Water Repellency in Calcareous Soils Under Different Land Uses in Western Iran

Soil wettability and water repellency, two important soil physical properties, play an important role in water retention and water conductivity in arid and semi-arid regions. To date, there is a lack of information on soil water repellency in calcareous soils of western Iran. In this study, soil water repellency and its affecting factors were studied using 20 soil series collected from Hamadan Province, western Iran. The effects of soil properties including organic carbon content (SOC), total nitrogen (TN), C:N ratio, texture, CaCO3 content, and both fungal and bacterial activities on water repellency were investigated using air-dried, oven-dried and heated soil samples. Water repellency index (WRI) was determined using the short-time sorptivity (water/ethanol) method. To distinguish the actual effects of SOC, a set of soil samples were heated at 300 °C to remove SOC and then WRI was measured on the heated samples. Relative water repellency index (RWRI) was defined as the change of WRI due to heating relative to the oven-dry WRI value. Results of the WRI values showed that the soils were sub-critically water-repellent. Pasture soils had higher WRI values compared to tilled soils, resulting from high SOC and TN, and high activities of bacteria and fungi. It was observed that SOC, TN, fungal activity, and SOC:clay ratio had significant positive impacts on WRI. Strong positive correlations of RWRI with SOC, TN and fungal activity were also observed. Pedotransfer functions derived for predicting WRI showed that the WRI values had an increasing trend with the increases in fungal activity, salinity, alkalinity and fine clay content, but showed a decreasing trend with increasing bacterial activity.