.1,.
A LEGUME-BASED, PASTURE PRODUCTION STRATEGY
FOR ACID INFERTILE SOILS OF TROPICAL AMERICA
by
Pedro A. Sanchez
This report is reproduced under an agreement between;lthe author- Dr. Pedro A. Sanchez of North Carolina State University, and the Office' of Agriculture, Bureau for Science & Technology, U. S. Agency for International Development, Washington, D. C. - August, 1981 I•. , ~f. . " 1"
" •• " 11 A LEGUME-BASED, PASTURE PROOUCTION STRATEGY FOR ,I 21 ACID INFERTILE SOILS OF TROPICAL AMERICAli I vi00 Pedro A. Sanchez~/ 41 ~I INTRODUCTION 6 Tropical America (from 230 N to 2305 of latitude) can be divided into 7,two broad soil regions at the highest level of generalization. I - Region ,A'I ~!with predominant high base status soils of the orders Alfisols, Incepti- ! I oc:::::= p I 91s01s, Mollisols, Entisols, Vertisols and Aridisols, covers about 30% of ;~ '-- ::::> - C> .. , , II 10 Itropi ca 1 Ameri ca, connnonly w.i th dense rural popul a ti ons . Regi on B, wi th I, l~:pr,dominant, aci4 infertile soils (Oxis91s,_ Ultisols,:u acid- Inceptisols 12iand acid sandy E~tisqls) covers the remaining 70% (1043 million hal, and _:;.,! 4C!> ..':has mainly lovi population densities (Sanchez and Cochrane, 1980). I-t~, Two main strategies for increasing food production exist in the'
15;tropical, portions of this hemisphere: 1) Increase yields in presently :':'cultivated, areas, mainly high base status soils, and 2) expand the agri- :7:cultural frontier in the vast areas of acid infertile soils mostly under lo:savanna or forest vegetation. Sanchez and Cochrane's analysis suggests
l~ithat these two strategies are complementary rather than competitive, and nol ' • - Ill/ThiS paper represents to a large extent the existing position and 21 strategy of CIAT's endeavor to bring marginal lands in Latin America into economic production. It draws heavily on the research carried 221 out by many investigators within the Tropical Pastures Program (for merly Beef Program) and associated special projects of CIAT. The 23 paper largely reflects the experience of the Program, synthetized by , the author, who was Program Coordinator from January 1977 to May 1979. 24' 25!S;presentlY the author is Professor of Soil Science and Coordinator, I Tropical Soils Program, North Carolina State University, Raleigh, nGI N. C. 27650. - , ! n--, , ~,------~ i, " ( ".. " " 11 2 i oJlthat the interacti~n between them i,s already playing a m~jor role in the :,o~erall agricultural development of many Latin American countries •. A I ~Ithird strategy, increasing irrigation, is very limited in areal extent, , . , although locally very important. " 6 ( The countries of tropical America have a combined population of 378 " 7 million inhabitants as of 1980, and are growing at an annual rate of
~ 2:7%, which doubles the population every 24 years. To maintain the ,Ipresent and largely inadequate level of per capita human nutrition, food .J I 10isuPPlies must also double every 24 years. FAD, (1979) estimates that 55% 1110f food production increases will come from opening new lands in Latin 121America and 45% from increasing production on land presently under culti-· , " "[vati on. The vast majority of the rural population is located in Region A,: .v. . , , / , . !mqinly in coastal or highland areas. Increases in population density
''''I • y size of traditional farms to decrease. Farmers then attempt to: 15!cause, the
,o:cultivate.1..': • marginal land beyond its limits of slope, causing severe soil I • . _'erosion. This, in turn, forces large scale migration of farmers to the , , .slums of major cities. Tropical America at present has two cities with .l.:: I ,clover 10 million people, three others with over 5 million, and 18 others ~~, 20 with over 1 mill ion people each (Sanchez and Cochrane, 1980). Displaced 21 rural populations add major unemployment and welfare problems to these • ?,!cities. An alternative for these displaced people is to settle in the acid • ::1, 1 n,jinfertile soil regions, and in certain cases this is a viable alternative! "'''I I 25lHowever, lack of sufficient knowledge on how to manage these soils, plus
~ ,lllimited infrastructure, credit, and accessibil ity to markets has caused _tl ! !many settlement efforts to fail. 27 ~ ------~~~------~ . .. \~~: .. , .' 1 .·3
2 It is not possible to quantify the consequences of soil erosion in
3 tropical America at this time; some generalizat;-ons, however, can be 4 made. Visual evidence of gully and sheet erosion are most prevalent in 51ustiC, densely populated, high base status soils, mainly on hillsides I 6 along the Andes and other steeplands in Central America and the caribbeani 7 The presence of a strong dry season is crucial because the soil is left i I R unprotected by a crop canopy at the beginning of the rainy season, when c I 9 the danger of water erosion is highest. The situation is worse in semi- I / ,I lolarid or arid climates. , In udic soil moisture regimes, where there is no significant dry III i, l~ season, soil erosion is less of a problem, since there is usually a plant!
., ~ cover protecti ng the soil throughout the year. This is the case in much ~VI I ; 1 l~iof the Amazon where secondary forest regrowth covers the soil when crops I • I. . . . .'. . . !, 15'lare not growing. Visual sheet or gully erosion in udic areas of the I IG.Amazon and other similar regions is mostly caused by civil engineering , __ :rather than agronomic mismanagement, along the roads, farm pathways, and 1,las a consequence of improperly designed drainage and sewage outlets. These observations do not imply that erosion is unimportant in udic 20 regions, but that it is more extensive and critical in ustic and aridic 21 regions. Erosion hazard is very important when the soil surface is 22 exposed by conventional plowing in udic regions, This is seldom done by 23 traditional cultivators, but newcomers to rainforest areas often cause 24jsevere soil erosion in steep mountain hillsides while planting food crops 25l(watters, 1971). The same occurs when pastures are overgrazed, or when 26iland in permanent crops or pastures. is converted to annual crop produc- o_lt1on.I . -, .LI ______~ " 4 POSSIBLE SOLUTIONS
r '. The best methods of erosion -control are good soil. and crop 'management .;. practices, particularly those that minimize water runoff and improve , , C water infiltration. (Lal, 1980). The adaptation of, this fundamenta'l ·con- G cept to tropical America involves both the stabilization of erosion-prone
~ , , areas under dense populations, and the development of prod.uctive. econom- , , ~ ical1Y and ecologically sound management systems for the acid infertile ." ( soilrregions, the latter in order to provide ~ viable alternative to :C urban mi gra tion. " ' The purpose of this paper is to describe the development, of one :~ strategy for the Oxisol-Ultisol regions, the use of low input. legume- , .c.;:: ,'. :lased pastures. Not all the components of this strategy are yet in ,. - .~ place,; therefore, several gaps are recognized in this paper. There are
. , other viable strategies for Oxisol-Ultisol regions such as changing from , annual .to permanent crops like rubber, oil palm or forestry (Alvim. . 1977). These crops keep the soil protected by a plant canopy the year "around. Another one is the continuous cultivation of annua'l crops under :: moderate to 'high fertilizer inputs to correct acid soil infertility, ·"')n -. ilhere economics and infrastructure considerations make i.t feasible
~. -- (Sanchez, 1977)'. By growing three crops per year, the soil is protected' 2~ ~y ! plant canopy most of the time. There is no question that most ~:o Oxisols and Ultisols with no serious physical limitations can be contin- , 2~ uou~lY and profitably managed for intensive food production in tropical ,= -~ Ame!'ica, provided the pric~ ratios of chemical inputs. to farm p'roducts , ~,: are sufficiently attractive (Vicente-Chandler et ~., 19711; $anchez,
1977; V.alverde et a1., 1919 . .,
" 5 In the majority of the savanna and rainforest areas however, the
?vi economics of high input use are seldom attractive, mainly because of a
'-,i:PQqrly developedsa transportation__ and marketing infrastructure, credit, 5 and the increasing cost of energy. ---Thus, --='~an alternative is presented S,here, at least in its initial stages. I ~I Legume-based pastures are a promising strategy for new land areas , I ~,because the low cost per unit area involved in producing beef with the , ,- 9,animals harvesting the pasture,· storing the product in their bodies and
1(' tr:ansporting themselves away from the farm, if necessary. Beef is one
II ot the basic staple foods in tropical America. Studies sho~1 that fami , l~ lies of lowest income strata spend from 8 to 18% of their total income
~~ buying beef (CIAT, 1979). Much of tropical America's beef is produced
l~ in high base status soils, where unfortunately it competes with inten-
" =,sive crop or milk production. Consequently, a gradual displacement l "'. ;r,:towards the acid infertile soils where beef has the comparative advan- • __ 'tage, could provide alternative uses for the better soils located closer 1, : to markets. · The importance of legume-based pastures in this strategy deserves l~) . • 20iemp1 haS1S. . Several million hectares of Amazon rainforests have been , ?,icleared within the last 15 years and planted to pasture grass species • --,, ??~such as Panicum maximum'without legumes or fertilization. This species ...... i ??!is not well adapted to severe soil constraints found in the Amazon and ~vl 24,sUCh pastures disappear after a few years, causing widespread bankrupt-
?_ c~es and a spreading belief that successful pasture-based beef production _:J , i~posSib1e in the Amazon (Hecht, 1979). ..
