Solubility and Physiological Availability of Phosphates in Sodium and Calcium Systems

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All Graduate Theses and Dissertations Graduate Studies

5-1948

Parker F. Pratt Utah State University

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All Graduate Theses and Dissertations Graduate Studies

1-1-1948 Solubility and Physiological Parker F. Pratt

PHOSPHATES IN SODIUil AriD CALCI UM SYSTEJI;l •'' ····· ····· by

Parker P'. Pratt ......

A theab submitted 1n partial 1'ult1111118nt of the requirements for the degree ot

MASTER OF SCI ENCE

Soil Chemistry

1H8

UTAH STATE AGRICULTURAL COt.LEGB Logan. Utah .-(rr

I wiah t o thank Dr . De w. Thorne for his help in nleotillg the probloa aDd for his vnluablo aa aiatanoe ill conducting the 1nveatisat1ona. Al ao, I

wiah to aoknCJWledge the auggeationa and ideu r;hen

by Dr. P. B. ann.

l'lu-ker P. Prw. tt TABLE OF COll'l'EDTS

Io Ill'l'RODUCTIO ...... 1 II. REVI V OF UTERA'l'tJRE • . .. 2 Ao Solubility of Phosphatee ...... 2 1. Solubility in oa lciua aystel!ll 2

2. Solubility in sodium s ystems , 4 s. The illlporte.nce of anion exehanj;e • • • 5 B. Physiological Availability In solution cultures • ...... 6 2., Physiological availability of HaP04 and uro: ions 7 III. TlTE SOtuDit.ITY OF PITOSP!TATES Ill SUSPENSIOilS

FERBJI1' DEGREES OF BODIUU AND OAJ.CIUY SATURJ.TION .... ~ .... 10 A• lllthod • • ...... " . . . 10 B. Results • . .... 11 IV. Tl'!E PE!UiEA.DIUTY

'· p3 relstionshipe •••• ' ' ~ ~ •• < r ... 15 2. Concentration relationships . . . 20 v. DISCUSSION • . . . ' . . . 24 VI • SUl.lWIRY . ._ .. • ft •••• ... 27 VII. Literature Cited • ...... 28 1

SOWBILITY Am> PHTSIOLOOICAL J.VAI IA!llLI'l'T CP

PHOSFRATES IN SODIUJI AND C.U.OIUll SYSf

Pllrker P'. Pratt

llll'R 000 CT I 011

One of the pr1noipal fertility probl- or oal04reou1 aoila 1s the lack of a..,.1lable phoephatea. !he factore which control thh a..,.1lab11- ity are not coapletely understood. One hindrance to the solution of the problema 1mol'n4 reiUlte from contulion or the concept• or eolub111ty and aT&ilability. AT&ilability is the net effect of the ohemioal etate of a plaut nutrient ele.. nt and the ability of the plant to utiliea the for. of the ele•nt preeent under the edati:nt; chemioal and phy8ical en vironmental oondit1one. In th11 paper, the toMB aclub1Uty will be uaed to deaignate the ch8lllioal aolubility or an elftllnt in -ter or in apaoi• fled oxtn.otin& reagent• • file tera phyaiolo&ioal aT&Uability will be uaed to deaignate the ability or the pla~ to aeaimilate the eoluble forme of tho element, and the tera net aT&ilab111ty will be uaecl to deeignate the not effect ot ohemioal aolub111ty and ph:yaio l ~ical availability. fheae ltmited def1nltione aeea juetified in thia atudy beoauae the aodiua and oaloiua ayate• innetigatod are alkaline and planta growing in thoae

•~atema would probably be largely lt.i~d tu ~oluble vhcephatea. Sol~ bility ia kno.n to be one of the main faotora whioh control aYAilability of phoapbat.. , but there 11 no oonolua1n evidence aa to the importance ot phya1ologioal aY&ilability.

Soms innatigatora (26,1!)1 ban prcduoed erldenee which they claim aupporta the hypotheaia that the HzPQI ion 11 the only phoapbate ion

lNilmberl in pareutheail refer to •titerature Cited•. 2

abaorbed by plarlta. SiDOe the relatin concentration of thla ion deoroaaea as the pH iDOreaaes above !liNtraUty, they then conclude that phyaiologwo ioal availability is largely a function of pH. other 1Dveat1gatore (41,7) have produced eYidenoe which auggeata that eolub111ty ie probably the only factor which limite the availability of phoaphatee in alkaline and oal oareoua aoib, The purpoee of thil ~tudy ill to add eridence which w1ll help ol&l'ify t >e ralative importance of aolub1lity and phyaiologioal avail• ability ot phoaphatee in 1.;.diua aDd caloiua aolle.

REVIEW f6 LI1'ERATORE

Solubility !!_ Pboaph&te•

Solubility.!!!,~ epten

!'he eolub111ty or phoephatee in oalciua dominated eyete~:~~~ 11 very lc:~~r, eepeoially in alkaline oollditioneo Bue!~Hr (U),. trca purely theoretical treat11111nt, hae calculated that,. in the ayatea C&HP0-&-

HJC0s 1 the phnephlte oonoentration at equ111br1ua 11 directly proportion al to the hydrogen ion oonoerltration and 1nnreely proportional to the oaloium ion oonoentrat1ono !'he ruulta of thil theoNtioal tNatment a re in a Nemant With the work ot 'l'ealtle (ftO),. who found that, in a oaloiua dominated eoll eyatem,. the •in taotor1 in the depl"'eaion of the aolu bUity of phoephatea are oaloiua ion conoentrat:ton and hydrmeyl ion oon oentratioao He also found 'that if the hyaro~l ion ooncentrat1on waa

1mreaeed, without add1t1o1'11 o~ oaloiua ion• the aolubiUty of phoephatea

11 inoreaeedo With varicul oationa in the eon,. Teakle found that tho11 aoila which contained oaloiuawere the only onee which ahawed a deoreaae in aoluble phoephatea ae the pH wa.a railed above 7o Benne, Perkine, and

Xing (8) found that oaloiua oxide wae 11101'1 effeotin than calcium car bonate in reducing phosphate solubility. They explained thia on the bal11 of the low aolubility of oaloiwa carbonate oompe.red to the aolub111ty ot calcium oxide. They alae found thAt when oaloiua oxide -• added, the

sninilmun solubility of phosphatee -• reaehed at a pH of 7oS6 and re•

•ined at the same lenl ae the pH -• inoreaaed.

