Residual Nitrogen In Soil And Its Utilization In Dryland

Nitrogen fertilizer has important role on food production. At present, it is common in many areas of China to use excessive nitrogen fertilizer. Excessive N applied leads to more residual N in soils of farmland. It not only reduces N fertilizer utilization efficiency, but also causes many environmental problems, like pollution of underground water .Two field experiments were conducted to investigate the effect of different cultivation methods on residual N in soils and N uptake by crops, and the effect of different crops on utilization of residual N in dryland. The main conclusions include:Both of film mulch and furrow planting increased wheat yield and N uptake by wheat, while straw mulch didn't increase wheat yield and N uptake.29.87～462.59 kg residual nitrate per hectare were found in the depth of 0-200 cm soil after 4 years cropping, whicn was greater than that in last year. There was a peak of accumulated nitrate around the depth of 80-100cm soil, which was deeper than that in last year.Much nitrate was found in soil depth of 0-200cm for film much treatment while fewer nitrate was found for furrow planting and straw mulch treatments, comparing with no mulch.When 240 kg N/hm2 was applied, accumulated nitrate in 0-200 cm of soil was 6 times of control (no N fertilizer application), and 3.5 times of N120 treatment (120 kg N/hm2 appilcation).Crop density had no effect on residual nitrate in soil depth of 0-200cm.When no N fertilizer was applied, 75.5% of residual nitrate in soil depth of 0-300cm decreased after 3 years of cropping of alfafa while 71.6% of that for winter wheat. Residual nitrate in soil depth of 100-300cm contributed dominating decrease for alfafa while residual nitrate in 0-200cm for winter wheat.