,6
COMPONENTS OF A LEGU~lE-BASED PASTURE PRODUCTION SOIL MANAGEMENT STRATEGY
A low input soil management strategy designed to take advantage of ,I , I, ' ~ acid soil infertility for pasture production is emerging as a result of I ., 6 mu.ltidisciplinary teamwork by various research institutions in tropical I, 7 America: CIAT's* Tropical Pastures Program; EMBRAPA's Cerrado Research ! " ,j SI'cen~er (CPAC), the UEPAE Sta ti on at Manaus, and the Humid Tropical Center! / , , 91(CPATU) at Be1em in Brazil; ICA's Carimagua Station in the Colombian , 10 III anos; INIA's Yurimaguas Station and IVITA's Pucallpa Station in the ! ,I -, I''Amazon of Peru, and North Carolina State University's Tropical Soils Pro-! ! 12lgram. Ninemain components of the strategy are described in the following: ,J, I ~~; pages. . 1. Land Resource Evaluation for Site Selection - The first step is to select the appropriate soils, avoiding certain ,_!groups of fertile, high base status soils that are best used for food , . , ,crop production, poorly drained soils that are seasonally flooded, and 1 ::-1 , isoils with severe physical limitations or with extreme infertility such .i..:J1 20las ?podosols. The acid infertile soil regions of tropical America'are , -..
21 mai,hly, under rainforest or sqvanna vegetation. The total area of rain- '/ ~ 22 forest is on the order of 700 million ha and the savanna areas about I 23 30D million ~ Lead .cal,:ula~~ns from the FAD-UNESCO (1971) world sojl .' 24lmap, modified by the author's observations (Sanchez, 1979) plus the re- 25 cent completion of the RADAM soil survey of the Amazon (Ministerio das I 26,Minas e Energia, 1973-1979) provide some estimates of'soil distribution J*See 1 ist of acronyms used at the end of the paper. -.?~, L-, ______~ ______~ :lin the rainforest areas of South Amer~ca. Well drained, high base status 3 soils cover about 60 million ha or 8% of the Amazon. Although many' of I , ~ them can support grass/legume pastures, their higher native fertility 5 gives the comparative advantage to intensive annual food crop production 6 or to export crops such as cacao. In addition, the Amazon has about 742 million ha of poorly drained soils either as flood plains or swamps,
. 8 accounting for 6% of the total. Many of the flood plain areas are al- ~!readY under intense use, such as many "varzeas" in Brazil and many ,- . • ,I 10 1"restingas" in Peru and Ecuador. ll\ Al~o to be avoided, but for different reasons are acid infertile 12'I'soils with severe physical limitations such as shallow depth or steep
-,.V\ 0 slopes, and coarse sandy soi 1s cl ass i fi ed as Psamments or Spodoso 1s wi th 14!extremely low native fertility, severe leaching and erosion hazards, 1510ften (:a 11 ed "Tropi cal Podzo ls . " These two groups cover about 33 mi 11 ion i , 161ha or 5% of the Amazon. Unfortunately a sizeable proportion of the data :7!gathered by ecologists to·warn about the extreme fragility of the.
The total area to which the proposed strategy may apply is there- 21 22 fore, on the order of 560 million ha or ~1% of the Amazo~ mainly 0;iso1sl
, 23 and Ultisol.s. Extremely steep slopes within these areas should also be I
24 a voi dec!. - In the savanna regions- it is less difficult-to identify the sojJs 2ci . • ?_Ito be avoided, but the criteria remain the same. Many o~he islands of "'°1 . __ ~ __ \..., ?_!high fertility soils are already under intensive production such as in -'~i ______-J 11 8 'lIthe Eastern Llanos of Venezuela. Steep and shallow soil s are read; ly -I o!recognized in the landscape. Large areas of seasonally flooded plains vi 4!suchI as parts of the Western Llanos of Venezuela and its extension into 5 Colombia, and parts of the Beni of Bolivia will require a different 6 management strategy.
7 Although the above generalizations provide an overall picture, ~ actuaJ selection is very site specific. Soil parameters per ~ are not -I , I qlsufficient for appropriate site selection. Land classification there- • I I loifore, is a more useful tool because it also considers climate, landscape, I . "' I llinative vegetation and infrastructure. The land systems approach use~ irl lzllCIATIS Land Resource Study of Tropical America (ClAT, 1978, 1979) ap~ears
~3 to be an appropriate method for evaluating the potential of these vas't ~ I ' 14!areas. Us,ng a scale of 1:1 million, about 500 land systems have been , . _!identified so far, each representing a recurring pattern of climate, l 23 saturati on at a specifi c depth. A fundamental modifi'cation of the USDA Land Use Capability C1assi- 24 25 fication, System has been developed in Brazil to take into account the o"irea,lities._0, of the tropical environment. Ramalho et !l., (1978) defined o_lsix group~, including three management levels for. crops, (low, moderate -I I . 1 9 zlland high input). Input use is interpreted in terms of fertilizer and 3 mechanization, but not irrigation. limiting the system to rainfed agri- I 4 1culture • The highest categories of this system are illustrated in 5 Table 1. Only land classified in groups 3 and 4 should be used for im- 6 proved pastures. Groups 1 and 2 although suited, may be' best used for 7 crop production. s 2. Appropriate Land Clearing Methods ,/ 81, Land clearing is not a major problem in savanna regions where trees I l°iare generally small and widely spaced. Clearing rainforests however. is 11!a tcrucia1 step which strongly influences the future productivity of the ·1 121soi1. The traditional slash-and-burn method is superior to mechanical , 131clearing with bulldozers. because it provides a sharp but tempor.ary in~ 14 ~rease in soil 7erti1ity due to the nutrient content of the ash. avoids 15 soil compaction and topsoil displacement commonly caused by bulldozing ~~Ioperations (Seubert et ~ •• 1977; Sanchez. 1979). The establishment and -~linitial growth qf grass and legume species is significantly retarded by 181mechanical land clearing. giving rise to more intense weed and jungle , 91 ~ regrowth problems. The tangled mass of partially burned logs and tree 20 stumps left by the slash-and-burn method provides an important degree of 21 protection against erosion to the soil while the pasture is being estab- 22lished. These effects have been demonstrated at the experimental scale :!3 in Yurimaguas. Peru (Table 2) and on a commercial scale in r'lanaus. Brazil 24i(~MBAAPA. 1979). :~I There are many cases where 'lack of labor forces mechanized land ~tilclearing., In such cases. the method used should strive to minimize 271 ,~------~ 1 ' 10 2 compaction and topsoil carryover and to include burning in order to take 3 advantage of the free fertilizer value of the ash. Toledo and Morales 4 (1979) bas{~d on their work in PUcallpa, Peru, recommend initial clearing 5 with tree crushers, followed by burning and overseeding pasture species. 6 3. Selection of Adapted Species Tolerant to Acid Soil Stresses 7 The basic principle of this component is to use plants adapted to 8 1the soil and climatic limitations rather than change the soil to meet the 9lp1~ntJs nutritional requirements (Spain et a1., 1975). The use of such 10!p1ants reduces the rates of fertilizer needed, ,but does rlot eliminate the 11 need to fertilize. Research has identified several species and ecotypes 12 ~ that are remarkably tolerant to the main stresses present in Oxiso1- 13!Ultisol regions: Aluminum toxicity, low phosphorus availability, water I 14' stress, insect and disease attacks, and occasional fires. In addition, 15 grass and legume species must be compatible with each other and must 16l_lpers1s . t'1n m1X. t ures un d er reasona bl e grazlng. pressures. -, I Aluminum tolerance. A wide range of GIAT's forage germp1asm bank is lEltolerant to high levels of exchangeable aluminum ~imply because much of 19', it has been collected from acid infertile soil regions of tropical 20 America. An example of differential tolerance to aluminum of four comman 21 tropical grasses is shown in Figure 1 from a culture solution study of 22 Spain (1979). Brachiaria decumbens shows even a slight-positive response • -23 t~ the first increment of 'aluminum, and no growth reduction at high con- 24 centrations. Panicum maximum exhibits strong tolerance up to half the ,'~ . 25 aluminum concentration as Brachiaria decumbens. In contrast. Genchrus 26Iciliar~s, .one of, the most ~idespread tropical grasses in ustic but not 271 :;, -: 1 11 2 acid areas of Australia, is severely affected by aluminum. This ex-' 3 cellent grass is well adapted to non-acid soils, but to grow well in 4 Oxisol-Ultisol regions it is necessary to completely neutralize the ex- 5 changeable aluminum by liming. 