Nitrogen (N) recycling in agricultural soils plays a key role in the terrestrial N cycle. A thorough understanding of N storage and its spatial distribution in Chinese paddy soils would be helpful to research on N cycle. Total soil N density and total soil N storage of paddy soils in China was evaluated based on the data of 1 490 paddy soil profiles and the 1∶1 000 000 soil database of China. Results showed that the mean nitrogen density of paddy soils at a depth of 0~100 cm was 12.4 Mg hm-2, and the N storage was 569 Tg. Nitrogen density varied substantially with the soil subgroups and regions. Submergenic paddy soils were the highest in mean N density (19.7 Mg hm-2) among all paddy soil subgroups, whereas Bleached paddy soils the lowest (8.71 Mg hm-2), and Southwest China was the highest (17.4 Mg hm-2), while South China had the lowest (11.5 Mg hm-2). The variation of N density in both paddy soil subgroups and soil regions are quite significant, but it was higher between soils subgroups than between regions. This indicates that spatial variation of soil N in paddy soils was sensitive to surface water regime rather than climate.
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Lin Jinshi, Shi Xuezheng, Yu Dongsheng, Wang Hongjie, ZhaoYongcun, Sun Weixia. Spatial patterns of nitrogen storage in paddy soils at regional and subgroups levels in China[J]. Acta Pedologica Sinica,2009,46(4):586-593.