摘要:华北平原潮土区是我国重要的粮食主产区，改革开放40多年来该区农业经历了以高水肥投入为主要特征的集约化进程，相应的氮淋失导致的面源污染自20世纪90年代以来不断加剧。本研究针对华北平原潮土为主要类型的粮田，对过去40多年间主要研究文献进行全面分析，梳理氮肥和水分投入与氮淋失之间的定量关系，比较主要农田管理措施对氮淋失的阻控效果及其机理，以期为我国农业面源污染提供决策支持。研究发现，氮肥和灌溉是影响华北平原潮土区粮田氮淋失的主要因素，其中氮淋失与氮盈余量之间呈指数关系，比与施氮量的指数关系更显著。基于机器学习的随机森林回归模型能够考虑包括施肥、灌溉、土壤条件和气象等多因素对氮淋失的影响，未来在定量预测中有较好前景。同等氮肥投入条件下，由于氮供应与作物吸收契合度高，有机无机配施能显著降低氮淋失。以缓控释肥、尿酶和硝化抑制剂为代表的肥料增效剂可以降低约1/3的氮淋失，值得重点推广应用。秸秆还田可以实现包括提高土壤有机物和微生物氮库、增加无机氮缓冲容量等综合效益，有利于降低氮淋失风险（降低比例达10%），但免耕的阻控效应较低且呈现较大不确定性。调整种植制度、休耕、间作套种和种植填闲作物等措施会影响粮食产量，推广过程中应慎重。氮淋失的阻控效果更多受到社会、经济和政策等因素的影响，今后应采取包括生态补偿等手段发挥农民主动性，从政策和法律法规层面创造实施氮淋失阻控措施的社会环境。
关键词:潮土区/
粮田/
氮淋失/
施氮肥/
灌溉/
肥料增效剂/
种植制度/
生态补偿
Abstract:The North China Plain is a grain production region with fluvo-aquic soil and has seen rapid agricultural development over the past four decades. Excessive fertilization and frequent irrigation have increased nitrogen (N) leaching and nonpoint source pollution since the 1990s. This study screened published nitrogen leaching data on the North China Plain grain farmlands to identify the relationship between fertilization and irrigation with N leaching and to evaluate the primary N leaching mitigation measures. The results showed that regional groundwater during the 1970s was shallow and then deeper. During the 2010s, the regional cropping system changed from one to two crops per annum, and the annual N fertilizer rapidly increased to 600 kg(N)·hm-2·a-1 but then slowly decreased to 500–550 kg(N)·hm-2·a-1. Since the 1990s, irrigation increased from zero (rainfed during the 1980s) to 150–400 mm per annum, crop straw had gradually been incorporated into farmlands, and the fertilizer synergist technology had been accepted. The soil organic matter and total N improved by 38%–47%, pH decreased by 0.5 units, and available potassium decreased slightly. Fertilization and irrigation were the main influencing factors of N leaching, and the exponential relationship between N leaching and the N fertilizer balance (N fertilizer rate - crop above-ground N uptake) was better than the relationship between N leaching and N fertilizer rate. Random forest (RF) regression modeling based on machine learning was used to determine the relationship between N leaching and impacting factors such as irrigation, soil properties, and climate; the prediction results were satisfactory. At the same rate of N fertilization, organic fertilization combined with chemical fertilization significantly decreased N leaching because the N supply and crop demand were synchronized. Fertilizer synergists, such as control-release fertilizers, ureases, and nitrification inhibitors, mitigated N leaching by 1/3 and should be used in the North China Plain. Crop straw incorporation microbially improved N fertilizer in the short term and increased the long-term soil total N stock and inorganic N buffering capacity and reducing N leaching by 10%. The no-tillage mitigation effects were low and variable among farmlands. Fallow farmland and rotation/intercropping of deep root and shallow root crops, leguminous crops with cereal crops, and grains with vegetable crops were effective at reducing N leaching, but the crop yields also reduced. Therefore, these techniques required careful examination during technical dissemination. Governmental support, technical training, and proper planning should be implemented during the 14th Five-Year Plan of China to prevent and mitigate N pollution. Ecological compensation and an agricultural sector water use charge could also be used to encourage farmer participation.
Key words:Fluvo-aquic soil area/
Grain farmland/
Nitrogen leaching/
Nitrogen fertilization/
Irrigation/
Fertilizer synergist/
Cropping system/
Ecological compensation
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