the Symposium on Wheats for More Tropical Environments - cimmyt

23~Tolerance to soil aciditySoil acidity is one of <strong>the</strong> majorconstraints for agricultural productionin tropical and subtropical soils inBrazil, and effects of excess aluminumon <strong>the</strong> wheat crop are well known.Advances in plant breedin,g, initiated byIwar Beckmann in sou<strong>the</strong>rn Brazil in1920, have led to <strong>the</strong> development ofaluminum-tolerant varieties which givereasonable yields under acid soilconditions, even when lime is notapplied; sensitive varieties give loweryields even when lime is applied(Figure 4). To arrive at appropriaterecommendations for farmers, <strong>the</strong>1.61.2variety tolerance level to soil aciditymust be considered, since soils arevariable in acidity levels and varietiesgive different performance on acid soils,even with liming. Under fieldconditions, a study was carried out inorder to characterize limit-values for %of soil-aluminum saturation:(% Al = Al x 100)AI+Ca+Mg+KThis formula can be used as aparameter to quantify <strong>the</strong> tolerance ofwheat varieties to soil acidity. Table 4_NoLime-;s''%'' ,.~ Liming for Al =0,--_I Liming for pH =6.00.4IAC-5 (Maringa)VarietySonora 64-RFigure 4. Effects of liming on yield of two wheat varieties in an OZl801 (redlatosol) soil, nor<strong>the</strong>rn Parana, BrazilTable 4. Criteria used to classify aluminum tolerance of wheat varieties, Parana, BrazilTolerance levelof varietyHighly susceptibleSusceptibleMedium tolerantTolerantHighly tolerantCritical value of soil-AI saturation(80 cm profile depth)Less than 5 0/0less than 20 0/0less than 35 0/0Less than 45 0/0More than 45 0/0