This study was carried out to investigate the relation between soil erodibility (Wischmeier- et al nomograph 1971) and aggregate stability (Kemper and Rosenaue 1985) in Oazvin soils. In this study the effect of elimination of calcium carbonate (leading to change in texture) on soil erodibility was determined. From 44 soil series and phases, 111 composite samples of top soil were taken for physicochemical analysis. Also 37 soil
samples were chosen for determining soil erodibility and the percentage of aggregate stability. For ordinary samples wet sieving, using distilled water was employed. In the case of soils with high SAR the sieving was done with both distilled and saline water. The soil texture was determined in the presence and
absence of CaCo3. The results showed that the soil texture in colluvial fans nearby ridges was medium to coarse(SL, SiL,L), by approaching plain and lowlands the texture becomes heavier (C,SiC,CL). The Maximum salinity in low lands in dS/m was 24.6. Maximum soil sodicity (SAR) was 50-70 in
Valadabad and Farsian series. The organic carbon and CaCo3 were in the ranges of 0-1.4% and 1-25% respectively. The Gypsum was present in Kohkin , Valadabad and Farsian series. The soil erodibility factor (K) was in the range
. of 0.22 -0.50 in UK system.The aggregate stability percentage (ASP) differed from 6.7 to 80%. There was low correlation between K and ASP (r=0.404), indicating that aggregate stability index is not reliable for the expression of soil erodibility. The clay fraction of the soil samples following elimination of CaCo3 was decreased significantly indicating that .CaCo3 mainly belongs to clay fraction of these soil samples. Therefore the nomograph developed for CaCo3
free soils, must be used with caution in such conditions. When soil mechanical analysis was done using distilled water (without dispersant) the clay content
was shown to be reduced significantly. The reduction was more pronounced in samples with more organic carbon. No significant correlation between clay dispersion and erodibility factor was found.
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