TILLAGE RESPONSES OF WHEAT IN RELATION TO IRRIGATION REGIMES AND NITROGEN RATES ON AN ALLUVIAL SAND IN A SEMIARID SUBTROPICAL CLIMATE

A 3 year field study was conducted to evaluate the effects of conventi onal tillage (CT, uniform soil disruption to 10 cm depth) and deep til lage (DT, sub-soiling to 40-45 cm depth with passes of a single tine c hisel 35-40 cm apart, followed by CT) in combination with frequent sma ll and infrequent large irrigation applications and a range of N ferti lizer rates on root growth, water and nutrient use, and yield of wheat . The trial with tillage and irrigation combinations in main plots and N rates in sub-plots was performed on an alluvial sand (Typic Ustipsa mment) in north-west India. Deep tillage decreased bulk density and so il strength (measured in the first year of experiment) in the tilled z one and increased the depth and density of rooting. Frequent and small irrigations also enhanced root growth during the dry year. In both of these cases, there were significant increases in dry matter accumulat ion and grain yield of wheat. At 160 kg N ha(-1), deep tillage and inf requent large irrigation increased mean grain yield by 1.0 Mg ha(-1) o ver 2.7 Mg ha(-1) obtained with conventional tillage and infrequent la rge irrigations. The corresponding increase of yield in conventional t illage with frequent small irrigations was 0.7 Mg ha(-1). A combinatio n of deep tillage and frequent small irrigations increased yield by 2. 3 Mg ha(-1). These results suggest that for higher wheat yields and in put use efficiencies on alluvial sands, deep tillage should be combine d with frequent small irrigations. (C) 1997 Elsevier Science B.V.