Seed engineering properties of common bean varieties for multi-crop planter design

Common bean, a key crop for over 100 million Africans, faces significant yield gaps due to planter inefficiencies and unquantified seed-property variability. This study quantifies engineering properties of five improved varieties ('SAB 632', 'Awash Meten', 'DAB 96', 'NAUS 17', and 'DAB 372') to derive quantitative design specifications for multi-crop planter components. Principal dimensions (length, width, thickness) of 100 seeds per variety were measured, and derived parameters, including elongation ratios, mean diameters, surface area, shape index, flakiness ratio, and sphericity, were calculated. True and bulk densities, thousand-seed mass, and angle of repose were measured in five replicates for each variety. All data were analyzed using one-way ANOVA (p < 0.05). Seed lengths mean spanned approximately 8.51-14.68 mm and geometric mean diameters 6.65-8.82 mm (sphericity 60.11-78.22%) across the varieties. These ranges indicate that metering-unit openings must accommodate seeds up to about 16.25 mm long by 5.28-6.57 mm mean thickness. Measured bulk densities (723-816 kg m^-3) and repose angles (26.3-33.3°) indicate favorable flowability for gravity-based handling systems. The maximum repose (33.3°) suggests hopper walls should be inclined at ≥ 35° to ensure mass flow. The derived engineering specifications support the use of interchangeable metering plates, approximately 19 mm metering unit length, hopper wall inclinations of 35-40°, tapered seed tubes, and optional vibration-assisted hopper systems to improve seed singulation and flow consistency across common bean varieties.