Abstract: 【Objective】 Ratios of microbial biomass C to total organic C (Cmic-to-Corg) could be an indication of a system at a new equilibrium after land use or managements changed. 【Method】 But few researches putted their emphasis on the impacts of land use or management on Cmic-to-Corg. Two small-scaled regions (Pantang region and Kenfu region) and six long-term experiments (1986-2001) in paddy fields were used to investigate the response of Cmic-to-Corg to land use and fertilization in subtropical region of China. 【Result】 The results from PT and KF regions indicated that there was no universal equilibrium Cmic-to-Corg constant in every land use. Mean Cmic-to-Corg amounted to (5.07±1.26)% for paddy field, (2.96±1.60)% for dryland, (2.40±0.34)% for woodland, (1.98±0.89)% for orchard in Pantang region, respectively. The effect of land use on Cmic-to-Corg in Kenfu region was a little different with that in PT region. Mean Cmic-to-Corg amounted (3.01±1.51)% for paddy field, (1.57±0.40)% for woodland, (1.29±0.56)% for dryland, (1.14±0.42)% for orchard, respectively. In both regions, responses of Corg to land uses were similar with Cmic-to-Corg, and the results also showed that anthrostagnic soil (paddy field) was not only in favor of the carbon sequestration but also helpful to the microbial biomass enhancement. Long-term experiments showed that Cmic-to-Corg of paddy soils with chemical fertilizer applied increased in recent 17 years in half of experiments but not significant. With the same amount of N applied, organic matter incorporation including middle-level (30% organic N+70% chemical N) manure, high-level (60% organic N+40% chemical N) manure and straw treatments contributed to the enhancement of microbial biomass in paddy soils, averaged by 6 experiments, Cmic-to-Corg increased by 17.94%, 19.91% and 17.51% (compared with control), respectively. 【Conclusion】Though significant relationships (P<0.01) exists between organic C and microbial biomass C in 6 long-term experiments, but the response of soil organic C to fertilization was not completely the same as that of Cmic-to-Corg. It indicated that Cmic-to-Corg could reflect the changes of Corg, but not precisely.

Key words: Cmic-to-Corg, Organic C, Land use, Fertilization