秸秆还田结合减氮调控旱地土壤硝化潜势维持作物产量的机理

  【目的】  氮肥过量使用所导致的氮素利用率低和环境污染等问题严重影响现代农业生产。研究秸秆还田改善旱地农田土壤性质、提升土壤肥力和氮素利用率的潜力和作用机理，为减少氮肥用量、提高作物氮素利用率和土壤肥力提供科学依据。  【方法】  本研究选取河南许昌潮土和云南曲靖红壤两种典型旱作农田，2016～2018年开展了田间玉米－大麦/小麦轮作定位试验，在两地同时设置以下4个处理:不施氮 (CK)、常规施氮 (N)、减氮20% (80%N)、减氮20%配合秸秆还田 (80%NS)，研究不同处理对土壤养分、土壤硝化潜势和作物产量及氮肥利用率的影响。  【结果】  与N处理相比，80%NS处理可稳定保持麦季抽穗期和玉米季抽雄期两种旱地土壤可溶性有机碳氮养分含量，促进土壤中NH₄+-N的积累并降低了NO₃–-N含量；80%NS处理使潮土和红壤硝化潜势分别降低了5.5%～33.9%和7.8%～37.5%；3年连续减施20%氮肥配合秸秆还田能够稳定产量并表现出一定的增产效果 (11.2%～20.4%)，提高氮肥利用率6.4%～10.3%；而80%N处理会使作物产量下降3.9%～13.4%，氮肥利用率降低1.8%～38.9%。  【结论】  连续3年减少常规氮施用量20%配合秸秆还田，不仅增加了土壤有机碳氮含量，还减缓了土壤的硝化作用，增加了土壤铵态氮积累，实现对作物所需养分的持续供应，因而在维持和提高作物产量的同时，提高了氮肥利用率。单纯降低氮肥用量则有降低作物产量的风险。

Mechanism of combination of nitrogen fertilizer reduction and straw returning in regulating dryland nitrification intensity and keeping stable crop yield in long run

  【Objectives】  Low nitrogen use efficiency and environmental pollution are common in modern agricultural production due to excessive use of nitrogen fertilizer. The potential and mechanism of combination of straw returning and chemical fertilizer reduction were studied to improve the soil properties and increase nitrogen use efficiencies in condition of not affecting or even increasing the yield of crop.  【Methods】  Field experiments were conducted in two typical uplands of north China and south China for three years. The north site was located in Xuchang of Henan, where was fluvo-aquic soil, and the south one was in Qujing of Yunnan, where was red soil. The cropping system in both location was corn-barley/wheat rotation. The field experiments had four treatments, including no nitrogen fertilizer control (CK), inorganic NPK fertilizer alone (N), reduced inorganic nitrogen by 20% (80%N), 80%N plus crop straw returning (80%NS). The soil nutrient contents and nitrification intensity were measured during growing seasons, and the crop yields were investigated and the nitrogen use efficiency were calculated.  【Results】  Compared with N treatments, reducing nitrogen by 20% and combined with straw returning for three years could maintain stable or even increase crop yields, increase the content of dissolved organic C and N in dryland soils at barley/wheat heading stage and maize tasling stage, promote the accumulation of NH₄+-N and reduced the content of NO₃–-N. 80% NS reduced nitrification potential by 5.5%–33.9% in fluvo-aquic soil and by 7.8%–37.5% in red soil. Consecutive three-years’ 80%NS treatment maintained stable yields and even increased yield by 11.2%–20.4%, and increased nitrogen use efficiency by 6.4%–10.3%. In contrast, 80%N treatment reduced yields by 3.9%–13.4%, and reduced N fertilizer utilization efficiency by 1.8%–38.9%.  【Conclusions】  Adequate N reduction along with straw returning could increase soil organic carbon and nitrogen contents, slow down nitrification intensity, therefore maintain the continuous supply of nutrients to ensure crop yield and increase nitrogen utilization rate. Reducing nitrogen input without straw returning shows risk of decreasing crop yields.