Determination of the Effect of Soil Compaction on Soil Physical and Hydraulic Properties Using Inverse Method

Many forces applied to soil surface during cultivation season cause soil compaction, which affects many soil physical and hydraulic parameters. Under field condition, different forces affect the soil and cause changes in its characteristics. The aim of this study was to determine the effect of soil compaction on soil physical and hydraulic properties. Four treatments including T₀ (no tractor pass), T₁ (one pass), T₂ (three passes) and T₃ (five passes), were selected. Treatments were irrigated regularly as local farmers’ schedule. After three months, soil samples were taken for determination of some soil properties such as particle and bulk density, shape of cumulative infiltration curve, soil moisture retention curve, and saturated and unsaturated hydraulic conductivity. Water infiltration rate was measured in each treatment using a double ring infiltrometer. Residual water content at a given water pressure head was obtained in laboratory. Inverse solution was used to estimate soil water retention and unsaturated hydraulic conductivity functions parameters by Hydrus 3D code. Results indicated that by increase in the number of tractor passes over the soil surface, bulk density of T₁, T₂ and T₃ treatments increased by, respectively, 17.41%, 26.87% and 35.65% compared to T₀. Total porosity of T₁, T₂ and T₃ treatments decreased 16.55%, 25.36%, and 33.04 % and saturated hydraulic conductivity of the same treatments also decreased 38.09%, 59.05%, and 61.43 % compared to T₀, respectively. Particle density was constant. Residual moisture, saturated , saturated,and van Genuchten  increased, while  and decreased due to increase of soil compaction. Soil compaction effect on, , ,  and parameters was significant, but the effect was insignificant on  parameter. Significant probability of these five parameters is different.