Abstract: Taking the adjacent 18-year-old pure Pinus massoniana pure forest (Ⅰ), P. massoniana, Liquidamber fomosana, and Schima superba mixed forest (Ⅱ), S. superba pure forest (Ⅲ), L. fomosana  (Ⅳ) pure forest, and natural  restoration fallow land (CK) in Taihe County of Jiangxi Province as test sites, a comparative study was made on their soil soluble organic carbon (SOC) and nitrogen (SON), soil microbial biomass C (MBC) and N (MBN), and soil urease and asparaginase activities. In 0-10 cm soil layer, the pool sizes of SOC, SON, MBC, and MBN at test sites ranged in 354-1007 mg·kg^-1, 24-73 mg·kg^-1, 203-488 mg·kg^-1, and 24-65 mg·kg^-1, and the soil urease and asparaginase activities were 95-133 mg·kg^-1·d^-1 and 58-113 mg·kg^-1·d^-1, respectively. There were significant differences in the pool sizes of SOC, SON, MBC, and MBN and the asparaginase activity among the test sites, but no significant difference was observed in the urease activity. The pool sizes of SOC and SON were in the order of Ⅳ> CK> Ⅲ>Ⅰ>Ⅱ, those of MBC and MBN were in the order of CK>Ⅳ> Ⅲ >Ⅰ> Ⅱ, and asparaginase activity followed the order of Ⅳ>CK>Ⅲ>Ⅱ>Ⅰ.With the increase of soil depth, the pool sizes of SOC,SON, MBC, and MBN and the activities of soil asparaginase and urease decreased. In 0-20 cm soil layer, the SOC, SON, MBC, MBN, total C, and total N were highly correlated with each other, soil asparaginase activity was highly correlated with SOC, SON, TSN, total C, total N, MBC, and MBN, and soil urease activity was highly correlated with SON, TSN, total C, MBC and MBN.

Key words: forest plantation in degraded red soil region, soil soluble organic carbon , and nitrogen, soil microbial biomass carbon , and nitrogen, soil enzyme activity, nitrogen fertilizer management, watermelon, yield, quality, nitrogen use efficiency.