto n &D.D . Stuthman,1970 .Geneti c variation ofqualit y traits inmaiz e (Zeamay sL. ) forage.Cro pSei . 10:365-367 . Russell,W.A. , 1968.Testcrosse s ofone -an d two-ear typeso fCor nBel tmaiz e inbreds: I.Performanc e at fourplan t densities.Cro pSei . 8:244-247 . Schmidt,W. ,1980 .Proteingehal t undProteinqualitä t beiMais .Chance nun d Möglichkeiten derZüchtung .Mais-Kolloquiu m 1980,Einbeck ,pp .27-45 . Semuguruka,G.H. ,W.A .Compton ,C.Y .Sulliva n &M.A .Thomas ,1981 .Som e measures of temperature responsei ncor n (Zeamay s L.). Maydica26 : 209-218. Sheldrick,R.D. ,1979 .Th equalit y of 'brown-midrib-3'mutan tmaiz egrow n forforag e under field conditions insouther nEngland .Gras s& Forag e Sei.34 :283-291 . Sibma,L. ,1977 .Maximizatio n ofarabl e cropyield si nth eNetherlands .Neth . J. agric.Sei .25 :278-287 .

240 Sorrells,M.E. ,J.H .Lonnquis t& R.E .Harris ,1979 .Inheritanc e ofprolificac y inmaize .Cro pSei . 19:301-306 . Stallings,C.C. ,B.M .Donaldson ,J.W . Thomas& E.C .Rossman ,1982 .I nviv o evaluationo fbrown-midri b cornsilag eb y sheepan dlactatin gcows .J . DairySei .65 :1945-1949 . Stamp,P. , 1980.Variabilitä t vonSpross -un dWurzelmerkmale n jungerMais pflanzen inAbhängigkei t vonGenoty p undTemperatur .Z .Pflanzenzüchtg . 84:226-239 . Stinson,H.T .& D.N . Moss, 1960.Som eeffect so f shadeupo ncor nhybrid s tolerant andintoleran to fdens eplanting .Agron .J .52 :482-484 . Struik,P.C. , 1982a.Productio npattern ,chemica l composition anddigesti bilityo f foragemaiz e (Zea mays L.). Mededelingno .64 ,LH ,Vakgroe p Landbouwplantenteelt &Graslandkunde ,Wageningen ,Netherlands ,pp .1-28 . Struik,P.C. , 1982b.Effec to fa switc h inphotoperio d onth e reproductive development of temperatehybrid so fmaize .Neth .J . agric.Sei .30 : 69-83. Struik,P.C. , 1983a.Th eeffect so f switchesi nphotoperio d oncro pmorphology , productionpatter n andqualit y of foragemaiz e (Zea mays L.)unde rfiel d conditions.Mededelinge nLandbouwhogeschoo l 83-2,Wageningen ,pp .1-27 . Struik,P.C. , 1983b.Th eeffect so fshor t and longshading ,applie ddurin g different stageso fgrowth ,o n thedevelopment ,productivit y andqualit y of foragemaiz e (Zea mays L.). Neth.J . agric.Sei . 31:101-124 . Struik,P.C. , 1983c.Effec t oftemperatur e ondevelopment ,dry-matte r production,dry-matte rdistributio n andqualit y of foragemaiz e (Zea mays L.). Ananalysis .Mededelinge nLandbouwhogeschool ,83-3 ,Wageningen , pp.1-41 . Struik,P.C . 8tB .Deinum , 1982.Effec to fligh tintensit y afterflowerin go n theproductivit y andqualit y ofsilag emaize .Neth .J . agric.Sei .30 : 297-316. Thiagarajah,M.R .& L.A .Hunt ,1982 .Effect so ftemperatur eo nlea fgrowt h incor n (Zea mays). Can.J .Bot .60 :1647-1652 . Thomas,V.M. ,D.V . Glover& W.M .Beeson ,1976 .Nitroge n andenerg y utilization ofne wendosper m typeso fcor nwit h growing steers.J .Anim .Sei .42 : 529-534. Thompson,D.L. ,1972 .Recurren t selection forlodgin gsusceptibilit y and resistance incorn .Cro pSei . 12:631-634 . Thompson,D.L. ,1982 .Grai nyiel do ftw osynthetic so fcor nafte rseve n cycleso f selection forlodgin g resistance.Cro pSei .22 :1207-1210 . Tollenaar,M .& T.B .Daynard ,1978 .Lea f senescence inshort-seaso nmaiz e hybrids.Can .J .Plan t Sei. 58:869-874 . Tollenaar,M .& T.B .Daynard ,1982 .Effec to fsource-sin k ratioo ndr ymatte r accumulation and leaf senescenceo fmaize .Can .J .Plan tSei .62 : 855-860. Tollenaar,M. ,T.B .Daynar d &R.B .Hunter ,1979 .Effec to f temperatureo nrat e of leafappearanc e and floweringdat e inmaize .Cro pSei . 19:363-366 . Tollenaar,M .& R.B .Hunter ,1981 .Quantificatio n of theeffect so f temperature andphotoperio d onmaiz e development.Agron .Abstr .1981 ,Amer .Soc . Agron.,p . 14. Twusami-Afriyie,S .& R.B .Hunter ,1982 .Evaluatio no fquantitativ emethod s fordeterminin gstal kqualit y inshor t seasoncor ngenotypes .Can .J . Plant Sei.62 :55-60 . Undersander,D.J. , L.F.Bauman ,V.L .Lechtenber g& M.S .Zuber ,1977 .Effec t ofcycli cselectio n forhig han dlo wcrushin g strengtho nrind ,pit h andwhole-stal k composition incorn .Cro pSei . 17:732-734 . VanSoest ,P.J. , 1967.Developmen to fa comprehensiv e systemo f feedanalyse s andit sapplicatio n toforages .J .Anim .Sei .26 :119-128 .

