Evaluation of the growth response of soybean (Glycine max L.) to some commercial fertilizers in the guinea savannah agro -ecological zone of Ghana

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Series of field experiments were undertaken in the Guinea Savanna agro - ecological zone of Ghana to assess the influence of some agricultural commercial products in optimizing soybean production. The field experiments were carried out using sixteen treatments at Akukayili, Cheshegu and Ghulahgu during the 2012 and 2013 cropping seasons. The treatments were replicated four times in a split – plot arranged in randomized complete block design. Soil chemical properties evaluated in the study areas before trial establishment indicated that the soil fertility status was below the optimum for soybean growth. The results showed that the use of starter N (25 kg N ha -1 ) is essential to increase soybean yields in the study area. Grain yields of 3321 and 3056 kg ha -1 were recorded respectively for Boost Xtra (BX) + 25 kg N ha -1 and BX + 5O kg N ha -1 at Akukayili where 25 kg N ha -1 + BX emerged as the best treatment in enhancing both Agronomic Efficiency (AE) and Nutrient Use Efficiency (NUE) of nitrogen. Furthermore, the sole use of Bradyrhizobium japonicum inoculum did not significantly (P > 0.05) enhance grain yield. At Cheshegu, Fertisoil and Bradyrhizobium japonicum inoculum treatments increased nodule dry matter accumulation by 51% and 407% respectively relative to the control. Moreover, P90 + FS, P60 + FS and P30 + FS produced grain yields of 3588, 3583 and 3524 kg ha -1 respectively, which were significantly higher (P < 0.05) than the control. Phosphorus application increased N uptake in the order, 30 > 60 > 90 kg P ha -1 . The use of 30 kg P ha -1 enhanced the AE and NUE of phosphorus when combined with Bradyrhizobium japonicum inoculum (INO) and /or Fertisoil (FS). The emphasis on the benefit of combining more than one nutrient at a time was clearly observed across the study locations, where combined use of the various treatments (especially FS + N25P30 ) led to an increase in nodule dry weight, biomass and grain yield relative to their sole treatments. Also, the uptake of N and P were enhanced with the treatment combinations than the sole applications. At Ghulahgu, the application of Boost xtra iv resulted in a value cost ratio (VCR) of 5 which was the highest relative to VCR‟s obtained at Akukayili and Chesshegu.
A thesis submitted to the Department of Crop Science, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science.