棉花/二月兰套作对棉田土壤氮素淋溶的阻控机制

Excessive application of nitrogen fertilizer in the cotton production of the Yellow River basin, resulting in environmental problems such as groundwater pollution by nitrogen leaching which have become increasingly prominent. Therefore, it is urgently necessary to explore chemical fertilizer reduction, green and sustainable cotton farming system. Cotton and February Orchid (Orychophragmus violaceus L.) relay intercropping system is a newly developed cropping system that introducing green manure as catch crop to winter fallow cotton field, and it has higher ecological benefit. Previous studies have identified that Cotton and February Orchid relay intercropping system could reduce nitrogen leaching, and improve the utilization efficiency of nitrogen fertilizer. However, the mechanism of reducing nitrogen leaching from cotton field through relay intercropping of Cotton and February Orchid is unclear. By conducting field experiment and 15N isotopic tracing micro plot experiment, this study aims to quantify the impacts of Cotton and February Orchid relay intercropping system on the spatial and temporal distribution of nitrate nitrogen in soil profile and the transformation characteristics of different forms of soil nitrogen pools; to analysis the difference of nitrogen absorption and utilization between green fertilizer source and chemical fertilizer source; and to analysis the nitrogen leaching difference between green fertilizer source and chemical fertilizer source. The study is supposed to illustrate the mechanism of reducing nitrogen leaching from cotton field through relay intercropping of Cotton and February Orchid, and the conclusion can provide theoretical basis for the build of high efficiency, green, and sustainable cotton farming system in the Yellow River basin.

黄河流域棉花生产中氮肥的过量施用，导致氮素淋溶污染地下水等环境问题日益突出，亟需化肥减量、绿色可持续的棉花耕作栽培制度。棉花/二月兰套作，是一种将绿肥作为填闲作物引入冬闲棉田，具有较高生态效益的新型棉花种植制度。前期研究表明棉花/二月兰套作能阻控棉田土壤氮素淋溶，提高氮肥利用效率。然而目前关于棉花/二月兰套作阻控氮素淋溶的机制尚缺乏深入研究。本项目拟通过大田试验与15N同位素示踪微区试验相互补充验证，定量研究棉花/二月兰套作对棉田土壤剖面硝态氮时空分布、不同形态氮库转化特征的影响，解析棉花对二月兰源和化肥源氮素吸收利用的差异，以及棉田对二月兰源和化肥源氮素淋溶的差异。研究以期阐明棉花/二月兰套作对棉田土壤氮素淋溶的阻控机制，为黄河流域棉花高产增效绿色可持续种植制度的构建提供理论依据。

本研究在大田条件下设置棉花单作（SC）和棉田种植翻压二月兰（FO）两种种植制度，每种种植制度中设置0（N0）、112.5（N1）、168.75（N2）和225（N3）kg/hm2 4个施氮量（纯氮）。研究不同施氮量下不同种植制度对棉田氮素去向和棉花生长的影响，从而探索可以解决棉花冬闲问题、减少化肥用量、实现低碳高产可持续种植目标的棉花种植制度。主要试验结果如下：. 土壤硝态氮（NO3--N）含量呈现棉花生长发育前中期含量高、生长发育后期含量低的时间变化特征。随着生育时期的推移，土壤NO3--N呈现0～20 cm土层含量最高、40～60 cm土层含量增加的空间变化特征，并且0～100 cm土体的土壤NO3--N累积量随施氮量的减少而降低，差异普遍达到显著水平。相同施氮量下，棉田种植翻压二月兰普遍增加了0～100 cm土体的土壤NO3--N累积量。棉田冬闲期种植二月兰可降低0～100 cm土体的土壤NO3--N含量。. 各处理的棉株生物量和氮素吸收量在棉花生长发育前期表现的差异不明显，而在棉花生长中后期表现的差异较明显。相同施氮量下，棉田种植翻压二月兰的棉株生物量和氮素吸收量普遍高于棉花单作。棉花籽棉产量和皮棉产量均随施氮量的减少而降低，且差异普遍达到显著水平。相同施氮量下，与棉花单作相比，棉田种植翻压二月兰增加了棉花籽棉产量和皮棉产量。. 与SC+N3相比，FO+N2在2018和2019年的氨挥发总量分别显著降低了1.24和0.85 kg/hm2；0～100 cm土体内的土壤NO3--N累积量在棉花花铃期显著增加了60.09 kg/hm2，在收获期略高于SC+N3；棉花生长发育中后期，FO+N2的棉株生物量明显高于或者相当于SC+N3；FO+N2的棉花整株氮素吸收量显著增加，产量略有增加。说明FO+N2是一种能够解决棉花冬季赋闲，减少化肥用量，增加棉花产量的种植制度。.