Model-Assisted Optimization of Nitrogen Fertilizer Rates for Maize in Dry Zone of Sri Lanka under Current and Future Climate Scenarios

Maize ( Zea mays L.) is the most vital upland cereal and a cornerstone of food security in Sri Lanka. The crop is extensively cultivated in the dry zone, a region highly vulnerable to climate change. Nevertheless, current nitrogen (N) fertilizer rates have not been recently climate-optimized, reducing yield efficiency and increasing environmental impacts. The objectives of this study were to model and optimize N fertilizer rates for maize, under current and future climate conditions for 2050 and 2100 by testing different nitrogen management scenarios by utilizing the Agricultural Production Systems Simulator (APSIM). Simulations were conducted using 30 years of past climate data from Mahailluppallama local weather station and 2023 IPCC climate projections to test multiple nitrogen management strategies. Results showed that the current Department of Agriculture recommendation of 315-425 kg ha⁻¹ N can be optimized to 345-435 kg ha⁻¹ under present conditions, increasing yields while reducing leaching losses. Under future climates, optimal N rates rose slightly to 375-465 kg ha⁻¹ to maintain productivity, though leaching risks increased. Findings highlight the importance of adaptive, climate-responsive N management strategies to sustain maize yield and minimize environmental impacts. The outcomes provide valuable guidance for developing data-driven, climate-smart fertilizer recommendations for dry zone of the Sri Lanka.