Basin scale impacts of nitrogenous fertilizer use on croplands from a grey water footprint perspective

Nitrogen fertilisers are frequently used at excessive rates to optimise crop yield, especially in irrigated agriculture. Pollution associated with the application of nitrogen fertilizer has become a critical concern globally. The aim of the study was to assess the grey water footprint (GWF) and water pollution index in the Banas River Basin over the period of 2008–2020. We estimated spatially explicit leaching run-off fraction (α) based on local data, which ranged between 0.075 and 0.093 (Mean 0.088) in the basin. During this period, based on fertilizer application rates and production statistics of principal crops in the basin, we estimated 1754 MCM/yr annual GWF. Approximately 76% of the annual GWF can be attributed to the following crops: Rapeseed & Mustard, Bajra/Pearl Millet, Wheat, Maize, and Gram. Water pollution index indicated that pollutant load exceeds the assimilation capacity in nine months of the year except for August, September, and October months during which there is sufficient runoff to assimilate the full pollutant load. Annual water pollution index (WPI) was found to be 133% in the Banas basin highlighting gross violation, which would lead to degradation of water quality over time resulting problems like algal blooms, fish kills, hypoxia and health related side effects for downstream users some of which have already been noticed in some stretches of the river, signifying the need of developing better policies to optimize fertilizer management for crop production and tackle this problem. Research highlights the necessity of improving our understanding of localized water quality impacts from nitrogenous fertilizer use, quantifying the pressure they put on our freshwater resources, and remediating them using suitable management strategies.