农田施氮对水质和氮素流失的影响

基于ISI Web of Science数据库,利用文献计量学方法分析了自1957年以来各国在农田氮流失领域的研究发展态势,综述了农田氮流失特征及氮流失防控措施。结果表明,目前各国对农田氮流失的研究主要集中在施氮对水体水质的污染和监测方法上,涉及的关键词主要有Groundwater、Water quality、Surface water、Nitrate pollution、Eutrophication、Contamination、Nonpoint source pollution、Lysimeter、Runoff、Subsurface drainage等。中国、美国和加拿大等农业大国的研究机构在这一领域的研究成果最多发文量最多的期刊主要分布在荷兰、美国和中国。文献分析表明,受降水、地形、土壤、施肥等诸多管理措施的影响,不同区域的农田氮流失量差别很大,中国各类农田的氮流失量(13.7—347 kg/hm~2)明显高于欧美国家(4—107 kg/hm~2)。我国单位面积化肥(357.3 kg/hm~2)和氮肥(165.1 kg/hm~2)施用量均远高于世界平均用量(87.5 kg/hm~2和52.9 kg/hm~2),当季氮肥利用率(17%)却明显低于世界平均水平(58%),表明氮肥施用过量且利用率过低是造成氮流失的关键因素。综合分析农田氮流失防控措施发现,从源头控制氮流失是最有效的措施,优化农艺管理措施和氮迁移过程拦截等分别可减少15%—92%、46%—77%的氮素流失,其中针对农田适宜施氮量的研究最多。然而,面对粮食生产需求与资源短缺、水体水质持续恶化的现状,未来的研究重点应从简单的表观平衡向整个农田生态系统的氮素循环过程转变,更为迫切的是加快探索以水质保护为目标的化肥氮施用阈值(造成环境污染的临界施氮量),并推广示范这些有效的氮流失防控措施。

A bibliometric analysis of status and trend of international research on field nitrogen application effects on nitrogen losses and water quality

A bibliometric analysis method was used to identify the developmental trend of international research on nitrogen losses in farmlands as affected by nitrogen applications, based on peer-reviewed studies available in the ISI Web of Science since 1957. We also reviewed control and prevention measures for farmland nitrogen loss, with the same method. The bibliometric analysis showed that the current focus of research regarding nitrogen losses worldwide involved assessing and monitoring of the effects of nitrogen fertilization on water pollution and quality. Keywords included Groundwater, Water quality, Surface water, Nitrate pollution, Eutrophication, Contamination, Nonpoint source pollution, Lysimeter, Runoff, and Subsurface drainage, etc. Research institutions that contributed to a large number of research findings are mainly resided in large agricultural countries, including China, United States, and Canada, and the mainstream journals that included most relevant papers are published in the Netherlands, United States, and China. Literature analysis showed that nitrogen losses are site-specific because it can be influenced by precipitation, topography, soil properties, and forms, rates, timing and placement of fertilizers, as well as other management practices. Nitrogen losses in China (13.7-347 kg/hm²) was significantly higher than that of countries in Europe and North America (4-107 kg/hm²). On average, the fertilizer use is 357.3 kg/hm² and nitrogen rate is 165.1 kg/hm² in China, which was much higher than the world average application rates (fertilizer rate:87.5 kg/hm²; nitrogen rate:52.9 kg/hm²). As a result, nitrogen use efficiency during one crop growth period in China (17%) was significantly lower than the world average (58%). These results indicated that excessive fertilizer application and underutilization of nitrogen were main reasons for nitrogen losses to surface and ground water. By comprehensively analyzing prevention and control measures for farmland nitrogen losses, we found that reducing nitrogen losses from the source was the most effective measure. Optimizing agronomic management practices and intercepting nitrogen migration could reduce nitrogen losses by 15% to 82%. Among a large diversity of studies, the largest group of studies focused on optimizing nitrogen applications. However, faced with resource shortage, water quality deterioration, and food production pressure, future research focus should shift from nitrogen balance to study of the nitrogen cycle in the entire farmland ecosystem. Further, there is an urgent need to determine nitrogen fertilization thresholds (critical nitrogen levels resulting in risk of pollution) for water quality protection. Effective prevention and control measures for nitrogen losses will provide theoretical and technical supports to balance the conflicts among food demand, resource conservation, and environmental protection.