红壤坡耕地氮素输移形态对土壤水文过程响应及机理

Nitrogen loss associated with soil loss not only leads to land degradation, but also behaves as a source of non-point source pollution. Nitrogen forms play an important role on crop growth and water pollution, and forms of nitrogen movement affected by soil hydrological processes. Surface runoff, infiltration and soil moisture affect nitrogen content and forms characteristics. In this study, taking typical red soil slope land as the research object and taking Jiangxi Eco-science Park of Soil and Water Conservation, China as the field test site, using large scale drainage lysimeter, field observations and simulation methods are used to make clear of nitrogen hierarchical morphology moving law duing surface runoff, interflow and groundwater runoff under rainfall in red soil slope farmland. By testing different forms of nitrogen such as nitrate, ammonium, organic nitrogen during soil hydrological processes, nitrogen forms’ characteristics will be analyzed. Using mathematical statistical methods, relationships between nitrogen content with runoff and soil moisture will be built. Response and mechanism of nitrogen and its forms to soil hydrological processes will be revealed and the effects of measure covered with grass to nitrogen movement will be clarified. The results will help to deepen the understanding of the nitrogen movement mechanism in red soil slope farmland for soil erosion and provide a scientific basis for non-point source pollution control and development of ecological agriculture.

降雨侵蚀造成的坡耕地氮素流失不仅导致土地生产力下降，而且成为非点源污染的来源，氮素形态对作物生长和水体污染都有重要作用，而氮素的输移形态受土壤水文过程影响，地表径流、水分入渗和土壤水分含量影响氮素含量及形态特征，目前相关研究尚不系统。本研究以典型红壤坡耕地为对象，以江西水土保持生态科技园为野外试验基地，利用大型土壤渗漏装置，采用野外观测与模拟试验相结合的方法，明确降雨条件下红壤坡耕地地表径流、壤中流和地下径流的分层输移过程中氮素的形态特征规律；通过对土壤水文过程中硝态氮、铵态氮、有机氮等不同形态氮素的测定，研究氮素输移的形态特征，采用数理统计方法，建立氮素含量与径流和土壤含水量之间的关系，揭示氮素输移形态对土壤水文过程响应及机理，阐明草被覆盖措施对氮素迁移的作用。研究结果将有助于深化红壤坡耕地氮素迁移机制的理解，为水土流失和非点源污染防治、发展坡耕地生态农业提供科学依据。

坡面氮素的输移受土壤水文过程影响，地表径流、水分入渗和土壤水分含量影响氮素含量及形态特征。本项目以典型红壤坡耕地为对象，采用渗漏小区定位观测、野外水冲试验与室内模拟试验相结合的方法，研究了自然降雨条件下红壤坡耕地氮素分层输移形态及途径、土壤水文过程对氮素输移及形态特征的影响、红壤坡耕地氮素输移对土壤水文过程响应机理等3个方面的内容。结果表明：（1）地下径流是氮素输出的主要途径，各形态氮素随地下径流输出占该形态总输出的66.8%-94.5%；（2）各形态氮素浓度均呈现地下径流>壤中流>地表径流的趋势，各组分径流中氮素浓度为硝态氮>有机氮>氨态氮，淋溶过程中氮素也主要以硝态氮的形态淋出；（3）60cm深度壤中流总氮浓度与60cm以上土层含水量呈正相关，相关系数达0.57-0.68，其余不同深度土壤含水量均对各径流组分氮素浓度输出影响较小，地表径流总氮浓度与降雨高度正相关，各径流组分对自身氮素浓度均具有明显的影响；（4）相比土沟，草沟减小了流速，加大了水深，使得坡面产流时间延长，并对污水中高浓度的氮素有较好的去除效果（劣Ⅴ类水氮素去除率达到48.0%-58.3%），两种坡面沟水流剪切力与水流总氮浓度、水流功率与水流总氮浓度的关系均无显著相关性；（5）秸秆覆盖具有缩短土壤和泥沙吸附平衡时间和解析最大值到达时间的作用，相较于土壤，侵蚀泥沙对氮素的吸附量更多、吸附平衡时间更短，氮素解吸最大值到达时间也明显更短；（6）虽然在长时间尺度上，由于养分归还作用，秸秆覆盖措施使壤中和地下氮素输出增加，但在短时间尺度上秸秆覆盖措施能够抑制红壤在淋溶过程中氮素特别是硝态氮的淋失。研究成果初步揭示了揭示氮素输移形态对土壤水文过程响应及机理，阐明了草被覆盖措施对氮素迁移的作用，可为水土保持生态建设和农业面源污染防治提供理论基础。