Xiaoyuan Yan1, Xuejun Liu2
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 (N) than any other country in the world. Total N 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 N input plays a vital role in ensuring food security, it has contributed to low nitrogen use efficiency in crop production systems. Much of the remainder N can be considered an expensive and environmentally damaging waste such as emissions of greenhouse gases, degradation of soil and freshwater. Average bulk N deposition, plant foliar N and crop N 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 N deposition in temperate grasslands. Meanwhile, large amounts of soil nitrate N accumulation were observed in major upland soils in China, threatening groundwater quality. Surface water eutrophication, air quality deterioration, both closely linked with reactive N, are increasingly being witnessed. China is facing a huge challenge to realize food security and protect the environment through maximizing N use efficiency and minimizing N negative effects.