Changes in soil fertility parameters in response to irrigation of forage crops with secondary treated wastewater

Field experiments were conducted to evaluate the effect of irrigation with treated wastewater on soil fertility and chemical characteristics. Three field experiments were conducted at a farmer's field near Ramtha Wastewater Treatment Plant. Corn (Zea mays) was planted for two seasons as a summer crop while vetch (Vicia sativa) for one season as a winter crop. Plots were irrigated with either potable water (PW) or wastewater (WW) in amount according to the following treatments: i) potable water equivalent to 100% class A pan reading (PW); ii) wastewater equivalent to 100% class A pan reading (WW1); iii) PW with application fertilizer equivalent to N and P content of WW (PWF) and iv) wastewater equivalent to 125% class A pan reading (WW2). Treatments were replicated 4 times in a randomized complete block design. Soil samples were taken before and at the end of the growing season and were analyzed for soil parameters. WW samples were taken and analyzed periodically for major characteristics. WW analysis indicates inefficient treatment and high values of Biological Oxygen Demand, salt content and reduced form of nitrogen. The results of the field experiments indicate that WW irrigation decreased soil pH and increased soil salinity, soil phosphorus (P), potassium (K), iron (Fe), and manganese (Mn) levels. Soil organic matter increased only in the topsoil and by the highest rate of WW irrigation. This effect could be attributed either directly through the addition of the nutrients and organic compounds to the soil or indirectly through enhancing solubility of soil nutrients. Soil zinc (Zn) and copper (Cu) were not significantly affected by WW irrigation. It can be concluded that secondary treated WW can improve soil fertility parameters, however, more efficient treatment is recommended to reduce salt content. In addition, proper irrigation management and periodic monitoring of soil quality parameters are required to minimize adverse effect on the soil.