Comparison the results of three methods for measuring the amount of Water-Dispersible Clay in Khuzestan soils

The fraction of clay that disperses in water, water-dispersible clay (WDC), is recognized as an important property with respect to predicting soil erosion, colloid leaching and soil development. The WDC is measured by different methods producing different results. In this study, three methods (Rasmussen, Mechanical stirrer and Ultrasound) were compared in terms of measuring the amount of WDC in soils. For this purpose soil samples with different physio-chemical properties were collected from different region of Khuzestan province and the WDC were determined by the proposed methods. The correlation between WDC and the soil properties were analyzed using regression model and equations were fitted for the three methods. The results showed that the WDC measured by Rasmussen, Shaker and Ultrasound methods were 72.6 (%), 33.4 (%) and 14.1 (%) from total clay, respectively. The results showed that the most important soil properties affecting the WDC for Rasmussen method were gypsum and clay, for Mechanical stirrer were linear extensibility coefficient (COLE), organic matter (OM), clay, gypsum and total sand, and for Ultrasound method were gypsum content, linear extensibility coefficient and silt. These varieties could be related to the nature of each method. Also, statistical analysis showed that the gypsum, COLE, and silt content had maximum effect on the WDC in Rasmussen, Mechanical stirrer, and Ultrasound methods, respectively. Organic matter, gypsum, sodium adsorption ratio (SAR), soluble sodium, and electrical conductivity had negative correlations with WDC, and the total clay content, lime, COLE, cation exchange capacity and pH had a positive correlation. Therefore, it is suggested that the selected method for measuring WDC should be according to the research emphasizes and soil characteristics. Also, the effect of aggregates size, type and organic matter composition on the WDC should be investigated in future study.