Rice Productivity, Nutrients Use Efficiencies and Water Productivity on a Biochar-amended Soil in a Typical Lowland Rice System in Benin

This study was conducted to evaluate the effects of soil amendment with biochar sources (corn cobs (CC) and rice husks (RH) biochar) and irrigation regimes (alternate wetting and drying (AWD) and continuous flooding (CF)) on rice productivity, nutrients use efficiencies and irrigation water productivity (IWP) of a lowland rice system in Benin during the 2022 and 2023 growing cycles. The experiment was arranged in a split-plot design with four replicates. The results reveal that the combined use of CC or RH biochar (15 tons/ha) with chemical fertilizers significantly improved paddy rice yields by 19% compared to control (no use of biochar and use of chemical fertilisers). The alternate wetting and drying (AWD) irrigation regime insignificantly improved paddy rice yields by 7% on average. The uptake of the three major nutrients (N, P and K) did not significantly vary with irrigation regime and biochar application. In the 2022 growing cycle, the combined use of CC or RH biochar and chemical fertilizers significantly reduced the apparent recovery rate by 42.07, 46.40 and 79.83%, and the agronomic N, P and K use efficiency by 39.91, 41.35 and 82.78%, respectively compared to control plots. In the 2023 growing cycle, the combined use of CC or RH biochar and chemical fertilizers increased apparent recovery rates by 29.09, 22.05 and 55.67% for N, P and K respectively, and their agronomic use efficiency by 40.36%. Soil amendment with CC or RH biochar significantly improved irrigation water productivity (IWP) by 18.5% on average compared to the control. AWD irrigation regime significantly improved IWP by 37% compared to the CF regime. Overall, the results of this study highlight the potential of: i) combining biochar amendment with the application of chemical fertilizers to significantly improve productivity and, ii) adopting the AWD irrigation regime without reducing yields in lowland rice systems in Benin.