Effect of water tankers traffic on soil hydraulic properties in winter rangelands of Aq Qala plain

The most important indices (or indicator) for soil quality assessment are water infiltration rate into the soil and soil hydraulic conductivity. They play key roles in various issues of watershed management, soil and water conservation and hydrological modeling. By definition, infiltration is the water entry from the thin surface layer of the soil into its profile. Numerous factors such as intrinsic properties of soil, amount of vegetation cover, land use type and soil compaction affect the rate of infiltration. The stakeholders of Aq Qala winter rangelands in northeast of Iran are facing the challenge of water deficit both for drinking water and wateing the livestock during almost the whole grazing period. To solve the problem, they buy and transport water by tractors and tankers. Due to the flat topography of the plain, tractors and tankers commute from many paths without considering the environmental consequences and causes surface layer soil compaction over vast areas. This reduces rainfall infiltration and destrucs vegetation cover of the rangelands at a significant level. This study aims at investigating and quantifying these consequences on the hydraulic properties of topsoil. Infiltration rate was measured by two methods of double cylinder in the field and Lab. with constant head water and disk infiltrometer, measuring saturated hydraulic conductivity by applying constant head of water on undisturbed soil samples contained in metal rings. Using independent t-test, the hydraulic properties of the soil were compared. Samples were taken from the controls and the whecle wheel passage areas. The results showed that there was a significant difference in 95% confidence level between them. In other words, the traffic of water tankers has caused soil compaction and reduced the permeability of the topsoil in the studied rangelands. Result of the study suggests that increasing traffic routes, will create serious ecological consequences in the long term. Also, the analysis of physical and chemical properties of the soil in the area showed that except for the pH parameter, other parameters have a significant difference between the traffic routes and control sites.