Effect of IW:CPE-Based Irrigation Scheduling and N-Fertilization Rate on Yield, Water and N-Use Efficiency of Wheat (Triticum aestivum)

Under emerging water scarcities in the face of global warming, optimization of irrigation and nutrient inputs is essential to maximize input-use efficiency. Thus, a field experiment was conducted with wheat for 2-years to evaluate the effects of N and deficit irrigations on yield formation, water productivity (WP) and nitrogen-uptake efficiency (NUE). Treatment consisted of combinations of four N application levels, i.e., 60, 90, 120 and 150 kg ha(-1) as main-plot factors and seven levels of irrigation water (IW; equaling 1.00, 0.85, 0.70, 0.55, 0.40, 0.25 and 0.10 times of the cumulative open pan evaporation, CPE) as sub-plot factors. After pre-plant and first post-planting irrigation through flood method, line-source sprinklers were used. Grain yield increased with applied N and was the maximum (3.39-4.66 Mg ha(-1)) at IW:CPE 0.85 and declined @ 0.67-0.81 Mg ha(-1) for every 0.1 IW:CPE. Application of 150 kg N ha(-1) improved the grain yield by 6.0-8.9% over 120 kg N ha(-1) under medium stress (IW:CPE 0.41-0.70) and no stress (> 0.70) conditions, but showed little impact under severe stress (0.10-0.40) conditions. Rather it declined by 45.3-66.1 and 13.0-26.1% at 60 and 90 kg N ha(-1) over 120 kg N ha(-1), respectively under the latter. The WP and NUE ranged between 1.28-1.36 kg m(-3) and 37.4-38.4%, respectively, with 120-150 kg N ha(-1), while the counter figures were 0.99 kg m(-3) and 30.2% with 60 kg N ha(-1). On the whole, results indicate basing N applications on the water availability for irrigation for optimal grain yields where, WP and NUE vis-a-vis benefits can be maximized under deficit irrigation conditions.