241

243 VanSoest ,P.J. , 1976.Th eestimatio n ofdigestibilit y fromchemica l compo sition. In:Carbohydrat e research inplant s and animals,Misc .paper s 12,Agric .Univ. ,Wageningen , pp.137-145 . mio DwokaKTiuot fflptnra

ora tth ebeginnin g ofAugust .Th edigestibilit y of thecell-wal lmateria l produced duringsubsequen tea rdevelopmen ti sstil lhig h atharvest .Thi s cell-wall formation endsdurin gearl y grain filling.I fpollinatio n andgrai n setar esuccessful ,th eendosper m cellsi nth ekernel s are filledwit h completely digestible starch.Som eo fth esucros enecessar y tosynthesiz eth e starch isproduce d duringgrai n filling.Th eremainde r comes fromth estalk , shank,co ban dhusks .Thes eplan tpart scontai n considerablepool so f previously stored solublecarbohydrate s andothe rcompounds .Dependin g onth e rateo fphotosynthesis ,thes emetabolite s areredistribute d anduse dfo r dry-matteraccumulatio n inth egrains .I fphotosynthesi s duringgrai nfillin g issufficientl yhigh ,th emas s fractiono fcellula r contentsi nth ewhol e cropincrease sa tsuc ha rat e thatth edeclin ei ncell-wal l digestibility is overcompensated.Thi sresult s ina smal lincreas e indigestibilit y ofth e whole cropunti lth erat eo fphotosynthesi sbecome s solo w (becauseo flo w lightintensit y andagein go f leaves) thatthi sincreas e reversesan dbecome s a smalldecrease . Thus theproductio n ofpoorl y digestible cell-wall components,o fver y digestible cell-wallcomponent san do fwholl y digestible cellularcontent s occursa tdifferent ,partl yoverlapping ,stages .Therefor e theamount san d nature ofthes ecomponent s canb eaffecte d separately.Th e crop'sdigestibilit y dependso nth ecell-wal ldigestibilit y andth erati obetwee n cell-wallyiel d anddry-matte ryield .Th eresult so fexperiment s reportedi nthi sthesi ssugges t thatth ecell-wal ldigestibilit y ofth ewhol eplan tmainl y dependso nth e plant'sgenotyp ean dphysiologica l age,an do ntemperature .Th emea n seasonal temperature doesno tvar y sufficiently toinduc eyear-to-yea rvariatio ni n cell-walldigestibility .Withi non ehybri d andwit hnorma lsowin gan dharves t dates,digestibilit y onlydepend so nth erati oo fcel lwal lt ocellula r contents.Thi smean s thatdigestibilit y isa roug hindicato ro fth e favourablenesso f theenvironmenta l conditionsafte rgrai nse tvis-à-vi sth e conditionsbefor e grainset . Theduratio no fthes e twoperiod si sdetermine db y thecrop' srat eo f development.I nturn ,thi srat ei saffecte db yenvironmenta l conditionsan d bygenotype .Developmen ti softe naffecte db y short-livedweathe rconditions , becausecertai n developmental stagesonl y lasta fe wday so rbecaus esom e transitions inth eplant' sdevelopmen tar edrastic . Inadditio n todigestibility ,dry-matte r contenti sa nimportan t quality characteristic,sinc e itinfluence s theprocesse si nth esil oan d inth eruminant .Developmen tinfluence s theultimat edry-matte r contentmor e

