Optimization of plant density and fertilizer application to improve biofortified common bean (Phaseolus vulgaris L.) yield on Nitisols of South-Kivu, Eastern D.R. Congo

Soil nutrient depletion and poor farming practices are serious challenges limiting crop productivity in soils of the eastern Democratic Republic of Congo (D.R. Congo). An experiment was conducted in two cropping seasons to assess the effect of plant density (25 plants m² and 33 plants m²) and fertilizer application (with and without NPK) on the yield and yield components of three biofortified common bean varieties (HM21-7, RWR2245 and RWR2154). The experiment involved two plant densities, two fertilizer rates and three varieties arranged in a split-split plot design with three replications. Results showed that yield significantly varied with plant density, variety and fertilizer rate (<i>p</i> < 0.05). The best performing variety in terms of grain yield was HM21-7 (1.5 t ha^-1) as compared to RWR2154 (1.09 t ha^-1) and RWR2245 (1.14 t ha^-1). The NPK fertilizer increased the grain yield by 38.2%. Grain yield increased also with the plant density, highest grain yield being recorded on higher plant density (1.37 t ha^-1) as compared to low lower plant density (1.25 t ha^-1). Agronomic efficiency (AE) was influenced by the variety, with the highest AE obtained on RWR2245 (23.27 kg kg^-1) and on high plant density (20.34 kg kg^-1). Therefore, we concluded that increasing the plant density by reducing the plant spacing, using NPK fertilizer and high yielding varieties provide with an opportunity to improving common bean yields on Nitisols dominating the highlands of eastern D.R. Congo.