摘要:合理水氮管理可以实现作物目标产量和品质、维持土壤肥力和降低环境污染。然而, 自20世纪90年代以来, 我国农田过量施氮和大水漫灌等问题突出, 引起农业面源污染日趋加重, 地下水硝酸盐污染成为一个普遍现象。本文以华北潮土区冬小麦-夏玉米体系为研究对象, 采用数据整合和文献分析的方法, 阐明了典型农田硝态氮淋溶的时空特征及影响因素, 研究了地表裂隙和土壤大孔隙对硝态氮淋溶的影响, 定量了氮素在地表-根层-深层包气带-地下水的垂直迁移通量及过程。结果表明, 农户常规管理的冬小麦-夏玉米轮作体系氮素盈余较高(299~358 kg·hm-2·a-1), 导致土壤根区和深层包气带累积了大量的硝态氮。冬小麦季硝态氮的迁移主要受灌溉影响, 以非饱和流为主, 且迁移距离较短; 春季单次灌溉量低于60 mm, 可以有效控制水和硝态氮淋溶出根区。冬小麦耕作和灌溉引起的地表裂隙对水氮运移的贡献不大。雨热同期的夏玉米季, 土壤水分经常处于饱和状态, 再降雨就可以导致硝态氮淋溶出根层进入深层包气带。夏玉米季极易发生硝态氮淋溶事件(占全年总淋溶事件的81%左右), 硝态氮淋溶量占全年总淋溶量的80%左右, 且单次淋溶事件的淋溶量较高。大孔隙优先流对夏玉米季根区硝态氮淋溶的贡献率在71%左右, 这些硝态氮脱离了作物根系吸收范围, 反硝化作用对硝态氮去除具有一定作用。在华北气候-土壤条件下, 特别应注意冬小麦收获后土壤不应残留过多硝态氮, 以避免夏玉米季降雨发生大量淋溶; 夏玉米季需要注意施氮与作物需氮的匹配。由于夏玉米追肥困难, 生产上提倡一次性施肥措施, 控释肥应该能够发挥更大作用。未来气候变化, 导致夏季极端高强度降雨事件的频率增加, 将会加剧包气带累积硝态氮通过饱和流或优先流向地下水的迁移。合理的水氮管理是从源头上减少硝态氮向深层包气带和地下水迁移的主要措施。
关键词:潮土/
冬小麦-夏玉米体系/
氮素淋溶/
硝态氮/
包气带/
裂隙/
大孔隙/
优先流
Abstract:Rationally managing nitrogen (N) and water results in high crop yield and quality, maintains (or improves) soil fertility, and reduces environmental pollution. However, since the 1990s, excessive use of N fertilizer and flood irrigation has created problems in Chinese croplands, causing agricultural nonpoint source pollution and groundwater nitrate contamination. Data integration and literature review of winter-wheat summer-maize farmlands in fluvo-aquic soil in the North China Plain was used to investigate the temporal and spatial variation of N leaching, the contribution of cracks and macropores to N leaching, and N movement through soil (along the surface to groundwater continuum). The results showed that the N surplus was very high (299-358 kg·hm-2·a-1) when conventional management was used, resulting in high nitrate accumulation in the root and deep vadose zones. Nitrate movement in the winter wheat season was primarily caused by unsaturated flow and affected by irrigation; the nitrate movement distance was short. Water and nitrate loss from the root zone was negligible if the irrigation amount was lower than 60 mm. In the winter wheat season, tillage- and irrigation-induced cracks contributed minimally to nitrate and water movement out of the root zone. In the wet and hot summer maize season, the soil was frequently water-saturated, and small precipitation amounts lead to nitrate leaching, accounting for 81% of the annual leaching events and 80% of the annual nitrate leaching. In the summer maize season, the leached nitrate amounts were much higher than in the winter wheat season, and 71% of the total nitrate leaching was preferential flow caused by macropores. Nitrate from the root zone could be partially removed by denitrification in the deep vadose zone. In the North China Plain, avoiding high nitrate accumulation after winter wheat harvest was effective at decreasing nitrate leaching in the summer maize season. Matching the N fertilizer supply with crop demand and controlled release fertilizer in summer maize season (to avoid costly topdressing N fertilizer) may also play important roles in leaching reduction. Frequent and heavy rainfall accelerates the movement of nitrate via saturated and preferential flow to groundwater. Therefore, rational water and N management is key to reducing nitrate movement to the deep vadose zone and groundwater.
Key words:Fluvo-aquic soil/
Winter wheat-summer maize rotation/
Nitrogen leaching/
Nitrate nitrogen/
Vadose zone/
Crack/
Macropore/
Preferential flow
?Equivalent contributors
注释:
1) ?共同第一作者：牛新胜, 研究方向为农业资源与环境科学研究, E-mail: xinshengniu@163.com张翀, 研究方向为农田氮素去向及管理, E-mail: zhangchong@hainanu.edu.cn
PDF全文下载地址:
http://www.ecoagri.ac.cn/article/exportPdf?id=d9ac2fbe-0bc1-4906-af45-78780baf5e05
