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 5 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/m 3 , 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 10 SOC (Giardina et al., 2003). Thus, studying the spatial distribution of paddy soil N will 856 BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 20 the soil N storage in China and investigated the spatial distribution of soil N. As for paddy soils, Tian et al. used the data from 525 soil profiles to obtain the paddy soil area (29.79×10 6 ha) and N storage (273.49-384.23 Tg). While each of these studies established a foundation for soil N storage of paddy soils in China, most only estimated the N storage and N density, and failed to investigate the 25 factors which affect N storage. Also, previous studies were conducted in limited areas (villages, experimental sub-areas, etc.), or used a finite number of paddy soil profiles. Abstract Introduction Conclusions References Tables BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 25 soils was 150 cm. According to the farming practice in China, surface layer depth is defined as 0-20 cm, and the depth of a profile is defined as 0-100 cm in the present 859 BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables Equation (1) was used to first calculate the soil N density of every soil profile. Then Eqs. (2) and (3) were used to calculate the N storage and N density of Chinese paddy soils. 860 BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 25 SOC and total N content. The North region's cropping system was fallow in winter, where dry conditions reduce paddy soil N content. 863 BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 25 864 BGD 7, 855-877, 2010 Abstract Introduction Conclusions References Tables 1996.

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