Abstract:
Objectives With the adjustment of agricultural cultivation structure in Ningxia Yellow River Irrigation Region, the area of greenhouse increased greatly. The objectives of this study were to investigate the nitrate nitrogen (N) pollution in shallow groundwater and to analyze its relationship with soil nitrate N in intensive greenhouse planting areas, and then to provide theoretical basis for effective control of groundwater nitrate N pollution in Ningxia and other similar areas of China.
Methods A total of 214 groundwater samples and 102 soil samples were obtained from seven typical greenhouse intensive planting areas in different periods, and the contents of nitrate N and salts of groundwater and soil were analyzed.
Results Results showed that the contents of nitrate N in groundwater samples exceeded the grade III standard of groundwater by 53.3% and there were great differences in the pollution degree of groundwater nitrate N among the 7 intensive planting areas. The contents of groundwater nitrate N increased from summer and autumn fallow period to winter planting period. There was a significant positive correlation between groundwater salinity and groundwater nitrate N concentration in intensive greenhouse planting area, especially when the groundwater nitrate N content was greater than 40 mg L−1, and the groundwater salinity increased dramatically. From the aspect of soil salinity, nearly 80% of the samples showed different degrees of salinization, in which moderate salinization accounted for 57.12%. There was an extremely significant linear relationship between soil salinity and nitrate N content in 0 – 20 cm soil, with a determination coefficient of 0.376. Meanwhile, there was a very significant exponential function relationship between soil nitrate N content and groundwater nitrate N content and an extremely significant linear function relationship between soil salinity and groundwater salinity.
Conclusion The groundwater nitrate N pollution in typical greenhouse intensive planting areas in Ningxia is considerably serious. The accumulation of nitrate N in soil and soil salinization are partly caused by nitrate N content and salinity of groundwater, and the large accumulation of soil nitrate N might be the main source of groundwater nitrate N.