244 thanth eultimat edigestibility . Untilgrai nse tth eamoun to fwate ri nth e cropincreases ,althoug h thewate r contentslowl ydecreases .Durin ggrai n filling theamoun to fdr ymatte r continues toincreas ebu tth ecro plose s water,especiall y ifth eear sar e large.Th erate so fvegetativ ean d reproductive development,th esiz eo fth este man do fth eear ,an dth erate s ofgrai nfilling ,o fmaturatio n ando fsenescenc e determine thedry-matte rconten t atharvest .Th eproportio no finsolubl e drymatte r inth e freshstove ri s probablymor e important forconservatio n losses than thedry-matte r content ofth ewhol e crop.Therefor e theintensit y ofredistributio n alsoplay sa role. The generalpatter no fproductio nan dquality"outline dabov e isbase do n theresult so f fieldan dphytotro n experimentsi nwhic h theeffect so f levelso f ando fchange si ntemperature ,ligh tintensit y andphotoperio d onth e development,dry-matte rproduction ,allocatio no fdr ymatter ,digestibilit y anddry-matte rconten twer einvestigated . Insom eexperiments ,genotyp ean d cultivation techniquewer e alsovaried .Th eexperiment sno tonl y increased theunderstandin g aboutth egenera lpatter no fproductio n andqualit yan d the factorsinfluencin g thispatter nbu tals oyielde d informationo nspecifi c ecophysiological reactionso fth emaiz e cropt oshort-live d changesi n weather.

Effects of climatic factors Temperatureshighe r thannorma ldurin gth eperio dbefor e tassel initiation increase forage-maizeyield si nTh eNetherlands ,sinc ethe yaccelerat e the growtho fth eseedlin g andtherefor eboos tth eproductivit y lateron .Hig h temperatures justbefor e the tasselinitiatio nresul ti nmor e leavespe r plant.A largenumbe ro fleave sma yincreas eproductivit y butnegativel y influencesdigestibilit y anddry-matte r content.Afte rth einitiatio no f tasselan dears ,a ris ei ntemperatur e causesa ris ei nth erate so fproductio n ando fdevelopment .A sth etemperatur e coefficiento fth ephotosyntheti c rate ismuc h lowertha ntha to fth erat eo fdevelopment ,th eultimat e effecto n yield isnegative ,unles sth e growingseaso ni scurtailed ,e.g .b y frosto r lowligh tintensity .Continuousl yhighe rtemperature sals olowe rth ecell-wal l digestibility asa resul to fincrease d ligninconten tan daltere dphysical / chemical structure.Th eeffect so ftemperatur eo ncell-wal l digestibility aremuc h lesspronounce d ifth erise si ntemperatur e areonl y temporary. During certainphase safte rtasse linitiatio nhig h temperaturesma yals ohav e someadvers eeffect so nea rdevelopment .

