Infiltration and bulk density dynamics with simulated rainfall sequences

Experiments with simulated rain on interrill plots were set up (2016–2017) at the Masse SERLAB station (42°59′34″N 12°17′27″E, Italy) to study the cumulative effects of the processes affecting the soil surface and the top 5-cm soil layer under a series of rainfalls separated by a no-rain period of several days. The modifications were quantified in terms of random roughness, bulk density (BD), porosity, and infiltration dynamics. Each experiment consists of an initial tillage and three rainfall events (intensity = 40 mm/h during wetting and 70 mm/h during runoff) in a silt-clay-loam with 51 % silt and 34 % and clay. The data confirm a quick and considerable decrease in porosity (derived through BD data). Nevertheless, the decrease is not monotonic and continuous; on the contrary, it is counteracted by an increase during the inter-rainfall period. When the porosity behavior is plotted versus applied pressure (rainfall impacts), as in oedometer tests, then it suggests a behavior on the verge of deterministic chaos with two attractors. The roughness behavior also shows a partial recovery during the between-rains intervals, confirming the BD trends. Introducing the decrease in pore size and the total porosity within a simple porous media hydraulic formula, it was possible to interpolate the infiltration data. The presence of the two BD attractors means that predictions can never be precise, unless the processes leading to the recovery of porosity are studied in detail in order to generate algorithms that evaluate the soil's recovery behavior, which can be used in advanced infiltration models. This study underlines that adequate data are needed to generate algorithms that can evaluate the soil's ability to recover and the total porosity between successive rainfalls.