6 Figure 2 also adapted from.Spain (1979) shows actual responses to 7 lime, applications in an Oxisol of Carimagua, Colombia with pH 4.5 and 8190% aluminum saturation before liming. Very tolerant grasses such as .' 91AndrOpOgOn gayanus, Brachiaria decumbens and Panicum maximum and the 10\legUmes Stylosanthes capitata and Zornia latifolia produced maximum \ II·growth either at 0 or 0.5 ton/ha of lime. The 0.5 ton/ha rate did not 12 alter soil pH or aluminum saturation, but provided calcium and magnesium , 'l3!to the plants. Other legumes, particularly Desmodium ovalifolium and I,, I 14 i'Puerari a phaseo 1oi des appear, to requi re ei ther more cal ci urn and magnesi urn: ,-lor a lower level of aluminum saturation than the previous group. Yet, J.~I I l,,!their performance is clearly superior to aluminum-sensitive species such I I , I ~~'as grain sorghum and Centrosema plumieri, a legume clearly not adapted tOI l~!acid soils. It is also relevant to point out that some species are ., ialuminum tolerant but do not grow vigorously in acid soils. This is the "~ I ~o case of Pangola grass (Digitaria decumbens), shown in Figure 2. • 21 . Low levels of available soil phosphorus. Phosphorus is the single 22 most expensive input needed in improved pastures in Oxisol-Ultisol i 23 savannas. It is not, however, the only nutrient that is deficient in I 24 these soils, but its correction is certainly the most expen'sive one. No I 25 improved pastures can be established or maintained without phosphorus i 1 ~6 fertilization. In order to maximize the efficiency of phosphorus fer- \ ! 27!tilization, it is possible to select plants that have. a lower requirement! I :. ! 12 '-. of phosphorus for ll!axiJllum growth than those c0llUl1on1y used. Fortunately, -: ' , 'a1 umi num tolerance and "low phosphorus tolerance" often occur joi nt1y "I ~ibecause the latter seems associated with the plant's ability to absorb sand translocate phosphorus from the root to the shoot in the presence of Q high levels of aluminum in the soil solution and in root tissue (Salinas,.J - 1978). I ,I . ,i Table 3 shows examples of promising grass and legume species that ~i I ~:require a fraction of the available soil test phosphorus levels required 1: :by annual crops and much less than other pasture., species. The general 1: SO~l test critical level used for crops in Colombia is 15 ppm P by the l::Bray II method (Marin, 1977). Promising, aluminum-tolerant ecotypes ·of i~:Sty1osanthes capitata, Zornia latifolia and Andropogon gayanus require ~~ 1/3 to 1/5 of that amount to attain maximum yields. Other forage species: Ie 'require considerably higher levels of phosphorus, such as Desmodium :: .leonii and Macroptilium sp. 535 .• They are not recommended for low input . _ systems. 1 : It should be noted that adapted grasses such as Andropogon gayanus 1- and Brachiaria decumbens require higher levels of available soil phos- 2.:. phorus than adapted legumes 1ike Stylosanthes capitata and Zornia 2: 1atifolia. The commonly held view that fertilization of grass-legume 0- mixtures should be based on the legume's higher nutritional requirement ~-, ? ?: . Field responses during the establishment year show significant dif- -. , n_'ferences in optimum levels of phosphorus fertilization at Carimagua in 1 13 ~,an Oxiso1 with about 1 ppm available P prior to treatment applications , 3i(Fi gure 3). Andropogon gayanus required 50 kg P205/ha to reach maximum 4i7ields, while Panicum maximum required 100 kg P20s/ha and Hyparrhenia s!rufa required 200 or perhaps more. The latter species, very widespread ~ 6 in Latin America, performs poorly in Oxiso1-U1tiso1 regions because of a ~ I generally, higher requirement of phosphorus and potassium and a lower 31to1erance to aluminum than the other two (Spain, 1979). These differen j ~ices are quite significant at the animal production level. At levels of 'I 10:inputs where other grasses produce good cattl~ liveweight gains, 11,Hyparrhenia rufa produced serious liveweight losses at Carimagua 12:(Paladines and Leal, 1979). It may be argued that the use of species that require less phos~ ,. phorus may provide insufficient phosphorus for animal nutrition. There ..!.~ '= is no evidence in the CIAT work that this is so (CIAT, 1978, 1979) but, ~y' I 'c,if it were it is probably cheaper to apply to the soil the quantities 'I ,_:required for maximum plant growth and supplement the rest directly to I . the animals via salt licks.' ~Jater stress. The ability to grow and survive the strong dry sea- 201sons of ustic environments under grazing pressure is necessary for these , ?1 jgrass and legumes, as irrigating pastures i·s prohibitively expensive in ::!most of the Oxisol-Ultisol regions. Because of their aluminum tolerance, 23\roots of adapted forage species are able to penetrate deeply into ex- r,. :tremely acid subsoils and exploit the residual moisture available. This ""'-::1 25;is in sharp contrast with aluminum sensitive crops that suffer severely 1 ~r,:from water stress even during short dry spells because their roots are -, , ,,_i'confined to the limed topsoil (Gonzalez et ~., 1976). • 1 1'4 2 Adapted legume species are generally more tolerant to drought stress ",than the grasses, and also maintain a higher nutritive value during the " 4 dry season. For example, Zornia latifolia 728 contained 23.6% protein inj _ 'its leaves at the height of the Carimagua dry season (CIAT, 1979). Among· ~ I 6 the itdap:t.ed· grasses, Andropogon gayanus is more tolerant to drought 7 stre~s than Brachiaria decumbens or Panicum maximum (ClAT, 1979). Its S pubescent leaves also permit dew drops to remain on the leaves longer 9 than in ~. decumbens or ~. maximum. It is common to get one's pant legs 10 'I wet while walking through an Andropogon pastur; at about 10 a.m. in the lllLlanos of the Amazon, when swar.ds of the other two species are already I 12ldry. -. _i Insect and disease attacks. Most of the adapted legume species have! ::l~heir center of origin in Latin America and therefore, have many natural ~ , 1s1enemies. Anthracnose caused by Collectotrichum gloeosporoides is a most :r,ldevastating disease of legumes (ClAT, 1977, 1978, 1979). Stemborers of :7!th~ genus Caloptilia also destroy several StYlosa~thes species (ClAT, , l .;, 979). Spi ttl ebug attacks caused by Deoi s i ncompl'eta and other species If, !have ~estroyed thousands of hectares of Brachiari a decurnbens pastures in 20ludiC regions of Brazil. The solution to these problems is varietal re- I • 21 sistance since applications of insecticides or fungicides to these pas- 22 tures are likely to be uneconomical. Screening for tolerance to these 23 and other pathogens has provided ecotypes that combine the adaptation to 24,adverse soil conditions with pathogep resistance. Examples of these to 25 date are several ecotypes of Andropogon gayanus, Sty10santhes capitata ry61and Desmodium ovalifolium. Several promising ecotypes of' Stylosanthes :7IgUianensis, a legume extremely well adapted to the soil limitations, 15 " 2 unfortunately have succumbed to insect and disease attacks (CIAT, 1978, 31979). As in other plant improvement programs, the search for new eco- 41types that combine tolerance to pathogens with other desirable charac _ teristics is a continuing activity. " 6 It is interesting to note that plant protection problems increase in ~ importance after the soil constraints are solved by plant selection, I g breeding or management in these Oxisol-Ultisol regions. This may be a 9 consequence of eliminating a previously limiting factor or of a pathogen loibUildup as new plants are grown on many hectares for the first time in a I 11lnew environment. The same is the case with crops. Tolerance to disease: 121and insect attacks, however, vary with ecological conditions and therefore,: I , ~Ithe degr'ee of tolerance of each promising ecotype must be validated '!LJI I 1-! 11 oca 11y. I ! Tolerance to burning. Accidental burning is common in savanna lsi iregions and intentional burning may be a necessary management practice in: lG: !cases where grasses grow too fast and lose their nutritive value. Conse-: ...... ! quently, the adap,ted species must be able to regrow after burning. ;Studies by Jones (CIAT, 1979) show that Andropogon gayanus, Panicum 1!~ ; imaximum, Brachiaria decumbens and Brachiaria humidicola regrow rapidly 201 lafter burni ng. 211 • 4. Supply Nitrogen with Acid-Tolerant Rhizobia 221 Nitrogen deficiency is a widespread limiting factor in most • 23 I !Oxisol-Ultisol regions, except during the first year or two after land 252411 c ear1ng.' I n mos t' 0 'f t hese reg10ns'th' e pr1ce 0f' Oltrogen f ertl'1' lzer 1S, very high relative to the price of beef. Nitrogen fertilization for 26 ?