INVESTIGATING NPK, MOLYBDENUM AND ZINC EFFECTS ON SOYBEAN NODULATION, NITROGEN FIXATION AND YIELD IN NORTHERN GUINEA SAVANNA SOILS

Soybean, like other grain legumes, requires some essential nutrients to accomplish the dual purpose of fixing atmospheric nitrogen and high yielding. A screen house experiment was then setup to investigate the effect of N, P, K, Zn and Mo on nodulation and growth of soybean. Soils from six farmers' fields in Kaya, northern Guinea savanna and seven fertilizer compounds were used in a factorial experiment laid out in completely randomized design. Data collected at 8 weeks after planting on biomass yields, nodulation variables, N2-fixation, mycorrhizal roots colonization, and N and P uptake were analyzed using SAS. Soils test revealed variation of soils' chemical contents among farmers field, especially for P with 51.7 mg kg-1 in Soil 1 to 2.7 mg kg-1 in Soil 4. Significant effects from soils and fertilizers were observed on biomass yield, nodulation and nutrient uptake. Nitrogen fixation potential of TGX 1448–2E, however, was not increased by soils or fertilizer treatments. Soil x fertilizer effects was significant on P-uptake, shoot and nodule dry weight. It was observed that K application reduced shoot dry weight and P-uptake in soil 1. Owing to these results in response to fertilizer treatments, soybean fertilization should be recommended according to soil inherent fertility.