垄作免耕下紫色水稻土有机碳的分布特征

DISTRIBUTION OF SOIL ORGANIC CARBON IN PURPLE PADDY FIELD UNDER LONG-TERM NON-TILLAGE RIDGE CULTURE

土壤有机碳的空间分布特征是研究土壤有机碳储量及其动态的重要内容之一。本文从土壤团聚体、剖面和田块等尺度研究了四川盆地紫色水稻土在垄作免耕下有机碳的分布特征。结果表明：紫色水稻土团聚体含碳量在大团聚体（2～0．25mm）中最高，但有机碳总量主要分布在0．25～0．02mm。其次是0．02-0．002mm；垄作免耕下团聚体有机碳主要富集在0—10cm土层的大团聚体（〉0．25mm）中（富集系数〉1．5），而常规平作、水旱轮作和垄作翻耕下，剖面中土壤有机碳含量分布自上而下缓慢降低；实验田表层土壤有机碳含量及相关土壤特性的空间分布呈条带状和斑块状格局，具有明显的空间变异性。土壤有机碳含量在垄作免耕处最高，达30．71g kg^-1，在常规平作处最低，为16．50g kg^-1左右。长期垄作免耕会导致有机碳向土壤表层大团聚体的相对富集及在土壤剖面的层次分异。

Spatial distribution of soil organic carbon （SOC） is one of the key issues of the study on SOC sequestration, and plays a crucial role in understanding SOC storage dynamics. A research project on distribution of SOC in soil aggregates, profile, and field of purple paddy soil that is widely distributed in the Sichuan basin, was initiated in 1990. Results show that the highest organic carbon content in aggregates was discovered in the fraction of 2 - 0.25 mm in particle size, while total organic carbon （TOC） in aggregates was mainly distributed in the fractions of 0.25 - 0.02 mm and 0.02 - 0.002 mm. The content of SOC in aggregates trended to be greater （enrichment coefficient, EC 〉 1.5） in macroaggregates （ 〉 0.25 mm） at depth of 0 - 10 cm under non-tillage ridge culture. In conventional fields under flat culture, paddy-upland rotation and ridge culture, SOC concentration decreased slowly with the increase in depth. Organic carbon content was significantly （ p 〈 0.05） different between treat- ments. Distribution of soil organic carbon and some related properties of the topsoil layer of the experiment field demonstrated significant spatial variation, forming stripes and patches. The treatment of non-tillage ridge culture was the highest in SOC content, reaching 30.71 g kg^-1, while the treatment of conventional flat culture the lowest being only around 16.50 g kg^-1. Long-term non-tillage ridge culture may lead to enrichment of SOC in macroaggregates of the surface soil layer and differentiation between layers of the soil profile.