Effect of genotype and plant population on growth, nitrogen fixation and yield of soybean [Glycine max (L.) Merrill] in the Sudan savanna agro-ecological zone of Ghana

Soybean genotypes vary in growth characteristics and require different plant densities especially at different ecological zones. It is unacceptable to use one plant spacing recommendation for all varieties in different ecological zones. An experiment was conducted to determine the effect of plant population on the growth, nitrogen fixation and yield of four soybean genotypes (Jenguma, Soung-Pungun, TGX1904-6F and TGX 1955-4F) in the Binduri District in the Sudan Savanna zone of Ghana. The experiment was laid out in a split plot design with four communities serving as replicates. Genotype was the main plot and plant spacing (45 x 10 cm, 60 x 10 cm and 75 x 10 cm), the subplots. Data collected was plant height, days to 50 % flowering, number of nodules, nodule fresh weight and effectiveness, biomass weight, percentage nitrogen fixed, total nitrogen in plants, number of pods per plant, grain yield per hectare, 100 seed weight and fodder weight. The data collected was subjected to the analysis of variance. The results showed that plant height was not affected by genotype and plant spacing interaction; however, it influenced days to 50 % flowering, nodule count, biomass weight and grain yield. Flowering was earliest in Soung-Pungun while TGX1904-4F was last to flower. Soung-Pungun gave the highest grain yield of 0.953 ton ha^-1 at plant spacing of 45 x 10 cm, followed by TGX1904-4F and Jenguma yielding 0.884 ton ha^-1 and 0.838 ton ha^-1 at plant spacing of 75 x 10 cm and 60 x 10 cm, respectively. TGX 1955-4F recorded the lowest grain yield of 0.590 ton ha^-1 at plant spacing of 60 x 10 cm. Overall, Soung-Pungun could give the highest grain yield to producers in the Binduri district if the production goal is to maximize grain yield. Nitrogen fixing ability was different among the soybean genotypes, with TGX1904-4F recording the highest percentage nitrogen fixed followed by Jenguma. TGX1904-4F is recommended for farmers if the goal is to support N fixation. The spacing recommended to farmers is 45 x 10 cm for Soung-Pungun.