Taihang Mountain region is the recharge area for groundwater in the North China Plain (NCP). In recent years, the elevated nitrate concentration in the groundwater in the Taihang Mountain has often been associated with the increased area of farmland and the excessive application of nitrogen. Thus, it is significant to study the soil nitrogen leaching process in typical farmland. In this study, the root zone water quality model (RZWQM) was used to simulate the nitrate nitrogen leaching of winter wheat/summer maize rotation systems in the Hilly Ecosystem Experimental Station in Taihang Mountain. The results showed that during the 2015-2016 winter wheat/summer maize season, the nitrate nitrogen from the soil leaching occurred mainly in the summer maize season (rainy season), with the nitrate nitrogen leaching amount reaching 59.9 kg·hm-2, while the nitrate nitrogen leaching amount during the winter wheat season was only 2.12 kg·hm-2. The soil nitrate nitrogen leaching condition was simulated using the RZWQM model for different nitrogen contents and years with different rainfall. Significant linear correlations were observed between nitrogen use and nitrate leaching in winter wheat/summer maize rotation systems. In summary, the results showed that the nitrate nitrogen leaching values were 10.5, 59.9, and 136.5 kg·hm-2 for nitrogen fertilizer applications of 0, 300, and 450 kg·hm-2, respectively, during extreme precipitation in a wet year (2015). The value of nitrate nitrogen leaching in the maize season of 2013 (dry year), 2015 (normal year), and 2016 (wet year) accounted for 9%, 10%, and 20% for the 300 kg·hm-2 of nitrogen fertilizer applied, respectively. However, the value of nitrate nitrogen leaching in the maize season of 2013 (dry year), 2015 (normal year), and 2016 (wet year) accounted for 11%, 17% and 30% of the 450 kg·hm-2 of nitrogen fertilizer applied. These results show that extreme precipitation events not only greatly recharge the groundwater, but also increase the leaching of accumulated nitrate nitrogen and potential nitrate contamination in the groundwater.
Keywords: extreme precipitation; hilly area of Taihang Mountain; nitrate nitrogen leaching; nitrogen application rate; root zone water quality model (RZWQM).