Depth-dependent heterogeneity of water flow in sandy soil under grass

The non-equilibrium water flow was studied on an aeolian sandy soil under grass using the dye tracer infiltration experiments. Two experiments simulating infiltration of 20 mm and 70 mm of rain water were conducted. The improved digital image analysis technique for estimating the effective cross section (ECS) and degree of preferential flow (DPF) from stained soil profiles was used to analyze the depth dependency and variation of the ECS and DPF parameters. It was found that the heterogeneity of water flow in sandy soil under grass increased with depth. Extremes of heterogeneity parameters (minimum value of the ECS and maximum value of the DPF) were almost the same for the two cumulative infiltrations, and the depth, in which the extremes of heterogeneity parameters occurred, increased with an increase in cumulative infiltration. Moreover, considerable variation of infiltration patterns was indentified in consecutive vertical sections.