牛新胜^{1, ?,},
张翀^{2, ?,},
巨晓棠^{2, 3,,}
1.中国农业大学曲周实验站 曲周 057250
2.海南大学热带作物学院 海口 570228
3.中国农业大学资源与环境学院 北京 100193
基金项目: 国家重点研发计划项目2016YFD0800102
国家重点研发计划项目2017YFD0200105
国家自然科学基金项目41830751
国家自然科学基金项目31861133018

详细信息

通讯作者:巨晓棠, 研究方向为农田生态系统氮素循环与温室气体。E-mail: juxt@cau.edu.cn

^?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
中图分类号:S14;S15

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收稿日期:2020-08-04
录用日期:2020-09-01
刊出日期:2021-01-01

Mechanism of nitrogen leaching in fluvo-aquic soil and deep vadose zone
in the North China Plain

NIU Xinsheng^{1, ?,},
ZHANG Chong^{2, ?,},
JU Xiaotang^{2, 3,,}
1. Quzhou Experimental Station, China Agricultural University, Quzhou 057250, China
2. College of Tropical Crops, Hainan University, Haikou 570228, China
3. College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
Funds: the National Key Research and Development Project of China2016YFD0800102
the National Key Research and Development Project of China2017YFD0200105
the National Natural Science Foundation of China41830751
the National Natural Science Foundation of China31861133018

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Corresponding author:JU Xiaotang E-mail: juxt@cau.edu.cn

^?Equivalent contributors


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摘要
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

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图1华北潮土冬小麦-夏玉米轮作周年气候、田间管理、土壤质量含水量、硝态氮累积量及硝酸盐淋溶量
红色箭头代表发生硝态氮向1 m以下土体迁移, 粗细和数字代表硝态氮淋溶量(kg·hm^-2)。降雨量和大气温度来自Gao等^[46]。土壤含水量和硝态氮累积量分布图引自李洪亮^[47], 硝态氮淋溶数据引自Huang等^[8]。
Figure1.Annual climate, field management, soil gravimetric water content, nitrate accumulation and leaching in the winter wheat-summer maize rotation in the North China Plain
The red arrows denote the moving down of nitrate from root zone (0-1 m), the width of arrows and numbers denote the amount of nitrate leaching. Precipitation and air temperature were cited from Gao et al. ^[46]. Soil water content and soil nitrate accumulation were cited from Li^[47], nitrate leaching was cited from Huang et al.^[8].


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图2模拟灌水后土壤水和温度对裂隙发育的影响^[52]
裂隙率=裂隙面积/灌溉小区的总面积×100%。
Figure2.Effects of soil water and temperature on soil crack development after the simulated irrigation^[52]
Crack area density=crack area/plot area×100%.


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图3模拟灌溉对优先流的影响
图a是亮蓝在土壤垂直剖面的染色情况, 图b是亮蓝在不同层次水平方向的染色面积比例。IS45、IS90和IS135分别指模拟灌水45 mm、90 mm和135 mm, -1、-2和-3分别指3个重复。
Figure3.Effect of irrigation on preferential flow under simulated rainfall
figure a is the vertical distribution of brilliant blue in the soil profile, figure b is the percentage of dyeing area in the horizontal direction of each soil layer. IS45, IS90 and IS135 denote irrigaiton of 45 mm, 90 mm and 135 mm, respectively.-1, -2 and-3 denote three replications of the same irrigaiton treatment.


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图4土壤垂直剖面不同级别大孔隙单位面积数量及比例
Ind.表示个数。
Figure4.Percentage and numbers of macropores of different sizes in soil profile
Ind. denotes individual.


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图5农户常规管理农田土壤剖面亮蓝染色面积占比
图例代表不同采样点。
Figure5.Preferential flow in the cropland under farmer's conventional management
Villages in the legend denote sampling sites.


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图6优先流对土壤水(a)和硝态氮淋溶(b)的贡献
CK、AC1、AC2和UC分别代表无大孔隙模拟土柱、少孔隙模拟土柱、多孔隙模拟土柱和原状土柱, 折线图代表发生连续的淋溶事件, 点状图代表不连续淋溶事件。
Figure6.Contribution of preferential flow to water (a) and nitrate leaching (b)
CK, AC1, AC2 and UC denote the artificial soil column with no, little and much macropores, and undisturbed soil column, respectively. Line plot denote the continuous leaching event, scatter plot denote the non-continuous leaching event.


