Effects Of Irrigation And Nitrogen Fertilizer On Water And N Use Of Wheat Under Straw Mulching

Water and nutrients are important factors which restricts wheat production increases in arid area in Southwest China. Appropriate nitrogen fertilization, cultivation modules and irrigation stage are key factors to enhance wheat production and nutrient uptake. Carried on the field experiments, effects of irrigation stage, different nitrogen fertilization under straw mulching conditions on yield of winter wheat, nitrogen uptake, nitrogen use efficiency, soil water content and accumulation of nitrate were studied. The main results obtained were listed as follows:1. Despite of mulching or not, supplementary irrigation in jointing stage could affect wheat yield and biomass obviously. Irrigation in filling stage could increase wheat yield under mulching conditions. Despite of mulching or not, irrigation in jointing stage could enhance nitrogen uptake by winter wheat, the N uptake amount by winter wheat cultivated under straw mulching conditions is higher than no mulching significantly. Effect of straw mulching on N uptake and utilization is in relation to supplementary irrigation in growing stage, Irrigated in seedling and filling stage, nitrogen use efficiency of winter wheat cultivated under straw mulching conditions is higher than no mulching. Despite of mulching or not, grains per ear was increased and 1000-grain weight decreased with the increase nitrogen fertilizer applied. Grains per ear and 1000-grain weight were both increased, and harvest index of wheat was enhanced under straw mulching conditions at higher nitrogen fertilization level.2 After harvests, there was a low water content layer exists in 80-120 cm of the soil profile, the low water content layer move downward in drought years. More precipitation in growing stage or pre-sowing soil water-storage capacity could result the shallower low water content layer, and there is no obvious difference exists between straw mulch and no mulch. No irrigation or irrigation in filling stage, straw mulch could reduce water consumption of growing stage, and also could increase the water use efficiency of wheat. Compared to no mulch, straw mulch could also increase the 2-m water-storage capacity under no irrigation conditions. In relative drought years, water use efficiency could be enhanced by mulching at high nitrogen applied level, and in relative humid years, no significant difference exists between straw mulch and no mulch. The water use efficiency increased significantly with the increase of nitrogen fertilizer application in despite of mulch or not. 3 Higher nitrogen application levels resulted higher cumulant of nitrate in soil profile, especially under no mulch conditions. And the cumulation of nitrate could be observed during the whole soil profile from 0 to 200 cm, especially in surface layer of the profile. Under irrigation conditions, average nitrate residue amount in 0-200 cm soil profiles under mulch conditions is 225.6 kg/ha, while it was increased to 281.3 kg/ha under no mulch conditions, which suggested that nitrate residual amount could be decreased by straw mulching.