Effects of Soil Amendments and Rhizobium Inoculation on Soybean Nodulation, Growth and Yield in the Semi-Deciduous Forest Agro-Ecological Zone of Ghana

Abstract

Ghana's soybean cultivation is primarily restricted to the Guinea savanna and the forest/savanna transitional agro-ecological zones. Although soybean can be grown in the semi deciduous forest zone, its productivity is limited due to low soil pH and limited nodulation. The study was conducted at the University of Ghana Forest and Horticultural Crops Research Centre at Kade in the semi-deciduous forest agro-ecological zone of Ghana between August and December, 2021.The objective of the study was to assess the combined effects of soil amendments, phosphorus fertilizer and rhizobium inoculation on soil chemical properties, nodulation, growth and yield of soybean. The experiment was laid in a split-split plot design with four (4) replications with main plot being soil amendments (No amendment, 2 tons/ha lime and 5 tons/ha rice husk biochar), subplot being P fertilizer at 0 and 20 kg P ha-1 and sub subplot with or without Rhizobium inoculation. Data on nodule number and effectiveness, shoot biomass, one hundred seed weight and grain yield were taken. Results from the study indicated that phosphorus application significantly influenced grain yield as grain yield was increased by about 60% due to P application. There wasincrease in soil pH from the initial 5.09 to 5.52 and 5.54 on plots that received biochar and lime respectively, 17 weeks after treatment application. The effect of inoculation on pH was also significant (p < 0.05). Rhizobium inoculation had significant effects on exchangeable K and Mg. The inoculated plots had exchangeable K and Mg values of 0.37 and 2.62 cmol (+)/kg soil, respectively, while the values for the uninoculated plots were 0.33 and 3.31 cmol (+)/kg soil for K and Mg respectively. Inoculation significantlyinfluenced nodulation parameters such as nodule number, nodule effectiveness and nodule fresh weight of soybean. The application of rhizobium inoculant significantly (p < 0.001) increased nodule number and nodule effectiveness by 44 % and 45 % respectively, over plantsthat received no inoculants. The sole application of P fertilizer increased the number of nodules by 44 % compared to the plots that received no P fertilizer However, this did not translate intoincreased grain yield. The interaction between Rhizobium inoculation and Phosphorus fertilizer significantly affected dry shoot biomass of soybean. Treatment interaction between soil amendments and P fertilizersignificantly influenced P-use efficiency. The results show that the three factors that were studied did not interact to significantly influence nodulation, growth and yield of soybean However, the three factors interacted to significantly enhance nodulation and improve P-use efficiency and some soil chemical properties (OC, Total N and exchangeable Ca and Mg). However, it is recommended that farmers can apply phosphorus fertilizer at the rate of 20 kg P/ha for increased grain yield of soybean on acid soil.