Infiltration and macroporosity of a silt loam soil under two contrasting tillage systems

Infiltration into soils is influenced by macroporosity. The properties of the macropore system are, among other factors, a function of the applied management and tillage system. Therefore, tillage practices are supposed to have considerable impact on surface runoff and generation of floods. On an experimental site with a silt loam soil partly treated with conventional and conservation tillage systems, two different methods for the characterization of the macropore system were performed: Visual inventarization of stained and unstained macropores and tension-adjusted infiltration measurements. Dye tracer experiments with methylene blue yielded a penetration depth of 120 cm on the plot with conservation tillage whereas on the plot with conventional tillage a penetration depth of only 50 cm were observed. The visual inventarization of stained and unstained macropores resulted, for both tillage treatments, in macropore densities ranging between 100 and 1000 macropores per square meter, with macropore numbers greatest in the topsoil and gradually decreasing towards depth. Infiltration rates at saturation were, in the topsoil, slightly higher at the conventionally tilled plot compared to the conservation till plot, whereas below 30 cm depth it was vice versa. For both methods, the macroporosities are at soil depths of 0 - 10 cm higher for conventional tillage, and below soil depths of 20 cm higher for conservation tillage. In combination with the greater depth penetration of dye tracer at the conservation till plot, this indicates a greater continuity of macropores in vertical direction for soils with conservation tillage system. Therefore, this tillage practice could possibly offer a means to reduce surface runoff and flood generation in agricultural landscapes with silty soils.