亚热带典型耕作土壤磷素淋失临界值及其主要影响因素

Control of agricultural non-point pollution has been become one of the main issues concerned by Chinese government. The subtropical region of China is being suffered from agricultural non-point pollution and eutrophication, which caused by intensive agricultural and fertilization practices. Phosphorus (P) loss from soil to water by erosion and surface runoff have been much studied and quantified. However, more recently, researchers observed the evidence that vertical movement of P through soil profile ascribing to long-term application of P fertilizers and the consequent soil P accumulation, which highlights the importance of investigating P loss by leaching and its relationship with land use and soil properties. In this study, soil P leaching change point, the variation of soil P leaching change point and their relationship with soil physical, chemical, biological properties will been established; and the effects of human activities such as fertilization and land management on soil P leaching change point will be revealed by conducting soil survey, laboratory simulation, In situ soil column trial and field observation on upland, vegetable plot and paddy field in sub-tropical area of China. This project will set up and improve the methods of soil P leaching change point and will also reveal soil P leaching change points in typical cropping soils of subtropical region of China. .Conclusively, this study will provides supportive arguments to retarding soil P transport and assessing soil P leaching potential capacity and environmental risks of crop fields in subtropical region of China , and it also will be further poses an important implication of maintaining regional agricultural sustainable production, reducing the cropland P movement and alleviating the headstream of agricultural non-point pollution.

农业面源污染已成为我国政府高度关注的重要环境问题之一，我国亚热带区在高强度农业生产和大量施用化肥的作用下，已成为农业面源污染和环境富营养化最为严重的地区。以往研究认为土壤磷素主要通过土壤侵蚀和地表径流进入水体，然而随着施肥量的增加和农业土壤磷的不断积累，农田磷有明显向土壤深层淋失的现象。本项目拟以亚热带区典型代表性旱地、稻田和菜地为研究对象，通过典型区域耕作土壤调查、室内模拟测定、原状土柱试验和田间定位观测等方法相结合。完善和建立亚热带耕作土壤磷素淋失临界值的测定方法；阐明亚热带区主要类型耕作土壤磷素淋失临界值变化状况；弄清土壤物理、化学和生物学特性及土地利用、施肥和耕作管理方式等因素对亚热带典型耕作土壤磷素淋失临界值的影响；评估亚热带耕作土壤磷素淋失环境风险。对于保障区域农业高效生产、减少农田磷素迁移和从源头上控制农业面源污染等方面具有重要意义。

随着化肥施用量的不断增加，亚热带区农田氮磷面源日益严重。本项目通过区域调查、室内模拟试验和田间小区试验研究了亚热带典型耕作土壤有效磷含量特征、耕作土壤磷素淋失临界值及影响因素、田间条件下土壤磷素淋失状况。建立了稻田小区施肥田间试验、稻田土壤氮磷淋失监测和稻田土壤有效磷饱和容量测定等方法。区域调查研究表明典型县稻田土壤有效磷含量低于旱地土壤，这与稻田长期淹水导致土壤有效磷流失有关。通过室内模拟试验和提取法测定土壤磷素淋失临界值结果表明，亚热带旱地土壤淋失临界值低于稻田土壤，旱地土壤磷素淋失风险高于旱地土壤，耕作土壤的pH、粘粒、CEC、有机质、交换性钙镁、氧化铁铝等影响土壤磷素淋失临界点Olsen-P含量。稻田田间小区试验结果表明，稻田土壤磷素淋失量较小，在亚热带稻田耕作管理方式和土壤条件下，发现当磷肥施用量到达一定量时稻田土壤有效磷可到达有饱和容量，首次提出了亚热带区稻田土壤有效磷饱和容量的观点，田间试验结果拟合表明长沙红壤稻田土壤有效磷饱和容量（47.6 mg kg-1）显著高于湘阴湖积物稻田（39.2 mg kg-1）。对于减少亚热带稻田磷肥施用，控制稻田土壤磷素面源污染等具有重要的科学意义。田间小区试验结果还表明，施用牛粪可显著提高稻田土壤pH值，对于防止稻田土壤酸化和控制污染稻田土壤重金属的活性等方面都具有重要意义。