Changes in soil hydrodynamic parameters during intermittent rainfall following tillage

Abstract

The changes in the soil hydrodynamic properties following soil tillage were investigated in rainfall simulation trials of intermittent rain at the Masse experimental station (Soil Erosion LABoratory, SERLAB) in central Italy. The experiments were designed to build a database as representative as possible of situations that may occur in nature. The data collected during the experiments were used to determine the saturated soil hydraulic conductivity, Ks, the soil sorptivity at the antecedent soil–water matric potential Ψi, S, and the flow-weighted mean pore size at Ψi, λm. It was also verified if the energy content of total rainfall after tillage explained the short-term temporal variability of Ks. The results showed that during a sequence of rainfalls with wetting and drying cycles, there was a reduction of both S and Ks by 2.9–3.1 and 1.4–2.2 times, respectively, depending on the plot. This decrease was abrupt for S and more gradual for Ks. The analysis confirmed that Ks decreased as the overall energy dissipated at the soil surface, E, increased. The range of possible Ks values should be expected to become smaller as the dissipated rainfall energy after tillage increases (<30 mm/h for E = 2 kJ/m2 and < 5 mm/h for E = 8 kJ/m2). For this reason, for the prediction and mathematical simulation of the rainfall-runoff transformation process, it is not advisable to limit the investigation to a single hydraulic characterization carried out immediately or shortly after tillage but data should be collected in a relatively long time span after tillage to properly characterize the soil in a condition favourable to surface runoff occurrence. For very high energy values, a recovery mechanism of the hydraulic properties of the altered/compacted layer was observed, but this behaviour should be confirmed by further investigations.