Effect of soil surface water repellency on the evaporation rate from three soils with different textures

Reducing irrigation losses due to surface evaporation by using water repellent soil surface can help in maintaining water in the current situation that our country is suffering from water deficit. In this research, the effect of creating a water-repellent layer on the soil surface in the form of anti-evaporation mulch layer was evaluated on three soil textures (sandy loam, loam and clay loam). For this purpose, soils artificially hydrophobized by Stearic acid at four different concentrations and water drop penetration time method to obtain four different degrees of water repellency. And its effect on the rate of surface evaporation from the small lysimeters (with height and diameter 30 cm) located at the ground was investigated in the form of water-repellent layer with three-centimeter thickness. All experiments were conducted at a field in Marand area (latitude: 38° 25' 16.87'' N and longitude: 45° 47' 30.30'' E) in summer 2016. The experiments were performed in a completely randomized design with five treatments degree of water repellency and three replications. After analysis by SPSS and Duncan test (5% level), the average comparison carried out between evaporation in the different water repellency degrees for three soils. The results showed that the surface the water-repellent layer significantly decreased the amount of evaporation in the mentioned three soils. Also, the surface evaporation reduction rate was increased with increasing the water repellency degree. The maximum reduction of evaporation with increasing in the water repellency degree compared to the control treatment (zero degrees of water repellency) was 78.3 %, 42.2 % and 30.1 % in the sandy loam, loam and clay loam soil, respectively.