Saturday, 15 July 2006

Response Of Cmic-To-Corg To Land Use And Fertilization In Subtropical Region Of China.

Liu Shoulong1, Wu Jinshu2, Su Yirong2, Huang Daoyou2, Xiao Heai2, and Tong Chengli2. (1) Huazhong Agricultural Univ, College of Resources and Environment, Wuhan, China, (2) Chinese Academy of Sciences, Key Laboratory of Agro-ecology, Institute of Subtropical Agriculture, Changsha, China

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. But few researches focus on the detailed impacts of land use or management on Cmic-to-Corg. 2 small-scaled regions (PT and KF) and 6 long-term experiments (1986~2003) in paddy fields were used to investigate the response of Cmic-to-Corg to land use and fertilization in subtropical region of China.

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

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