~ipasture-based beef production is seldom profitable (0. Paladines, personali ~l: I 16 ; .) ;communication). Consequently, the majority of these pastures must rely - ! ~ i 3;on, symbiotic nitrogen fixation by legumes for their nitrogen supply. ·.4i Until recently it has been assumed that most tropical pasture 5 legumes growing on acid soils develop effective symbiosis with native 6 "cowpea-type" strains of Rhizobium, and therefore, the selection of 7 specific strains for individual 'legume species or cultivars is the ex s ception rather than the rule (Nor.ris, 1972). Recent work by Halliday ~1(1979) and collaborators clearl; shows that this is no longer the case. 10 A five-stage screening and matching procedure involving laboratory, 11 greenhouse and field stages has shown a high degree of strain specificity: l?ifor obtaining effective symbiosis in the most promising legume ecotypes. : --! i ,~IRecent recommendations including inoculation technology are available . ..1.'-', ' , H!(ClAT, 1979). 15: Long-term field experiments hOI-lever, show that the response to ; .,[inoculation with selected Rhizobium strains generally decreases with , ._'time. Protecting the inoculant scrain with lime or rock phosphate pel- l~!leting permits an effective infection in an acid soil. The critical ,(.~point however, is reached two to three months afterwards when the primary. -~ I : 20!nodule population decomposes. Then the Rhi zobia must fend for themselves: in an acid soil environment in order to reinfect the plant roots (ClAT, i t, 21 ! 1979) The selection of effective acid-tolerant strains is therefore, 22 . ,. 23 highly desirable. Date and Halliday (1979) developed a simple laboratory! I 2~ltechni~ue to screen for acid tolerance at the early stages of strain i 25 selection, using an agar medium buffered at pH 4.2. Rhizobium strains itolerant to acidity grow in such a media while those suscepcib1e die. ~61 271 ~------~ . , '. I! 17 I 21Acid soil tolerance of the Rhizobia, therefore, is probably as important 3\as acid soil tolerance of the pasture species. , 41 Differences in aluminum tolerance of Rhizobium strains for cowpea 5 have also been identified (Keyser et ~., 1979) suggesting that similar 6 relationships may take place in aluminum-tolerant annual crops. 7 The potenti al of associative symbios i s by nitrogen-fi xi ng bacteri a 5 ,such as Spirillum lipoferum in the rhizosphere of tropical grasses 1 / 9icreated" expectations about possible important contribution of nitrogen , , I lO!fixation by grasses (National Academy of Sciences, 1977). Unfortunately,! , ll;evidence to date indicates that the practical exploitation of such sym-' I 12!biosis, appears to be minimal (Hubbell, 1979). This is an example of a '13110\'1 input component that did not work. 14 5. Use Low Cost, Low Reactivity Rock Phosphates As previously mentioned, phosphorus is the single most expensive • r. _. ,purchased input used in establishing and improving pastures in Dxisol 'savannas, particularly since many of these soils have a high phosphorus , . , , ' -"fixation capacity. The use of grass and legume species requiring lower I ~8ilevels of available soil phosphorus decreases phosphorus application -?O'.Irates appreciably. Still greater efficiency can be attained if the cost 3 21 per unit of ferti1izer phosphorus can be decreased by direct application 22 of rock phosphates. This is possible in tropical South America which is • 231blessed with large rock phosphate deposits, shown in Figure 4. 24 All these deposits, except for Bayovar in Peru, are classified as 25!low reactivity materials which are considereq u~suitable for direct ap- 2C!Plication (Lehr and HcClellan, 1972). Low reactivity rock phosphates -,~-I , "10, ", 1 18 2 need to react with acids in order for their solubility to increase, which 3 is done in superphosphate manufacturing. I 4' If the soil is acid, the same process occurs naturally, but few crop 5 plants can tolerate the high levels of exchangeable aluminum present at '6 such low pH values. When aluminum-tolerant plant species are grown. how- 7 ever, these low reactivity rocK phosphates can be as effective as super- 8 phosphates. Table 4 shows the effect of various rock phosphate sources 9 and placement methods on pasture production in an Oxisol of Carimagua. 10 with a pH of 4.8 and about 85% aluminum saturation. The acid-tolerant -, 11 grass used, Braciliaria decunbens is well adapted to these conditions. 12' Rock phosphate fl"om all tropical South America sources performed in a -13 fashion similar to triple superphosphate. regardless of reactivity rating 14 Apparently the chemistry of acid soils can effectively replace a super- 15 phosphate factOl'.'Y when acid-tolerant plants are grown. Since the cost 16 per kilo of phos.phorus as rock phosphate costs 1/3 to 115 as much as ,-1superphosphate" considerable savings can be made. Thus, low reactivity ~'I Islrock phosphates are suitable for direct application under these condi- 19 tions. High r,eactivity rock phosphates are also suitable, but are less 20 coman in trop;ical America. Since pho!sphorus is particularly critical during the establishment 21 '. 22 phase, it is -important that these rock phosphates react quickly with the 23 soil and prov,'i de the needed boost to get the pasture established. This occurred Wit/,l the high (Bayovar) and medium (Huila) reactivity rock 24 , _ phosphate at the recol/lllended rate of 50 kg P205/ha in the Carimagua ex- 2v ; periment shown in Table 4. The dry matter production of Brachiaria 26 27 decumoens during the first cut (three months after planting) with these " 1 19 2 two sources was equivalent to that with superphosphate. Similar results 3 with the high reactivity Bayovar rock phosphate on an acid, unlimed 4 Ultisol from the Amazon of Peru have been reported by North Carolina 5 State University (1975). The pasture growth pattern with the low reac- 6 tivity Pesca rock in the Carimagua experiment, at the same rate (50 kg/ha 7' of P20S)' was slower during the first year than with Bayovar and Huila. ~ 8 but it caught up with the others within the first year (CIAT, 1978). 9 Results with another low reactivity rock,·Araxa, on Oxisols of Bras~lia, 10 Brazil sr.ow that it took about two years to produce the same dry matter 11 yields of Brachiaria decurnbens as high reactivity rock phosphate 12 (Sanchez, 1977). A combination of low reactivity rock phosphate with '13 banded superphosphate app 1i cati ons may be desi rab 1e in some instances. 6. Correct Other Nutrient Deficiencies 15 • Oxisols and Ultisols are often deficient in calcium, magnesium, ~:IPotassium, sulfur and several micronutrients particularly zinc, copper, "[boron, and molybdenum. Unfortunately, very little is known about the geo- l~!graphical occurrence of these deficiencies, particularly sulfur and 1~ micronutrients, in terms of critical levels in the soil and the require- 20 ments of the promising grass and legume species. There are no known • 21 ways to overcome these deficiencies except by conventional fertilization. 22 Hutton (1979) attributed most of the lack of legume persistence in mixed 23 pastures of LatHI America to uncorr'ected nutrient deficiencies. Many 24 ranchers in tropical America feel that applying triple superphosphate is 25 sufficient for grass/legume pasture$. This fertilizer source provides ? • -olonly phosphorus and some calci~m. In tropical Australia rnolybdenized ,,~ I -'IL-_____ ' ______~ 1 20 2 simple superphosphate is widely used as the only fertilizer in Alfisols 3 very deficient in ni trogen, phosphorus, sul fur and mo'lybdenum. This 4 source corrects phosphorus, sulfur and mOlybdenum deficiencies, allowing _ the legume to provide nitrogen to the mixture. Given the fundamental ;) 6 differences in soil acidity between soils of tropical Australia where 7 improved pastures are grown (mainly Alfisols) and the Oxisol-Ultisol re- B gion of tropical America, it is not possible to extrapolate the Australian I' .' 9 fertilization practices directly (Sanchez and Isbell, 1979). Surveys of I 10 the nutritional status of Oxisol-Ultisol regio~s such as the one Lopes 11 and Cox (1977) did in the Cerrado of Brazil, plus on-site field experi-' 12 ments'on the nutrients such as those conducted in Carimagua, Colombia (CIAT, 1977, 1978, 1979, Spain, 1979) and in Yurimaguas, Peru (VillachicaJ 13 14 1978) contribute significantly to identifying which nutrients are defi- , I 15 cient and which are the best practices to correct them, including pos- I 16 sio'le nutrient ilTbalances which may be induced by fertilization. These ,~!studies, however, show that nutrient deficiencies other than phosphorus I -, , 1& lare in the Oxisoi-Ultisol regions. Therefore, site-specific identifica- I 19 tion is necessary. These efforts must be related to the nutritional re- 20 quirements of the main grass and legume cultivars, of which very little 21 is known about the species mentioned in this paper. Insufficient knowledge of nutrient deficiencies is the weakest com- 22 ? ponent in this strategy. This gap can be corrected by systematic deter- .3 " 24 minations of critical nutrient levels in the soil and in the plants. 