The 8 year-field experiment was carried out to study the effecls of nitrogen application rate on soil nitrate nitrogen distribution,accumulation and crop yield. The results showed that the change rule of soil nitrate nitrogen content in 0 - 200 cm soil layer was N575 > N400 > N225 > NO after 8 wheat-maize rotation cycle. With the increasing of soil depth, soil nitrate nitrogen content in 0 - 80 cm soil layer of each treatments decreased, in 60 - 80 cm reduced to minimum value. With soil depth increasing,the soil nitrate nitrogen in 80 -200 cm firstly increased and then decreased, the differences among different treatments increased significantly. The difference reached a significant level for nitrate nitrogen of the same soil layer in 80 - 200 cm of different treatment. After 8 wheat-maize rotation cycle,the ratio of 100 -200 cm soil nitrate nitrogen accumulation of N575 treatment in the total cumulative volume increased 15. 18%. By volume of nitrogen and soil nitrate nitrogen accumulation with mathematical model simulation, found two in accordance with the linear relation, nitrogen and soil nitrate nitrogen accumulation amount of regression equation is γ = 1. 34χ + 75. 58( R2 = 0. 84 ** ) . From the winter wheat and summer maize rotation cycle, the optimum amount of nitrogen is 400 kg/hm2 . Considering the effect of nitrogen application rate on soil nitrate nitrogen residue and crop yield, total amount of nitrogen fertilizer application should be about 225 - 400 kg/hm2 in wheat - maize rotation system at piedmont plain of Huabei. This could basically control soil nitrate nitrogen leaching loss to deep soil and reduce groundwater pollution risk caused by soil nitrate nitrogen leaching.%通过8年田间小区定位试验研究不同施氮量处理对土壤硝态氮分布、累积以及作物产量的影响.结果表明,在小麦-玉米轮作8个周期后,0～200 cm土体中各土层的硝态氮含量变化规律为N575＞N400＞ N225＞N0,随着土壤深度的增加,在0 ～ 80 cm土层各施氮量处理土壤硝态氮均呈下降趋势,各处理在60 ～ 80 cm降到最低.各施氮量处理在80～200 cm土壤硝态氮随着土壤深度的增加均呈先升高后降低的趋势,同一土层不同施氮量处理间硝态氮的差异明显增大.经过8个小麦玉米轮作周期后,N575处理100 ～ 200 cm土壤硝态氮累积量所占总累积量的比例提高15.18％.通过对施氮量与土壤硝态氮累积量用数学模型模拟,发现二者符合线性关系,施氮量与土壤硝态氮累积量的回归方程为y=1.34x+ 75.58(R2=0.84**).从冬小麦-夏玉米轮作周期考虑,全年的适宜施氮量为400kg/hm2.综合考虑施氮量对土壤硝态氮的残留量与作物产量的影响,提出华北平原区小麦-玉米轮作周期中总施氮量应控制在225 ～ 400 kg/hm2之间,基本上能控制土壤硝态氮向深层土壤的淋失,能明显降低土壤硝态氮向地下水淋失的风险.
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