Soil sealing and its influence on erosion rates for some soils in the Mediterranean area

In the vineyards of the Anoia-Alt Penedes region of NE Spain, erosion probl ems arising from a combination of soil and climate characteristics and thei r relief have been accelerated in the last few decades as a consequence of new cropping/planting patterns and soil management practices involving cont inuous tillage, which leaves the soil bare most of the time. In the rain-fe d vineyards of the area, rainfall water conservation in situ has also becom e a problem that influences the production of high quality wine. The determination of the actual and potential erosion processes required fo r rational selection, design, and application of soil and water conservatio n practices requires identification and quantification of the hydrological properties and processes that induce runoff and soil erosion. Laboratory st udies in 10 representative surface soils of the region, using simulated rai nfall, proved that erosion losses were highly related to the surface sealin g susceptibility of the soils, which reduced minimum rainfall water intake rates to 1 to 7 mm h(-1) or less after only 10 minutes of rainfall. This su sceptibility was highly correlated with the high silt and low organic matte r content of the soils. In most of the soils, surface protection by a cover was found to increase t he minimum rainfall water intake rate 50 to 200 times. A simple laboratory test, based on the measurement of saturated hydraulic conductivity and the time to reach its minimum value, measured efficiently the sealing susceptib ility of the studied soils and the relative effect of a protective cover. T he minimum value of saturated hydraulic conductivity was highly correlated to runoff and soil erosion losses in soil boxes under simulated rainfall.