the Symposium on Wheats for More Tropical Environments - cimmyt

234Alternatives toMinimize Soil ConstraintsSoli conservationand water retentionSoil tillage practices utilized in <strong>the</strong>soybean-wheat rotation are leading tosevere soil erosion in <strong>the</strong> Braziliansemitropical area. Burning wheat strawafter harvest. followed by landpreparation using heavy disc harrows.are common practices. Theseoperations result in an intensivedisturbance of <strong>the</strong> arable surface layer(0 to 10 cm). destroy organic maUer.decrease water infiltration and build upa compacted layer (hard-pan) between<strong>the</strong> 10 and 15-cm depth. causing strongrun-off and inadequate conditions forroot penetration and development. Soilerosion losses can be reduced 70 to90% by adopting a more appropriateconventional tillage method (plowingplus two light harrowings) or a notillagesystem (Figure 3). No--tillageenhances surface mulching by leaVingcrop residues and helps to increasewater retention and water aVailabilityfor <strong>the</strong> wheat crop (Figure 2).30~253$20oe15~34--No-tillage ----- Conventional tillage ,--------.... ....-,/',....,-.. -.,. ..---', ..." ... - ....---\ I, I,------_.'--------...._--. ,-,'"26 --.'".--------.-...-.10 20 30Days after planting-""Figure 2. Soli-water availability under conventional and zero tillagesystems in an o.1l:lsol soli. nor<strong>the</strong>rn Parana. Brazil"5-5It) 0.• il)0'0~--jeo.(.):;::l0 0~CI)6-60_Traditional (burning + 1 heavy harrOWing+ 2-5 light harrowings)Conventional (1 plOWing + 2 light harrowings)__......1 No-tillage15Tillage systemsFigure 3. Soil losses by erosion as related to tillage systems in an o.1l:isol(red latosol) soli, nor<strong>the</strong>rn Parana, Brazil