Long-term impact of wastewater irrigation and nutrient rates II. Nutrient balance, nitrate leaching and soil properties under peri-urban cropping systems

Since irrigation with under-treated wastewater is growing in many underdeveloped countries, its regulation should follow more efficient and less polluting approach. Therefore, the nutrient balances and soil properties were monitored in an 8-year experiment where the food grain (FGPS, paddy–wheat), fodder (FPS, sorghum-Egyptian clover) and vegetable (VPS, gourds/okra-cabbage/cauliflower) and agroforestry (AFS, poplar–paddy–wheat) production systems were irrigated either with sewage water (SW, BOD 82 ± 11, NO3–N 3.2 ± 0.4, NH4–N 9.6 ± 0.5 and P 1.8 ± 0.3 mg L−1) or good quality groundwater (GW) along with variable doses of N & P (25–100% of the recommended). The concentration and uptake of both N and P increased with SW and NP doses. SW enhanced N uptake by 29, 23, 18 and 37% in FGPS, AFS, FPS and VPS, respectively, while the corresponding values were 28, 21, 29 and 35 per cent for P uptake. The crop N removal obtained at 100% NP dose in GW were at par with 25% NP doses in AGF and VPS and 50% NP doses in FGPS and FPS with SW. The positive balances of nutrients with SW resulted in improvement in soil organic carbon and available status of nitrogen and phosphorus. Soil microbial biomass carbon (MBC) and activities of dehydrogenase, urease and phosphatase also improved substantially with SW. The most of nitrate-N was retained in the surface 0.3 m soil especially its leaching was minimal under AFS. Overall results indicated for improvement in the awareness of the growers for adjusting NP doses and non-dependent on water guzzling crops like paddy to minimise the fertiliser costs and the contamination of groundwater.