Moderate N fertilizer inputs under proper water management enhanced off-season rice production in central Benin, West Africa

Effective water and nitrogen (N) management strategies are critical inputs to avoid unstable crop yields and minimize environmental pollution. Our study aimed to identify the best combination of water management and nitrogen rate (N) that improves water productivity and nitrogen use efficiency without compromising grain yield for irrigated rice production in central Benin. Two-year field experiments were established at Koussin-Lele, central Benin, in 2021 and 2022 using a split-plot experimental design. The main plot was assigned to water management technologies that include continuous flooding (CF) and two thresholds of alternate wetting and drying (AWD) irrigation (AWD₁₅ and AWD₂₅). The subplot was assigned to the N fertilizer regime (0, 90, and 120 kg ha^− 1). Results showed that both shoot dry weight and the leaf area index were higher in the CF regime with N120 whereas the highest root dry weight of 5.77 T ha^− 1 was recorded under the AWD₁₅ regime. Averagely, the highest grain yield of 6.04 T ha^− 1 was recorded under the CF regime with N120 which is statistically similar compared to the AWD₁₅ regime. The AWD₁₅ and AWD₂₅ regimes saved 31.75% and 52.30% of total water inputs compared to the CF regime, respectively. Furthermore, the AWD₁₅ regime with N90 recorded the most efficient nitrogen use, the highest harvest index, and the highest water productivity. Our findings emphasize the adoption of the AWD₁₅ regime with N90 is advantageous over farmers’ practices and should be promoted to reduce fertilizer inputs and cope with water scarcity without yield loss in central Benin.