245 Shortperiod swit h lowligh tintensit yearl y inth egrowin gperio d strongly reduce the dimensionso fth e stemwithou treducin gultimat eyiel d orquality .Lo wligh tintensit ydurin gcritica l stageso freproductiv e developmentundoubtedl yha sfar-reachin grepercussion so nyield ,digestibilit y anddry-matte rcontent .Durin ggrai n filling,th ereaction so fmaiz e tolo w lightca nals ob edramatic .However,th eexperiment s suggested thatafte ra whileadaptatio no reve nrecover y ispossible .Lo wligh tintensit y atth e endo f theseaso nca nmak e the cropmor esusceptibl e to Fusarium. Longperiod so flo wligh tintensit yresul ti nlarg eyiel ddepressions . Ifsuc hperiod sd ono tstar tto oearl yi nth egrowin gseason ,lo wligh t intensity alsoreduce sdigestibilit y andretard sth edry-dow no fth ecrop . Bymean so fswitche si nphotoperio d applieddurin gearl ydevelopmen ti t appeared tob epossibl e tosynchroniz eo rdesynchroniz e vegetativean d reproductive developmento fth emai nste man do fth eea rshoots .Simultaneously , thesiz eo fth evegetativ e andreproductiv eorgan swa sals oaffected .Researc h intoth econsequence so fsuc heffect sma yb eusefu lt oimprov e thedescriptio n ofa nideotyp eo f foragemaize .

Ideal weather conditions in The Netherlands for growing forage maize TheDutc h climate issuitabl e forth eproductio no fhigh-qualit y forage maize.However ,productivit y isseverel y limitedb yth elo wsoi lan dai r temperatures insprin gan dt oa smalle rexten tb yth e lowai r temperatures duringSeptembe ran dOctober .Durin gthes emonths ,ligh tintensit y ismor e limiting.Becaus eo fth eprolonge d absenceo fkillin g frosts,however ,yield s of foragemaiz e intemperat e regionsar e fairlyhigh .Th e idealweathe rfo r growingmaiz e inTh eNetherland si scharacterize db y sufficient,frequen t rainfall (butno tto omuch) ,hig h temperatures fromsowin gt ojus tbefor e tasselinitiatio n anddurin ggrai nfilling ,an dmuc hirradiance ,especiall y aftertasse linitiatio nunti lharvest . Itseem spossibl e topredic t thedigestibilit y offorage-maiz e crops fairlyaccuratel yo nth ebasi so f thegenotype ,cro pcharacteristic san d weather.

Ideotype of forage maize for North-West Europe The ideotypeo fmaiz e forforag eproductio n inNorth-Wes tEurop eshow s thefollowin gcharacteristics : - agoo dcol dtoleranc ean dearl yvigou r andals oa goo dtoleranc eo fhig h plantdensitie s

246 a fastrat eo flea fappearance ,a nexcellen tstay-gree n indexan d thehighes t possible rateo fphotosynthesi s early flowering,a smal ltasse lan da larg eea rwit h aslo wgrai n filling a stockystem ,wit ha hig hproportio no fstron gpit h lowsusceptibilit y topest san ddisease s ahig hpotentia l cell-walldigestibilit y anda fas trat eo fcell-wal l digestion amoderat e formationo fbrac eroots .

247 SAMENVATTING

Deopbrengstpotentie sva n snijmalsi nNoordwest-Europ a zijngedurend ed e laatstedecenni aaanzienlij k gestegendan k zijd eintroducti eva nproduktiever e rassen endoo rverbeterin gva nteelttechniek .He tkolfaandee le nhe tgehalt eaa n droge stofwerde nvoornamelij k verhoogd doorwijziginge n inteelttechniek .Nieu w geïntroduceerde rassenbleke ndaarentege n ietsminde r goedverteerbaar . Fundamenteel inzichti nhe tproduktiepatroo n enhe tverloo pva nd everteer baarheide nva nhe tdroge-stofgehalt ebi jsnijmaï se ni nd e factoren,di edaarbi j eenro lspelen ,ontbreek t echterno ggoeddeels .I ndi tproefschrif tword tonder zoekbesproke nda tto tdoe lha ddi tinzich tt evergroten .

Produktiviteit in het algemeen Malsheef tee naanta lecofysiologisch e eigenschappen,di ee rd eoorzaa kva n zijn,da the tgewa s zichi nhe ti nNoordwest-Europ a heersende klimaatnie t optimaalka nontwikkelen .Va ndez eeigenschappe n isvoora lhe tthermofiel e karakter vand eplan tva nbelang .Bodem -e n luchttemperaturen gedurended e eersteweke nn ainzaa i zijnva ndoorslaggevend ebetekeni svoo rd euiteindelijk e opbrengst.Nadie n isd eprodukti e sterk afhankelijk vantemperatuur ,licht intensiteite nvochtvoorziening .Dez e factorenbepale n zoweld eproduktiesnel - heid alsd eduu rva nd eproduktiev eperiode .Voora ld eomstandighede n tijdens debloe ie nd e lichtintensiteitn ad ebloe i zijnvaa kbeperken dvoo r (het instandhouden van)d eproduktiviteit .D eweersomstandighede n inNederlan d zijni nhe talgemee ngunstige r tijdensd etweed ehelf tva nd evegetatiev egroe i end eontwikkelin g vand ebloeiwijze n dantijden sd ebevruchting ,zettin ge n vullingva nd ekorrels .

