Soil and plant mineral composition and productivity of Acacia nilotica (L.) under irrigation with municipal effluent in an arid environment

Abstract

Municipal effluent is becoming an increasing environmental threat and needs appropriate disposal measures to safeguard soil and environmental quality. As an important source of water and nutrients, municipal effluent could be used to increase productivity in nutrient deficient dry areas. Acacia nilotica L. (Babool) seedlings were grown using municipal effluent. Five treatments comprised: irrigation of soil (without seedlings) with municipal effluent at potential evapotranspiration (PET) (treatment T₁), irrigation of seedlings at 0.5 PET (T₂), PET (T₃), and 2 PET (T₄), and canal water irrigation of seedlings at PET (T₅). Seedlings in the T₃ and T₄ treatments attained greater height and collar diameter, and produced 22% and 54% more biomass than those in T₅. After 24 months, biomass production was 7.43–12.96 t ha⁻¹ as compared to 5.73 t ha⁻¹ in T₅. Nutrient concentrations in the seedlings were positively correlated with effluent quantity (r = 0.82, p < 0.01), being greater in foliage than in stems and roots. Uptake of nitrogen (N) was 2.70%, and of iron (Fe) 0.11%, of seedling biomass. Relative increase in metal concentration was greater than that in nutrients. The availability of potassium (K), copper (Cu), Fe, manganese (Mn) and zinc (Zn) in the soil increased twofold and that of NH₄-N and PO₄-P by 4.5- and 7.9-fold, respectively, in T₄ relative to T₅. Available NH₄-N, PO₄-P, Mg and K were highest in the 0–15 cm depth soil, whereas NO₃-N, Na, Cu, Fe, Mn and Zn availability were highest in deeper soil layers. Relatively low soil nutrients in T₃ compared to T₁ indicated withdrawal and accumulation of these nutrients in the seedlings. In several respects municipal effluent benefited A. nilotica seedlings and soil properties, and produced 5.59–12.96 t ha⁻¹ dry biomass. Municipal effluent could help to meet the fuel need of suburban areas, although long-term application of effluent would lead to metal accumulation in soil and plants.