THE EFFECT OF BIOCHAR AND INOCULANT WITH COMPOST OR PHOSPHORUS ON SOIL FERTILITY AND SOYBEAN YIELD IN GUINEA SAVANNA ZONE OF GHANA

The yield of soybean in Ghana stands at 1.45 t ha-1 out of an achievable harvest of 3 t ha-1 and among the contributory reasons for the low yields are inherent low soil fertility and lack of adequate indigenous bacteria in the soils used for soybean production. Amendment of the soil is believed to hold the key to improve yields of soybean. The objective of the study was to determine the effect of Bradyrhizobium japonicum inoculant (USDA 110 and USDA 136 stains) in combination with soil amendment on soybean yield and improvement of soil fertility. A plant house experiment was conducted in a 3 x 5 factorial combination and laid out in a randomized complete block design with three replications. The factors were Bradyrhizobium japonicum (3 levels) and soil amendment (5 levels). The treatments were biochar at a rate of 20 t ha-1 , biochar (10 t ha-1 ) + compost (5 t ha-1 ), biochar (10 t ha-1 ) + rock phosphate (60 kg ha-1 P205), biochar (10 t ha-1 ) + triple superphosphate (60 kg ha-1 P205) and the farmers practice, no amendment (control). These treatments were added to 5 kg of soil in a bucket and planted with Sung-pugun soybean variety inoculated with the two rhizobium strains. Non-inoculated control was kept. It was observed that the addition of compost to the biochar led to a higher plant height and grain yield than when TSP or Rock phosphate was added. The addition of Bradyrhizobium japonicum strain USDA 110 produced more nodules than that of Bradyrhizobium japonicum strain USDA 136, and the inoculants promoted more nodule development than the non-inoculant treatment. Soil amendment improved P, K and Na concentrations of the plant more than those on non-amended soil. Biochar + Compost recorded the highest Cation Exchange Capacity. The various soil amendment highly influenced the carbon concentration of the soil. The study concluded that the combination of biochar with compost improves the soil's biological, physical and chemical properties, which led to higher grain yield and has to be encouraged.