Yan Xiaoyuan1, Liu Xuejun2
1 Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China
2 College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
China now creates more nitrogen than any other country in the world. Total nitrogen input to the terrestrial ecosystem of mainland China increased from 25.2 Tg in 1980 to 61.0 Tg in 2010, while the amount of natural N2 fixation changed little during this period (9.3–11.0 Tg). Though large amount of nitrogen input plays a vital role in ensuring food security, it has contributed to low nitrogen use efficiency both in crop and livestock production systems. Much of the remainder nitrogen can be considered an expensive and environmentally damaging waste such as emissions of greenhouse gases, degradation of soil and freshwater. Average bulk nitrogen deposition, plant foliar nitrogen and crop nitrogen uptake from long-term unfertilized croplands all significantly (p<0.05) increased from 1980 to 2010, in agreement with rapidly increased NH3 and NOx emissions. As a consequence, significant soil acidification was reported in major Chinese croplands, grasslands and forestlands. Clear evidence showed that plant species richness and soil bacterial diversity declined with increased nitrogen deposition in temperate grasslands. Meanwhile, large amounts of soil nitrate nitrogen accumulation were observed in major upland soils in China, threatening groundwater quality. Surface water eutrophication, air quality deterioration, both closely linked with reactive nitrogen, are increasingly being witnessed. China is facing a huge challenge to realize food security and protect the environment through maximizing nitrogen use efficiency and minimizing nitrogen negative effects.