Ca~~eron and Bell (14), in 1907, ade an n:tenlive atudy ot •ell phoe

phatea. 'l'he;y .tated that aoil phoBpbatn, whether aolid •olutione or

definite chemical compounds, are of IUoh a mture a• to give Yery uall

quantities ot soluble phosphate•• They IUggeated that eoil pholphates are of the mture of hydrox;yapatite or oarbon&te apatite. aa ..ett (6)

concluded that aince the soil reaction range 11 well within the range in

which hydroxyapatite 11 tho etablo oaloiua phoephate, thh t'ol'lll of phoa•

phate 11 the only one that can ex11t pe~nently in the aoil. 'McGeorge and Breaaeale (2i) aay that the law aclub111t;y of phoaphatea in calcarecue

soil8 reeulta t'r0111 the t'onation of carbonate apatite, which hu the

t'oraula SC&s{P04)zoC&CO$o They 1tate that carbonate apatite ia the loaat

•oluble fOI'la of phOllphate in oaloaJ'Cioul 1oila1 and that it• •olubllity b g0'1'8rned by tho common ion oalciua and the eolid phue oaloiwa oar bonate. McGeorge and Breazeale ae1ign a definite atruotural formula to

oarbomte apatite. Xramer and Shear (28) point out that it i• i ncorrect to a .. ign a definite foJ'liUla to carbonate apatitao Logan and Taylor (26)

say that the ocapolition ct carbonate apatite or hydroJcy&pati te 11 not

conetant and depend• on the oonoentra~ion of such ions ae ca ++ 1 t!J'Of, on-, Cti in the Bolution at the ti• of preoip1tat1on. l!lbenberger, tehran

and Turner (18) wggeat that the apat1to• are not •toichi0118trio oompowlda,

• but typu of oryatal lattioea which for111 oontinuou• eorin of 1olid sol• utionso They cite the apatite t&llily ae an example ot an ionic ory1tal capable of di••ol'l'ing a large .-riety ot components, in large or 1mall

proportions, without fundamental change in lattice,

Ensminger and IAraon (19) in atudying orop re•ponae to pholphate !'or-t1lhat1cm found that eoib containing Oo6 to 1.0 peroettt lt. ah~

lout reaponae, aoib containing loO to z.o peroent 1~ ~owed D*!iua

ruponu, aoUa oonta1nin~ 2 peroent or mo.·• 111111! ehowe4 good reaponao, and that there -• no 1noroaae in reeponae aa tho pel'oent 11• 1ncnaee4

above 2 peroent• !hh sugg.. ta that 2 peroent Ume •Y be j uat aa

effeotin ae higher percentages in reducing the aoluble phosphatee ln

eoile.

Solub111tx _!! ~ syate•

Tho solubility ot phoaphatea in aoU ayate• dOillinated by nohange

able sodium or eodiua carbonate 1a lllOh hit;her than in oaloiua d0111inate4

eoil ayate•• In a aodiua eyetea there ia a decrease in oaloiua ion

oonQentraticm ·and a release of phosphates into the soil aolutiono 'l'hia

deoreaee of oalo1Uil ion oonoentration and inoreaae in eoluble phoaphorul

11 well 1llu1tratH by tbe 'tJOrk or fhol"'l8 (n-•2) Who found that, when

the exoh&n!!Mble aodiua inoroaeed; the oaloiua content of plontl ct..

oreaae4 and the phoaphor111 content 1noreaee4• Bower anil '!'urk (9) report

that naturally OOOUJT1ng aolla, high 1n eaban«<&ble eodiua, •:r not t'lar

niah an adequate supply of oalo1ua to plante ~n though oaloiua carbonate

11 proaent. Teakle (<&<>) found that ~1 ot the oaloiua iona !'rca the

aoll solution With oxalate oaueed a 20 to 60 fold 1noroaae 1n eolublo

phoaphatea·• Willia• («) oonduote4 an ntunination or t he 1olubillty or ftl'ioue phoephatic -.teriala and 1bund that the only typea whic.h oan be

plaoed in the aodiua hydrOKide inaoluble oatocory are thoee haYing an apa• tite lltruotl!reo Oard!lllr and Xelly (20) ay that b-u•e ot the 1011' ooa oontrat1cm of calciua ion 1n eodlla eoila, the rate ot !'oration or carbonate apatite 11 greatly red~d it not .topped cOIIPletely,. and there• tore soluble phoephatea aooumlatea Xobe and ~n1 (22) found that the

eolubility of oaloiua photphate• in 1odium carbonate eolutiona inorea1ed 6

aa the concentration of aodium carbonate inoreaeed, and that srinding t he

phoephatee inoreaeed their eolubil1ty. other inveati~tora {S6, 26, 28, 8)

agree t~t phosphatee are more aoluble in eod1uatr an in calcium dominated a on• •

!!!.!. importance !!, ~ exoh&n!j!

In eodiwa and ce.lo1u• doailliLted aoile, anion exohange 18 not an iao

portant factor in reducing the solubility of phoephatee. stout {89),

1r0rk:!.ng with kaol:!.nite olay, fcund tlw.t the ability ot thie clay to tix phoephate as an exchAngeable anion waa greatly r educed in alkaline aol•

uti one. Stcut reports that the phoephate fixed at pH value a of 7, a, 91 10, and 11 wu u . 7, 6. 9, <& .s, a.z, and 0 percent reapecthely ot the

IUIICJUnt fixed at pH So Thia 11 in a~-nt with the results obtained by

Jllrphy {ISO) who conducted a ailll11ar .inwat1gat1on Yith the same type olayo

Dean and Rubina {17) atate that the phosphatee retained by eoila aa ex

ohan aable anions are almoet completely removed by hydroxide aolutiODa•

lbi.Tilcciv1toh {SS) found that, when caloiu• hydroxide or aodium hydr oxide

1e added to an acid aoil; the exchange reaction takes place in two etepa. The f'irat atep h a cationic reaction which prooeecla until the hydrogen

iona are ooaipletely remowcl f'roa the olay• llhen there are no hydrogen

ions being released to unite with the h;ydroz;yl lone being acldecl; the second atep beginh rhb 1tep cODailtl of an anionic exchange in which hydr oxyl iona replace phosphate ions helcl aa exchangeable ionet It caloiUlll hydroxide 1a the baae added, the releued phoaphatea are preolpoo itated aa oaloiua phoaphateu It aodiua hydroxide 1a the baae added, the reloaaed phoaphatea 'Will relllllin in aolutiCJile

Phy!lol opoal .&:wailabiUt y

In aolutlaa oul turea

The dii'fioult:y or measuring the phyaiolog1oal avaUabiU ty of nutr1enta 6

1n auch a ooaplex ayatea aa the soil, haa led to the uae of aolut1cm oul turea for auoh atudiea. Reaulta obtained by the atudy of eolut1oa culturea cannot, 1n all oasea, be applied direotly to the son. But with phosphates in calcareous and alkaline aoila, where planta are probably Uaited to aoluble phoaphatea, there should be aoaD application. rhe effect ot pH on the phyaiolor ioal availability ot phoaphatea in aolution culturoa haa been atudied by aneral 1Jmtatiga.tora. Arnon,

Fratske, an4 Johneoa (o&) report the uptake of phoaphatea by lettuce, to-.to and bel'IU!& gran planta f'roa aolutlon over a pH r~ frOID S to

9o Plante ,..,re gram in a balanced nutrient aolution until they -re 6 waeka old. t'hey ,..,re then plaoed in nutrient aolut1ona 1n which the pH

