Patterns of soil nitrogen storage in China

We have investigated the storage and spatial distribution of soil nitrogen (N) in China based on a data set of 2480 soil profiles and a map of Chinese soil types at a spatial resolution of 1:1,000,000. Our estimate indicates that the total N storage in China is 8.29x10(15) g, representing 5.9-8.7% of the total global N storage. The total N storage in China is on average or slightly above the average of its share in the global N storage, even though low nitrogen content soils cover a large area in China. N density varies substantially with soil types and regions. Peat soils in the southeast of Tibet, southwest China, show the highest averaged N density with a value of 7314.9 g/m(3) among all soil types. This is more than 30 times of the lowest N density of brown desert soils in the western desert and arid region. The highest N storages among all the soil types are the felty soil in southeast of Tibet, dark-brown earths in northeast China, and red earths in southeast China with values of 921.1, 611.4, and 569.6 Tg, respectively. N density also varies with land cover types in China. Wetlands in southwest China exhibit the highest N density at 6775.9 g/m(3) and deserts in northwest China have the least at 447.5 g/m(3). Our analysis also indicates that land cover types are poor predictors of N content. Further research is needed to examine how transformation from organic agriculture to increased use of fertilizers and pesticides has influenced N storage in China