Evaluation of nitrogen fixing potential of some grain legumes and their residual effects on maize yield in the semi-deciduous forest zone of Ghana.

Field experiments were conducted at the Plantation Crops Section of the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana during the 2014 and 2015 major and minor rainy seasons to evaluate the nitrogen fixing potential of some grain legumes and their residual effects on yield of maize. In the 2014 major cropping season, five varieties each of groundnut, soybean and cowpea were planted out in a randomized complete block design and replicated four times. In the minor season of the same year, the haulms were left on their respective plots and maize variety Abontem was planted on each plot with a plot treated with recommended fertilizer rate (90 kg N, 60 kg P2O5 and 60 kg K2O /ha). In the 2015 major season, four varieties of soybean inoculated at a rate of 10 g of inoculant per1 kg of soybean seeds and three levels of inorganic N (0, 30 and 60 kg/ha) were laid out in a randomized complete block design and replicated four times. In the following minor rainy season of the same year, the haulms were left on their respective plots. Maize variety Abontem was planted on all plots and a plot treated with recommended fertilizer rate. Results of the study indicated that groundnut produced the highest haulm N followed by soybean and cowpea. Among the groundnut varieties, Manipinta, Nkatiesari and Jenkaar produced the highest haulm N, while Manipinta produced the highest grain yield. Among the soybean varieties, Quashie and Songda produced the highest haulm N than other varieties, while Sonqu-panqu produced the highest grain yield. Among the cowpea varieties, Hewale produced the highest haulm N than other varieties, while Asontem produced the highest grain yield. All haulm-incorporated plots produced higher grain yield of maize than the plot treated with recommended fertilizer rate except Asetenapa and Asontem cultivated plots. Residual N from groundnut produced higher grain yield of maize than the soybean and cowpea treatments. The Haulm produced from Quashie significantly gave the highest grain yield of maize (2482 kg/ha). In 2015, under sole inoculation, Salintuya-1 and Songda produced the highest haulm N. Quashie and Songda produced the highest haulm N at 30 kg/ha N while Quashie produced the highest haulm N at 60 kg/ha while Sonqu-panqu produced the highest grain yield under all conditions. All haulm-incorporated plots produced lower grain yield of maize compared to the recommended fertilizer rate. Under sole inoculation, haulms from Quashie and Sonqu-panqu produced higher grain yield of maize. Haulms from Songda produced the highest grain yield at 30 kg/ha N and that of Salintuya-1 gave the highest maize grain yield at 60 kg/ha N. Manipinta and Jenkaar among the groundnut varieties were found to have the highest nitrogen fixing potential while Manipinta produced the highest grain yield. Quashie and Songda among the soybean varieties were observed to have the highest nitrogen fixing potential, while Sonqu-panqu produced the highest grain yield. Hewale among the cowpea varieties emerged as having the highest nitrogen fixing potential and Asontem produced the highest grain yield. Inoculation and inorganic N are beneficial to soybean production as indicated in this study, but further research is needed to ascertain the actual level of N for the different varieties of soybean. As par the economic evaluation of grain legumes production in this study, under favourable weather conditions, farmers can obtain financial benefits, ranging from earning more income from the sale of the grains to utilization of the haulms for the production of maize. These, will not only improve their standard of living, but also contribute to the country’s GDP.

Source: KNUST