-• controlled by additiona of aodiua h)"'!roxide or aul.t'\u'io aotd. The phoaphate oonoelltration -• held at the 881!18 le"Nl in all aolutionat !'he uptake of phoaphatoa -• r.awred for a per1od of 91 houra. 'l'oato an4 bel'Blda craa• plallta ehond ax1Jma abaorpt101l ot phoapbatee at pH 7. t.ttuoe ahond .ax1Jma abaor-ption at pH 6, !fOI' all planta ttwre •• a lignitioant deoroaae 1n phoaphate uptake at pH levela abaft 7 • At pH B the uptake -• approd•tely 66 peroellt of t~ .•rlllllWI uptake. At pH 9 the uptake waa 7 peroellt of the •:n.- for tcaato plant a, 26 pereellt of the ax'-- for lettuce, a!ld 12 percent ot the III&X1Jma for bel'll.lda gra••• Al'llon, Prabte and Jabmoa ooaol uM that, prOY1d1ng a 11Upply ot aoluble phoapbatea 1a -.1ntained1 planta will be able to abaorb adequate UIOUJlta or phoalilatea over a pH range f'rca ' to a. Tbia augpata that within thia pH ra e the phyliologioal anilabillty 11 not u b1portant aa solubility in the control of phoaphate a.,..UabUity. J«

Tidmore (43) reporta the abaorpt1on of phoapha.toa troa aolut1on culture•

by wheat and oorn plautl at pH ftlues of 4, 51 a, and 7o5o There -•

no appreciable d1tferenoe in the absorption at pH valuel of 4, S, and s.

But at pH 7•5 the ab1orption was a1gni1'ioant:ly lCIWer than at pH a. Breuet.le (10) report• a decreaae in phosphOl'Ua content ot rye planta with

increase in sodiua carbonate content of solution oulturea. An inoreaae in sodium carbonate concentration is oOIIIp&rable to an inoreaae in pH.

Samokh"'llt.l ov (S7) reporta the abaorption of phoaphatea trOll aolution cul•

tures by wheat and vetoho The highest absorption wa1 at pH 7. .A.t pH 5

and 8. 4 the abaOi'pticm ns le11 than at pH 7. Breaseale and lloGeorge (11) oollduoted eolution culture investigations

in which the pH and phosphate oonoentration ware detendned every hour• Proa the result. of this investigation, they concluded that phoaphatee in

alkaline oolutiona are not abeorbed by plaut1 until the pH of tho eolutione

hu been reduced to at least 7 Thb report 1111 contrary to the re~lte . .e. . obtained by Arnon, Pratcke, aD4 Johneon (4), and Sall!okhw.l oT (37), who

report phoaphate absorption at pH value• above So

Phyaiolor;ioal a"'llt.~lability !!£ ~ !!!!!_ HPO; !!!!!!. Duehrer (lS), u1ing the di11001ation oonetanta of phoapborio acid, bas calculated the relatiTe concentration of varioul orthophoapbate lone

OTSr a pH range i'Poa 4 to 9o Figure 1 ehowe thi!l relathe oonoentratioDII

of and lone at var1ou1 pH valuea. conoentratione of H P0 HzPO; IJPOt 8 4 and Pd.t are too small to be represented graphically. The po1itiona

of Ifa~ and " curves depend lllllnly on the aeoond dillooiation cOD'" etant of phosphoric aoid. 'l'here 1s oonaiderable T&rlat.ion among the value• reported in the literature tor thb constant. 'l'able I give• a Uet

of value1 found, '1'he solid line curve• in figo 1 are b6aed on oaloulationa uaing a value of 1, 95 x lo-7, taken troa.A.bbott and Bray (1), for the 8

rr------.------~.------.------.------~0

oL------m~------~w------vL------~~------oJv

N 01111 ~ 1 N 3 c.> N 0 c.> 3Aill1l3~ 9

eecond dieeooiat1on oonatant ot pholphor1c ao1d, which 11 the hl~e1t .aluo

t'oundJ and t ho broken lin., ourw1 are ba11d on oaloulat1one u81n a ..alue

Table Io ~luee p;hen for the 1ec011d di8Sooiat1on coMtant of ph01phorio acid

Souroe of Inf~tion 'l'lt.lue Reported

Abblrl:t aDd Bray (1) lo96 X 10·~ Britton (12) 1o4 X 10• silla (as) 9o66 x 1o-B at 260c Chem1.t~ aDd ~ioa ltllnclbook (16) 7oS x 10:: at lBOC Cohn (16 6o9 x 10 Bates and Acree (6) 6o3 X 10-8 at 250c 6o07 x lo-B at 2000 ·-Prideaux(Sl) and 11ard (3') 6o86 x lo-B

found-. Buehrer ue_ed the .alue reported by Abbott and Bray, which 11 111oh

hi her than any of the other w.luee reported• The ,.. lative concemratto:ll

or the B';PO'i and ~ 10111 are thue a tunct1on or pH, anc!. the oorNOt

ftluee probably He Within the range ehad.ed. in fig,. 1. '!'he PH ftlue at which tho rol~tthe concentration of B't~ 1on beco.ee ••11 clepend.l on the eeoond d1II001at1on oonetant ot phoaphor1o acid•

UoGecrt;e {26) oonoludoe tha.t the Hz~ ton 1e the phoepbate ion uti.. Uaed by plant•·· He etatee that! 8111041 HzP04 1e the doat.Dt phoephate

ion in the pH range of plant n-p0 anc!. e1nco plant• exilt on lawer ooncen- trationl ot pi\Oilpbt:tee 1n eliglltly acid soile, plant. prefer thh 1on for.

nutritiona.l purpoee•·· Re 1tat11 that phywiolog1oal ua1lab1lity of phoe•

phate1 11 t hus lugely a ~~atter of pU. Buehrer (13) 1tat11 that allc.alble

eolutione •:~· affect the mJIIbranee of roots in eucha 'lilLy that they - - not readily ab1crb phoephat11, but that 1t 11 equally oonrtnc1ng to argue that the roote don't roadily ab•orb phoaphate• fra. alkal1De 1oluti0D1 be cauee of the low concentration of EzP06 i011e

rhorno (U) rou'nd a politive correlation between the piT of eynthet1c 10

soils and tho concentration of phosphoruo in plants grawn in these soils.

Tho pH valuoe were closely related to the degree of sodium uturation or

the oilc. Since with calcium carbonate in tho soil there was no close

relationship between pH and phosphorus content of plants, Thorne oonolude1

that the prilrlley oanee of tho 1ncreesed pboephoru• uptake was the degree

or sodium llaturation with the resulting inoreue in soluble pho1phatee.

