Combined biochar and compost or P applications improve soybean yield and inoculation in tropical acidic soil

Abstract

Abstract: Most crops grown in tropical savanna ecosystems have a 30%–60% yield gap, primarily due to poor soil fertility, low nutrient bioavailability, and limited effectiveness of conventional fertilization practices. This study used an integrated soil management approach involving Bradyrhizobium japonicum inoculant and rice husk biochar combined with compost or phosphorus fertilizer for soil fertility improvement, soybean (Glycine max L.) growth, and grain production. In the Guinea savannah zones of Ghana, we conducted a two-factorial pot experiment under greenhouse conditions. The treatments were as follows: (i) 1% w/w (20 t ha−1) rice husk biochar (B); (ii) 0.5% w/w (10 t ha−1) compost (CM); (iii) co-application of 0.5% w/w (10 t ha−1) biochar with compost (B + CM); (iv) rock phosphate (B + RP); and (v) triple superphosphate (B + TSP) at 0.5% w/w (10 t ha−1), 0.003% w/w (0.06 t ha−1), and 0.003% w/w (0.06 t ha−1), respectively. Non-inoculated and B. japonicum inoculated soybeans were grown for 91 days. Soybean yield indicators and soil chemical fertility were measured. A significant increase in pH, cation exchange capacity, and P availability was observed in combined biochar treatment with compost or P sources, resulting in increased grain production. Compared to the non-inoculated plant, B. japonicum increased nodule numbers of plants grown in soils treated with B (+26), B + CM (+53), B + RP (+39), and B + TSP (+40). The combined biochar and compost amendment was superior, producing 93 nodules per plant compared with 51 in the control. Combined biochar and compost treatments most effectively minimized soil-limiting factors for soybean nodulation and grain production in weathered tropical acidic soils. Core Ideas: Biochar and compost modified edaphic properties and increased chemical fertility of the weathered acidic soil. Biochar-compost amendment improved Bradyrhizobium japonica’s symbiosis with soybean roots and increased nodules. Combining biochar with either compost or P source increased soybean production in the acidic soil. Rock phosphate and triple superphosphate had similar effects on soybean yield in the biochar-amended soil.