Abstract: 【Objective】In order to assess the impacts of land use change on soil organic carbon (SOC) and soil microbial biomass carbon (SMBC), the contents of SOC and SMBC of surface soil samples (0-20 cm) were investigated. 【Method】The dense sampling (the density of sampling for paddy and dry land is 3-4 per ha, for orchard is 2-3 per ha and for woodland is 0.2-0.5 per ha) and the field surveys in Kenfu demonstration area of environmental immigrants of the northwest of Guangxi, a hilly landscape of red soil area of subtropical China were carried out. 【Result】The average contents of SOC, SMBC and the ratio of SMBC and SOC were respectively (17.53±5.02) g·kg-1, (278±174) mg·kg-1 and (1.56±0.84)% in the area, respectively. The average contents of SOC, SMBC and the ratio of SMBC and SOC of the woodland were (17.53±5.02) g·kg-1, (278±174) mg·kg-1 and (1.58±0.39)%, respectively. Compared with the woodland, the contents of SOC and SMBC and the ratio of SMBC and SOC of the paddy field increased by 15.5%, 84.0% and 73.9% (P<0.01); The content of SOC of the dry land (17.50±4.89 g·kg-1) decreased slightly (P>0.05) compared with the woodland, that of SMBC and SMBC/SOC decreased by 29.1% and 24.2% (P<0.01); The content of SOC, SMBC and SMBC/SOC of the orchard decreased by 26.8%, 46.1% and 26.1% compared with the woodland (P<0.01). In addition, there were significant correlations between SOC and SMBC in different land use except the paddy field. 【Conclusion】This study indicated that the conversion of woodland into paddy field increased the accumulation of SOC and the microbial activity evidently in the hilly landscape of red soil area of subtropical China. However, the conversion of woodland into dry land or orchard reduced the content of SOC and the microbial activity to different degrees.

Key words: Land use, Subtropics, Hilly red soil region, Soil organic carbon, Soil microbial biomass carbon