25 Fortunately, the relatively long-term residual effect of calcium, mag nesium. zinc and copper fertilization may reduce application costs. 26 Also, maintenance of suitable levels of these nutrients plus potassium 27 L-______~ 1 21 2 and sulfur is also favored by a degree of recycling via animal excreta. ?!Nevertheless, it should remain dear that deficiencies of these nutri'ents vi 41must be identified and corrected in order for the improved pastures to ,J- persist. 6 7. Use Low Cost Pasture Establishment Methods 7 Conventional pasture establishment methods in savanna regions com- S manly consist of one or two passes with a disk harrow, followed by seed- 91ing with a grain drill equipped with a fertilizer attachment. These are lolrelativelY easy to do during the rainy season but the cost is high, on 11 the order of U.S.$133/ha in the Llanos of Colombia (Spain 1979, CIAT, 12 1979 ). Low establishment costs are possible by two mechanisms, one ap- '13lplicable to Oxisol savannas, and another applicable to most Oxisol HIUltiSOl regions. 15 In Oxisol savannas, weed growth after land preparation is very slow 1 lEi'due to the extremely low native soil fertility, as long as the soil is l';' .. not limed or fer.tilized. Taking advantage of this situation, Spain 1:,(1979) developed a low density planting system where considerable savings 1& can be accomplished in terms of seed costs and initial fertilizer appli- 20 ~ations. After the land is prepared with one or two passes with an off- 21 set disk harrowing, grass and/or legume seeds are planted in holes spaced 221 at about 3.16 m giving a population of 1000 plants/h~ during the rainy 23 season. The pla;.t:s receive a localized high rate of phosphorus and 24 potassium, but on a per hectare basis the highest rates used w~re 9 kg 251P205/ha and 1.5 kg K20/ha. One man equipped only with a ~h~ve1 can Plantl ~~iand fertilize one hectare in one day (Spain, 1979). I -, I . ~------.------~ l' 22 .J 1 These I'J ants ,grow vi gorously duri ng the rai ny season due to thei r -I 3!high soil fertility status and absence of competition from weeds or 4iplants of their own species. Stoloniferous species cover the ground 5 within eight months. at the beginning of the next rainy season (CIAT. 6 1979). Tussock-type grasses such as Andropogon gayanus and Panicum 7 maximum produce seed at the end of the rainy season. At Carimagua. these q seeds aligned themselves in the furrows left by the disk harrow and ger -I 9jminated with the first rainy season showers , starting ahead of the weeds. " 10iThe new seedlings have to be fertilized shortl~ after emergence or they 1 lliwill die because of phosphorus and potassium deficiencies. With such a 12lsystem, pastures were ready for grazing within nine months after plant '3 ing, which is about three months later than with conventional land pre- • 1 1 14iparation. The details are explained more thoroughly in reports by Spain - I 151(1979) and CIAT (1978, 1979). Although this system does not reduce the ~6!fertilizer requirements relative to conventional plantings, the seed I -.~!costs, are reduced from U.S.$34' to $3/ha (CIAT, 1979). Since seed of ! :slimproved pasture species is generally scarce, an additional advantage is !8!that vegetative propagation can be used. 20 This low density planting system is not likely to be successful in 21 savanna areas that have been previously fertilized or in recently cleared 22 rainforest areas where vigorous weed and jungle regrowth takes place. :!3 In many of these a,' 25 tion practices r~quired by the crops but interplanting pasture species so 26 when crops are harvested; the pasture is established (Shelton and 23 2 Humphreys, 1975; Kornelius et ~., 1979; Toledo and Morales, 1979). In 3\effect, pasture establishment costs are largely paid for by the cash crop 4 1 Recent results with a Colombian Ultis01, shown in TabJe 5, clescribe 5 some of the relationships involved. When cassava (Manihot esculenta) and 6 Stylosanthes guianensis were planted simultaneously, cassava yields ~ere 7idecreased somewhat ~nd stylo production halved, but a stylo pasture was 8 ready for grazing after the cassava harvest. When cassava was inter- 9 plqnted with a mixture of Brachiaria decumbens and ~. guianensis, crop lO!yieldS were adversely affected by the vigorous, grass growth. Although th I 11 sum of' relative yields is identical to the previous case, this combina- 12 tion seriously decreases cassava yields. 13 When a crop with short growth duration is used, the results are dif- 14 ferent. Table 5 also shows the same two pasture species planted at the 15 same time with Phaseolus vulgaris. Bean yields were not affected by the I 16 tresence of ei ther the legume a 1one or the gras~ -1 egume mi xture. a 1though I :7'pasture growth was retarded by the presence of the bean crop. Neverthe 1 l~iless, a pasture was established after the bean harvest. I 19' Intercropping between pastures and crops is extremely site specific 20 and weather dependent. The actual systems to be used must be validated 21 locally, particularly in tenns of relative planting rates, row spacing, 22 crop varieties and fertility. On the same location in Colombia, the • 23 first upland ricP,rasture experiment failed because ri.:e growth was so 24 vigorous that the pastures could not compete with it. A second trial in 25 which relative planting dates and spacings were studied showed excellent 26 associations of short-statured upland rice with a mixture of Brachiaria '2.7 decumbens and :Jesmodi urn ova 1Ho 1i urn (CIAT. 1979). " 1 24 2 It is li'kely that pastures established i,n such a manner would enjoy 31a higher soil fertility level if fertilized with the recommended rates for 4ithe crops, which would provide a beneficial residual effect to the pastures. _ If managed in conjunction with other conventionally established pastures, '" ' 6 they could serve as a source of protein or energy for the herds. 7 8. Use Low Cost Pasture Reclamation Technigues After the pasture is established, management is aimed at maintaining '. / 9,its initial productivity and botanical composition by manipulating stock- 10ling rates, grazing pressure, fertilization and,weed control. Unfortu Illnately, most of the existing data is related to stocking rates and graz- 12\ing pressure, with extremely limited knowledge of maintenance fertiliza- , "13!tion and weed control in Oxisol-Ultisol regions. It is generally be- I 1411ieved that maintenance fertilization rates should be less than half of 15 the established rates of all nutrients applied. Soil tests and plant 16 analysis could quantify which are the most economical rates and what I 17'their fr~quency of application should be, either every year or every two , Isiyears. ,\lso these techniques would identify nutritional deficiencies or 19'imbalances that arise with time. 20 Pasture degradation in the Amazon Jungle has received considerable 21 attention. According to Hecht (1979) most of the Panicum maxil1JJm pas- 22 tures in the Brazilian Amazon are in some stage of degradation. In the 23 P~ragominas area elf the State of Para, Hecht reports that about 70% of ' 24 the cattle ranches went out of business because of degraded pastures. , , 25 The main causes of degradation are the use of a grass species with high 26/nutritional requirements, no fertilization, no legumes and often exces- 271sively high stocking rates. The costs of controlling. jungle regrowth 1 25 2 becomes too high when the Panicum maximum population decreases, and the 3 fields ar-e gradually transformed into a secondary forest. 4 Serrao and coworkers (1979) have found that phosphorus deficiency is 5 the factor that sets this process in motion. Phosphorus availability is 6 high right after burning the forest, remains above the critical level up 7 to four years, and then declines. The correction of this problem is re- 8 markably simple and of low cost. ~errao et ~., (1979) recommend to cllt 9 the jungle regrowth with a machete and burn the field, then broadcast 10 50 kg P20S/ha half as simple superphosphate and half as rock phosphate. " 11 U~der these conditions, the Panicum maximum popUlation increased from 12. about 25 to 90%. Broadcasting legume seeds has also been incorporated :13 into the system. 