Effect of Applying Urban Wastewater in Irrigation of Sorghum on Some Soil Physical Properties

In this study, effects of short-term domestic wastewater application on some soil physical properties were analyzed for determining the impacts of four factors including quality of irrigation water (normal water, raw wastewater and treated wastewater), soil texture (two loamy soils), methods of irrigation (surface and subsurface), and presence or absence of plants. The study was carried out in the green house with three replications in 2008. Experimental period was four months and the crop was sorghum. Physical properties of soils, namely, bulk density and basic infiltration rate were measured with completely randomized design in three replications and water retention curves were determined with RETC software and compared with the measurements at the end of the experiments. The analysis of the results on water retention curves for different treatments indicated that the use of wastewater for irrigation resulted in an average increase of the available water capacity of soils by 4% (volumetric) and 24% relative value. Soil water retention on volumetric basis was increased at some tension points in the wastewater irrigated treatments by 9.5 to 10% at 0.1-bar, 4.5 to 5% at 0.33-bar and 1.5 to 2% at 1-bar, on the average. Such results could be related to the improvement of the soil structure. Overall, the basic infiltration rates were somehow increased in soils irrigated with raw and treated wastewater. However, the differences were not statistically significant. Also, soil bulk density was not affected by various treatments because duration of this study was not long enough. Generally, according to the current and previous studies, soil water retention was increased, particularly in the presence of plants, due to addition of organic material to the soil by wastewater and increasing magnesium concentration, in line with the improvement of the soil structure.