Study on Soil Organic Carbon and Its Change of Activity in Continuous Cropping Cotton Field under Mulched Drip Irrigation

【Objective】 To elucidate the variation characteristics of soil organic carbon in cotton fields under drip irrigation in different continuous cropping years in the hope of provilding data and theoretical support for estimation of organic carbon reserves and analysis of carbon sequestration potential in continuous cropping cotton fields. 【Methods】 Field investigation and sampling were used to analyze the changes of soil organic carbon content, oxidizable organic carbon, organic carbon density, soil bulk density, carbon pool activity and carbon pool management index in 0-40 cm soil layer in different consecutive cropping years (L₅, L₁₂, L₁₇ and CK). 【Results】 With the increase of continuous cropping years, the soil organic carbon content in cotton fields showed a trend of increasing and then decreasing on the time scale. The total organic carbon content in cotton fields increased when continuous cropping was 1-5 a, and decreased significantly when continuous cropping was 5-17 a. On the spatial scale, the surface layer of organic carbon content was the largest, which decreased layer by layer with the increase of soil layer thickness. The total organic carbon content of 0-20 cm soil layer was greater than 20-40 cm soil layer. The soil organic carbon and soil organic carbon density of different continuous cropping cotton fields also showed the same trend as the total organic carbon. With the increase of planting years, the overall trend of soil bulk density changes in each soil layer was gradually increasing: L₁₇ > L₁₂ > L₅ > CK. In spatial scale, soil bulk density increased gradually with the increase of soil depth. In time and space scale, soil carbon pool activity decreased gradually. 【Conclusion】 In the context of long-term drip irrigation under the membrane, short-term continuous cropping could improve the soil total organic carbon and oxidizable organic carbon content. With the extension of continuous cropping years, soil organic carbon and active organic carbon content significantly decreased, soil carbon bank management index decreased, soil quality decreased, and soil fertility was affected.