14 9. Strategic Use of Improved Pastures 15 The combination of some of these components in actual grazing trials 16 is provi d'i ng promis i n9 results. Legume-based pastures on Carimagua 17!Oxisol savannas" planted conventionally, with an initial fertilization i 16 rate of 50 kg P 0S/ha, 25 kg K 0/ha, 20 kg S/ha and 20 kg Mg/ha and an : j 2 2 19 annual maintenance rate of half that amount are expected to produce an 20 average liveweight gain of steers on the order of 400 to 500 g/day, with 21 a carrying capacity of about 2 animal units/ha during the rainy season 22 and 1 animal/ha during the dry season. Total beef pr~duction per hectare , .- 23 in fattening aile)'" "ions is expected to be on the order of 200 to 300 24 kg/na/year (Nores and ~strada, 1979), Actual grazing trial data at Cari- 25 magua have exceeded these estimated (ClAT, unpublished). This flgure is 26 approximately twice the production with ifllprove 27 tures wi thout h. umes and about 10 ti mes as much as the roducti vi t of 1 26 2 the native savanna. Although such liveweight gain levels have been ob-, "tained during the first or second year in Oxisol regions (CIAT, 1978; 0) " . 4 Rolon and Primo, 1979); they have to be validated for persistence for a _ period of time. Under Colombian Llanos conditions, a minimum' persistence ;) 6 of six years is necessary according to economic analyses (CIAT, 1979). . , If these legume-based pastures are indeed persistent as they appear 7 5 to be at the time of this writing, the i.ncreases in pr.oduction per unjt 9'of land.. are so large that several cost cutting alternatives become fea- I , ' 10 sible. In areas relatively close to the markets where cattle can be I I I lllattened, most of the grazlng area could' be put into such improved, pas- i I 12,tures. In the case of the Colonbian Llanos this could double the rate of! ., 3 ,return ~>n investment (Nores and Estrada, 1979). I :41' In udic rainforest areas, the prodU,ctivity of well managed grass- I 15 legume pastures ~s even higher than in the savannas because of the ab- i. I 16 sence of a strc,r:g dry season. Toledo and Mora,les (1979) report an annual I' 1711ive~ei~ht gain of 450 kg/ha with a mixtur~ of Hypa;rhenia rufa and I i .; IS iStylosanthes guianens'i s ferti,l i zed with si ngl e super~hosphate for a 1~ three-year period in an Ultisol from Pucallpa, Peru. This is three times 20 the amount obtained with the pure grass, without fertilization. In areas devoted ,to cow-calf operations and far away from the mar- 21 22, kets, putting about 10% qf the grazing area in improved legume-based 23 pastures appears to be a promising alternative. Such dn area would ,be •• 2 s,trategically grazed in relation to the 90% left as unimproved native 4 , 25 savanna. Strategic g~,azin~ consists of placing the animals with higher o nutritional requirements such as lactating cows and recently weaned ~6 . . . ' 27 c~lves on the improved pastures while other animals graze the native ; II 1 ' 27 [ 2 savanna. Also, intense grazing periods by much of the herd are done when 3 the pasture seems to be growing too fast and is in danger of decreasing 4 its nutri ti ona 1 value. 5 A breeding herd experiment was established in Carimagua. in 1977 to 6 test this hypothesis. Three identica·l herds with 54 cows each were sub- 7 jected to native savanna plus the best animal management and health prac~ 8 tices including ad libitum mineral supplementation·. Three other identical .- 9 herds were given the same treatment except that 10% of their grazing area 10 had Brachi ari a decumbens and Stylosanthes gui anensi s grown in separate 11 paddocks. At the end of the first fl.jll year, the strategic use of im- 12 proved pastures in 10% of the area increased the annual liveweig~t output - 13 by ~50 .percent (CIAT, 1979). 14 Although these results need more time for validation, they show the 15 promise of strategic use of improved. pastures, either as energy or·pro~ 16 tein banks or both. The concept could also apply to rainforest areas 17 with degraded pastures such as those described by Serrao et ~., (1979.). I i', ' " 18 In cases where lt is not feasible to have a pasture regeneration program .. 19 for the entire farm. complete regeneration of part of it could have a .. 20 similar effect as that observed in the savannas. , . " 2;1. EFFECTS OF IMPROVED LEGUME-BASED 22 ?ASTURES ON SOIL PROPERTIES 23 24 Most of the present improved pastures in Oxisol-Ultiso1 regions of 25 tropical America are inherently unstable because they lack one or mpre" 26 of the key components described in this paper. The princ.ipal l~mitations 27 are the use of a poorly adapted grass species, lack of fertilization, the 1 28 2 absence of Pfilrs;,stent legumes or sufficient s.eed supplies. The proposed 3 strategy, if successful, should have the opposi te effect. Persistent, 4 legume-based pastures can provide continuous cover to protect against 5 soil erosion, as long as they are not overgrazed. Such well managed " / . 6 pastures have maintained the o.rganic matter cO,ntents of an U1tisol from 7 northern Australia for 16 years at the same levels as before clearing 8 the rainforest, as shown in Figure 5. In the eastern Amazon of Brazil. 9 an additional advantage in the maintenance of soil chemical properties 10lhas been recorded. Serrao et a1., (1979) sam~,led soils in unfertilized 11lpanicum maximum pastures of known ages in two areas of Brazil. The re- 12jsults summarized in Figure 6 indicate that soil pH increased from about " , " J4.5 to between 6 and 7 right after burning, and remained constant up to .~, i 14:13 years. Aluminum toxicity was completely eliminated and calcium and I .",_,'magneSium levels were maintained at fairly high levels, as well as or- .oiganic matter and nitrogen. Potassium values remained close to the }. f; : :~!critical level while available phosphorus decreased below the critical ! , I, 1~:leve1 rather qui'ckly. These results are from samples of different fields lulof known a'le after clearing taken at the same time; t~erefore. they con- , 20 found time and space variability. Nevertheless, ,it seems clear that 21 many of the chemical properties of these Oxisols were definitely improved ~~ when cleared and grazed. These soil dynamics are in sharp contrast with ~- , 23 the rapid fertiiity decline observed after clearing ra1nforests and ., 24 gr.owing annual crops in udic areas of Peru and Brazil (Sanchez. 1977, 25 1979). The reasons for these differences are not clearly understood and 26 deserve more thorough study. Some factprs favoring a less marked de- cline in easte:-n Amazonia may be an ustic soil moisture regime which 27 .1 29 2 allows for a more thorough burn and more ash and possibly upwards move- 3 ment of cations and anions during the dry season. Also, the periodic 4 burning every few years practiced in these areas and some degree of nu- 5 trient recycling by the grazing animal may contribute to the effects 6 shown in Figure 6. Whatever the reasons are, the improvement in the 7 chemical properties of acid infertile Oxisols is remarkable. and shows g promise for better managed grass-legume pastures in the Amazon region. I ' ,,- 9 SUt-111ARY 10 III Results from a multidisciplinary effort by CIAT's Tropical Pastures 121program and collaborators in Colombia, Brazil and Peru suggest the emer- , l~lgence of a low input soil management strategy designed to take advantage "'/ 14iof acid soil infertility rather than overcoming it by large applications I 15iof lime and fertilizers. legu~e-based pastures for beef production have lC!comparative advantages for expanding the agricultural frontier of trop ,_!ica1 America into its vast Oxiso1-U1tiso1 regions. This may provide an 1 ~: a lterna~ive for allevi ati ng popu1 ati on pressures from eros ion-prone, hi gh I 191base status soil regions. Although not all the components of this 20 strategy are sufficiently well known, the main ones are: 1) Use of land 21 resource evaluation studies to select ,soils suitable for crop-pastures 22 systems, avoiding those with severe physical constraints; 2) use of ap- - , 23 propriate lqnd clepring systems in forested areas t,lat prevent soil co",: 24 paction and include burning to take advantage of the free fertilizer 25 value of the ash; 3) selection and/or breeding of productive, persistent 26 and compatible pasture grass and legum~ cultivar? tqlerant to high levelsl of Al saturation, low levels of available soil P, major disease and ' 27 1 3D 2 insect attlcks, drought stress, and burning; 4} supply nitrogen to the 3\System by inoculating legumes with ~ffective, acjd-tolerant Rhizobium I 4 strains; 5) use low cost, low reactivity rock phosphates which become 5 readily aVdilable when the soil is kept acid and Al-tolerant plants are 6 grown; 6) correct other nutritional de~icienci'es, particularly potassium, . . 