INFLUENCE OF MINERAL NITROGEN-LEVELS AND FOLIAR FERTILIZER ON INOCULATED SOYBEAN NODULATION, GROWTH AND YIELD

Abstract

The need for N in Soybean production has been confirmed by so many reseachers; however the need for nutrient supplement at leaf senescence stage to sustain successful seed formation, pod filling and quality seed harvest has not really been reported in the Northern region of Ghana. The influence of N rate and time of application on soybean cultivation has also aggravated a lot of research questions. Therefore, an experiment was conducted to evaluate the response of soybean plant height, canopy spread, nodulation, pod formation and grain yield to mineral fertilizer (30 kg P2O5 and K2O each as basal application) with ammonium sulphate as starter N (25kg Nha-1), then a top dressing (25 or 50kg Nha-1) at mid-vegetative stage, foliar fertilizer (Boost xtra 4 litre ha-1, at vegetative/early podding stage) and 5 g seed-1 of Bradyrhizobium japonicum inoculant. The experiment was a Randomized Complete Block Design replicated three times. The results obtained shows that the appropriate timing of N and foliar fertilization could enhance soybean growth and grain yield. Plant height and canopy spread response to the application of initial 25kg Nha-1 was an indication that a minimum level of N is a necessity for soybean establishment. Also soybean pod formation and seed grain were all proofs of significant (P<0.05) influence of the applied treatments on soybean development as compared to the Control. Infact, an impressive grain yield (94% increase) was produced from the plot treated with 50kg Nha-1+BX compared to Control. However, the lowest N-level (25kg Nha-1) used as sole and better still it’s combinations with BX or INO and the combination of the three (25kg Nha-1+INO+BX) also gave substantial increase of 50% and above grain yield over the Control. Hence, the use of fertilizer (mineral, foliar and bio-fertilizer) is paramount in augmenting soybean production in the study area. The choice, rate and time of application depend on the farmer’s financial capability.