EFFECTS OF SOIL WATER REPELLENCY ON INFILTRATION CHARACTERISTICS OF TWO SANDY LOAM AND CLAY LOAM SOILS

s Soil water infiltration and its characteristics are important in water management both in agriculture and hydrology. Water repellency of soil, a phenomenon that often occurs in forest soils, reduces infiltration greatly and enhances soil degradation by various ways. In this study two clay loam and sandy loam soils were sampled from Kaleybar forest area, East Azarbaijan province. They were artificially hydrophobized into five different degrees of water repellency by using stearic acid. Water drop penetration time test (WDPT) was applied to assess the severity of the repellency. Effects of the repellency were investigated on cumulative infiltration and infiltration coefficients of the Kostiakov and Philip models. Results indicated that in the both soils, cumulative and average infiltration rate (average of triplicate infiltration measurement data) at the beginning of the experiment and the average steady state infiltration rate decreased with increasing of repellency from degree 1 to 5. The average value of the initial infiltration rate decreased from 1.37 to 0.31 in sandy loam soil, and from 1.50 to 0.23 in clay loam soil with increasing the severity of the repellency from degree one to five. Steady state infiltration rate was greatly reduced from 0.037 to 0.0001 in sandy loam soil, and from 0.02 to 0.008 in clay loam soil. Water repellency significantly affected Kostiakov c and Philip sorptivity S. The Kostiakov model in comparison to the Philip model was more appropriate for estimating cumulative infiltration in different degrees of water repellency.