不同施肥水平对长期麦豆轮作体系土壤氮素及产量的影响

探索施肥对长期轮作下土壤氮素变化及产量的影响，对优化氮素管理具有重要作用。通过优化施肥方案，对关中地区冬小麦-夏大豆长期轮作模式下作物产量及土壤全氮、硝态氮、铵态氮、微生物生物量氮含量动态变化进行定位研究。结果表明：土壤全氮、硝态氮、铵态氮含量秋冬季较高，春夏季较低，微生物生物量氮变化趋势与之相反。土壤中氮素各组分含量均表现为表层土高于下层土，土壤全氮、硝态氮、铵态氮平均含量及铵态氮层化比、土壤硝态氮与铵态氮比值随着化肥施用量的增加而增加，硝态氮层化比随施肥量的增加而减少。与不施肥相比，优化施肥促进微生物生物量氮含量的提升，而常规施肥导致微生物生物量氮含量下降。试验连续运行9 a后，施肥导致土壤pH和水分含量下降，对小麦、大豆产量有显著影响，与不施肥处理相比，小麦、大豆平均增产50.20%、45.29%。麦豆长期轮作种植模式下优化施肥在基本保证作物产量的同时，降低土壤中全氮、硝态氮、铵态氮含量，增加微生物生物量氮含量，减少化肥施用量。

Effects of Different N Fertilization Levels on Soil Nitrogen Content and Crop Yield in Long-term Wheat-soybean Rotation

Exploring the effects of different N fertilization levels on nitrogen change in soil and yield under long-term crop rotations will play an important role in optimization of the nitrogen management.In this field experiment,different fertilization treatments were set up to assess the change of different fractions of soil nitrogen and crop yield in winter wheat and summer soybean under long-term rotation.The range of total nitrogen(TN),NH⁺₄-N,and NO^-₃-N content in the soil during autumn and winter was higher than that during the spring,but the opposite trend was in microbial biomass nitrogen(MBN) content.The different N fertilization levels enhanced the TN,NH⁺₄-N,and NO^-₃-N contents,and it had significant difference between the different treatments.The TN,NO^-₃N,NH⁺₄-N contents and NO^-₃-N/ NH⁺₄-N rates increased with increase of the fertilizer application,and the fractions of soil nitrogen contents were higher in the surface soil than in the subsoil.The MBN content increased in response to the optimized fertilizer(0.8TF) treatment compared to the no fertilizer(NF) treatment,but decreased in response to the total fertilizer(TF) treatment.After nine years of continuous operation of the experiments,soil pH and water content under treatment plots decreased,but the yield of wheat and soybean increased significantly; Winter wheat yield increased by 50.20% and summer soybean increased by 45.29%,compared with the unfertilized plots.Under long-term wheat-soybean rotation system,optimized fertilizer application can basically ensured the crop yield,at the same time,can reduce total N,nitrate N and ammonium,can increase N content of bio-mass in microorganism,finally,the chemical fertilizer application is reduced.