Nitrate in groundwater is increasing in many aquifers worldwide due to excessive use of fertilizers. However, the behavior of N-based fertilizer as it leaches through thick vadose zones is still poorly understood, and the long-term effects on groundwater quality in such settings may yet to be fully realized.

Prof. Chunsheng Hu has been carried out long-term experiment on nitrogen fertilizer gradient in the North China Plain for more than 20 years since 1997. The results of this study were based on these experiments. No much of the leachate from chemical N-fertilizers (abundantly applied throughout the region since the 1970s) has entered groundwater via matrix flow. Manure and septic waste are the major sources of nitrate in groundwater to date. Increased nitrate concentrations in groundwater may also result due to preferential flow in sand layers and/or lateral flow from headwater areas. Denitrification (particularly in the upper 4m depth of soil) appears to have limited the flux of fertilizer-derived nitrate to some degree.

The large N stock and generally weak denitrification potential in the deep unsaturated zone, pose a major threat to future groundwater quality. The results have major implications for groundwater quality management in the future.

This work was supported by National Natural Science Foundation of China, the National Key R&D Program of China, and the Hebei Province Science Foundation for Youths.

Fig.. Leaching speed and denitrification rate in various texture soils in the N0, N400 and N600 treatments. 

Website: https://doi.org/10.1016/j.jhydrol.2019.06.012