Effects Of Nitrogen Application Amount And Time On Ammonia Volatilization, Nitrogen Leaching And Use Efficiency

The research was carried on in large-scale percolation pond in the College of Agriculture in Yangzhou University in2009-2011, under rice-wheat rotation, effects of different soil types, nitrogen application rates, fertilizing season, seepage volume on density of NH4+-N and NO3--N in surface water and leakage water, nitrogen accumulation in rice plants, grain yield and yield components and the vertical migration of soil nitrogen and leaching, loss of ammonia volatilization from paddy field and rice yield were studied, for rational fertilization, controlling the loss of nitrogen in paddy fields, reducing non-point source pollution to provide theoretical and practical basis. The main results are as follows:1. After fertilizer nitrogen application, ammonia volatilization rapidly happened in paddy fields, and reach the peak in1to3days, the amount of ammonia volatilization with the increase of nitrogen, ammonia volatilization losses in clay soil was lower than that in sandy soil. Total ammonia volatilization losses from sandy soil was101.9kg·hm-2the proportion to nitrogen application rate was10%, total ammonia volatilization losses from clay soil was1133.65kg·hm-2, the proportion to nitrogen application rate was13%. The ammonia volatilization losses from bigger to smaller were the tillering stage>4leaves from top panicle stage> basal stage>2leaves from top panicle stage. Ammonia volatilization from the best fit model to follow the mathematical simulation formula:Y=AeBx(Both A and B are coefficients; Y is ammonia volatilization;X is nitrogen application), and the correlation coefficient R2>0.9.2. The main form of nitrogen in surface water after fertilizer nitrogen application is NH4+-N.The concentration of NH4+-N in surface water increases rapidly and reaches the maximum in1to2days after fertilizer nitrogen, then gradually reduced. The concentration of NH4+-N in surface water on the fifth day after the basal fertilizer is12.5-34.5%of the first day in sandy soil. Behavioral characteristics of NH4+-N in the application stage of panicle fertilizer is consistent with the basal and tillering fertilizer application stage. The concentration of NH4+-N in surface water is a bit lower than its in basal and tillering fertilizer application stage under the same application amount.The average concentration is2.67-12.16mg·L-1,while the number is3.52-16.96mg·L-1in in basal and tillering fertilizer application stage. At the same time NH4+-N concentration in surface water in clay soil is about0.5-4.8mg·L-1lower than which in sandy soil at the same fertilizer application amout and fertilizer season.3. The main form of nitrogen is NOP3--N in the leakage water in rice ecosystems. Nitrogen loss in the leakage water from leaching increased gradually with the increased nitrogen application amount. The inorganic nitrogen in the leakage water was dominated by NO3--N. The concentration of NO3--N in the leakage water reached a level as high as6.065mg·L-1in the treatment of high nitrogen application amount. In all the treatments, the concentration of NO3--N was about3.5times as high as the concentration of NH4+-N. The concentration of NH44+-N in the upper soil was lower than that in the lower soil, showing a trend that was contrary to the concentration of NO3--N. Compared with other stages of nitrogen application, the concentration of NO3--N and NH4+-N were higher after the application of basal nitrogen. The period after basal fertilizer should be a critical period of preventing nitrogen contamination.4. With the increase of nitrogen application amount, the rice grain yield, dry matter accumulation and nitrogen accumulation in rice plants increased, but nitrogen use efficiency was decreased. The nitrogen use efficiency in the treatments of high nitrogen application amount was only30%more or less. Compared with the sandy paddy soil, rice grain yield, dry matter accumulation and nitrogen accumulation were slightly higher in sandy soil. At the nitrogen application amount of300kg·hm-2, the highest rice grain yield was recorded and the paddy soil was kept environmentally secure. With the increase of nitrogen application amount, average yield, marginal yield, partial factor productivity and elasticity of productivity (abbreviated as EP) were decreased. The marginal yield has been negative at the level of N4both in clay soil and in sandy soil.