Abstract: In this paper, mesh-bag method is used to study the decomposition of straws and roots of maize and wheat, and isolated pot alkaline liquid assimilation method is used to determine soil respiration. Based on these, the yearly mineralization rate and balance coefficient of soil organic carbon are calculated. The decomposition dynamics of organic materials doesn't show any difference between middle and high yield fields, but the soil respiration rate of these two fields are 1725.7 and 1878.5 g CO₂·m^-2·yr^-1,respectively. The yearly mineralization rates of soil organic carbon are 5.48 and 5.64%, and the balance coefficients are 1.86 and 1.84 respectively. The results suggest that intensive management of crop field doesn't decrease the content of soil organic carbon.

Key words: Intensive agriculture, Organic material decomposition, Soil respiration, Soil carbon balance, cotton, spatial and temporal distribution, trend analysis, fiber quality