Effects Of Continously Applying Nitrogen On Soil Nitrate Accumulation In Rain-fed Agriculture Region Of Mid Loess Plateau

The production and application of chemical nitrogen fertilizer promote mightly the decelopment of agriculture. From the later of 20th century, the amount of the production and application of chemical nitrogen fertilizer of world and China are increasing. High amount of nitrogen fertilizer result in continous nitrogen surplus in agro-ecosystem. Companyed with development of the regional economy, the nitrogen rate is increasing. Nevertheless, the NO3--N content and ammont of the NO3--N accumulation were not seen clearly, as well as their residual efficiency to the succession crop in the soil profile of agro-ecosystem in the Mid Loess Plateau.On the base of researching Huangmian soil nitrogen mineralization, nitration by incubation experiment, to study the NO3--N accumulation amount affected by nitrogen rate and its residual efficiency to the succession crop, exhaust and uptake of nitrogen by crops through spring wheat nitrogen rate experiment and nitrogen exhausting culvtivating exteriment. The main conclution was as follows.1. The mineralization of Huangmian soil is very weak and its main production is NO3--N. The NO3--N content increase as the moisture increases. But nitration is intense. After urea is applied into intense Huangmian soil, nitration will finished completely after 7～14 days when the soil moisture is≥13%. The peak value of nitration rate increases as the soil moisture increases.2. The results of spring wheat nitrogen rate experiment show that the nitrogen rate influence the average nitrate content of 0～200cm soil profile at spring wheat harvest. The verage nitrate content of 0～200cm soil profile at spring wheat harvest, for 3 years continuously applying nitrogen is 3.9～16.7mg kg-1, and increases as the nitrogen rate increases except nitrogen rate 105kg hm-2.As well as after ontinuously applying nitrogen for 2years and the 3rd year no applying nitrogen,it is 3.4～7.5mg kg-1, and increases as the nitrogen rate increases.The distribution of soil nitrte in 0～200cm soil profile at spring wheat harvest takes on"parabola"shape. Continously applying nitrogen for 3 years, The peak of soil nitrate is in 80～110cm or 110～140cm layer. The peak value is 6.3～38.3mg kg-1. The peak of soil nitratecontent is different from that of other layers'significantly. Continuously applying nitrogen has not resulted in the deep layer movement of the soil nitrate. When the spring wheat harves, there are no big changes of the soil nitrate comtent of the 170～200cm layer...