基于RZWQM模型模拟太行山低山丘陵区农田土壤硝态氮迁移及淋溶规律

Simulation of the Migration and Leaching of Nitrate Nitrogen in the Farmland Soil Profile in a Hilly Area of Taihang Mountain with the RZWQM Model

太行山低山丘陵区是华北平原地下水补给区,近年来山区农田面积增加,农田过量氮肥投入造成地下水硝酸盐浓度逐年升高,因此,研究典型农田土壤氮淋溶过程对保护补给区地下水具有重要意义.本文以位于太行山低山丘陵区的中国科学院太行山生态试验站冬小麦-夏玉米轮作农田为研究对象,应用根区水质模型(root zone water quality model,RZWQM)对太行山低山丘陵区2015～2016年冬小麦-夏玉米的1个轮作周期内1m土壤剖面水分和硝态氮运移进行模拟.结果表明,土壤硝态氮淋溶主要发生在夏玉米季(雨季),当全年施氮量为300 kg·hm^(-2)时,夏玉米季硝态氮淋失量达到59. 9 kg·hm^(-2),而冬小麦生长季硝态氮淋失量仅为2. 12 kg·hm^(-2).不同施氮量和不同降水年型下玉米季土壤硝态氮淋溶模拟结果表明,当施氮量为0、300和450 kg·hm^(-2)时,2016年(丰水年)极端降水后,玉米季土壤硝态氮潜在淋失量分别为10. 5、59. 9和136. 5kg·hm^(-2);当全年施氮量为300 kg·hm^(-2)时,2013(枯水年)、2015(平水年)和2016年(丰水年)玉米季硝态氮淋失量分别占轮作周期总施氮量的9%、10%和20%;当全年施氮量为450 kg·hm^(-2)时,2013(枯水年)、2015(平水年)和2016年(丰水年)玉米季硝态氮淋失量分别占总施氮量的11%、17%和30%,表明大降水事件不仅对地下水形成大量补给,很大程度上也增加了累积在农田土壤中的硝态氮淋溶损失,增加了对区域地下水硝酸盐潜在污染威胁.

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.