7 sulfur and micronutrients; 7) use low cost pasture establishment methods 5 su~h as low density seedings or interplanting with crops; 8) use low cost 9 pasture reclamation techniques; 9) for extensive cow-calf operations 10iplace about 10% of the grazing area. in improve? pastures. ni Preliminary results show that this strategy is very promising. Well I ; 12imanaged pastures provide a continuous protective cover against soil I . "u!erosion, promote nutrient recycling and improve certain 'soil chemical I 14 properti es. i, I 15i :61 I - . 161 , 1:' !I I 20' 21 22 23 .' 24 25 26 27, 1 31 2 LIST OF ACRONYMS OF' RESEARCH, INSJITUTION~ 3 MENTIONED' IN THIS PAPER' 4 CIAT = Centro Internaciona'1 de' Agricultura Tropica.l 5 CPAC = Centro de Pesquisa Agropecuaria dos Cerrados , 6 CPATU = Centro de" P'esquisa·.Agrope,cuaria; do Tropjco, Umido, 7 EMBRAPA Empresa' Brasi lei ra, de! Pesquisa· Agrop-ecuario: ,~, = 8 ICA = Ins ti tuto Co] omb.i'ano Agropeeuari o· " 9 INIA = Instituto Naciona'l de Invest; gadai!' Agrari'ac 10 IVITA = Instituto Veterinario'de Investigaciorl'.de,r Tropico' y de,AHura', 11 UEPAE i" Uni dad de Execuc;ao de, R"esquisa no .. Ainbi-to~ ES,ta:dUiET. I 12 I " 3 1 ~ I I ,I 141 'j , i 1~; ! IG I I .: .... : ,1 ~t, I I 1 CI, " I 20 21 22 ,;.. , 23 24 25 26 ?"-I 1 32 2 LITERATURE CHED 3 Alvim, P . .T. 1977. The balance between conservation and utilization in 4 the humid tropics, with special reference to the Amazonia of Brazil. Pages 347-352. In: G. T. Prance and T. S. Elias (eds): Extinction is Forever. New-Vork Botanical Gar:~en, N_. Y., I 6 Bruce, R. C. 1965,. Effect of Centrosema ubescens on soil fertility i.n , the humid tropics. Queensl. J. Agr. mm. Cl. 22:221-226. ' ~ , , Buol, S. W., P. A. Sanchez, R. B. Cate and -M. A. Granger.- 1975. Soi'l fertility capability classification: A technical soil classification for ferti 1 i ty management. Pages' 126-'141 . In: E. Bornemi sza and A. Alvarado (eds): Soil. Management in Tropical America. _ North 9 Carolina State University, Raleigh. 10 CIAT.. 1977, 1978: 1979.- Beef Program. Annual'Reports for 1976, 1977 and 1978. Cen,tro Internacional de Agricul tura Tropi ca.l, Cali, 11 Colombia. ... ' 23' Fenster, W. E. and L. A. Leon. 1979. Management of phosphorus ferti1i- 24' zation in establishlng and maintaining improved pastures on acid, infertile soils of tropical America. Pages 109-122. In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in ACid Soils 25 ,of tpe Tropics. Centro Internaciona1 de Agricultura Tr9pical, Cali, Co.J ombi a. 26 27 " <' E., E. J. Kamprath, G. C. Naderman, W_ V. Soares e E. Lobato. 1975. Efeito da profundidade e inc6rpora~ao de calcareo na cultura do milho em solo acido de Cerrado do Brasil Central. .. Pages 299-302. Em: Anais XV Congr. Bras. Ciencia de Solo, (campi,nas!,1 - ! , ~ Halliday, J. 1979. Field responses by tropical legum~s to inoculation I , with Rhizobium. Pages 123-138. ~: P. A. Sanchez and L. E. Tergas ' " 6 (eds): Pasture Production in Acid Soils of the Tropics. Centro Internacional de Agricultura Tropical, Cali, Colombia. 7 I Hancock, J. K., R. W. Hill and G. H. Hargreaves. 1979. Potential 'evq.po-! B , transpiration and precipitation deficits for tropical America. A I resum(~ of the pre 1 imi nary c 1 imati c data used for the Land Resources I ," 91 Evaludtion Study of Tropical America. ClAT, Cali, Colombia. 398? 10!Hargreaves, G. H. 1977. World water 'for agriculture. Climate, preciPi-! tation probabilities and adequacies for rainfed agriculture_ Utah 11 State University, Logan. 12,HeGht, S., [. 1979. Amazonian cattle-pasture research. Unpub- I lishec, data. Geography Dept., Univ. of California, Berkeley. "13 I 'Hubbell, D H. 1979. The potential of associative symbioses between 14! nitrogen-fixing bacteria and forage grasses. Pages 139-144. In: " i P. A. Sanchez and L. E. Tergas (eds): Pasture Production in Acid ' 15 Soi ~ s ~f _th~ , Tropi cs. Centro Internaci ona 1 de Agri cultura Tropi ca 1, : i1 Cal., ColomDla. 1 r; , ,Hutton,I E. M. 1979. Probl ems and successes of 1egume-grass pastures, i' especially in tropical America. Pages 81-94. In: P. A. Sanchez and, ' L. E. Tergas (eds): Pasture Production in Acid Soils of the TroPics.,' Ibi Centro lnternacional de Agricultura Tropical, Cali, Colombia. ,I 1!J iKeyser" H. H., D. N. Munns and J, S. Hohenberg. 1979. Aci d tolerance of I Rhizobia in culture and in symbiosis with cowpea. Soil Sci. Soc. 20 Amer. J. 43:719-722. ~, 21 Kornelius, E., M. G. Sauressig and W. J. Goedert. 1979. Pastures estab i Hshment and management in the Cerra do of Brazi 1. Pages 147-166. , - 22 In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in Acid i ,\..,, Soils of the Tropics. Centro Internacional de Agl-,cultura Tropical, , 23 Cal i, Colombia I I 24Lal, R. 1980_ Erosion dS a constraint to food production in the tropics. I In: Priorit~es for Alleviating Soil Constraints in the Tropics. 25 International Rice Research Institute, Los Banos, Philippines (in press) . 26 1 34 2 Lehr, J. A. and G. H. McClellan. 1972. A revised laboratory scale for evaluating phosphate- rock for direct application. Tennessee Valley 3' Authority BuJl. Y-43. , .. ILopes, A. S. and F. R. Cox. "977 • A survey of the ferti 1ity status of surface soils under Cerrado vegetation in Brazil. Soil SCi. Soc. '5 Amer. J. 41 :742-747. 6 Marin, J. G. 1977. Fertilidad de Suelos con Enfasis _en Colombia. Instil r- tuto Colombiano Agropecuario, Bogota. 299 p. 7 Ministerio das Minas e Energia, Brasil. 1973-79. Projeto RADAM-~rasil. 8 Vol. I-XI. Departamento Nacional da Produ9ao -Mineral, Rio de Janeiro. Brazil. / 9 Na'tional Academy of Sciences. 1977. World food and nutrition study: 10 The potential contributions Qf research. National Academy of 'I Sciences, Washington, D. C. 192 p. ~ I11lNores, G. A. and R. D. Estrada. 1979. Economic evaluation of beef pro- 12 ducti on sys terns in the Ll anos Ori enta 1es of Col ombi a. Pages 327-341;, i In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in' ACi'dl '131 §Jils of the Tropics. Centro Internacional de Agr;cultura Tropical, I Cali, Colombia. 14\Norris, D. 0,. 1972. Leguminous plants in tropical pastures. Trop. 15i Grassl. 6:159-170. , ) North Carol ina S ta te Uni vers i ty . 1975. Agronomi c-economi c research on ~"' tropi ca 1 soi,l s. Annual Report for 1974. Pages 42-47. Soi 1 Sci ence, Department, N. C. State Univ., Raleigh, N. C. ! I ,,;Paradines, O. P. and J. Leal. 1979. Pasture management and productivity ~oi in the Llanos Orientales of Colombia. Pages 311-322. In: P. A. "'j Sanchez and L. E. Tergas (eds): Pasture Production in ACld Soils of _0 the Tropi'cs. Centro Internaci ona 1 de Agricultura Tropi ca l, Cal i , 20 1 Colombia. 21 Ramalho Filho, A., E. G.- Pereira e K. J. Beek. 1978. Sistema de avalia- 9aO da aptidao agrlcola das terras. Servi90 Nacional de Levanta 22 mento e Conserva9ao de Solos, EMBRAPA, Rio de Janeiro, Brazil. ?3 Rolon, J. D. ancl ;~,. 1. Priroo. 1979. Experiences in regional demonstra- ., - ticn triaL ' ?~_I 1 35 2 Sanchez, P. A. 1977. Advances in the management of Oxisols and Ultisols in tropical South America. Pages 535-566. In: Proceedings Int. 3 Seminar on Soil Environment and Fertility Management i'n Intensive .Agriculture. Society of the Science of Soil and Manure. Tokyo, Japan. 4 Sanchez, P. A. 1979. Soil fertility and conservation considerations for 5 agroforestry systems in the humid tropics of Latin America. Pages 79-124. In: H. O. Mongy and P. A. Huxley (eds): Soil Research in 6 Agroforestry, Nairobi, Kenya. . 7 Sanchez, P. A. and T. T. Cochrane. 1980. son constraints in relation to major farming systems in tropical America. In: S9il Constraints Conference. International Rice Research Institute, Los Banos, Philippines (in press). , 9iSanchez, P. A. and R. F. Isbell. 1979. A comparison of the soils of 10' tropical America and Tropical Australia. Pages 25-54. In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in AC1Q Sojls of the Tropics. Centro Internacional de Agricultura Tropical. Cali, 11 Colombia. 12 Serrao, E. A. S., 1. C. Falesi, J. B. Veiga and J. F. Texeira. 1979. '13 Productivity of cultivated pastures in low fertility soils of the , I Amazon of Brazi 1. Pages 195-226. In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in~cid Soils of the Tropics. 14i I, 1 Centro Internacional de Agricultura Tropical,Cali, Colombia. .j 15!seubert, C. E., P. A. Sanchez and C. Valverde. 1977. Effects of land ,r.! clearing methods an soil properties and crap performance in an i ·"1 Ultisol of the Amazon Jun91e of Peru. Trop. Agric. (Trin.) 54: r 307-321 . ; ,jShelton, H. M. and L. R. Humphreys. 1975. Undersowing rice ~Iith .';, Stylosanthes guianensis. Exptal. Agric. 11:89-112. l~II'spain, J. M. 1979. Pasture establishment and management in the Llanos 20 Orientales of Colombia. Pages 167-176. In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in~cid Soils of the Tropics. 