Algemeen patroon van groei, ontwikkeling en kwaliteit Devormin ge nuitgroe i vanbovengronds e vegetatieve delenvinde nplaat s vanopkoms t (mediomei )to tenig eweke nn ad evrouwelijk ebloei .Dez eperiod e gaatgepaar dme td eopbou wva nstevigheidsweefse l dati nd e loopva nhe t groeiseizoen steedsslechte r verteerbaarwordt .Al sd evegetatiev edele n uitgegroeid zijn,houd td evormin g vanslech tverteerbaa r structuurweefsel indez edele nop ,maa rd ekwalitei tva nd ecelwande nblijf tlangzaa machter uitgaan. Degroeipunte nva nhoofda s enzijasse nworde nein dme io fbegi njun i

248 generatief.D eplui me nd ekol fontwikkele n zichvervolgen s enbloeie nein d julio fbegi naugustus .D edaaropvolgend eontwikkelin g vand ekol fgaa tgepaar d metd evormin gva nstructuurweefse lda too kbi jd eoogs tno ggoe dverteerbaa ris . Deze celwandvorming houdttijden she tbegi nva nd ekorrelvullin g op.Al sd e bevruchting enkorrelzettin g geslaagd zijn,worde nd eendospermcelle n ind e korrels gevuldme tvolledi gverteerbaa r zetmeel.D esucros edi enodi gi svoo r devormin gva n zetmeel,word tdeel s tijdensd ekorrelvullin g geproduceerd eni sdeel safkomsti gui td estengel ,d ekolfsteel ,d ekolfspi le nd eschut bladen. Indez eorgane nworde nonde r gunstigeomstandighede n aanzienlijke voorradenoplosbar e assimilatenopgeslagen .Afhankelij k vand efotosynthese snelheid tijdensd ekorrelvullin gworde n dezeassimilate n geredistribueerd enaangewen dvoo rd ekorrelgroei .Bi jvoldoend ehog eprodukti e tijdensd e korrelvulling neemthe tgehalt e aanstructuurweefse l zosne la fda tdaarme ed e afnameva n verteerbaarheid vandi tweefse lmee rda ngecompenseer dka nworden . Hetresultaa ti sda td everteerbaarhei d vand ehel eplan tn ad ebloe i iets toeneemttotda td eproduktiesnelhei d inoktobe r tengevolgeva nd elag elicht intensiteito fd everouderin gva nhe tbla d zolaa gi sda tee n geringeafnam e vand everteerbaarhei d weermogelij kis . Deperiode nwaari n slechtverteerbar e celwanden,goe dverteerbar e celwandeno fvolledi gverteerbar ebestanddele nva nd ecelinhou d gevormd worden,valle ndu svoo ree ndee lnie tsame ne nzij nverschillen d vanduur .D e hoeveelheid enkwalitei tva ndez ebestanddele n zijnda noo kdeel safzonderlij k tebeïnvloeden .D everteerbaarhei d vanee ngewa si safhankelij k vand everteer baarheid vand ecelwandbestanddele n end everhoudin g tussen celwandopbrengst endroge-stofopbrengst .Ui td ei ndi tproefschrif tbeschreve nproeve nkom t naarvore nda td ecelwandverteerbaarhei dva nhe thel egewa svoora lafhankelij k isva nhe tgenotyp ee nd efysiologisch e ouderdomva nd eplan te nd etempera tuur.D egemiddeld e temperatuur tijdenshe tgroeiseizoe n vertoont teweini g variatieo mjaarverschille n incelwandverteerbaarhei d teveroorzaken .Binne n éénhybrid e enbi jnormal e zaai-e noogsttijdstippe ni sd everteerbaarhei ddu s afhankelijk vand egewichtsverhoudin g tussenstructuurweefse l encelinhoud . Grofwegbeteken tdi tda td everteerbaarhei d aangeeftho e gunstigd eproduktie - omstandigheden nad ekorrelzettin gware n tenopzicht eva ndi evoo rd ekorrel zetting.