He 1tates that the pH was probably only an aooCI!lpiUlying relationllhip. This

suggests that plants are able to absorb adequate amounts of phosphate• re

gardless of the pH and the relative concentration of HeP04 i on, ~r~tding soluble phoephatee are present. Behrens (7) grew oat1 in pure sand to which pure chemicals -re added. Several phosphatic oCIIIpounds -re used with and without calcium oa~bonate. He ooncludca th•t the ~eat deerea1a

in phosphate utilization wlth calcium ocrbonata . -s a re>sult of tho sol ubility rather than pH.

li!Oeo.l"ge (27)• using the lleubauer test, determined phosphate absorp tion from soilll satUl"ated with oaloiua, mgneliUlll end sodiua. P'nosphate absorption from the calcium and magna11um a turated soils waa about the

1ame as from the original soil. but the absorption fr0111 tho sodium satu rated eoil -• appraoiably lower. Thora is IQIIII! question as to the w.l

idity or the Neubauer te•t under such condition•• !be 1eadlinga used in the tests probably mde very poor growth, ii' any, on the eod1Ulil eature.te

TJ1E SOLUBILITY CF PHOSPHATES I N SUSPENSIONS OF ClAY WITH

DIFFERE!l'i' DEGREES OF SOD!UII AND CALCIUM SATUI!A'l.'ION

~ The ole.y uaod in this 1nvest1ee-t1on was a montmorillonite typo of olay aeparated from a natural bentonite ater1al obtained about three miles 11

north o!' Garland in Box Elder County, Utaho The olay waa freed of buee

by leaching with dilute bydroohlorio &old and -~ auapended in ftter to taoil1tate handling. Sirleen 1foEo ot monopotaeeiua phoaphate per 100 P • ot olay wae added to the suapendon and t he suapendon thoroughly shaken

in a ID!Iohanioal ehakero Titration ourves were made by plotting pH againlt

lf. E. of aodiua hydroxide or Jt.E. or calcium aatide added per unit weight

of olay in the auspens1on. Plfty mla. of clay euapeneion fts put into

eaoh of S2 Brle!1111!1y8r flaebo Malt were treated with 't'llrying qualltlt1ea

ot sodium ~roxide and half with varying quantitiea of oaloiua oxide, The amount of base added to eaoh Pllple fta oaloulated fr0111 the titration

ourvee 10 aa to ~ iw pit valuoe ranging tram 4 to 10 inolulive, at inter fth of 0, 5 pH unit. Dupl1oate aamplea were prepared tor each pH "ffllue , water was added to each aaaple to brin the clay-water ratio to l alOo

!he eamplee were t hen atcppered and let stand for 6 dayc w1 th vigor~• ahald. ng twice daily. A water extract waa obtained by oentl"ifuging a auitable portion of the samplea in 100 1111. centrifur;e tubea. Phoaphorua waa determined on the water extract, according to the method of Allen

(S), using a Fieber A.o , model electrophotometero

~ The -ter aoluble phoaphorua in clay auepensiona at different pH valuea and dH't'•rent degreea of sodiua a'!ld cd.,1ua 111tuN.t!.on h •~own graphically in figo 2o At all pH "fflluea the clay suapenaiona titrated with aodiua hydraatide gaw higher &l!lounta or ftter soluble phoaphorua than those titrated with calclua oxide, Th11 difference waa r;reateat over the alkaline pH ranr;e . The large increaae in water aoluble phoaphorus in the clay suapena1ona titrated with aodiua hydroxide, over the pH range fro111 7 to to, probably r eaulta from tho releaae of phoephate ionl t'raa the anion cxch≠e complex. For every unit increase in pH there is a 12

16 / I

U'l ::;; "' I 2 I 0 0

0:: 10 UJ I a.. ui :i 8 I I 1/rNAOH INDUCEC a.: ALK LINITY w 6 _J CD ::l _J 4 I 0 (f) ~ 0 ~ N 2 I I 1---L/ ~AO INDUCED r-----_ ALK ~ L1 N I TY 0 4 5 6 7 8 9 10 pH

5 15 34 66 81 97 105 'l'. NA SATURATION

15 45 70 87 96 103 120 % CA SATUR ATION

Figure 2. The water soluble phoapborua 1n clay auapendcma 1n relation to the pH induced by add1tioD8 ot dlttereut quautitiea ot calcium oxide or .;o!i•nn hydraxlde, 13

ten told inoreue 1n eydroxyl ion oonoentNt1Qno 'llben the pH exoeedl 7

the hydroxyl ion oonoentNtion reach.. the point where, by at~a action,

they replace the phoaphate iona held by the ~ion exchange oa.plex (SO, 17.156). The w.ter aoluble phoaphorua in the olay auapendona treated with

calcium oxide waa leas than '! K.E. per 100 ~ · of clay tor all pH values

over ' • Prca pH 7 to 8 there waa a aUght lnoreue in soluble phoaphorua.

The probable oauae of thil inoreaae ia that the increment inoreaae or

phoephate 1ona releaaed from the anion exchange complex tor 1norement in-

creaae 1n pH 11 greater than the 1norement increaae of oala11}Jil. 1on tor the

a.- increase 1n p!I. Above pH 8 thil relationship 11 ·····~~raed ····· and the ····· . ... soluble phosphorus decreaaea with riae in ~R · tbla rel&itont.hip.... ~ be .·...... expreaaed aa rolla... ror pn 7 to 8 .!·· .~·· ··~·: .·..... ·:. ....··· · and for pH valuea above 8 (I'Ioa~~t.. ) <(c::> where panntheeea are und to 1nd1oate 10!llo aotirlty. At pH alightly above 8 the clay ._. 100 pereent oalo1ua aatuNted. Below thil ntuNtton point the oat1on exchange ccaplex or the clay abeorbe addad oala1ua tone and grel\tly ndl!on their w.otlvity b ~o oclut1on or th6 clay auepenl1on.

Above the nturation point the cation exchange complex haa greatly re duced capacity to abaorb added caloiua lone and they re11111in tree in inoreaeing quantitiea to react with phoaphate 1cn1 0 thua reducing the W&ter aoluble phoaphorue.

'l'he reaulta obtained are 1n general agreement with repcrtl by

RaTiko'lltoh (:55). llbo oonduated almilar etudiu with an acid ao11.

:2~523 The clay auepensiOilll titl"&te4 with aodiua hydroxide contaiDed no cal

oiUIII ions and thoee treated with c&loiull oxide contained no eodiUIII ion••

Therefore, the reeulte repreeent ertre• situation•• In naturally occur ring baaic and alkaline eoill, the chancel of obtainin~ a aoil with either

1oclium or oaloiuaa• the only exchangeable oation ia rather impr obable.

