Abstract: The observations of 26-year long-term experiment in Zhejiang paddy soil showed that: soil organic matter could increase continuously with applying organic manure, and the increase rate enhanced with the application rates of organic manure. By mathematic modeling, the soil organic matter will be increased by 22 kg with applying 1 t fresh FYM. The more the application rate of organic manure, and the more the root residues, thus the more the CO2 emission from the mineralization of soil organic matter. From the expectation, the CO2 emission will be at 10.04-21.61 t·ha-1·a-1 with applying 16.5-49.5 t·ha-1·a-1 of fresh FYM. The soil organic carbon from the mineralization and release of applied organic carbon (fresh FYM and root residues) will affect the CO2 concentration in the atmosphere. So, the more the application rates of organic manure, and the more the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t·ha-1·a-1 with applying 16.5-49.5 t·ha-1·a-1 of fresh FYM. Thus, the CO2 fixation will be increased by 46.7 kg with applying 1 t fresh FYM. To apply organic manure continuously in rice fields may be helpful to reduce the contribution to the increase in CO2 concentration in the atmosphere.

Key words: Paddy soil, Organic manure, Carbon cycle, Carbon dioxide, Global climatic changes