Evaluating the Long-Term Effects of Recycled Wastewater Irrigation on Soil Health, Crop Yield, and Ecological Sustainability in Arid Regions

Abstract

Water scarcity poses a significant global challenge, particularly acute in arid and semi-arid regions with limited freshwater resources and high agricultural water demands. This study investigated the impacts of recycled wastewater irrigation using hybrid poplar trees as a model crop in the Kyzylorda region, characterized by extreme climatic conditions and water scarcity. A randomized complete block design (RCBD) was employed to ensure robust comparisons between two irrigation treatments: the control using water from the Syrdarya River, and the experimental treatment involving biologically treated wastewater from the Kyzylorda Wastewater Treatment Plant. Chemical analysis revealed that the soil irrigated with wastewater exhibited higher pH levels (7.5 ± 0.3) compared to the control (7.0 ± 0.2), indicating increased alkalinity. Electrical conductivity, a measure of soil salinity, was significantly elevated in wastewater-irrigated soil (2.3 ± 0.2 dS/m) relative to the control (1.2 ± 0.1 dS/m), reflecting higher salinity levels. Moreover, organic matter content was substantially greater in wastewater-irrigated soil (3.5 ± 0.4%) compared to the control (2.1 ± 0.3%), suggesting enhanced organic enrichment. Nutrient levels, such as nitrogen (45 ± 5 mg/kg), phosphorus (30 ± 4 mg/kg), and potassium (189 ± 16 mg/kg) were markedly higher in the wastewater-irrigated soil compared to the control (27 ± 3 mg/kg, 15 ± 2 mg/kg, and 121 ± 10 mg/kg, respectively), highlighting the nutrient-rich nature of recycled wastewater. Seasonal dynamics in flora and fauna were also assessed. From January to March, both control and wastewaterirrigated plots exhibited a decline in species richness, reflective of winter dormancy. In January, for instance, control plots averaged 23 ± 4 species per square meter, whereas wastewater-irrigated plots had 18 ± 3 species per square meter. Fauna abundance followed a similar pattern, with both groups showing gradual increases from January to March, peaking in summer. The control plots consistently maintained higher fauna abundance levels compared to the wastewater-irrigated plots throughout the study period. Overall, this study provides insights into the complex interactions between recycled wastewater irrigation and soil health, crop performance, and ecological dynamics in arid environments.