Ronnr, the reeulte are incUoatin of the aolub111ty of ph01ph&tee in aoib dOIIdnated by exchangeable eodiua or exchangeable oaloiua. In 1o1la wh1oh are doiii1QI.te4 by oalclua and contain cOillliderable quanttt1.. of oal• oium oarbomte, the -tor eoluble phoephorua I.e undoubte4ly 1-r than the

'ftluea found in the clay eu1penaloaa treated. with oaloiua cu:ldeo In 10111 dominllted by exchanceable eodlua the activity or the oaloiua iona 11

reatl y re4uoed, and therefore the reaulte obtained repre1ent trende ot' the eolub111ty or phOiphorue 1n lodiua aou..

fHE PBRK!W!ILlTY OP P!IOSI'fTORUS TO ROOTS aP I!EAN AND

TCW.TO PIAB'l'S OVER A pH lWTGB PROM FOUR TO lfiWB

~ The 1111Jtho4 ueed in thh atudy h a 11041f'1oatlon ot a •thod dewloped and deaoribed by t.uritaen ( lo&) . r-to and bean planta wre gown in the greenhouH in ,.allon pote filled with PJre quarta 8&nd o 11\ltriente wre aupplied to the plant• troa a nutrient 1olution whioh wal dripped - t., +.htt ll&nd~ The p<'ta ~CIItained hoba in the ba!;tome 'll'hich t.llond frea drablageo 'l'he baane wre allond to grt1ft for 6 weeka and tbe t-toe• ft:~r

6 week.. 1'hen, for a three-day period• they wre g1't'en a nutrUnt eol• ution to llhioh no phoephatee ..re addedo At the end of' thb period, the tope of the planta were out orr. leaving about 2 inohea of the etema standing abow the lando 1'he pate were brought into the laboratory and the aand aJJd roote wa1hed with a 1olutlon of lcnt1fiD pH and knt1fiD phoaphate 15

content. The washing was continued until the aolut1on coming out of tho

sand Will of the desired PH• The hole 1n the bottom of eaoh pot waa then

se&.led with a rubber etopper and sufficient solution was added to ocmpleto•

ly saturate the sand. The pote were then tranafered to a preuure chari>ero

Rubber oonnectione were uaed to connect the abort atema to glaee tubing which led to the outeideo TWenty- five lba. per Lq. in. air praeaure waa then applied to the chamber and the solution forced throuKb the roots.

The solution Which cs.me from the roots waa oaugh:t in sall Erlenmeyer flaskso P'1!PlreB 3 and 4 show the aPI*ntua u1edo The preaeure was minoo tained for a period of 4 houn. The eolut1ca was then drlined from the land and the pli determined. Samplea were taken of the aolutioa 1n the sand both 'before am arter the pressure pariodo The p1J of the solution in the sand during the four-hour period was aeaumed to be the IIJ!Ian or the pH before an4 the pH after. The aample1 of the eand solution and the aamplea of the solution Whioh came through the roota -re analysed for phoaphoru•• The solution which came from the roots 11111 be called the ex preeaed eclut1ca and the aolution 1n the eand will be called the aolut1cm around tho roots.

pH relat1omhipe

F1gurea 6 and G 1h01r the relationship between pH ef the aolut1on al'ound tho roots and the oonoentrat1on or phcsphorua 1n the expressed sol• ut1on. The phoaphorua concentration of' the solution around the roota waa held at approxt.ately 46 p. p. m. Each small circl e representa the reaulta for one plant for one prcseure period. Regression linea are ahmrn where there h a aignitioant correlation and no· linea are ahmrn where the cor relation ie not eignifioant. The reeulta obtained with toato roots are not llr;ni!'ioantly different from the resulte obtai.ned with bean roots. XC

F1~re 8., ~otograph of the a,::.paratue used ill forcing soluti Oil throuljh plEil!'t rootc. Aptlll"'tul'i b s OWD 1111 Qper&t:iOlh

Figure '• Photograph of the apparatus u1ec! ill foro1nr; eoluticm t hrOUI';h plant roots • ApparU.tua it shown with the top of the PI'"•~• chQI)er "mnec! ehCJII"o 1ng tho method ot oo~m&oting roo".ol to t he delS:vory tubee. 25

0 ~ 0 a: - 0 a: 0 0 I 20 0 z 0 0 0 0 0 0 0 ..... ::I oi 0 ..J 0 0 0 I 0 0 0 0 0 o0 I I Cll I 5 0 ~ u 0 0 0 UJ 0 0 IS36.8-3.24X (/) 0 I (/) 0 0 0 UJ 0 0 I og 0 0:: ~ n a.. 10 X 0 '0 UJ uu~0 8J I 0 ° 0 z 0 8 0 a.: 0 0 5 " ~

4 5 6 7 8 9 10 pH 0 F SOLUTION AROUND ROOTS

P1gure 5. The relationahip b~Ml the pH of the eoluticm around the root& &nd the phosphorus content of the soluti

~ 0.: 0.: I z 20 0 0 0 0 0 0 I- 8 0 0 :::::> 0 _J 0 0 0 0 (/) 0 15 0 0 ~ w 0 0 0 r---Y= 34. 4- 3.02X (/) 0 0 0 (/) 0 0 oo 0 0 0 w 0 0 0 a:: 10 c.. ~0 0 0 0 0 X 0 0 w 0 0~ 0~ 0 ~ z 0 0 §0 8 0 rs 0 a.: 5 !81

4 5 6 7 8 9 10 pH 0 F SOL U T I 0 N AR OU NO ROOTS

Figure 6. The relationship between pU of tho solution arouod roots and the phosphorus oontent of the solution after foreinf, thr ougb the r oots of tomato plants. ( ~cspborus oontent of the Polution around roots held at 45 P•p•m.} 19

There waa no Jmaaureable ohe.nge in phosphorul content of the expre1eed aol ution with ohe.nge in pH over the acid range. Oftr the alkaline range there wae a deoreaae i n phouphorua content of the expressed solution with in oreue in pRo There was no obaernd correlation between pH and the amount of expreeaed solution collected during a four-'-.our preaaure periodo The pH of the expressed solution, for all pH ·value• of the solution around the roota, varied between 6o5 and 7.2.

The solution around the recta -• prepared tr011 a o0009 molar 1olution of acetic acid by adding phoaphorua ae orthopboaphorio acid and titrating with aodiUII hydroxide to the dea1red pn. Subatitution of potaadUII bf droxide for eodiUII hydroxide gne aimilar reilulta. Furthel"lllore, the addi tion of aodi\111. bicarbonate and aodiUII carbonate to the aodiUII hydroxide solution to inoreue the buffering power in tho alkaline pii range did not change the results. This i ndioatea that t he roault1 obtained are not unique to eodiUII hydroxide induoed alkalinity.

The dooreaee in phoephorua content of the expreaaed solution, with inoreaae 1n pll of th.e aolution around tho roots over the alkaline pH range

1a interpreted as a decreaae in permeab ility of tho i'oota to phosphate ions.

