Impact of wastewater irrigation on soil physico-chemical properties, growth and water use pattern of two indigenous vegetables in southwest Nigeria

The indiscriminate use of wastewater for irrigation as a result of freshwater shortage could impair soil functions and cause environmental pollution. The objective of this study was to evaluate soil physico-chemical properties, growth parameters and water use pattern of two indigenous vegetables irrigated with three kinds of wastewater in southwest Nigeria. The study was a 2 x 4 factorial (wastewater versus vegetable) pot experiment, laid out in randomized complete block design (RBCD) with three replications in a screen house. The tested vegetables were SM - Eggplant (Solanum macrocarpon) and CA Spinach (Celosia angentea) while the wastewater treatments were abattoir wastewater (AW), bathroom, laundry wastewater (BW) cassava effluent (CE) and rainwater (RW) as control. The wastewaters were analyzed for physical, chemical and biological properties while the soil samples collected from the field at 0-20 cm soil layer and pots at 0-10 and 10-20 cm layer were analyzed for physico-chemical properties before and after the experiment, respectively. Soil hydrophobicity was determined using the water-droplet penetration time (WDPT) method, plant growth parameters were monitored every 5 days while leaf area was determined shortly before harvest. Consumptive water use was determined using the soil water balance technique. The wastewaters had moderate to very high degree of restriction for use in relation to salinity and sodicity. Except for CE treatment, wastewater irrigation increased the soil pH, Mg, K, Ca, TOC, TN and CEC at harvest. SAR surpassed the threshold value of 6 in the surface layer of CA soil irrigated with BW wastewater. Wastewater irrigation caused the occurrence of soil hydrophobicity, with the highest hydrophobic degree from CE treatment. The plant growth indices showed that the SM vegetable performed better under AW treatment while the CA vegetable performed better under BW treatment compared with RW treatment. The vegetables differed in relation to water use and there was no discernible trend among the different wastewater treatments as regards the temporal distribution of the consumptive water use. The CE wastewater had the most negative impact on both soil function and plant growth. The study showed that wastewater resources are valuable because of improvement of soil fertility and enhanced crop growth compared with rainwater, however they need to be managed with caution, preferably treatment, before reused in relation to soil functions and crop quality. (C) 2016 Elsevier B.V. All rights reserved.