Replacing blanket agronomic recommendations with agroecology-specific decision support: a simulation-based framework for irrigated dry-season rice production in coastal deltas

Context Irrigated dry-season (Boro) rice (Oryza sativa L.) is a major contributor to food security in Bangladesh and inland West Bengal, but its cultivation is limited in the coastal Sundarbans due to high salinity, tidal influences, and scarcity of fresh irrigation water. Current policy frameworks promoting uniform transplanting windows and cultivar choices disregard the marked spatial heterogeneity of abiotic stress regimes in these deltaic agroecosystems. Aims This study aimed to characterize genotype × environment × management (G × E × M) interactions and identify location-specific sowing date–cultivar combinations to improve Boro rice productivity, irrigation water productivity, and yield stability under coastal saline conditions. Methods The Agricultural Production Systems Simulator (APSIM-Oryza) was calibrated and validated using multi-location field experimental data from Bangladesh and India collected during 2016–2018. Model performance was evaluated for phenology, above-ground biomass, and grain yield, with root mean square errors (RMSEs) of 6.7 days, 996 kg ha−1, and 1574 kg ha−1, respectively. Subsequently, 35 years of climate-driven simulations (1984–2018) were conducted to assess the effects of sowing dates and cultivar choices on crop performance, stress exposure, irrigation requirements, and irrigation water productivity across contrasting environments. Results Thirty-five years of climate-driven simulations (1984–2018) showed strong spatiotemporal variability in stress exposure. Early sowing (October) predisposed crops to cold-induced spikelet sterility, whereas late sowing (mid-December onwards) intensified exposure to terminal salinity and heat stress, elevating irrigation demand while reducing water productivity. Mid-November sowing consistently minimized risk trade-offs, achieving the highest probabilities of exceeding 5.0 Mg ha−1 with superior irrigation water productivity (9–11 kg grain ha−1 mm−1). Salt-tolerant cultivars (e.g. BRRI Dhan67, WGL20471) maintained yield across variable stress environments, whereas susceptible genotypes (e.g. BRRI Dhan28, IET4786) exhibited high interannual yield variability and frequent failure. Conclusions Sowing date and cultivar selection jointly determine Boro rice productivity and yield stability in coastal saline environments. Mid-November sowing, combined with salt-tolerant cultivars, emerged as a promising strategy for reducing climatic and salinity-related production risks. However, the magnitude of these benefits depends on local stress conditions and hydrological characteristics. Implications The findings support a shift from blanket regional recommendations towards dynamic, simulation-based decision-support systems that integrate sowing windows, stress-resilient cultivars, and location-specific hydrological and salinity conditions. Integrating these systems into agricultural extension services and policy frameworks could improve climate resilience, irrigation water productivity, and sustainable Boro rice production across the coastal saline zones of South Asia.