21 Centro Internacional de Agricultura Tropical, Cali. Colombia. 2" Spain, J. H., C. A. Francis, R. H. Howeler and F. Calvo. 1975. Differ- ~ ential species and varietal tolerance to soil acidity in tropical crops and pastures. Pages 308-329. In: E. Bornemisza and A. 23 Alvarado (eds): Soil Management in Tropical America. North Carolina State Univ., Raleigh. 24 2- Toledo, J. M. and V. A. ~lorales. 1979. Establishment and management of " improved pastures in the Peruvian Amazon. Pages 177-194. In: P. A. Sanchez and L. E. Tergas (eds): Pasture Production in~cid 26 Soils of the Tropics. Centro lnternacional de Agricultura Tropical, 27 Cali, Colombia. '. • 1 36 ? Valverde, C., D. E. Bandy, P. A. Sanchez and J. J. Nicholaides. 1979. ~ Algunos resultados del Proyecto Yurimaguas en la Zona Amazonica. 3 Instituto Nacional de Investigacion Agraria, Lima, Peru. 26 pp. 4 Vicente-Chandler, J., F. Abruna, R. Caro-Costas, J. Figarella, S. Silva and R. W. Pearson. 1974. Intensive grasslands management in the humid tropics of Puerto Rico. Univ. Puerto Rico Agr. Exp. Sta. Bull. 223. . 6 Villachica, J. H. 1978. Maintenance of soil fertility under continuous 7 cultivation in the Amazon Jungle of Peru. P.h.D. Thesis. North Carolina State University, Raleigh. ~ Watters, R. F. 1971. Shifting cultivation in Latin America. FAD Forestry Development Paper 17. 305 pp. 9 10 11 12 14 15 10 ,J-, , i 20 21 22 23 24 25 26 27 • ; Ii 1 ,! 37 I· 2 Table 1. Land use ca,pability groups used in Brazil for ra.infed agricul 3 culture '(from Ramalho et .!l..• 1978). 4: .~ and capa- 6 bil ity 1 7 j roup 't> ! ti 1 9 2 101 3 1 11! 4 1J 5 .J 6 ""1 I 14il/ f- Management 15 1 H = High input use: fertilizer, new technology, largely mechanized 16 I - I M = Moderate input use: limited fertilizer, technology and mechaniza- ·-1 tion i· l~ I L = Low input use: primarily manual 1abor, few purchased inputs .i 1 1£1 0 = Zero use. 20 21 j~ I ' - 22 ! .,. I 23 I 24 25 26 271 .. 1 38 2 31Table 2. Effects of land clearing methods on pasture dry matter produc tion within the first 10 months and soH ,properties (0-10 cm depth) in Yurimaguas, Peru ~~------Slash r- 6 and Bulldozer 71~arameter Burn Clearin,g ~I ------~------~-- S!Dry Matter Production (ton/ha): 9 P. maximum 7.8 3.2 10 P. maximum - P. phaseoloides 6.3 3.5 I 11 P. maximum + N P K + 1 ime 32.2 24.2 12 ,Soil Properties: ! 13, Infiltration rates (cm/hr): 11. 7 0.5 1~! Exch. A1 (meq/1 00 g) 1. 70 2.07 r Exch. Ca + Mg (meq/100 g) 0.88 0.5S 15i 'I I 161 Exch. K (meq/100 g) 0.32 0.19 I I ,i Avail. P (Oisen-ppm) 16.5 11.0 H! % A1 saturation 59 73 I 'C' ..' :Adapted from Seubert et a 1 ., (1977). i 201 -- , 21 i I r .,/ I, i 25 26 27 1-, I '. 1 39 2 3 able 3. .Difference in requirements of available soil; phos'phorus for I maximum growth of various grass 'and legume species growing on an Oxiso1 of Co1omb;'a in ·re1ation: to general soil test 41 recommendation for crops. ~I i I~' ------~------6 Critical i 71"1 . Bray II J I so;i 1 tes'c :!Speci es or Ei:otype level ~: r------~------ppm 10 :Gen. crop recommendation (Co·lombia) 15.0 ., 11 ;Desmodium 1eoni; 3001 11.4 , I. 12 ,Macropti1 ium ~ 545 9.5 1 • . . , .. Brachiaria decumbens 606 7.0 • ..l,, ,<,Desmodium ova1ifo1ium·350 6.6 -~, - ~ndropogon gayanus 621 5.2 1 ~I I 16iZornia 1atifo1ia 883 3.4 , l~ 'Stylosanthes capitata 1019 3.J r, :Stylosanthes capitata 1078 2.5 l~q :Source: CIAT (1978, 1979). 20' 21 25 26 2711 ~------~ 1 40 2 :Table 4. Relative agronomic effectiveness, expressed as percent yields 31 with superphosphate of various rock phosphate sources in rela-, , ,;1I tion to the cumulative dry matter yield of Srachiaria decumbens in an Oxisol of Carimagua, Colombia (sum of cuttings over 28 months after planting). ' 6,f---~------~------'"-- r 7 II? . Source 25 50 100 '400 ~~, : ------" % Relative Agronomic Efficiency c' ~- ; , 10: Triple superphosphate 100 100 100 100 100 11' Gafsa R. P. (high reactivity) 110 75 108 '99 98 12' , .' _:Sayovar R. P. (high. 125 90 87 98 100 ,l" reactivity) l';,Huila R. P. (med. reactivity) 90 110 96 109 . 103 I 15,Pesca R. P. '(,low reac'tivity) III 81 101 1'04 99 i : I6,Tenn.. R. P. (low reactivity) 112 78 88 106 96 Source,: CIAT (1979). 1 ~, 'f_ ..I. .... : 20; 21 24 25 26 271 ~------~ I, I .' • 1: 1 !" 41 ! 21 T:ab 1e 5. Crop and pasture production in row intercropped systems planted I 3 simultaneously on an Ultisol from Quilichao, Colombia ferti1iz I with 0.5 ton/ha of dolomitic lime and 100 kg P20S/ha of triple "" superphosphate .. 5 !'1 Crop Yields Pasture (Dry Matter) I 6 S ecies Sum Pasture* Mono- Inter- Mono- Inter- of p (# cuts) culture cropped RY** culture cropped RY RY ['" 7fro 81 ----- ton/ha ----- % ----- ton/ha ----- % % 9 !cassava S.g .• (3) , 45.6 38.2 84 2.1 1.0 48 132 !( roots) 101 i 111 " B. d. + 42.4 17.0 40 7.0 6.4 92 130 1 S.g. (3) 121 I, . Beans S.g. (1) 1.08 1.08 100 0.80 0.37 40 146 , , ,- '(grain) I ~"[ I , " B.d. + 1.22 1.24 102 1.70 0.93 55 157 14 - i S.g. (1) 15 ,i ~r, lA.dapted from CIAT (1979). I :7:*S.g. = Sty10santhes guianensis 136; B.d. = Brachiaria decumbens. l~I**RY = Relative Yields = Intercropped x 100 i Monoculture , 9 i ~ I 20 21 ; 22 I~ 23 24 25 26 ?~_I ; . 100 --- -- Brachiaria 0 ----4 ., -J - ...... decumbens lJJ ...... 0 __ ...... , ,,. >- 80 ...... a:: '6 Pani~um lJJ ...... maximum I- ...... ~ 60 "0 Hyparrhenia ::a: rufa a:>- 0 40 ~ ::l ::E X ::e0 . ciliaris 0 0.5 I, 2 4 ; AI IN SOLUTION ( ppm) Figure 1. Differential tolerance to aluminum in culture solution by four tropical grasses. Source: I _ Spai-n (1979). , " GRASSES ., 8 _-----6 Panlcum maximum _--- Brachiaric decumbens 6 b..--~r=-:..:-::..;-=-=-:::,::-:,,:-==:;:'-=:";-;;:;;":;;~ Andropogon gaycnus 621 --::I ~ .rr"----o-----'------DHypcrrhenia rufa C .c: 4 " ,/ r· en c: o __ ~--~r------__ Digitaria decumbens ~I -- 2 __ "Grain sorghum :z ---- o -- ..... --..-.-. ----- U o 0.5 2 6 :J o 4 a:: LEGUMES 0.. 0:::: 3 W I- ><~=::::::::::::.-=:---__ Zorn ia latifolio 728 Stylosanthes capitato, 10/9 ~ ----:0--'-.-----.,------D~smodium ovalifolium 350 ~ 2 _._--a Centrosemc plumieri 470 > a:: --:-....--....-.--_~....:::.:::..-~. Pueraria phcseoloides 9900 ..- o I' "...""" -- .... .J;iil~ _..-'" o Q5 2 6 LIME APPLIED (tons/he) I I 9085 60 15 % AI SATURATION Figure 2. Field response to ·lime applications by several grass and legume forage species in an Oxisol of Carimagua, Colombia. Mean of 4-5 cuts for the grasses and first cut for legumes. Adapted from' Spain (1979) . ..., P' '-.-: .,~, c -.s;;. 8 "c: P APPLIED ( kg P2 Os Iha) Fl gure 3. Different; a 1 response to phosphorus fer tilization of three grass species during the establishment year in an Oxisol of Carimagua, Colombia. Sum of 3 wet season cuts. All ~reatments received 400 kg N/ha. Source: Jones (CIAT 1979). .f _-....-••"...... "." ... ~.. __ r " II. (" , l VENEZUELA Sard i nata~~ Lobatera :'V '~_') \ eAzufrada \ ...... J ( f· COLOMBIA ePesca \. r ..... -· "> i ) ./ I \.- (. )...... -« ...... " { I \. "" Tesalia ,..._ . ..j-. ~ .../ V' • ".~ (Huila) :> ...... -._.\ \ .I-, ...... _ ...... \ / , . . ( I . ./ .oJ. ( / / f BRAZIL \ \.-.\. /) ..... , L r' . PERU ''''( \ ...... i ..... - ...... \ Catalao !- \ .Patos de Minas I ...... \ • \ . , I, I • Araxo I 1 . \ ( . ( "'-",1 • Tapira I \ \ '{ I' I. 'i \._ I' }."-'-'-''''''i.. \ .Ipanema \ ',- " Juquio • J ~ , .,,' '-, 1-', • J cupiraranga ( - i . " i. . / / " ' ...... -. i I ( .~. ~, I Figure 4. Rock phosphate deposits in tropical South America, 1977. Source: Fenster and Leon (1979). '. I, .. 0.40 ..... E ,, C.) \ !:Q 0.35 , Grass / Legume I 0 " .....~. " 0.30 " ."\ ~ '0 *'Z ...... _------0--._ j,\ -1 :--0 ~ 0.25 Grass alone 0 I- 0.20 0 4 . zz 4.5 ..... E C.) . \ 10 4.0 \ . \ I , Grass I Legume 0 \ \ --...... ::e0 3.5 '" " . -- '0- Grass alone i U ------0 , U --', Z ~o " , « ) (!) '0 , a:: 0 I 4 8 12 16 22 '" YEARS OF PASTURE " Figure 5. Long-term effects of unfertilized guinea grass (Panicum maximum) pastures, with and without Centrosema pu6escens, on the topsoil organic matter after clearlng a rainforest in South Johnstone, Australia. Source: Adapted from Bruce (1965). . " ,.1 , t" ' -I.- ( .' e pH 10 Co +Mg (meq/IOOg) 7 .0--0. p- -0-<1..-0 6 '0' 5 Clayey Oxlsol, Parcgomfnas,Pa Loamy Oxiso~N. Mato Grosso • 4 f"Burnlng :3 ~ 0.5 2.5 K (meq/IOOg) AI (meq/IOOg) 0.4 2.0 '" p, .I 0.3 I \ I \ I , 0.2 po.d \ I I 0.1 0 100 % AI Saturation Available P (ppm) 80 60 20 2 0 0 '5 .25 % Organic Matter % Total N 4 .20 " 2 .1 ... ;, I), ..0...... 0.. .0-<>.0... '0...0 '0_-.0. -0-.0-0...0--0. '0' "().-¢' '0-0 .05 '0-0 0 I ' 3, 5 7 9 \I 13 0 3 5 7 9 \I 13 Age of Pasture Sampled (years) Figure 6. Changes in topsoil properties of Pancium maximum pastures of known age in eastern Amazonia (sampled at the same time). Adapted from: Serrao et ~., (1979).