the Symposium on Wheats for More Tropical Environments - cimmyt

240Soil Fertility ProblemsThe soils most suited for cropping in<strong>the</strong> Cerrados are <strong>the</strong> red-yellow latosolsand <strong>the</strong> dark red latosols. A surveycarried out by Lopes and Cox (8) showsthat <strong>the</strong>se soils are extremely low infertility in every aspect except organicmatter (Table 1). Virgin soils normallyhave a reasonable level of organicmatter. but this is decreased bycropping. and nitrogen needs to beadded to obtain high yields ofnonleguminolls crops. The two mainsoil problems are 1) low pH with itsaccompanying high exchangeablealuminum saturation and 2) low soilphosphorus levels. These two problemsmust be resolved. and <strong>the</strong>ir solutionwill be costly.Low pHThe problem of low pH and highexchangeable aluminum saturation canbe solved by liming. Two formulas arenormally used for making limingrecommendations:CaC03(tlha) :: 2 x meq exch AVl00 gorCaC03(tlha) :: (2 x meq exch AJI100 g) +12 - meq exch (Ca + Mg)/I00g]As a result of <strong>the</strong>se formulas.recommendations usually range from 2to 4 tons of lime per ha; this results ingood crop response.The lime is usually incorporated to adepth of 30 em. which corrects <strong>the</strong>problem only to this level; in o<strong>the</strong>rwords. with <strong>the</strong> application of lime.<strong>the</strong>re is an effective rooting depth ofonly 30 em. Under Cerrados conditions.e 400e-I:~.= 300oooooDTOPp• PETooo oo30- 20 C,)of~200>v't:l~~ 100I:~jv 0.e10 ~J F M A M J J A s°MonthNDFigure 2. CUmatic conditions ofBrasiUa, D.F., Brazil (average monthlytemperature (T) 21°C, annual rainfall (PP) 1570 mm and annual potentialevapotranspiration (PET) 1280mm)Source: EMBRAPA-CPAC(2)