Effects of Long-Term Irrigation with Treated Wastewater of Parkand Abad Refinery on Some Soil Chemical and Biological Properties

Reusing of treated waste water (TWW) for agricultural irrigation is one of the common management strategies for dealing with water deficit in arid and semi-arid regions. The aim of this study was to investigate the effects of irrigation with TWW for ten years on some chemical and biological properties of irrigated soils in surrounding land of Kashafrud River located in Mashhad (Iran). The soil samples were collected from 8 points and 3 replications at intervals of 1 Km from surrounding lands of river. Also the soil sample that irrigated with underground water and had the same agricultural management practices was selected as control. The results showed that irrigation with TWW increased the soil pH and electrical conductivity (EC) in comparison to the control. Also¡ the TWW increased the concentration of zinc (Zn)¡ iron (Fe)¡ and lead (Pb)¡ so that they were less than toxicity limits and the concentration changes of cadmium (Cd) and nickel (Ni) in soil due to TWW was negligible. Application of TWW significantly increased the ratio of Cmic/Corg¡ respiratory activity and microbial biomass in comparison to the control. The metabolic coefficient (qCO2) values of irrigated soil samples with TWW were significantly less than that of control. The results of this research demonstrated that the irrigation with TWW did not only have adverse effects on soil properties and it also improved them. Furthermore¡ due to the different entrances of waste water into river¡ the soil chemical and biological properties were various in different points.