Inoculation and n fertilizer effects on the growth, grain yield and n remobilization in soybean (Gylcine max [L] Merrill) in the guinea savanna zone of Ghana

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October, 2015
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Experiments were conducted at Nyankpala and Savelugu both in the Guinea savanna zone of the northern region in the 2012 and 2013 cropping seasons to determine the effects of N fertilizer and inoculant applications on the growth, grain yield and N remobilization in soybean (Glycine max [L] Merril). Soil samples were taken before and after the experiment to determine initial fertility level and the effects of the system on soil fertility. The experiments were laid in a 3 X 5 factorial arranged in Randomized Complete Bock Design (RCBD) with four replications at each location. The factors were the three varieties (Jenguma, Quashie and Anidaso), inoculation and four levels of N fertilizer which include 0 kg N/ha, 15 kg N/ha, 30 kg N/ha and 45 kg N/ha. The inoculant was applied at the rate of 5 g to 1 kg of soybean seed through the slurry method that was estimated to give 107 of viable rhizobia cells. Planting was done manually on the flat by drilling and later thinned to 2 plants hill-1 at 0.1 m (10 cm) within rows and spaced at 0.5 m (50 cm) between rows. Each plot had 8 rows with 30 stands giving an approximate plant population of 400 000 plants ha-1. A non-legume crop used was maize cv Obantampa spaced at 80 cm x 40 cm. The N fertilizer was applied to the plants two weeks after planting (2 WAP), except where inoculant was applied. Growth parameters measured were plant height, leaf area, number of branches, number of nodules, percent effective nodules, nodule dry weight and shoot dry weight. Yield parameters measured were number of pods per plant, number of seeds per pod, 100 seed weight, grain yield, harvest index (HI) and crop residue yield. N remobilization and N distribution index (NDI) were also determined between 80 and 120 DAP. The results indicated that the inoculant effects produced the highest nodulation of 21.2 to 23.0 nodules plant-1 across locations. There was also promiscuous nodulation where no inoculant was applied that produced 15.9 to 17.0 nodules plant-1 across experiments. The amount of N fixed ranged from 59 to 81 kg N ha-1. In all parameters measured, the inoculant treatment was superior to the uninoculated control. Additionally, the 45 kg N/ha produced greatest grain yield that ranged from 2,146 to 2,302 kg ha-1 across locations compared to the other rates of N. Nitrogen remobilization was observed in all plots that ranged from 50.0 to 115.7 kg N ha-1, which indicate that soybean needs greater levels of N during grain filling.
A thesis submitted to the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Agronomy, 2016