This decrease i n pen.ability ay be explained in at leaat two waya 0 The a,ro; ion •Y be tho phoaphate ion IIIOrt easily aaaiailated by plant., aDd the deereue in pel'lleability illlly reault trOll the deoreue in concentration of t hia ionJ or, the increase in hydroxyl 1011 concentration, associated with 1norsue in pH, •Y produce phyaiologio&l changes in the rcot anabranea resulting in a deoreued per.eability to phosphate iona. The d1.ta presented in figs. 5 and 8 do not favor the decreaae 1n RzJ'Oi ion u an ex-planat1011 because in the pii range tr• 4 to 7 the rel.athe concentration of thia ion ie decreased a pproximately 50 percent {see fig. 1), but there waa no de crease i n permeability over thia pH range. A phyaiologioal change in the 20 root membranae, associated with increase in pH, seem. a more logical ex planation for the result• obtained in thie study. Buehrer (1~) after a consideration or solution culture data presented by KoOenrge (26) and reazeale and McGeorge (11), d1eouaeed both or theee poaaibilitie1 and placed more emphasis on the explanation involving the H2PO. phoaohate ion. Data from a more recent aolution culture atudy by Arnon, Fratcke, and

Johnaon (4) favor tho explanation 1nvolT1ng a phyliologioal change in the root membrane•, a.,ociated with inoreue in hydroxyl ion coll,centration, beoauae only at pH wluea above 1 was there a lignifi<'ant deoreaee in phosphorus assimilation with increaee in pHo

The reeult1 obtained agree with the work ot Pierre and Pohlman (~2), who amlysed the el

Concentl'!!.1~ relationehiR,•

There wa1 aOIIIIS difficulty esperienoed in keeping the aolution around the roots at a .constant phoephorue concentration. The aolution al-ya contained a hi&her concentration of phoaphoru1 at the end or the preaeure period than at the beginning. For a great majority of the teatl the average or the phosphorus concentration at the be,;inning and the end or the pressure period was oloae to 46 P•P••• Beoauee the increaee in phoa• phorue concentration was greateat at acid reaction• moat ct it was attributed to the diasolving action of the uffer aolution on the pho .. phatee precipitated in the eand• Some or the inoreaaed phoephorus concentration in the eolution around the roote probably resulted alae trom the relatively low phoaphorue content of the exprepeed &Q!ution. Because of the "f&riatione in phoephorua concentration in the solution around the roots a study was conducted to find the relationship between 21 such variations and the concentration or phosphorus in the expreesed eol• ution. The phoephorue concentration in the solution around the roota •s varied trom l to 85 p. p.m. with the pB held at 7 for one series of teats and at 9 for another eorielo The reeults obtained with rooh ot tamato plant• are presented graphically in tigo 7 and those for bean roots in fig. So 'lllth tomato roota there waa no lign:l.tioant correlation between the phosphorus concentrations of the expressed eolution and the aolution around the roots at either pH value. The phosphorus concentration in the erpreaaed solution at pH 9 was consistently lowor thAn that at pH· 70 in dicating that over the entire range ot phosphorus concentration, the permeability or the roots to phoaphate ione was lese at pH 9 than at pH 7. Similar results were obtained with bean roota and with t,..to roota, e,.. oept that with beana in the pH 1 aeriea a poeitive correlation wae obte1ned between phoephorua in the expressed solution and that in the solution around the roots over the ranr,e ot 46 to 86 p. p.m. Jo auoh trend waa ob served with tomato roota. The abeenoe or a positive correlation between the phoephorua ooncen• tration or the eolutlon around the roots and the phoaphorua concentration or the erpreeaed eolution aug~ate that the roots -re able to concentrate or screen out phosphorus Aepend1ng on the phoaphorua concentration around the roote. It also su r,ests the poeaibil:l.ty that the phoaphorue ooatent or the expressed solution depends to acme ertont on the amount of phos~ phorue already in the roote ,; There 11 evidence tor and against thia poedbility. Tomato root a frOII ·IiX planta -re -•had olean of aand , w1 ped dry. and then placed without water in the preuure ohalllber . !he expresaed aolution obtained woold then be that which wae .. lready in the roota. Preuure wae applied until no more aolution could be obteined from the roots.

From 6 to 14 IIIla . of erprened eolution waa obtained froa each plant and ::£ a: 20 ll a: I I z AT pH 7-- 0 0 4> t AT pH 9-- + => s ...J 5 -I- --C 0 (f) 0 C• c " 0 "" 0 " I ., ~ 1 0 r rr (l (' -t c I") :< w ,... ( 0 8 c ' r (f) ~B 9 (f) 10 -"- ---<)-- r -+ - w >n4> " ic c i c:: t • it ~ ... (l_ " ~ 't ... t ,. ~ X t (J + + w ' i -. ' t + t ~ _,_t 1 z sr-- - - - t a.:

' _j 0 '------0 10 20 30 J40 50 60 7 0 B 0 85 P. IN SOLUTION A R 0 UN 0 R 0 0 T S- P. P. 1'-4.

Figure 7. '!'he phoephorue content or solution preaeed through t..ato roota in relation to the phoaphorua con tent of the aolution around the roota. 30 ') :f I 13 a: a: _)n I 25 z AT pH 7 ---o 0 ty;2. 2+ .2 0 I- pH 0 AT 9---+ 0 ::::> n .....1 20 ">f' 0 8 13 (f) 8 oo 0 0 0 0 0 Qo~ v 0 w 15 •n 0 (f) 8 (f) 0 t- 0 w + + a:: + 0 a_ 0 oo 0 0 X 10 n + w + " + 0 +- 0 + 0 +++.... t z 0 t t+ + + t 3: +- + + a.: 5 + + + r:t:- T

0 10 20 30 4 0 50 60 70 eo 85

P I N S 0 l U T I 0 N A R 0 U N 0 R 0 0 T 5- P. P. M.

Figure a. The phosphorus content of solution pressed through bean roots in relation to t he phoaphol'lla cont!!lnt of the aolution around the roots. 21

these solutions varied in ph os phorus oonoe~rat1 on ~o~ 8 to 18 p. p. m.

This shows that there was so~ phosphorus a lread~r in the roots whioh rra.y have tnrluenoed the results and whioh undoubtedly caused some ot the var iations found. Another group of tomato roots frOIIl six plants were put under pressure lll'ith distilled water around thQ roots. The awra .. e phos phorus concentrat i on of the expreaaed solution for the tirat two-hour

period was 11 P•P•nh For the aeoond two-hour period it waa 7.6 P•P•m• and t hen it dropped to 4.4 P •P•~• Thia indicate• that without a aupply of phos phorus t he phosphorus in the roots is soon washed out. However, all of the roote used in obtaining the results were used for three pressure periods, and most of them used for four pressure periods with no unusual reaults noted for the first period. Therefore, the phosphorus alreaay in the roota probably can be dismiaaed as a major factor in producing the o ae~ved re• aulta.

The results presented do not agree with the results obtainu~ br POhlman and Pierre (33) who found a positive ocrr.lation between the exuded sap of corn plants and the water soluble p osph orua in the soil. The different type of plants used and the different technique and method used in oolleot i n ~ the sap may account for this di•orepanoy.

