摘要:更多证据表明, 储存在深层包气带中的硝态氮在全球氮循环中具有重要作用。本研究在华北平原农田不同包气带深度(2~50 m)分别采集土柱, 分析不同深度土层的硝态氮含量和分布; 从资料与文献收集到华北平原不同省区及其县域的42年(1978—2019年)氮肥投入与农田面积变化数据, 计算不同区域(地下水埋深区域和县域)的农田包气带硝态氮存储量。首次利用区县氮肥投入与对应区域包气带硝态氮存储量的比值, 即存储率(NR), 研究氮肥投入对包气带硝态氮存储的影响程度。结果表明: 1)在2~50 m的地下水埋深范围内, 随着包气带深度的增加, 华北平原农田(粮田与菜地)的单位面积硝态氮存储量也随之增加; 2)在2 m、3 m、6 m、10 m、16 m、25 m、40 m和50 m深包气带, 粮田硝态氮存储量分别占42年(1978—2019年)氮肥总投入量的14%、18%、26%、30%、33%、35%、38%和39%, 菜地硝态氮存储量分别占42年(1978—2019年)氮肥总投入量的15%、20%、28%、32%、34%、36%、40%和41%; 3)进入2 m以下地下水的粮田与菜地硝态氮淋失总量分别为675.65万t和199.56万t, 分别占粮田与菜地42年(1978—2019年)氮肥总投入的13%和14%。本研究表明, 华北平原农业区高氮肥投入导致大量的硝态氮淋失进入包气带-地下含水层系统, 厚包气带对硝态氮截留和存储具有重要作用, 在地下水埋深较浅区, 高氮肥投入提高了地下水硝酸盐污染的风险。
关键词:农田关键带/
包气带-地下含水层系统/
硝态氮存储量/
硝态氮淋失量/
华北平原
Abstract:After the reform and opening in 1978, China’s nitrogen (N) fertilizer input increased sharply, increasing grain yield, but also causing serious soil nitrate accumulation and leaching problems that threaten groundwater security. This study aimed to explore the effects of N fertilizer input on nitrate storage in the vadose zone of farmlands (grain and vegetable fields) in the North China Plain (NCP) and to quantify the total amount of nitrate leaching from the 2–50 m underground aquifer of the NCP. We collected soil profiles from areas with different groundwater table depths (2–50 m) of the NCP farmlands and measured the nitrate content in different soil layers. Concurrently, data on N fertilizer input and changes in the farmlands of different provinces and counties of the NCP were collected from literatures and relevant websites for 42 years (1978–2019). Nitrate storage in the vadose zone was calculated using a geographic information system (GIS). The ratio of nitrate storage to nitrogen fertilizer input (NR) in the vadose zone was proposed from the perspective of regional blocks. The NR value of grain and vegetable fields in the NCP ranged from 0.14 to 0.39 and from 0.15 to 0.41, respectively. This provided scientific data and a theoretical basis for reducing the leaching loss of nitrate from the vadose zone to the aquifer. The relationship (NR value) between N fertilizer input and nitrate storage in the vadose zone at different groundwater table depths reflects the degree of influence of N fertilization on the amount of residual nitrate in the vadose zone. Moreover, under the same N fertilizer conditions, the leaching loss of nitrate from the NCP farmlands was estimated at groundwater table depths of 2–50 m. The results showed that high fertilizer application in the NCP farmlands led to large amounts of nitrate leaching into the vadose zone-aquifer system. The total nitrate leaching from grain and vegetable fields under 2 m of groundwater was 6.7565 and 1.9956 million tons, respectively, accounting for 13% and 14% of the total N fertilizer input from grain and vegetable fields in 42 years (1978–2019). Under ideal conditions (depth of vadose zone >10 m, the same farmland area and soil texture), higher N fertilizer input was associated with greater total nitrate storage in the vadose zone. Nitrate storage per unit area of farmland (grain and vegetable fields) in the NCP increased with increasing depth of the vadose zone at areas with 2–50 m of groundwater depth. This study also indicated that a thick vadose zone played an important role in nitrate nitrogen interception. In the 2, 3, 6, 10, 16, 25, 40, and 50 m vadose zones, grain field nitrate storage accounted for 14%, 18%, 26%, 30%, 33%, 35%, 38%, and 39% of the total N fertilizer input over 42 years (1978–2019), respectively. Vegetable field nitrate storage at the same depths of the vadose zone accounted for 15%, 20%, 28%, 32%, 34%, 36%, 40%, and 41% of the total N fertilizer input over 42 years (1978–2019), respectively. This study suggests that the relevant departments and agricultural workers should consider the depth of the vadose zone to comprehensively evaluate nitrate nitrogen accumulation and groundwater safety issues from a regional perspective.
Key words:Critical zone of farmland soil/
Vadose zone-aquifer system/
Nitrate storage/
Nitrate leaching/
North China Plain
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