THE EFFECTS OF SECONDARY TREATMENT ON NODULATION OF ALFALFA (MEDICAGO SATIVA L.) AND NUTRIENTS SUPPLY IN DOMESTIC WASTEWATER

The use of domestic wastewater in irrigation is becoming widespread. The aim of this study was to determine the effect of Secondary Treated wastewater (STW) irrigation on alfalfa nodulation, agronomic parameters, exchangeable cations and heavy metals in soil and plant. Three levels of STW diluted with distilled water and distilled water were applied for 6 months with three replications in randomized plots in laboratory. Negative binomial regression was applied to model the overdispersion. Diluted STW reduced the total and active nodule number by at least 79.5% and 91.2%, respectively. Diluted STW decreased total biomass of alfalfa compared to distilled water. STW increased the EC and Mg ratios in the soil and the Na ratio in the soil, root and shoot. However, it did not affect the K and Ca ratios in the soil, root and shoot. Co, Ni, As and Pb uptake were inhibited in roots, however elements such as Fe, Cu, Mo, Mn, Al, Cr and Cd accumulated in high concentration in the root. Increasing Zn concentration in shoot may be attributed physiological selectiveness of the alfalfa. Consequently, the use of STW cannot be recommended in alfalfa irrigation as it could reduce the biomass and prevent nodulation.