Optimizing soybean (Glycine max L. Merr.) performance through rhizobial inoculation and planting density in Kétou, Benin

Declining soil fertility, particularly nitrogen deficiency, remains a major constraint to soybean productivity in Benin. This study evaluated the effects of rhizobial inoculation and planting density on the growth and grain yield of soybean (Glycine max (L.) Merr.) variety TGX1910-14F under field conditions in Kétou, central Benin. A factorial field experiment comprising two inoculation levels (inoculated and non-inoculated) and three planting densities corresponding to row spacings of 50, 60, and 70 cm (20 cm within rows) was conducted in six farmers’ fields. The six treatment combinations were replicated six times, giving a total of 36 experimental units. Plant height, leaf number, leaf length, and leaf width were measured at four growth stages (S1–S4), while grain yield was determined at harvest. Data were analyzed using two-way analysis of variance (ANOVA) followed by Tukey’s HSD test at the 5% significance level. Rhizobial inoculation significantly increased leaf number (p= 0.0125) and plant height (p= 0.0055), whereas planting density had no significant effect on these traits. Inoculated plants also exhibited greater leaf dimensions than non-inoculated plants throughout the growth period. Grain yield was significantly affected by inoculation (p < 0.001), planting density (p < 0.001), and their interaction (p= 0.0014). The highest grain yield (1,855.53 kg ha⁻¹) was obtained from the combination of inoculation and 50 cm × 20 cm spacing (T1), while the lowest yield (677.77 kg ha⁻¹) was recorded in the non-inoculated treatment at 70 cm × 20 cm spacing (T6). The results demonstrate that rhizobial inoculation substantially improves soybean growth and productivity and that its benefits are maximized at a planting density of 50 cm × 20 cm. This management combination is recommended for sustainable soybean production in the Kétou agro-ecological zone of Benin.