The results from PT and KF regions indicate that there is no universal equilibrium Cmic-to-Corg constant in every land use. Regression analysis showed that significant relationship (p<0.01) existed between microbial biomass C and total organic C in the same land uses except paddy field in KF. The regression line of paddy field is obviously steeper than other land uses (dryland, orchard and woodland). Mean Cmic-to-Corg amount 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 PT region, respectively. Total organic carbon contents in KF region is higher than that in PT region for corresponding land uses. But mean Cmic-to-Corg is just on the contrary. Besides, land use impact on Cmic-to-Corg is a little different with that in PT region. Mean Cmic-to-Corg amount 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. Concluded from 2 regions, response of Corg to land uses was 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.
Cmic-to-Corg of paddy soils with chemical fertilizer applied increased in last 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 contribute to the enhancement of microbial biomass in paddy soils. Averaged by 6 experiments, Cmic-to-Corg increased 17.94%, 19.91% and 17.51%(compared with control), respectively. Though significant relationships (p<0.01) exists between organic C and microbial biomass C in 9 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