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

Abstract

The post-tillage dynamics of the surface soil saturated hydraulic conductivity, K_s, 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, K_s 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 K_s were expected to be specifically attributable to mechanical modifications of the porous medium due to the raindrop impact. For each individual experiment, K_s decreased with cumulative rainfall energy, E, according to an exponential or power relationship, denoting that raindrop impact had a noticeable effect on K_s when it occurred on an initially tilled soil. The developed experimental methodology appears usable to determine raindrop impact effects on the surface soil K_s in highly controlled field conditions and it could be applied to develop K_s versus E relationships usable for numerically simulating surface soil hydrological processes.