The Role of Nitrogen-Levels and Foliar Fertilizer at Critical Stages for Inoculated Soybean Growth and Yield Improvement in Northern Savannah Zone Of Ghana

Need for the nutrient supplement at certain critical stages of soybean development to sustain successful growth, seed formation, pod filling and quality grain yield cannot be underestimated. Hence, the response of soybean “Jenguma” growth, nodulation and grain yield to Bradyrhizobium japonicum inoculum and mineral fertilizer application at various growth stages was evaluated on the research farm of CSIR-Savanna Agricultural Research Institute (SARI), Ghana. The experiment consisted of three factors i.e. Inoculation (+INO and –INO), Nitrogen levels (0, 25, 50 and 75 kg N ha-1 (as starter and top dressed at beginning bloom, R1 - stage)) plus Foliar fertilizer (Boost extra (BX) applied at R1 – R4 stage) 4 liters ha-1 (+ and -)). Giving sixteen combinations in all, replicated thrice. Basal application of 30 kg P2O5 and K2O ha-1 each was applied. The experiment was a Randomized Complete Block Design. The plant height and canopy spread response to starter N (25 kg N ha-1) is proof that a minimum level of N is necessary for soybean establishment. The treated plots indicated a significant (P<0.05) influence on soybean pod formation and grain yield performance as compared to Control. In fact, a significant (94 %) grain yield increase was produced from 50 kg N ha-1+BX compared to Control. Likewise, the lowest N-level (25 kg N ha-1) and it's combinations with BX or INO and the use of 25 kg N ha-1+INO+BX also gave substantial grain yield increase (50 % and above) over Control. These are an indication that the appropriate timing of N, it's top dressing and foliar fertilizer application at certain growth stages of soybean enhanced inoculated soybean growth and grain yield. Hence, the use of fertilizer and its top dressing (N and foliar fertilizer) is paramount in augmenting inoculated soybean production in the study area. The choice of fertilizer, rate and time of application depend on the farmer's choice.