Can agricultural Nitrate leaching to groundwater be reduced without compromising crop yields?

Intensive agricultural production in the Indo-Gangetic Plain has led to widespread overapplication of fertilizers, particularly in sugarcane-based systems, resulting in elevated nitrate concentrations in groundwater. In the Hindon River Basin, the Central Ground Water Board (CGWB) has reported significant nitrate contamination, which poses a threat to both agricultural sustainability and drinking water security. Addressing this degradation while maintaining productivity requires quantitative tools to evaluate management interventions. This study employs the SWAT+ model to evaluate the impact of reduced fertilizer application and alternative irrigation practices on groundwater nitrate leaching and sugarcane yield in the sugarcane-dominated Hindon Basin. The model's ability to represent basin hydrology and crop growth was evaluated through calibration and validation using observed streamflow at two gauging locations, and sugarcane yield data from three districts. The model demonstrated satisfactory performance, with streamflow calibration and validation producing average KGE values of 0.74 and 0.73, respectively, and an average percent bias (PBIAS) of 12% and +9%. Crop yield simulations yielded average KGE values of 0.76 and 0.83 during calibration and validation, respectively, with PBIAS values of -4% and -6%. These results confirm the model's reliability for management-oriented assessments. Four management scenarios were simulated against a baseline that reflected current farmers' practices, as identified through field surveys. Scenarios included fertilizer reductions of 15% and 30%, implemented under both furrow and drip irrigation systems. Groundwater quality responses were evaluated using annual average nitrate percolation below the root zone for leaching, while sugarcane yield was used to assess productivity trade-offs. Across all alternative scenarios, nitrate percolation decreased by 46% to 68% relative to the baseline. Changes in sugarcane yield were minimal, remaining within 1-2% of current practices. Drip irrigation demonstrated greater nitrate reduction compared to furrow irrigation at the same fertilizer levels, highlighting the importance of irrigation efficiency in mitigating nutrient loss. These findings suggest that moderate decreases in fertilizer use, combined with drip irrigation, can significantly reduce groundwater nitrate contamination in the Indo-Gangetic Plain without compromising yields.