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图7降雨量与土壤淋溶液体积和硝态氮淋溶量的关系
CK、AC1、AC2和UC分别代表无大孔隙模拟土柱、少孔隙模拟土柱、多孔隙模拟土柱和原状土柱。
Figure7.Relationship among the losses of water and nitrate nitrogen and rainfall
K, AC1, AC2 and UC denote the artificial soil column with no, little and much macropores, and undisturbed soil column, respectively.


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图8氮素在地表-根层-深层包气带-地下水的垂直迁移过程及消减机制
所有数字单位均为kg·hm^-2·a^-1, 氮素投入、作物吸收氮引自Wang等^[24]和Ju等^[2]的结果, 氨挥发依据Ju等^[2]的氨挥发损失率估算。根层和深层包气带反硝化根据Wang等^[24]的结果估算。根区氮淋溶为氮投入减去作物吸收、氨挥发和根层反硝化。深层包气带淋溶为根区氮淋溶减去深层包气带反硝化。
Figure8.Mechanism of nitrogen movement and removal in the surface soil-root zone-deep vadose zone-groundwater continuum
Units for all numbers in the figure are kg·hm^-2·a^-1. Input, uptake, NH₃, Deni.(root), Leaching (root), Deni. (deep), Leaching (root) denote total nitrogen input, crop nitrogen uptake, ammonia volatilization, denitrification and nitrate leaching in the root zone, denitrification and nitrate leaching in the deep vadose zone (> 1 m). Nitrogen input and crop nitrogen uptake was cited from Wang et al. ^[24] and Ju et al. ^[2], ammonia volatilization was calculated based on the ammonia volatilization rate of Ju et al. ^[2], denitrification in the root zone (0-1 m) and deep vadose zone (>1 m) were estimated from Wang et al. ^[24]. Nitrate leaching from root zone was calculated by deducting crop nitrogen uptake, nitrogen losses via ammonia volatilization and denitrification in root zone from nitrogen input. Denitrification in deep vadose zone was calculated by deducting denitrification in deep vadose zone from nitrate leaching from root zone.


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表1华北平原冬小麦-夏玉米体系氮素收支平衡与盈余
Table1.Nitrogen budget and surplus in the winter wheat-summer maize rotation system in the North China Plain?kg·hm^-2

输入Input	数据Data		输出Output	数据Data
化肥Fertilizer	474±139		籽粒Grain	301±33
有机肥Manure	15±77		淋溶Leaching	119±35
生物固定Biological nitrogen fixation	15		氨挥发Ammonia volatilization	108±35
大气沉降Deposition	63		反硝化Denitrification	17±16
灌溉Irrigation	24±24
种子Seed	8±25
总输入Total input	600±162		总输出Total output	545±84
土壤氮库变化Change of soil nitrogen stock	54±95		盈余Surplus	299±167
数据来源包括实地调研(n=420)和文献调研。其中, 化肥、有机肥、灌溉、种子输入氮和籽粒输出氮通过实地调研投入量后, 结合其氮含量(除化肥外, 其他输入和输出项氮含量均为实测值)换算获得, 如灌溉投入量为农户提供的灌水量乘以实测灌溉水含氮量获得。生物固氮数据来自赵荣芳等[44], 氮沉降来自Xu等[43], 淋溶、氨挥发和反硝化数据根据赵荣芳等[44]建立的氮损失与施氮量的经验模型计算获得。Data were obtained from farmer survey (n=420) and literatures. N input from fertilizer, manure, irrigation and seed and N output from grain was calculated by multiplying survey data (e.g., irrigation amount) by corresponding measured concentration (e.g., nitrogen concentration in irrigation water). Biological nitrogen fixation was obtained from Zhao et al. [44], nitrogen deposition was obtained from Xu et al. [43]. Leaching, ammonia volatilization and denitrification were calculated by using nitrogen loss models obtained from Zhao et al. [44], based on the relationships between ammonia volatilization, leaching, denitrification and nitrogen application rates.

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