Study of Saturated Hydraulic Conductivity Variations in Different Aggregate Size Distributions in an Agricultural Soil

Saturated hydraulic conductivity (Ks) is one of the most important soil physical characteristics that plays a major role in the soil hydrological behaviour. It is mainly affected by the soil structure characteristics. Aggregate size distribution is a measure of soil structure formation that can affect Ks. In this study, variations of Ks were investigated in various aggregate size distributions in an agricultural soil sample. Toward this aim, eight different aggregate size distributions with the same mean weight diameter (MWD= 4.9 mm) were provided using different percentages of aggregate fractions consisting of (< 2, 2-4, 4-8 and 8-11mm). The Ks values along with other physicochemical properties were determined in different aggregate size distributions. Based on the results, significant differences were found among the aggregate size distributions in Ks, particle size distribution, porosity, aggregate stability, electrical conductivity (EC), organic matter and calcium carbonate. The aggregate size distributions with a higher percentage of coarse aggregates (4-8 and 8-11 mm) also showed higher Ks as well as clay percentage. A positive correlation was also observed between Ks and clay, aggregate stability and EC, whereas sand showed a negative correlation with Ks. No significant correlations were found between Ks and silt, porosity and organic matter. Further, multiple linear regression analysis showed that clay and aggregate stability were the two soil properties controlling Ks in the aggregate size distributions (R2=0.80, p<0.01). Aggregate stability was recognized as the most important indicator for evaluating the Ks variations in various aggregate size distributions.