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 b een well studied. This research was conducted in this concern by jointly us ing 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 cou nterparts. Furthermore, subgroups of the cultivated soil gave a C density a bout 20-63% lower than their natural counterparts (except subgroup 'young s imilar to'), showing remarkable C losses caused by cultivation. For soil gr oups 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 s oil, 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 a t a medium level. In the west, podzolic soil ranked the highest (17.9 and 5 5.8 kg C m(-2), idem), followed by dark brown soil, brown soil and limeston e soil (6.9-11.6 and 21-29 kg C m(-2), idem), and again torrid red soil, pu rplish soil and fluvo-aquic soil ranked the lowest (3.9-5.1 and 11.4-14.1 k g C m(-2), idem). Finally, a total of about 26.8 +/-7.4 Pg organic C was es timated being stored in soils of the entire region.