Assessing Soil Quality and Biomass Productivity Under Wastewater Irrigation in the Indian Arid Region

Indiscriminate discharge of effluents in rivers, waterbodies, and croplands is a common practice contaminating food chains through water and soil. Plantations using treated wastewater can help restore degraded lands and reduce soil and environmental pollution. One-year-old plantations of Azadirachta indica, Eucalyptus camaldulensis, Prosopis cineraria, Prosopis juliflora, Tamarix aphylla, Salvadora persica, and Salvadora oleoides were irrigated with borewell water at ½ET (Evapotranspiration, I₁) and treated wastewater at ½ET (I₂), ¾ET (I₃), and 1ET (I₄) for 4 years (September 2013–September 2017), to assess the remedial impact of these species on soils while reusing wastewater in urban greening and biomass production. Wastewater irrigation enhanced soil pH/EC (<1.0 unit) and SOC and nutrient contents (1.23–13.25-fold). Such increases were highest (p < 0.05) in 0–15 cm and lowest in 45–60 cm (50%–70%) soil layers. Species types and irrigation levels influenced soil salts and nutrient concentrations. Variations in pH/EC (<0.50 unit), SOC/nutrient contents (1.59–2.11-fold), and total biomass (3.26-fold) were greater between species than between irrigation levels (<0.30 unit, 1.14–3.33-fold and 1.81-fold variations, respectively). Salt and nutrient uptake were highest in S. oleoides and P. cineraria, medium in T. aphylla and E. camaldulensis, and lowest in S. persica, A. indica, and P. juliflora plots. Leaf mineral contents were below toxic levels. The former three species and S. persica responded by increasing biomass allocation to roots. In contrast, other species maximized root biomass to augment added water and nutrient uptake to sustain growing biomass. Conclusively, tree species influenced soil properties and biomass more notably than irrigation level, where adaptation mechanisms were allocated to/or maximized root biomass. Increased SOC and nutrients, and consequently plant biomass highlight the reuse of treated wastewater in plantations that remediated soil and promoted greenery and biomass in water-deficient dry areas.