Long term effects of pretreated municipal sewage water on some physical and chemical properties of soils under semiarid conditions

Abstract

The long term effects of applying pretreated sewage water to irrigate two forage crops: alfalfa (Medicago sativa. I) and barley (Horduem vulgare. 1) under semiarid conditions were investigated. The irrigation water had an EC 13 mS/cm, and SAR 26. The soils (Torrifluvents) were deep. clayey, low in organic matter and calcium carbonate. The two irrigated fields were furnished with an artificial subsurface drainage system. field and laboratory ivestigations revealed that an average annual rainfall of 280 mm was apparently sufficient to leach excessive soluble salts that might have accumulated during dry seasons when irrigation is practiced, but not the exchangeable sodium to the extent that partially irrigated soils became marginally sodic and the continuously irrigated soils strongly sodic. However, the hydraulic condctivity of these soils and their structure did not deteriorate. The fact that the characteristics associated with sodicity were not clearly manifested at such high ESP values was attributed to the high salt concentration of the irrigation water and its low RSC, the buffering effect of the solubilized Caco, and possibly the dominance of nonexpanding clay minerals. The decline of Caco, content of the soils of the two irrigated fields suggests a need for the application of calcium source to counterbalance the possible bad effects of high exchangeable sodium in the future.