A Check of Water Drop Impact Effects on Surface Soil Saturated Hydraulic Conductivity

The post-tillage dynamics of the surface soil saturated hydraulic conductivity, Ks, was studied at the Masse experimental station (central Italy, silty-clay-loam soil). A sequence of experiments was performed by rainfall simulation on two replicated micro-plots (width 1 m, length 0.92 m, slope 16%) established on bare soil. Each high-intensity rainfall simulation was preceded by a low-intensity wetting phase. The soil water content, w, was measured before wetting and both before and after simulation. Runoff was measured at 5 min intervals. The infiltration rate was calculated as the difference between rainfall intensity and runoff rate. Finally, Ks was assumed to be equal to the infiltration rate under the nearly steady conditions reached at the end of each simulation. The pre-wetting w values were quite low and they increased during wetting, reaching at the end of this phase a value that remained more or less stable during the simulation phase. Consequently, all changes of Ks were expected to be specifically attributable to mechanical modifications of the porous medium due to the raindrop impact. For each individual experiment, Ks decreased with cumulative rainfall energy, E, according to an exponential or power relationship, denoting that raindrop impact had a noticeable effect on Ks when it occurred on an initially tilled soil. The developed experimental methodology appears usable to determine raindrop impact effects on the surface soil Ks in highly controlled field conditions and it could be applied to develop Ks versus E relationships usable for numerically simulating surface soil hydrological processes.