GEOCHEMICAL AND PHYSICOCHEMICAL RESPONSES OF AGRICULTURAL SOILS TO LONG-TERM TREATED WASTEWATER IRRIGATION IN DAVANAGERE, INDIA

Abstract

Reuse of treated municipal wastewater for irrigation is increasingly practiced in water-scarce regions; however, its long-term impacts on soil
physicochemical and geochemical properties require systematic evaluation. This study investigates the effects of prolonged treated wastewater
irrigation on agricultural soils in Davanagere, Karnataka, India. Thirty composite surface soil samples (0-15 cm) were collected from agricultural
fields located within Zone 3 (2-3 km) of the municipal sewage treatment plant (STP). The samples were analysed for physicochemical properties,
macronutrients, micronutrients, and heavy metals using standard analytical techniques, including pH and Electrical Conductivity (EC)
measurements, wet oxidation for organic carbon, Olsen’s method for phosphorus, flame photometry for potassium, and atomic absorption
spectrophotometry for micronutrients and trace metals. The soils exhibited moderately alkaline pH (7.50-7.97; mean 7.80) with low salinity (EC
0.03-0.46 dS/m). Organic carbon ranged from 0.97-1.45%, indicating enrichment due to organic inputs from treated wastewater. Macronutrients
showed substantial accumulation, with Total nitrogen ranging from 1258-1854 kg/ha, phosphorus 145.83-322.81 kg/ha, and potassium 105.5-
278.55 kg/ha. Micronutrients were within agronomically optimal ranges. Trace metals including Pb (0.98-2.15 ppm), Cr (0.17-0.32 ppm), Cd
(0.19-0.405 ppm), and Ni (1.46-2.22 ppm) were detected but remained within permissible soil quality limits. The findings indicate that treated
wastewater irrigation enhances soil fertility through increased organic matter and nutrient availability while causing gradual accumulation of
trace metals. Although current levels remain within acceptable limits, continuous monitoring is necessary to ensure the long-term sustainability
of wastewater reuse in agriculture.