Deduu rva ndez ebeid eperiode nword tbepaal d doord eontwikkelingssnelhei d vanhe tgewas .Dez e snelheidword to phaa rbeur twee rbeïnvloe d doormilieu factoren,maa roo kdoo rgenotype .Omda tbepaald eontwikkelingsstadi a slechts enkele dagendure no fomda tsommig eovergange nabrup tzijn ,word td eontwikkelin g

249 vaakbeïnvloe d doorhe twee rva nslecht senkel edagen . Naastverteerbaarhei d ishe tdroge-stofgehalt eee nbelangrij kkwaliteits kenmerk,omda tdaardoo rd eprocesse n ind esil oe ni nd eherkauwe rbeïnvloe d worden.He tuiteindelijk e droge-stofgehaltei svee lafhankelijke rva nd eont wikkeling dand euiteindelijk e verteerbaarheid.To taa nd ekorrelzettin g neemtd ehoeveelhei dwate ri nd ebovengronds e delentoe ,hoewe lhe tvocht gehalte langzaamdaalt .Daarn aneem td ehoeveelhei d drogesto fno gsteed stoe , maarhe tgewa sverlies twater ,voora lal se rfors ekolve nontwikkel dzijn . Desnelhei d vanvegetatiev ee ngeneratiev eontwikkeling ,d eomvan gva nstenge l enkol fe nd esnelhei dva nkorrelvulling ,afrijpin ge nafstervin gbepale n hetdroge-stofgehalt ebi jd eoogst .He tgehalt eaa nonoplosbar e drogesto f ind evers emass ava nd evegetatiev e deleni swaarschijnlij kbelangrijke rvoo r conserveringsverliezen danhe tdroge-stofgehalt e vanhe thel egewas .Daaro m speeltoo kd emat eva ndroge-stofredistributi eee nrol . Hethierbove nbeschreve n algemenebeel dva nprodukti e enkwalitei ti s gebaseerdo pd eresultate nva nveld -e n fytotronproeven,waari nd eeffecte n vannivea uva ne nveranderinge n intemperatuur ,lichtintensitei te ndaglengt e opd eontwikkeling ,droge-stofproduktie ,droge-stofverdeling ,d everteerbaar heide nhe tdroge-stofgehalt ewerde n onderzocht.Teven swer d inenkel eproeve n hetra so fd eteelttechnie k gevarieerd.Dez eproeve n leverden inzichti nhe t algemenepatroo nva nprodukti e enkwalitei te ni nd e factoren diedaaro pva n invloed zijn.E rwer doo kinformati e verkregenove rspecifiek e ecofysiologische reactiesva nee nma'isgewa so ptijdelijk everanderinge n inklimaatsfactoren .

Effecten van klimaatsfactoren Hogeretemperature nda nnormaa ltijden sd eperiod evoo rd epluimaanle g verhogen deopbrengs tva nsnijmal si nNederlan d sterk,omda tzi jd egroe i vand ezaailin gversnelle ne nd eproduktivitei t lateri nhe t groeiseizoen bevorderen.Hoger e temperaturenkor tvoo rd epluimaanle g leidento tmee r bladeren.Ee n groteraanta lbladere nka nopbrengstverhogen dwerken ,maa rheef t eennegatiev e invloedo pverteerbaarhei d endroge-stofgehalte .Nada td eplui m end ekolve ngeïnitieer d zijn,leid tee nverhogin gva nd etemperatuu r totee n verhogingva nd eproduktiesnelhei d enee nversnellin gva nd eontwikkeling . Omdatd etemperatuurcoëfficiën tva nd e fotosynthesesnelheid veellage ri s danva nd eontwikkelingssnelhei d ishe tuiteindelijk eeffec to pd eopbrengs t negatief,tenzi jhe tgroeiseizoe n aanhe teind eduidelij kbegrens dwordt , bijvoorbeeld doornachtvors to flag elichtintensiteit .Permanen thoger e temperaturen leidenoo k totee n lagereverteerbaarhei d vand ecelwande nvan -

