an investigation of the occurrence and intensity of soil water repellency in talesh forest sites, guilan province

the occurrence of soil water repellency and its intensity were studied in three sites under pinus teada, petrocarya fraxinifolia and sombucus ebulus in talesh township, western part of guilan province. seventy nine undisturbed soil samples from 0–5 cm depth were collected for water repellency and water-soil contact angle to be determined in a dry season. soil water repellency was assessed using sater drop penetration time (wdpt) and molarity of ethanol droplet (med) tests. a significant and positive relationship (r= 0.77) between med and wdpt tests was obtained. water-soil contact angles were found out as greater than 90, using med test in water repellent determining samples. the soil contact angles raised with increase in water repellency. as with samples of wdpt 5820-6000 s, contact angles were estimated between 108.8 and 109. the average water repellency, measured (using wdpt and med tests) in site 3 were significantly higher than those in the other two sites. this trend was observed in the calculated water-soil contact angles too. high coefficients of determination were detected between the elements of log wdpt, med, as well as contact angle and organic matter content (r= 0.8, 0.83 and 0.77 respectively). the correlations of these parameters (log wdpt, med and contact angle) with soil solution ph were negative and meaningful (r= -0.78, -0.69 and -0.72 respectively). the correlations between hydrophobicity (log wdpt, med) and soil contact angle in soil of high sand percentage were positive, while being negative in high clay containing woil. however, the relations between soil texture parameters and hydrophobicity were estimated as weaker than the correlations between the factors of organic matter content and soil acidity vs. hydrophobicity. results finally show that soil organic matter content, texture, and acidity are important factors affecting the occurrence and persistence of water repellency in such soils of the studied region.