Evaluation of nitrogen fixation potentials of some soybean genotypes and their residue nitrogen effects on succeeding maize crop

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An experiment was conducted at CSIR- Crops Research Institute of Ghana to determine the nitrogen fixation potentials of some soybean lines and varieties and subsequently, their residue nitrogen effects on a succeeding maize crop. The experiment was a randomized complete block design with four replications. The varieties were ‘Anidaso’, ‘Nangbaar’, ‘Salentuya 1’, ‘Jengumah’ and ‘Quashie’. Soybean lines used were TGX 1990-5F, TGX 1987-62F, TGX 1989-20F, TGX 1904-2F and TGX 1990-8F. ‘Obaatampa’ maize variety was used as the reference crop. Data collected were plant height, number of primary branches, number of leaves, nodule count, nodule dry weight and effectiveness, number of pods per plant, number of seeds per pod, hundred seed weight and grain yield per hectare for soybean. Data collected on maize were plant height, stem girth, shoot dry weight, number of leaves, number of cobs per plant, number of seeds per cob, hundred seed weight and grain yield per hectare. The data were analyzed using ANOVA and means separated by LSD (P< 0.05) using GENSTAT. The results showed that all the soybean varieties and lines nodulated freely with the naturalized cowpea rhizobia. N fixation differed significantly (p<0.05) among the varieties and the Anidaso variety fixed the greatest amount of 59.1 kg N/ha. However, soybean grain yield was not the greatest in this variety. Again, the Anidaso variety left the largest amount of 14.3 kg/ha of N in its residue for succeeding crop. Maize grain yield results showed that applying the traditional fertilizer recommendation (100 kg N/ha of NPK and top dressing with ammonia fertilizer) was not significantly different from incorporating the soybean residue without any fertilizer application. The results indicate that farmers can reduce their cost of producing maize by incorporating soybean residue instead of fertilizer application.
A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture of the College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. This is in partial fulfillment of the requirement for the award of Master of Philosophy Degree in Agronomy,