The biological soil crusts (BSCs) in the NW Negev cause local water redistribution by increasing surface runoff. The effects of pore clogging and swelling of organic and inorganic crust components were intensively investigated in earlier studies. However, the effect of water repellency (WR) was not addressed systematically yet. This study investigates subcritical WR of BSCs in three different study sites in the NW Negev. For this purpose, three common methods to determine soil WR were used: (i) the repellency index (RI) method (ii) the water drop penetration time (WDPT) test and (iii) the Wilhelmy plate method (WPM). Furthermore, the potential influence of WR on local water redistribution is discussed and the applied methods are compared. We found the BSC to be subcritically water repellent. The degree of WR may only affect water redistribution on a microscale and has little influence on the ecosystem as a whole. The RI method was clearly the most appropriate to use, whereas the WDPT and the WPM failed to detect subcritical WR.
The fact that flash floods initiated in arable catchments are often accompanied by massive sediment and nutrient loads often leads to the assumption that surface runoff is the principle pathway by which runoff reaches watercourses. On the basis of an evaluation of several rainfall-runoff events in a representative agricultural catchment, we show that runoff from cultivated land may be generated in a way similar to that seen on forested slopes, where shallow subsurface runoff is the predominant pathway by which runoff makes its way to watercourses in most runoff events. To identify the predominant runoff pathway, we employed a combination of turbidity measurements and stream discharge data. Suspended sediment flux, a newly introduced index representing the ratio between precipitation duration and total sediment yield, and direction of the discharge-turbidity hysteresis loops were proposed as reflective indicators of the frequency of runoff via different pathways. In our study, most of the events initiated by rainstorms of various intensities and durations resulted in rapid increases in stream discharge. Although we observed temporal variability of topsoil properties attributable to seasonal weather changes and agricultural activities, e.g. bulk density and porosity, runoff generation was mainly driven by precipitation characteristics and the initial catchment saturation.
The paper deals with the effects of agricultural soils management on surface runoff in winter and early spring period. Cryogenic processes that take place in soils can cause temporary reduction of infiltration capacity of soil. In the periods of snow-thawing and rain these phenomena induce conditions promoting the occurrence of surface runoff and floods. Effects of agricultural soils management on surface runoffs were studied at the research station in BrnoKníničky, Czech Republic, from 1965 to 2002. The aim of this research was to find out the differences between the winter surface runoff from experimental plots under winter wheat crop sown after plowing and under perennial forage crops without tillage. On soils without plowing, the decrease of soil infiltration rate occurred faster and was more intensive than on loose soils. During ten winter periods the average surface runoff from perennial forages was significantly higher (2.05 times) than from wheat crop (runoff coefficients 0.239 vs. 0.489). and Příspěvek se zabývá hodnocením vlivu kultivace zemědělských půd na povrchové odtoky v zimním a předjarním období. Kryogenní procesy v půdách mohou způsobovat dočasnou redukci jejich infiltrační rychlosti. V obdobích tání sněhu a dešťů vytváří podmínky pro výskyt povrchového odtoku a povodní. V letech 1965-2002 byl sledován na výzkumné stanici v Brně-Kníničkách vliv kultivace zemědělských půd na povrchové odtoky. Cílem tohoto výzkumu bylo najít rozdíly mezi zimními povrchovými odtoky z pokusných ploch s ozimou pšenicí vysetou po orbě a s víceletými pícninami bez zpracovaní půdy. Na půdách bez orby došlo k redukci infiltrační rychlosti rychleji a tato redukce byla intenzivnější než na kyprých půdách po orbě. Během deseti hodnocených zimních období byl povrchový odtok z víceletých pícnin průkazně vyšší (2,05 krát) než z pšenice. Průměrný koeficient povrchového odtoku u ozimé pšenice dosáhl hodnoty 0,239 a u víceletých pícnin 0,489.