Organic carbon storage in soils of tropical and subtropical China

Tropical and subtropical China occupies a total area of about 215 Mha, but the contents and storage of soil organic carbon (C) on this land have not been well studied. This research was conducted in this concern by jointly using soil survey data and the regional soil map. It was estimated that the 0-20 cm C density of the soil subgroups in the region varied from 1.2 to 9.7 kg C m(-2). In the major zonal soils, soil subgroup 'young similar to' had generally a C density about 1.2-4.4 times lower than its other natural counterparts. Furthermore, subgroups of the cultivated soil gave a C density about 20-63% lower than their natural counterparts (except subgroup 'young similar to'), showing remarkable C losses caused by cultivation. For soil groups in the east, brown soil had the highest C density (6.8 and 21.4 kg C m(-2), for the upper 20 and 100 cm soil, respectively), followed by yellow soil, yellow brown soil and limestone soil (4.6-5.5 and 12.3-14.5 kg C m(-2), idem). Torrid red soil, purplish soil and fluvo-aquic soil had the lowest C density (2.0-2.2 and 5.8-7.5 kg C m(-2), idem) with the others ranking at a medium level. In the west, podzolic soil ranked the highest (17.9 and 55.8 kg C m(-2), idem), followed by dark brown soil, brown soil and limestone soil (6.9-11.6 and 21-29 kg C m(-2), idem), and again torrid red soil, purplish soil and fluvo-aquic soil ranked the lowest (3.9-5.1 and 11.4-14.1 kg C m(-2), idem). Finally, a total of about 26.8 +/-7.4 Pg organic C was estimated being stored in soils of the entire region.