Effect of rain on the macroporosity at the soil surface

Rainfall on soil causes slaking, mechanical disruption of aggregates and compaction. Too few data exist to predict the changes likely to occur in particular soil, landscape, and management conditions. Experiments with simulated rain were set up in order to study and to model mathematically the changes of the pore system within the surface layer of a soil when rain was applied on a field cropped with maize. Macroporosity, pore-size and pore-shape distributions, and fractal dimensions of the pore surface roughness, and the pore volume were measured by image analysis of thin sections. The general trends of changes in porosity indicated the presence of two different sets of processes at the surface (0-3 cm) and in the layer immediately underneath (3-6 cm). In both layers most of the variation in macroporosity was due to loss of elongated porosity. A theoretical approach recently developed to link rain and erosion to sealing properties was extended to describing the effect of rain on the amount of elongated pores and the pore volume fractal dimension in these two layers. Our approach could be useful when modelling the effects of sealing processes in soil erosion.