Title: Optimal Supply of Water and Nitrogen Improves Grain Yield, Water Use Efficiency and Crop Nitrogen Recovery in Wheat
Abstract: Little information is available on the role of optimized application of irrigation and N on crop N recovery and NO3-N build up and movement in soil profile.A field experiment was carried out to evaluate the effects of irrigation and N management practices on wheat yield, water and fertilizer use efficiency and NO3-N distribution in soil.The treatments included were three levels of irrigation; 0.7, 1.0 and 1.3% of the estimated evapo-transpiration (ETc) and four levels of N; 0, 110, 160 and 210 kg N ha -1 in split plot design.The N was applied either in two splits (50% at sowing + 50% at maximum tillering) or three splits (50% at sowing + 25% at maximum tillering + 25% at spike initiation).Nitrogen applied at 110 kg ha -1 in three splits produced higher wheat yield, N recovery and water use efficiency (WUE) than two splits.Further, application of N in three splits had considerably lesser accumulation of NO3-N in soil as compared to two splits.A significant irrigation effect was observed on grain yield, N recovery and WUE.The highest levels were achieved with water application according to crop water requirement (1.0 ETc).The deficit irrigation produced significantly lower grain yield (3.15 t ha -1 ) than full (3.80 t ha -1 ) and excessive (3.80 t ha -1 ) irrigations.Response of WUE to irrigation levels was in the order, 1.0 ETc (11.03 kg ha -1 mm -1 )>0.7 ETc (10.63 kg ha -1 mm -1 )>1.7 ETc (9.84 kg ha -1 mm -1 ).Deficit irrigation resulted in higher build up of NO3-N in surface soil.In contrast, excessive irrigation resulted in greater concentration of NO3-N in lower depths of soil.The results from this research show that there is great potential for decreasing N leaching and increasing wheat crop yield and N use efficiency thorugh controlled irrigation and N application according to crop demand.