Effects of irrigation and nitrogen application on water consumption and yield of winter wheat in different precipitation years

Abstract: Irrigation and nitrogen fertilization are two major factors influencing the grain yield production in agroecosystem, and appropriate irrigation and nitrogen fertilizer application can improve grain yield and water use efficiency by alleviating the stress of drought and nutrient deficiency, enhancing photosynthetic area and photosynthetic rate. In this study, we investigated the impact of precipitation year patterns on crop yield, water consumption and their relationship under different water and nitrogen management practices. A field experiment during 2011-2014 was conducted with 3 irrigation levels and 4 nitrogen input levels in Guanzhong Plain of Shaanxi Province. Irrigation levels included no irrigation, irrigation 46 mm at the jointing stage, and irrigation 46 mm at the jointing and wintering stages, respectively. The nitrogen input levels included nitrogen application rate of 0, 105, 210 and 315 kg/hm2. The fertilizer was urea. The other field management followed local traditional methods. The experiment was carried out by completely randomized design. Soil water content and grain yield were measured and the water use efficiency was calculated as the ratio of yield to ETa under various water and nitrogen management in different year patterns. Meanwhile, soil water storage was calculated based on the volumetric water content. Water consumption (ETa) was calculated by the field water balance equation. The results showed that soil water content before sowing was affected by irrigation, nitrogen fertilizer application rate and precipitation. The soil water storage before sowing increased as more irrigation and less nitrogen application rate were applied. The 0-100 cm soil water storage before sowing would be supplemented majorly when the total precipitation from July to September was below 400 mm, and the 0-180 cm soil water storage before sowing increased by 0.47 mm as the total precipitation from July to September increased 1 mm. The 0-180 cm soil water storage at harvest improved with more irrigation but decreased first and then leveled at a certain value as more nitrogen was used, and it was greatly influenced by the precipitation of 2 months before harvest. Water consumption increased with more irrigation while the effect of nitrogen and interactive effect of irrigation and nitrogen on water consumption was not significant, and it has a linear relationship with water input during the growing period with the coefficients being influenced by initial soil water conditions, i.e. less water would be consumed led by unit water input when the soil water storage before planting was higher. Irrigation enhanced both the yield and actual water consumption, while the yield was only improved significantly in relatively dry year 2012-2013 and the water use efficiency were not boosted in all years; Nitrogen fertilization had no significant effect on water consumption but improved yield and water use efficiency significantly, which showed that nitrogen application rate increased the proportion of crop transpiration to total water consumption. Additionally, the maximum (boundary) yield and water use efficiency were explored by developing a boundary function of winter wheat yield and evapotranspiration in Guanzhong Plain. From the function, we found that when the water consumption exceeded 388 mm, the grain yield would level at 8 184 kg/hm2 and the maximum water use efficiency was 2.52 kg/m3. In this research, the interactive effects of water, nitrogen and precipitation year patterns on yield and field water consumption were analyzed, aiming at providing valuable information for developing reasonable water and fertilizer management practices in winter wheat production.