Nitrogen storage and variability in paddy soils of China

Abstract. Paddy soils support important croplands in many parts of the world, especially in Asia. A thorough understanding of nitrogen (N) in Chinese paddy soils would be helpful to comprehend N cycling on farms from a national perspective. The N storage and density of paddy soils in China were evaluated employing 1490 soil profiles and a map of Chinese soils at a scale of 1:1 000 000. Results showed that the mean N density of paddy soils at 0–100 cm was 1240.0 g/m³, with N storage of 569.0 Tg. Paddy soil N density varies with different soil-water regime. In fact, waterlogged conditions can enhance paddy soil N content. Different rotation systems and various fallow systems also can affect paddy soil N density. There are significant relationships of N between both SOC and sand content. But the sensitivity of paddy soil N to climate was weak because of human activity. While this GIS-based analysis is a relatively coarse evaluation of the database, it does provide the first quantitative assessment of paddy soils N storage across China using commonly available digital databases.