DISCUSSION

Ths phya!ologieal availability or p~oaphatea, ~£ ~aQUrod by tho permeability of roots to phosphatea, is a fUnction of pH. There was no change in pel'lllaability of roota to phosphatee with change in pH froa 4 to

7• but ~om pH 1 to 9 there was a decrease in pel'lll"ability with increase in pH. This decrease doea not seriously reduce the amount of phosphorus coming through the roots until the pH 8 1a exceeded. Therefore, it' the discussion is limited to pH valuea from 4 to 9, which is the range in which moat plants grow, physiological availability 18 only ot' importance in the 26

alkaline range and of major importance only where pii 8 1a exceeded. The net availability of phosphates is a function of their solubility and pbyaiolo ical availability. Fr011 pn: 4 to 7 the net availability 1a large l y determined by solubility. From pH 7 to 8 aolubility ia probably the dominRDt factor with physiological availability taking a place of minor importanoe. When pH 8 1a oxoe&ded, aolubility and phyaiological availability may be of equal importance. However, there ie a possibility

that, i~ a b ! g~ leT&l of soluble phoe phatea ie maintained over the entire pH range, plante will be able to assimilate adequate amounte of phoaphatee.

At hir,b PH valuee, where the phyeiolo~ioal availability of phosphatee ie low, plants are ueually reatricted in uowth because of factors other than the lack of phosphatee, producing a low phoephate requirement. In a eoil eyatem dominated by aodium the net availability of phoe• phatee probably ie, in moat oaaea of poor growth of planta, not the limiting factor, Solubility of phosphate• in lodium ao11 ayateu ia uaually high and ueually increases with increase in pHo Whe~ the pH of a sodium 1oil 1ystem is high enough that tho physiological availability of phosphatee 11 low, the plantl are probably ao restricted in growth by other factor• that tho phyaiolo ioal availability of phosphate• 11 no hindrance to t heir nutritiono In tact, under theae conditionl planta may show an increue

1~ phoaphOrue , on a percentage basil, with increase in pH (41 ). In calcium dominated soils the net availability of phosphate• ia usually low because of their low aolubllityo If the pH i1 increased to the point where physiol ogical availability il important, the not avail• ability is reduced to an extremely l ow value beoauae in a calcium system both solubility and phyeiologioal availability decreaee with 1ncreaee in pH. Howo"Nr, the pH or moat naturally ooourring calcar eoua aoill in their natural state in the field probably seldom exceeds 8. 6. Therefore, in 26

oalo1um dominated soils, phya1ologioal availability ie undoubtedly not as important as solubility in determining net availability. Phosphate solubility studies show that phoephate solubility in soils

cannot be directly related to pH ·unleu the type of' soil ayatem 1a apeo• ified. With a sodiua system the solubility oharacteriatica tor certain pH ranges are directly opposite from the characteristios round in calcium eyatema . How.wr, when the aoil syatem 11 specified, pH may poaaibly hAve

acme value eG ~n approximate index to the phosphate aolubility. Emph&lil ahould be placed on reaotion and changes which ooour with

chance in pH rather than on pH itself. The physiological availability of phosphatee is a flmotion of pH, yet, owr moat of the pH range of impor tance to the culture pf plants, solubility of phosphate• is the more

important faotor and at any pH value the aolubil1ty a;y nry tram one ex• treme to the other, depending on the t 3~ or soil aystem. .Albrecht (2) 1 in diaeuasing the significance of pH, stated that pH oannot be oloaely related to orop production if the pH r-ina o0111tant and other faotora fluctuate widely. Hoagland and Arnon (21) atate that pH oan only haw

1111aning '!hen used as a mea~rurelll8nt reflecting the interaction of several factor• peculiar to a epeoifio aoil.

With ~!ally aoib the -.tor aoluble phosphorue h aeldom greater than

1 p. p. m. and most phyaiologioal availability ltudise haw involved phoe• phorue concentrations hi~er than this. A 1110re thorou~ underatanding of how phyalologioal availability affect• the net availability or phosphatee under oollditiona of low solubility, •hould be uset\11 inf'oration. The rate of movement of phoaphate iona through plant root• h&l been auggeated as a factor which Day have affected the phoapborua oonoentration in·the expresaed solution obtained by foroing aolution through roota. The uae of radi o-active phoaphorua should give information on the rate of 27

movemont of phosphate 1ona, under these apeoific condit1ona, which would

un4oubt~dly help improve the ~thod &nd hel p interpret the results ob•

tainecl.

SUl!I4ARY

1. Inveatigationa· of' the sol ubility of' phosphatee i n eodiwa and oal•

ciuM clay auapenaiona and of the permeability or plant roota to phoeph&tes

onr a pH range f'r'oa 4 to 9 h&ve been conducted, A measure of the perm~Ja bility of' roots to phosphatee wae obtained by forcing aolution thr ou gh roots of tomato and bean plt.nta by tneane of air preeeure.

2, The aolubility or phoaphatea, tor all plj' wlu81 between 4 and 10, was hi~er 1n eodiu111 t han in calcium olay suapensiona. Thia difference was greatest at alkaline reaot1ona.

s, There waa no meaaureable change in the pe,._bil1ty of roots to phoephate i n the aoid pH range. In the alkaline pit rants there wa1 a d. oreaao in permeability with lncrea1e in pRo

-'• The phyeiologioal auilability of phosphatee, &I meaeured by the permoability of root• to phosphatea, ia a function of' pH, and ia important at alkaline reaotiODio

6. The net a'V&ilability of' phoapbat ee ia a fUnction of' their aolu• bility and their phyliol ogical availability. OYer the acid pH range from

4 tQ 7 f:h<'l net1 P.w.ilabili ty 11 largely a t\Jnot1on of a o l"b~Hty . t'ver the alkaline range f'r'om pH 1 to 9 phyaiologic&l auilab1Hty ia illportant, but

1olubility ia probably the ~e ~ortant of the two taotor ao s, The physiological aT&i labi lity of phoaphatea 1n aodiua and calcium aoU eyste11111 my seldoa be the liaiting factor in pl ant vowth, providing phoaphate solubility is held at a high le~l , 28

Literature Cited (1) Abbott, G. A•• and Bray, w. c. 1909 The ionization relations of ortho- and pyrophosphoric ac1de and their sodiua salta, Jour. Amero Chem. Soc.• 3la729-76l5o

(2) Albrecht, l'lln. A. 1941 Soil organic matter and ion availability for plants. Soil s.cio 51 a 4~7- 494 o

(S) Allen, Ro Jo L. 1940 The 'estimatlcn of phciephorua . Biochem. Jour. Mt858·8G5, (4) Arnon, Do I ., Fratzke, w. E., and JcbJJaon, ·c. 11. 1942 Hydrogen ion concentration in relation to abaorpUon of 1n~rganic nutrient• by higher planta. Plant Fbyaiolo 17t515-624o .

(5) Banett, H. 1917 The phosphatee ot calclum. Jour. Chem. Soc, (London) 11lt620.642o ·

(6) Bate•• Ro Go, and Aoroe, So Po 1943 pH valuea of certain phosphate chloride ~rea and the aeoond diaeoc1at1on constant of phoaphorio acid f'r'om 0 to 60°, Jour. Rea. Natl, Bur. Standarc!a. SO t 129-166o (7) Behrene, Wo u. 1935 The aaaim!lation by planta of phoaphoric acid combined with calc.1um, ztachr. Pflanzenernahro Dung. Bodenk. S9tl50l• 309, (Chem, Abl o 20a6999)

(8) Benne, !. J,, ~rkina , A, I ., and Kin«, R, u, 1916 fbe effect of calcium ions and reaction upon the aolubillty ot phoaphorua, Soil So1 . 42t29- se.

