Soil hydrophysical properties resulting from the interaction between organic amendments and water quality in soils from Southeastern Spain—A laboratory experiment

The use of treated effluents for irrigation as well as the addition of amendments could have an impact on the physico-chemical properties of soils. The main objective of this study was to evaluate, at laboratory scale, the combined effect of solid organic amendment and treated wastewater on the hydrophysical characteristics of four agricultural soils in a semiarid area. Soil texture varies from clay to sandy loam; calcium carbonate is abundant and organic C content for natural soils is always below 1%. Urban sewage sludge and a commercial organic fertilizer were added as ameliorants, whilst treated urban wastewater and distilled water were used as influents. A D-optimal design with soil type, amendment and irrigation water quality as factors was used for evaluating the hydraulic characteristics from laboratory infiltration experiments. Main effects as well as factor interactions were considered. Results indicated that soil hydrophysical properties were significantly influenced by soil type and irrigation water quality, with an interaction effect. Soil hydraulic properties such as saturated hydraulic conductivity and sorptivity showed a negative relationship with both soil electrical conductivity and organic C, whereas a positive relationship was noted with the amount of Na in the irrigation water. On the other hand, chemical properties of the leachate were affected by amendment and soil type, also with significant interaction effect. The addition of amendments increased leachate organic C and results indicated that the soil matrix retains the less complex organic matter promoted by bonds with Ca2+ from the abundance of calcium carbonate content in the soil.