[Spatial distribution of preferential flow paths in paddy field in the Karst Area of Guangxi.]

The spatial distribution of the preferential flow path in soil affects the occurrence and movement of preferential flow. In afield soil staining and tracing experiment, with the help of morphological image analysis technology and community ecological analysis method, we examined the spatial distribution characteristics of preferential flow path in paddy fields under straw mulching (CM) and non-mulching (CK) in karst areas of Guangxi. The results showed that, under the same external water supply conditions, with the increases of soil depth, soil horizontal dyeing changed from overall distribution to clump aggregation distribution in paddy field under straw mulching. In the non-mulching paddy field, the main dyeing was branch, with an average shape coefficient of staining patch of 21.69. The dyeing morphology in the non-mulching paddy field was 1.04 times of straw mulching paddy field. The preferential flow paths of straw mulching and non-mulching paddy fields showed both clustered distribution. In straw mulching paddy field, the Morisita index was 1.28 as the preferential flow paths with radius of influence less than 1.0 mm were the main ones (importance value 0.31). The importance value of preferential flow paths with radius less than 1.0 mm was 0.28 in non-straw mulched rice field. Straw mulching affected the preferential flow paths in paddy fields, which could help to improve water and fertilizer utilization of crops in the field.