Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv An experimental study to assess the effect of the energy and the electrolyte concentration of rain drops on the infiltration properties of naturally crusted soils G. Carmi * , I. Abudi, P. Berliner Wyler Dept. of Dryland Agriculture, The French Associates Institute for Agriculture and Biotechnology of Drylands, The Jacob Blaustein Institutes for Desert Research, Ben- Gurion University of the Negev, Sede Boqer Campus, 84990, Israel ARTICLE INFO Keywords: Rainfall simulator Soil crust Infiltration Drop energy Electrolyte concentration Runoff ABSTRACT The main objective of the study was to assess the relative importance of the electrolyte concentration of rain drops and their kinetic energy on the infiltration rate of naturally crusted loess soil. A highly accurate portable rainfall simulator was used in this study. The effect of electrolyte concentration on infiltration rates was studied by comparing the runoff patterns observed using distilled or tap water. Similar infiltration curves were obtained for both treatments indicating that the effect of the electrolyte concentration of the applied water on infiltration was negligible. The effect of raindrop energy on infiltration rate was assessed by comparing the runoff characteristics of three treatments: fog, plot covered with dense mesh and no-surface protection. No runoff was observed in the fog treatment and the infiltration rates in the protected treatment were significantly higher than those of the un- protected treatment. The results of this study suggest that the momentum of drops hitting a naturally crusted loess soil significantly affect the infiltration process while the electrolyte concentration of the rain water does not meaningfully con- tribute to further crust development. Runoff coefficients derived from studies carried out with rainfall simulators that do not mimic the natural distribution of drop size and energy should be viewed with care. 1. Introduction Rainfall generated floods are not very frequent occurrences in arid regions, but are of great consequence as they have a major impact on the environment (Sponseller et al., 2013) and can also be used for the irrigation of agricultural fields using appropriate water harvesting systems (Ben Asher and Berliner, 1994, Carmi and Berliner, 2008). Linking rainfall characteristics to runoff generation for catchments of varying sizes has been an elusive goal of dryland hydrologists for dec- ades (Beven et al., 1988; Kirkby et al., 2005; Mirus and Loague, 2013). The generation of floods is affected, amongst others by the size of the watershed, the fraction of the watershed that was affected by the storm, topography, cover, etc. (Mirus and Loague, 2013). The main driver for large-scale process is however the local generation of runoff at micro- scale that commences when the rainfall intensity is higher than the absorption capacity of the soil; the latter being frequently the result of the presence of a raindrop-induced structural crust. Structural crust is a term used for a type of crust that results from the breakdown of ag- gregates due to the impact of drops and the colloidal dispersion that may follow in its wake (Carmi and Berliner, 2008). Crust development and its effect on the infiltration process have been described in detail during the last decades (McIntyre, 1958; Römkens et al., 1990; Shainberg, 2000; King and Bjorneberg, 2012). Crusts are usually the result of the combined effect of raindrop mo- mentum and the subsequent chemical dispersion of clays (Valentin and Bresson, 1992, Singer and Shainberg, 2004), the latter affected by the salt concentration of the soil solution, which is strongly influenced by the chemical composition of the applied water (Agassi et al., 1981, 1985, 1994; Morin et al., 1989). The interaction of the raindrop momentum, the electrolyte con- centration of the soil solution and the different physico-chemical characteristics of the soil matrix (clay content and type, presence of soluble and non-soluble salts, etc.) is complicated and most of the studies mentioned previously were carried out using laboratory rainfall simulators in which the effect of the various parameters could be se- parated and studied with more ease (Agassi et al., 1981; Morin et al., 1989; Singer and Shainberg, 2004; Mamedov et al., 2000; Neave and Rayburg, 2007). One of the salient results of these studies was that the https://doi.org/10.1016/j.jaridenv.2018.01.009 Received 4 December 2016; Received in revised form 14 December 2017; Accepted 15 January 2018 * Corresponding author. E-mail address: genadi@bgu.ac.il (G. Carmi). Journal of Arid Environments 152 (2018) 69–74 Available online 01 February 2018 0140-1963/ © 2018 Elsevier Ltd. All rights reserved. T