1. $lt;span class='magtech_ref_source'$gt; W, He R, Jiang P, He J, Yang W, Zhou J, Ma Y Liu . Estimating soil nitrogen balance at regional scale in China’s croplands from 1984 to 2014. $lt;i$gt;Agricultural Systems$lt;/i$gt;, 2018, 167: 125–135 $lt;/span$gt;
2. $lt;span class='magtech_ref_source'$gt; X, Yan C, Ti P, Vitousek D, Chen A, Leip Z, Cai Z Zhu . Fertilizer nitrogen recovery efficiencies in crop production systems of China with and without consideration of the residual effect of nitrogen. $lt;i$gt;Environmental Research Letters$lt;/i$gt;, 2014, 9(9): 095002 $lt;/span$gt;
3. $lt;span class='magtech_ref_source'$gt; J, Zhou B, Gu W H, Schlesinger X Ju . Significant accumulation of nitrate in Chinese semi-humid croplands. $lt;i$gt;Scientific Reports$lt;/i$gt;, 2016, 6(1): 25088 $lt;/span$gt;
4. $lt;span class='magtech_ref_source'$gt; X T, Ju G X, Xing X P, Chen S L, Zhang L J, Zhang X J, Liu Z L, Cui B, Yin P, Christie Z L, Zhu F S Zhang . Reducing environmental risk by improving N management in intensive Chinese agricultural systems. $lt;i$gt;Proceedings of the National Academy of Sciences of the United States of America$lt;/i$gt;, 2009, 106(9): 3041–3046 $lt;/span$gt;
5. $lt;span class='magtech_ref_source'$gt; B, Gu X, Ju J, Chang Y, Ge P M Vitousek . Integrated reactive nitrogen budgets and future trends in China. $lt;i$gt;Proceedings of the National Academy of Sciences of the United States of America$lt;/i$gt;, 2015, 112(28): 8792–8797 $lt;/span$gt;