Variation of Soil Hydraulic Parameters and Unsaturated Water Infiltration Due to Wastewater Application Under Potato Plantation in Lysimeters

In this study، raw and treated wastewaters were used for potato cultivation in lysimeters. Five irrigation water treatments were included as: raw wastewater، treated wastewater، fresh water، a combination of 50% raw wastewater and 50% fresh water and a combination of 50% treated wastewater and 50% fresh water. The experiments were run within greenhouse during a period of four months. After construction and preparation of the lysimeters، they were filled with a two-layered soil. The textures of the upper and lower soil layers were sandy loam and sandy clay loam، respectively. In order to create the structure and conditions of the natural soil and develope macropores and preferential pathways، lysimeters were irrigated systematically each week during a period of five months before plantation. A total of eight irrigation programs with an interval of eleven-days were applied during the growth season. Unsaturated water infiltration into the soil was measured using a disk infiltrometer at the beginning and at the end of growth season. In order to evaluate the irrigation effects on soil physical properties، DISC Software (numerical) and Wooding (analytical) methods were employed to analyze the infiltration data. The results of saturated hydraulic conductivity were compared with direct measurements of the constant-head method، in which the numerical method (DISC software) was identified as the best method. The results showed that in all treatments، the saturated hydraulic conductivity and steady-state infiltration rate at matric suctions 5 and 10 cm increased after irrigations when compared with the initial values. Result also indicated that the unsaturated hydraulic conductivity and steady-state infiltration rate increased significantly in the wastewater treatments compared to the fresh water. Also، the maximum values of the steady-state infiltration rate and saturated hydraulic conductivity were observed in the raw wastewater and the combination of treated wastewater and fresh water treatments. The minimum value also belonged to fresh water treatment. Moreover، the highest changes in θs، αVG and nVG were recorded in the combined fresh water-treated wastewater treatment. The lowest variations of these parameters (except θs) were observed in fresh water treatment.