潮土小麦–玉米轮作体系氮肥用量阈值及土壤硝态氮年际变化

  【目的】  合理施氮是粮食高产、稳产的重要保证。研究不同施氮水平下作物产量的可持续指数以及土壤硝态氮年际迁移特征，对指导黄淮海地区冬小麦–玉米轮作体系下农田氮肥的合理施用具有重要意义。  【方法】  长期定位试验始建于2006年，设置10个施氮水平:0、60、120、180、240、300、360、420、500和600 kg/hm2。测定冬小麦和夏玉米产量及土壤剖面 (0—200 cm) 硝态氮含量的年际变化特征。  【结果】  施氮水平显著影响冬小麦–夏玉米轮作体系下作物产量，施肥年限以及施肥年限与施肥量间的交互作用对小麦、玉米产量也存在极显著影响。施N 0～240 kg/hm2的处理，小麦、玉米产量随施氮量的增加逐渐增加；施N 300～600 kg/hm2的处理作物产量基本稳定，处理间差异不显著 (P > 0.05)。施氮能显著提高冬小麦产量的可持续性指数 (P < 0.05)，但对夏玉米产量的可持续指数影响较小。随着施氮量增加，土壤硝态氮含量呈现逐渐增加的趋势，且施N量低于300 kg/hm2时，0—200 cm土层硝态氮含量均处于较低水平，施氮量超过300 kg/hm2后，土壤硝态氮含量显著增加。另外，随着试验年限的延长，土壤硝态氮累积峰逐渐下移，2008、2011和2017年土壤硝态氮含量峰值分别在40—60 cm、80—120 cm和80—160 cm。  【结论】  黄淮海盐化潮土区，冬小麦–夏玉米轮作制度下氮合理用量在冬小麦上的阈值为240 kg/hm2、在夏玉米上的阈值为180 kg/hm2，在此氮肥用量下，长期施肥既可保证作物 (小麦、玉米) 稳产，又不会显著增加土壤硝态氮残留及向下迁移。

Optimal nitrogen rate and the down movement of soil nitrate nitrogen in wheat-maize rotation system in fluvo-aquic soil

  【Objectives】  Application of nitrogen (N) fertilizer plays important roles in maintaining soil fertility and crop production. Responses of grain yield and soil NO₃?-N concentration to N application rates were studied to guide efficient and sustainable fertilization under winter wheat-summer maize rotation system in Huang-Huai-Hai region of China.  【Methods】  The objective of this study was achieved through a long-term (2006?2013) winter wheat-summer maize rotation experiment conducted on a fluvo-aquic soil in Huang-Huai-Hai region of China. The ten N application rates were: 0 (control), 60, 120, 180, 240, 300, 360, 420, 500, and 600 kg/hm2. The wheat and maize yields were recorded, and soil NO₃?-N in 0–200 cm profile were measured.  【Results】  Nitrogen application rate, fertilization year, as well as interaction between fertilization year and N application rate significantly affected the yields of both wheat and maize. Winter wheat yield increased with increase in N application rate, but N 300 kg/hm2 reached the highest wheat yield. Increase in N application rate increased summer maize yield, but the increment became stable from N 120 to 600 kg/hm2. The N rate increased the sustainable yield index of winter wheat, but did not affect that of summer maize. The N rates above 300 kg/hm2 increased the soil NO₃?-N content. The cumulative peak of soil NO₃?-N content gradually decreased with increase in the year of experiment, and the peak of soil NO₃?-N content in 2008, 2011 and 2017 were found in 40–60 cm, 80–120 cm and 80–160 cm soil depths, respectively.  【Conclusions】  Based on our results, N 240 kg/hm2 and 180 kg/hm2 could be recommended as optimal nitrogen application rates for winter wheat and summer maize cultivation in fluvo-aquic soil of Huang-Huai-Hai region. These N application levels could ensure the stability of wheat and maize yield and prevent the increment and accumulation of nitrate N in deep soil.