Water is the most limiting factor for crop production in arid and semiarid areas. The search of promising water management strategies is foremost for achieving highly productive and sustainable agriculture. Irrigation water management, water conservation, and nonconventional water use for agriculture are key issues to be considered by the National Agricultural Research Systems (NARS) in these areas. According to climate change scenarios and population growth predictions, these countries will undergo even severe water scarcity levels. Failure of resolving food production challenge will exacerbate tensions between countries, wars, and illegal immigration and compromise human, social, economic, and sustainable development in these areas. However, the search for innovative solutions to water scarcity must comply with societal values, environmental sustainability, and market growth.

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 unprotected 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 contribute 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.

Microcatchment is a technique for collecting, storing and conserving local surface runoff in order to grow trees/shrubs. In this system, runoff water is generated on a plot and stored in the soil during runoff events, and trees/shrubs may utilize this water during the next dry season.Microcatchments have relatively small runoff generation areas (from dozens to hundreds sq. m) and are cheap and simple to implement Their collection area is usually a small depression located nearby the runoff generating area in which one or a few trees/shrubs may be planted Due to the short overland flow path runoff generation is efficient and even short low intensity storms may generate runoff. The drawback is however that due to the small size of the generating area small volumes of water are conveyed to the storage plots. Another drawback is susceptibility of the augmented water to evaporation. The main objective of present research presented hereafter was to estimate the effect the depth of the depression has on the efficiency of the water conservation in the soil profile. In the present study the storage plots were circular pits and the effect their depth had on evaporative losses and water distribution were studied.The results clearly show that the depth of the pit significantly affects evaporative water losses. The losses were separately computed for the soil cylinder whose upper surface is the bottom of the pit and for the surrounding shell. No differences between treatments were evident for losses from the inner cylinder. Significant differences in water losses were however observed for the surrounding shell where the shallow pits losing as much as six times more than the deeper pits. (C) 2013 Elsevier Ltd. All rights reserved.

Rain simulators (RSs) are used in soil crusting and soil erosion laboratory and field studies. The energy flux produced by RSs is usually high in respect to the intensity of the application. The high energy flux applied on the soil surface by these RSs becomes a crucial disadvantage when low intensity rainfall is considered. Moreover, crust formation under natural field conditions is very different from crusting in disturbed soil samples.The main purpose of this study was the design and the construction of a portable RS to be used in the field for simulating rainfalls that induce soil crusting and thus lead to the generation of runoff and eventually soil erosion. A high accuracy portable RS for field rainfall simulations was designed and built. The D-50 of the drops is 1.5 mm with a ground hitting velocity that nearly matches the theoretical terminal velocity without the necessity of a tower (Barros et al., 2008). The energy flux of the simulated rain is 76% of the energy flux expected for a natural rainfall of the same intensity. The spatial distribution of water is homogenous for a wide range of rain intensities. This RS can be a powerful tool for field infiltration, soil crusting and soil erosion field trials. (C) 2012 Elsevier B.V. All rights reserved.

In and zones, runoff is frequently generated as a result of the crust development on the soil surface. This crust is a thin layer of greater density, high shear strength, finer pores and has a lower saturated hydraulic conductivity than the underlying soil. The objective of the research reported herein was to study the factors that influence the generation of runoff in small plots under natural rainfall conditions. Factors studied were crust permeability, roughness, soil salt content and time gaps between the rain showers.The field trial was carried out in the Mashash experimental runoff farm in Israel's Negev desert. Runoff was measured on eight plots using a tipping-bucket system (resolution 0.01 mm, s(-1)). Rainfall intensity was recorded on-site with a rainfall gauge (resolution 0.25 mm s(-1)). Two treatments were studied: long-term rainfall-induced crusts (LTC) that had developed over a period of years (three plots), and complete destruction of the crust (ICU) by cultivation to a depth of 0.2 to with a rotary tiller before the beginning of the trial (five plots).Surface roughness was characterized by the surface RMS height obtained from laser micro-relief measurements before and during the season. Prior to the onset of rain, roughness was similar for all the ICU plots. One month thereafter, roughness had decreased sharply, but exhibited no further change until the end of the season. Roughness of LTC plots did not change during the season and was lower than that of the ICU plots. After similar to 21 mm of cumulative rain, the average runoff yield was similar for both ICU and LTC plots, even though roughness in the former did not reach the low values of the LTC plots.Although the variability in roughness among individual LTC plots was very small, large differences were observed in the collected runoff. The same phenomenon was observed for the ICU plots. Moreover, the runoff yields in two ICU plots were consistently higher than those in two LTC plots while three other ICU plots produced much less runoff.Apparent saturated hydraulic conductivity (AHC) was measured on mounds and depressions. In the ICU plots the average AHC of the mounds was markedly higher than that of the depressions while the AHC values of mounds were very similar.No mounds or depressions were observed in the LTC plots, and their AHC was similar to that of depressions in ICU plots. The results indicate that the apparent saturated hydraulic conductivity of the upper soil layer was not directly linked to the runoff generation.Treatment effect was significant only for the first two rainfall events, but the presence of salts in the upper soil layer significantly affected runoff generation during the last four rain events of the season. Analysis of runoff and time gaps between the runoff-producing rain showers showed a clear relationship between runoff yields and average rainfall intensity, the degree of correlation between them improving with a decrease in the length of the gap. (c) 2008 Elsevier B.V. All rights reserved.