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Surface crusts are frequently found on fallow land in the semi-arid Ebro Basin (Spain) and are an important factor in land degradation. Soil surface seating leads to a decrease in infiltration rates and a consequent increase in runoff, thereby accelerating sheet wash and rill erosion. Thin sections were used to analyse the development and structures of the different crusts found across the ridge/furrow field pattern. Rainfall simulations experiments and infiltration measurements show the runoff generation and the soil erosion rates on the crusts. The spatial distribution of crusts was documented using large-scale aerial photographs, taken from a remote-controlled hot air blimp.

Splash and slaking cause structural crusts to form on the ridges, while eroded material leads to a build-up of sedimentary crusts in the furrows. A platy structure as well as vesicles then develop in these crusts, depending on the amount of time that has elapsed since ploughing and the frequency of wetting and drying cycles. Alluvial fan crusts develop on material accumulated at the end of erosion rills. The increase in the runoff of up to 81% and the decrease in infiltration rate up to 4.6 min h-1 on surface crusts were quantified. (c) 2007 Elsevier B.V. All rights reserved.