Catena 218 (2022) 106542 Available online 4 August 2022 0341-8162/© 2022 Elsevier B.V. All rights reserved. Infltration and bulk density dynamics with simulated rainfall sequences Francesca Todisco a, * , Lorenzo Vergni a , Alessandra Vinci a , Dino Torri b a Department of Agricultural, Food and Environmental Sciences, University of Perugia, Borgo XX Giugno 74, 06121 Perugia, Italy b CNR-IRPI, Perugia, Italy A R T I C L E INFO Keywords: Interrill Infltration Bulk density dynamics Roughness dynamics Porosity dynamics Infltration dynamics ABSTRACT 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 modifcations were quantifed in terms of random roughness, bulk density (BD), porosity, and infltration 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 confrm 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, confrming 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 infltration 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 infltration 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. 1. Introduction Raindrop impact is considered the main factor in forming the soil crust, as it detaches particles and soil aggregates, modifying the soil surface structure and causing compaction. Tackett and Pearson (1965) found an exponential increase in bulk density due to cumulative rain. Farres (1978) found that the increase in seal thickness during rain was related to the cumulative rain logarithm. Boiffn (1984) observed a hyperbolic decrease in the upper soil layer porosity with an increase in the time of exposure to rain. Mualem et al. (1990) ascribed the maximum change in the bulk density at the surface to the rain kinetic energy. Roth (1997) suggested that the exponential decay function proposed by Mualem et al. (1990) better represents the initial stages of surface compaction. By contrast, a sigmoidal function better describes bulk density changes in the later stages of structural seal formation. Bielders & Baveye (1995) linked clay eluviation and the thickness of the “washed in” layer to rain kinetic energy by means of linear regressions. In a study on the effects of raindrop impact on soil micromorphology under various crop systems, Panini et al. (1997) found that most of the reduction in macroporosity is due to the loss of elongated pores. They developed a simple approach for linking the size reduction of elongated macroporosity to causative factors through an exponential decay func- tion in a quantitative, physically-based manner. The sealing/crusting process causes a decrease in the infltration rate and an increase in runoff and soil erosion (Duley and Kelly, 1939; De Ploey, 1981), and, if disregarded, it may be harmful to both the natural and the anthropic ecosystems. Besides the expected infltration rate decrease due to soil void saturation (Philips, 1957; for stable pore system networks), the destruction of aggregates seals the pores and adds a further decrease in pore space and pore connectivity in the sealed layer, as shown by many studies pioneered by Horton (1939). Sealing of soil pores, which occurs as the frst step toward crusting, decreases infl- tration rates rapidly and pronouncedly (Horton, 1939). Hence, it in- creases runoff coeffcients. The interpolation curve, which is most often used to describe the change in the infltration rate due to sealing, is a negative exponential of time, which can be substituted by cumulated rain, or by rainfall kinetic energy, with more or less empirical * Corresponding author. E-mail address: francesca.todisco@unipg.it (F. Todisco). Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena https://doi.org/10.1016/j.catena.2022.106542 Received 3 December 2021; Received in revised form 22 July 2022; Accepted 23 July 2022