Rainfed cereal production in northern Ghana is highly variable due to rainfall uncertainty, soil constraints, and low-input fertility management. Integrated soil fertility management (ISFM) can improve productivity, but outcomes depend on climate and site conditions. Using the SIMPLACE model, this study evaluated interactions among ISFM practices, sowing dates, soil depth, and climate risk at a representative site. Simulations combined four fertility treatments (control, inorganic, organic, combined), contrasting soils, multiple sowing dates, historical climate, and +2.0 °C warming across >300 GCM-based ensembles. Kernel density estimates of yield and biomass showed that control and organic treatments had low yield potential but high stability. Inorganic fertilization maximized yields but was most unstable, while combined organic–inorganic management improved biomass stability and yield distributions, supporting ISFM as a climate-resilient adaptation strategy in northern Ghana.