Residual Nitrogen In Soil, Its Utilization And Influence Factors In Dryland

Nitrogen fertilizer has important role on food production in world. More than 2×107t of N fertilizer has been applied every year in China since 1994. Excessive N fertilizer applied leads to more residual N in soils of farmland. It not only reduces N fertilizer utilization efficiency, but also causes many environmental problems. Three field experiments were conducted to investigate the effect of different cultivation methods on residual N and N uptake, availability of residual N for next crops and the effect of different crops and different cropping patterns on utilization of residual N in dryland. The main conclusions include:(1) Plastic film mulching and furrow planting increased wheat yield, N uptake by wheat and N fertilizer utilization efficiency, compared to no mulch, indicating that both of them were important to reach the good harvest. However, they also increased the accumulation of NO3--N in soil because of the accelerated mineralization of organic N under higher soil temperature and water content, suggesting it was necessary to increase organic material input along with these two cultivation methods.(2) There were no significant differences of wheat yield and N uptake by wheat for the first two years between straw mulching and no mulch, while they had significant differences for the third year, indicating that it needed some years to see the effect of straw mulching on crop yield.(3) Wheat yield, N uptake by wheat and residual nitrate N throughout the profile of 0~200 cm were significantly higher when 240 kg N/hm2 was applied than 120 kg N/hm2. N rate of 120~240 kg/hm2 was reconmened for the winter wheat growth in the local region in order to reach the goal of high yeild and low residual N content in soil.(4) Wheat yield, N uptake by wheat and N fertilizer utilization efficiency increased significantly with the increase of wheat density, while residual nitrate N showed a reduction in the deeper layer of soil, suggesting that the appropriate increase of wheat density was a way to obtain high production and high efficiency.(5) After 3 years cropping, 446 kg/hm2(292~686 kg/hm2 )of residual mineral N (NH4+-N+NO3--N) were found in 0~200 cm depth of soil, which were equivalent to...