250 wegeee nhoge r ligninegehalte enee nveranderd e fysisch-chemischestructuur . Diteffec tva ntemperatuu ro pd ecelwandverteerbaarhei d isvee lminde ruitge sprokenwannee re rslecht ssprak e isva nee n tijdelijkeverhogin g vand e temperatuur.Hog e temperaturenn apluimaanle gkunne n inverschillend e gewas stadiaoo knegatie fwerke no pd eontwikkelin gva nd ekolf . Korteperiode nme tweini g lichtvroe gi nhe tgroeiseizoe n reduceren sterkd eafmetinge nva nd estenge l zonderda tz ed euiteindelijk e opbrengst enkwalitei tverlagen .Weini glich ttijden s crucialemomente n ind egeneratiev e ontwikkelingheef twe lverregaand e consequentiesvoo rzowe lopbrengs tal s verteerbaarheid endroge-stofgehalte .Tijden sd ekorrelvullin gka nmaï soo k nogzee rhefti greagere no pverminderd e instraling.Ui tsommig eproeve nblee k echterda tn averloo pva ntij dee nopvallend e aanpassing ofzelf sherste l mogelijk is.Lag e lichtniveausaa nhe tein dva nd eveldperiod ekunne nd e gevoeligheid voor Fusarium sterkvergroten . Langereperiode nme tee nlag elichtintensitei t gevengrot eopbrengst depressies.Mit snie tt evroe gi nhe tgroeiseizoe nbegonnen ,verlage nderge lijkeconditie sd everteerbaarhei d envertrage nhe twaterverlie sva nhe tgewas . Metbehul pva ndaglengteveranderinge n inhe tvoorjaa rblee khe tmogelij k devegetatiev ee ngeneratiev eontwikkelin gva nd ehoofda se nva nd e (kolfdragende) zijassenmee ro fminde r synchroon telate nverlopen .Tegelijkertij d wordtda n ook deomvan gva nd evegetatiev e enreproductiev e organenbeïnvloed .Onderzoe k naard econsequentie sva ndergelijk e effectenka nbehulpzaa m zijnbi jhe t verbeterenva nd eideotypebeschrijvin g vansnijmaïs .

Het ideale weer voor de snijmaïsteelt in Nederland HetNederlands eklimaa ti sgeschik tvoo rd eprodukti e van snijmaïsme t eenhog evoederwaarde .D eproduktivitei tword techte rernsti gbelemmer d door delag ebodem -e nluchttemperature n inhe tvoorjaa re nd elag eluchttempera tuuri nhe tnajaar .I nseptembe re noktobe ri sd elichtintensitei techte r sterkerbeperken d dand etemperatuur .Omda td eeerst e schadelijke nachtvorsten gewoonlijkpa s laati nhe tnajaa roptreden ,i she tgroeiseizoe n ind egematigd e gebieden lang;daardoo r zijnhog edroge-stofopbrengste n tochmogelijk .He t idealeweertyp evoor ,maï si nNederlan dword tgekenmerk tdoo rvoldoend e (maar niett eveel )e nregelmati gverdeeld eneerslag ,hog e temperaturenvana finzaa i totvla k voord epluimaanle g entijden sd ekorrelvulling ,e nvee lstraling , vooralvana fd epluimaanle g totaa nd eoogst . Hetlijk tmogelij k opgron dva nhe tgeteeld e ras,gewaskenmerke n enhe t weerd everteerbaarhei d vansnijmaï sme tee nredelijk ebetrouwbaarhei d te

251 voorspellen.

Ideotype van snijmaïs voor Noordwest-Europa Hetideotyp eva nmai svoo rd esnijmaisteel ti nNoordwest-Europ abezi t devolgend e eigenschappen: - goedekoudetoleranti ee n "earlyvigour" ,alsmed eee ngoed e tolerantievoo r hoge standdichtheden - snellebladafsplitsing , langgroenblijven dbladapparaa te nd ehoogs tmogelijk e fotosynthesesnelheid - vroegebloei ,ee nklein eplui me nee ngrot ekol fme tee nlag ekorrelvullings - snelheid - eenkorte ,dikk estenge lme tvee le nstevi gmer g - geringevatbaarhei d voorziekte ne nplage n -ee nhog everteringssnelhei de nverteerbaarhei d vand ecelwande n - eenbeperkt evormin gva nsteunwortels .

252