{9) Bowar, c. A., and Turk, L. v . 1946 Calcium and l!ap!eaiua deficienoies in alkali eoUs, Jour. Amero Soc, Auon, S8 t'723-727,

(10) Breazeale, J , Po 1916 Effect of sodium salta in water culture• on the absorption or plant food• by 'Wheat aeedlinga, Jour. Agr. Rea , 7t407-416.

(11) and MoGeorge , w, t'o 19S2 Jlutritloml dilordera in alkaline eoils ae oaueed by deficiency of carbon dioxide, Ariz , Agro 'Expo sta. Teob. Bul. U . (12) Britton, Ho To s. 1927 Blectrometrio study of the precipitation of phosphatee, Jour. Chem. Soc, (London) 1SO t614-6SO.

(lS) Buehrer, T. F. 1932 The phyeioo-chemlcal relationah1pe of aoil phos• phateao Arb o Agr. Expo Sta, Tech. Bulo 42, (14) Cameron, F. r., and Bell, J, 11. 1907 The action or water and aqueoue eolutiona on soil phosphatee. u. s, Dept, Agr . Bur• Soil Bul o 41 o

{15) Handboolc or Chemietff and Pbydo•• 'l'wentiy•nintli Edition. 1945 Ch8ili!cal Rubber PUb shin& Co , Cleveland, Obi~ ,

(16) Cohn, e, J. 1927 The activit~ coefficient• of the lone in certain 29

phosphate 1olutione. A contribution to the theory of buffor action, Jruro Amero Chem. Soo . 49t17S.192o

(17) DMn, L. A., and RubiM, Eo Jo 1947 Anion exchange 1n eoilao I Ez• changeable phoephcru1 and anion-exchange capacity, Soil Sci. Gilt 1177-387.

(18) Ebenberger, s., and tehran, A., and Turner, 11'. D. 1940 Tho bailie calcium phosphate• and related eyeteme o Some theoretical and prac tical aapecta 0 Chemo RaY. 26a267•296. (19) Eneminger, L. E., and Lareon, H. w. g, 1944 Carbonic and soluble phosphorua and lime content of Idaho soila in relation to crop re• aponae to phosphate fertil1cat1on. 8011 Sol. 68a26S.268o

(20) Gardner, Re, and ~alley, o. J. 1940 Relation of pn to phosphate aolubllity 1n Colorado •ella. SoU Sci. 60a91·102.

(21) Hoagland, J) , R., and Arnon, D. I . 1941 J'hya1oloc1oal upeote of an1lab1Uty of mtrienta for plant owl:h o Soil SoL. 6lt431.....,.

(22) ~obe, Xo At, and Drusni, 'ro F.. 1937 Uml.etzung &Wiaohen felton Steffen und Loaungen. I Caloiumphoephate und m&tr1umoarbonat. Ztaohro Anor~ . Allgem. Chem. 2112a319-S2t. (211) l[,.,.r, B.,. and Sh&ar, v. J. 1928 Compolition of bone- primary oal• cifioationo Jruro B1olo Ch.mo 79al47•160o

(24) Lauritsen, c. 11'. 1934 Diaplacement of eoil eolublea thrrugh plant roots by -n• of air preaaure a• a method of 1tudyinr; 1o1l fertll• ity problema. Jour. Amer o Soc. A.grono 26t80'1•819o (25) Logan, v. A., alld Taylor, a. L. 1938 Solubllity of bona •alt. II Factora affecting ita formation. Jour. Biol. Che-. 125tS77-S90o

(28) JfoGeorp, ll'o T. 19S2 Bleotrodialylia 11 a -eure of phoephate availability in eoile and the relation of soil reaction and ionbation of pbospbat81 to phosphate aadmilation. Arb. Agr. Ezp. sta. Tech• Bulo sa. (27) 19S9 Faotora 1nfluanoing the availability of native totl ~~oe~~~ and ph~aphate fftrtilic~rs tn Ari1~ eoilaa A~ic ~ Agro Expo Sta • .1'eob o Bul. 81.

(28) 1935 The relation of potential alkalinity to the available phoapbatea in oaloarecua • o1la. (29) , an4 Breaaeale, Jo r. 1931 The relation of phoapbate aftilabiHty, soil permeability, and carbon dioxide to the fertility of oe.lcarerue ao1la. Arb .. Agr. Exp. Sta. Teoh. Bul. S6o

(SO) lbrpby, Ho Fe 1939 The r ole of kaolinite in phosphate fixation. Hl l~rdia 12a343-S82o

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(33) Pohl~, G. G. , and Pierre, w. H. 1933 Phoaphorua concentration of the exuded sap of corn aa a measure of the aftilable phoaphorua 1n the soil. Jour. Allier. Soo. Agron. 26t1G0.170. (34) Prideaux, E. a., and r..rd, A. T. 1924 The diasooiation oonatanta of phosphoric acid. Jour. Chem. Soc. (London) 126t,23-42G. (35) Ravikovitoh, s. 19M Anion exchanger II • Liberation of the phos phoric aoid absorbed ions by soils. Soil Sci. 38t279-290. (36) 1938 Influence of exchGngeabl e cations on the availability of phosphate 1n eoila. Soil Sci. 47t367•366. (37 ) Samokhvalov, c. z: . 1938 The influence of the transpiration atream, the pH and the phos ph orus concentration or the 11111diwa on the absorp tion of phosphorus by plants. Chemisation Socialiatic Agr. (U.s.s.R.) No. 7•8t26-29. (Chom. Aha . 3lt6284)o

(38) Sima, ~niti 1939 The numerical valuoe of tho aocond dissociation oxponont of phoaphoric acid and factors influencing it. I Experi• mental studies on the d1aeoo1at1on oonatanta of phosphoric acide Jour. Biochem. (Japan) 29~121•146.

(39) Stout, Po R. 1939 Alteratiom in the crystal atructure of clay min erala aa a result of phoaphate fixation. Proo. Soil ~o\o Soc. Ame ro 4tl77•1Bl. (40) Toakle, t . J. H. 1928 Phosphate in the soil solution aa affected by reaction and cation oonoentrationae Soil Sci. 26tl43•16l0 (41) Thorne, o. w. 1946 Calcium carbonate and exchangeable sodium 1n re• lation to the awth and composition of plants. Proo. Soil Sci. Amer. lls397-40l. (42) 1944 Growth and nutrition of taato planta as in-

fluenced by exchangeable eodiu1110 oalo1wn, and pot...uiua. Pl•oc:.. Soil Solo Amer o 9tl85-l89. (43) Tidmore, J. w. 1930 Phosphate studies 1n solution culturee. Soil Soio 30sl3-3l. (44) Wi lliams , a. 1937 The solubility of soil phoaphorue and other phos phorus co:npounda in sodium hydroxide solutions. Jour. Agr. Sci. 271 269-270.