Numerous innovative climate-smart agricultural practices are being implemented across Africa, contributing to increased productivity and enhanced resilience. However, their efficiency remains relatively low at the continental and even regional levels. This study aims to assess the water use efficiency (WUE) of soybean (Glycine max) under the combined application of biochar and manure. A randomized complete block design (RCBD) with three replications was used for the experiment. The factor studied was organic amendment, with four levels: no amendment (T0), manure (T1), biochar (T2), and a combination of biochar and manure (T3). The methodology included rainfall and soil moisture measurements to monitor water availability in each experimental unit. Data on growth and yield parameters were collected. Analysis showed that manure, particularly when combined with biochar, significantly improved growth parameters. Furthermore, the biochar-manure treatment enhanced soybean grain yield by up to 37.34% compared to the control (i.e., 1642 kg/ha). It also resulted in the highest water use efficiency, with an improvement of up to 37.03%. Therefore, applying manure combined with biochar appears beneficial for soybean cultivation. The combination reduces nutrient loss by limiting leaching, thanks to the biochar’s retention capacity. Further research involving different application rates of biochar and manure would help determine the optimal quantities for maximizing water use efficiency.