基于作物生长过程的坡耕地夏玉米-冬小麦轮作体系氮磷流失效应

Nutrient loss is an important way of agricultural non-point source pollution with the seasonal changes in soil-crop system. In the system, crop growth accompanied by factors such as changes in background value of soil, vegetation coverage, the plants absorb and rainfall characteristics affect nutrient loss; Nutrient loss have resulted in seasonal changes of soil-crop nutrient balance, lowered crop yields and increased environment nutrient loading, thus revealing the coupling relationship between crop growth and nutrient loss seasonality and prevention and control of agricultural nonpoint source pollution are important. The project intends to study the system-crop system of winter wheat and summer maize rotation,.combining with field monitoring and laboratory simulation, to 1) monitor the changing forms and amounts of nitrogen and phosphorus in soil, the height of crop plant, leaf area index and nitrogen and phosphorus content in plant during crop growth to clarify seasonal dynamics of crops-nutrient interactions; 2) Simulate the runoff and nutrient loss process under rainfall conditions, monitoring runoff paths, runoff volume, sediment, and changing forms and amounts of nitrogen and phosphorus loss to obtain the seasonal dynamics of nitrogen and phosphorus loss from soil-crop systems; 3) Based on the soil-plant nutrients annual conservation, quantify nitrogen and phosphorus balance of inputs and outputs, and seasonal differences to obtain the optimal weighting coefficients of crop yield and.environment nutrient loading, and reveal the seasonal effect of nutrient loss in soil-crop system, providing the prevention and control of agricultural nonpoint source pollution.

坡耕地氮磷流失主要来源于土壤-作物系统。作物生长会导致系统内生物性状和土壤理化性质的改变，进而改变氮磷流失；同时，氮磷流失又会影响系统内氮磷的分配和平衡，进而影响作物生长，因此作物生长和氮磷流失之间存在耦合关系，阐明该关系有利于揭示坡耕地作物生长过程的氮磷流失效应。本项目以坡耕地夏玉米-冬小麦轮作体系为研究对象，采用大田试验，研究不同氮磷水平和作物株高、氮磷含量、叶面积指数、土壤孔隙度、氮磷形态及数量的相关性，探明氮磷-作物相互作用；通过对轮作体系模拟降雨，监测产流路径(地表径流和壤中流)中氮磷和同期作物生物性状变化，获取各生物性状对氮磷流失的贡献权重；基于氮磷-作物相互作用和各生物性状的贡献权重，阐明作物生长和氮磷流失的耦合关系；量化轮作周期内氮磷在植株-土壤-径流中的分配平衡，明确作物产量和氮磷输出负荷的最优加权，揭示土壤-作物系统的季节性氮磷流失效应，为防控农业面源污染提供依据。

本课题执行时间为2017年01月-2019年12月。项目通过分别监测天然降雨和模拟降雨条件下的夏玉米-冬小麦轮作体系作物生长过程和坡面氮磷流失过程，研究获取了轮作体系中生物性状变化特征和氮磷流失变化特征，并对氮磷流失过程及其影响因素进行相关性分析和回归分析，取得了以下研究成果：（1）天然降雨条件下施肥水平通过影响夏玉米和冬小麦的植株氮含量和收获指数，从而影响整个生长期内植株从土壤中带走的氮含量；（2）天然降雨条件下夏玉米坡面径流中可溶性氮（氨态氮和硝态氮）流失更多地发生于生殖生长阶段，而可溶性磷流失则更多地发生于营养生长阶段；（3）模拟降雨试验中同雨强条件下，不同生长期内的产流特征差异明显；施肥水平较低的小区其径流体积最高值出现在四叶期，施肥水平较高的小区出现在抽雄期；土壤表层孔隙度和深层孔隙度对产流的影响差异明显，表层孔隙度和径流体积相关性更强；（4）模拟降雨试验中同雨强条件下，夏玉米坡面径流中总氮流失浓度随生长过程延长而加剧，总磷流失浓度随生长过程延长而减轻，两者均体现了坡面产流过程中养分流失的时段性；（5）影响总氮流失浓度最大的因素是径流产流时间，影响总磷流失浓度最大的因素是覆盖度，影响径流体积最大的两个因素是土壤深层含水量和土壤深层孔隙度，上述所有因素都随植株生长过程而变化，因此作物生长过程对氮磷流失的影响确定且重要；（6）氮磷流失在整个生长过程中不同生长期内的比例分配结果表明四叶期和完熟期流失量最大，但是随着施肥水平的增加，养分流失在各生长期内的分配比例趋于平均。综上，本课题的研究结论可以为该地区时段性、针对性地防控农田玉米氮磷流失提供理论依据。