Coffee‐husk biochar application increased AMF root colonization, P accumulation, N2 fixation, and yield of soybean grown in a tropical Nitisol, southwest Ethiopia
Low soil fertility and soil acidity are among the major bottlenecks that limit agricultural productivity in the humid tropics. Soil management systems that enhance soil fertility and biological cycling of nutrients are crucial to sustain soil productivity. This study was, therefore, conducted to determine the effects of coffee‐husk biochar (0, 2.7, 5.4, and 16.2 g biochar kg−1 soil), rhizobium inoculation (with and without), and P fertilizer application (0 and 9 mg P kg−1 soil) on arbuscular mycorrhyzal fungi (AMF) root colonization, yield, P accumulation, and N2 fixation of soybean [Glycine max (L.) Merrill cv. Clark 63‐K] grown in a tropical Nitisol in Ethiopia. ANOVA showed that integrated application of biochar and P fertilizer significantly improved soil chemical properties, P accumulation, and seed yield. Compared to the seed yield of the control (without inoculation, P, and biochar), inoculation, together with 9 and 16.2 g biochar kg−1 soil gave more than two‐fold increment of seed yield and the highest total P accumulation (4.5 g plant−1). However, the highest AMF root colonization (80%) was obtained at 16.2 g biochar kg−1 soil without P and declined with application of 9 mg P kg−1 soil. The highest total N content (4.2 g plant−1) and N2 fixed (4.6 g plant−1) were obtained with inoculation, 9 mg P kg−1, and 16.2 g biochar kg−1 soil. However, the highest %N derived from the atmosphere (%Ndfa) (> 98%) did not significantly change between 5.4 and 16.2 g kg−1 soil biochar treatments at each level of inoculation and P addition. The improved soil chemical properties, seed yield, P accumulation and N2 fixation through combined use of biochar and P fertilizer suggest the importance of integrated use of biochar with P fertilizer to ensure that soybean crops are adequately supplied with P for nodulation and N2‐fixation in tropical acid soils for sustainable soybean production in the long term.