冬小麦-夏玉米轮作体系还田秸秆氮的释放与作物利用特性

In the North China Plain, a large amount of nitrogen in crop straw has been returned to the field accompanying with crop straw in the wheat-maize rotation system every year, and crop straw nitrogen has already been a major source for soil nitrogen pool in this agricultural system. To our best knowledge, no systematical studies have investigated the characteristics of release and mineralization of nitrogen in crop straw and quantified to which extend the availability of straw-N to subsequent crop. In this study, we will investigate the various fates of nitrogen in wheat and maize straw returned to the soil adopting 15N isotope tracer technique. Firstly, applying 15N-labeled nitrogen fertilizer in crop growing season, partial nitrogen in the straw would be labeled by 15N as a result of crop N uptake. Secondly, 15N-labeled crop straw would be returned to the soil in the new micro-plots after crop harvest, and then in these micro-plots winter wheat-summer maize rotation is conducted. Different N-fertilizer rates and straw-rotting agent treatments are then arranged for during wheat and maize growing seasons, respectively. 15N content in the residual straw and soil after crop harvest would be monitored to explore the characteristics of release and mineralization of nitrogen in the returned crop straw, and further to study its response to exogenous N-fertilizer and straw-decomposing agent. The availability of nitrogen released from straw to subsequent crops would be also clarified by measuring 15N uptake by wheat and maize. The results of the research might play a significant role in the nitrogen nutrition management and rational utilization of crop straw nitrogen in the winter wheat-summer maize cropping system in the North China Plain.

华北平原冬小麦-夏玉米轮作体系中，每年都有大量的氮素随秸秆一起还田，还田秸秆氮已成为该种植体系土壤氮库的重要来源之一，但目前有关秸秆氮的释放、矿化特征及其作物利用特性等问题尚未得到完全阐明。本项目拟在大田条件下施用高丰度15N肥料(15N丰度≥50%)，通过作物吸收实现对秸秆氮素的标记。15N标记秸秆还田到新的空白微区后，进行冬小麦-夏玉米轮作种植，并在作物生长季内分别设置施氮量和秸秆腐熟剂处理。作物收获后通过检测残留秸秆和土壤中的15N含量以探究还田秸秆氮的释放与矿化特征及其对外源施氮量和腐熟剂的响应；通过测定后茬作物对还田秸秆释放的15N的吸收量以明确还田秸秆氮的作物利用特性。有关研究结果理论上将丰富对还田秸秆氮释放特征与作物利用特性的认识，实践上将为华北平原冬小麦-夏玉米轮作体系的氮肥管理、秸秆氮素的合理利用以及作物氮营养调控等提供科学依据。

华北小麦-玉米一年两熟种植体系中秸秆还田是一项十分重要的农艺措施，还田秸秆氮已成为该种植体系土壤氮库和作物氮素营养的重要来源之一，但目前有关秸秆腐解、秸秆氮释放特征及其作物利用特性等问题尚未得到完全阐明。基于此，本项目在大田微区控制条件下利用15N同位素示踪技术标记秸秆氮，秸秆还田后设置腐熟剂和施氮量处理，研究小麦、玉米秸秆还田后秸秆腐解的时空变化动态，秸秆氮的释放特征及其对作物的氮营养贡献。主要结果如下：（1）小麦秸秆还田3个作物季后玉米秸秆还田2个作物季后秸秆腐解率和秸秆氮释放率均超过或接近90%，小麦秸秆氮的释放速率比秸秆自身腐解速率快，玉米秸秆氮的释放速率比自身腐解速率慢。秸秆腐熟剂在小麦秸秆还田第1季有显著促进腐解作用；腐熟剂和施氮量对还田玉米秸秆腐解未发现有显著影响。（2）小麦秸秆还田后秸秆营养性成分的释放速率表现为：钾>可溶性碳水化合物>氮>秸秆自身>磷，秸秆结构性组分的释放速率表现为：全碳>半纤维素>纤维素>秸秆自身>木质素。（3）小麦秸秆还田3个作物季后秸秆氮作物吸收率、秸秆残留率、土壤残留率和损失率依次为13.9%、1.1%、58.0%和42.6%，玉米秸秆还田2个作物季后上述四个指标依次为18.6%、11.5%、27.6%和42.3%。小麦秸秆氮对后茬作物氮营养贡献率在0.8%-1.1%之间，玉米秸秆氮在2.4%-4.8%之间。研究结果对华北麦-玉种植体系秸秆氮合理利用、氮营养调控及氮肥减施增效有重要意义。