Soils from semi-arid environments have traditionally been considered to have poorly stable aggregates. The use of aggregate stability methods for erosion research seems of particular interest. However, its use to predict crusting and erosion have yielded conflicting results. In this study, we investigate the possible relations between aggregate stability and soil physical properties, and soil water erosion parameters using the mean weight diameter concept, based on dry and wet sieving method. We introduced also a new aggregate stability parameter based on the stability quotient which takes into account the percentage of soil fraction larger than 2 mm. Twenty soil sites were sampled from a Mediterranean semi-arid watershed for aggregate stability test. This study is part of a research work about erosion processes in semi-arid regions of Tunisia conducted during the period 1999 to 2013. Results indicate a correlation between aggregate stability indices and quotients with organic matter content (r = 0.70), a positive correlation with clay content (r = 0.30), but a negative correlation with the amount of soil loss and splash (r = -0.49 and r = -0.40 respectively) as collected in a laboratory rainfall simulation experiment. The stability quotient is the best soil parameter that explains soil erosion. It shows that more than 80% of the soil samples have poor structure stability. The fractal dimension, a characteristic property of the number-size distribution of fragments as a mass of material is broken down, was calculated for all soil samples. After wet sieving all samples follow the law of fractal dimensions.
Key words: Aggregate stability, erosion, rainfall simulation, stability quotient, fractal analysis.
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