Effect of cashew (Anacardium occidentale) biochar on soil chemical properties and agronomy of soybean (Glycine max L. merril)

The experiments were conducted at the Teaching and Research Farm, Faculty of Agriculture, Nasarawa State University, Keffi, Shabu-Lafia during the 2018 and 2019 cropping seasons to evaluate the effects of different levels of biochar on soil properties, growth and yield of soybean. The experiments were laid in Randomized Complete Block Design (RCBD) with three replications. Biochar at the rates of 0, 4, 8 and 12 tons/ha were incorporated into the ridges of soybean at planting. The results showed that soil organic matter, organic carbon, total nitrogen, potassium, available phosphorus, calcium, sodium and base saturation decreased with soil layers. Soil pH (4.67 and 4.69), magnesium (1.52 and 1.62 cmol/kg), exchangeable acidity (0.67 and 0.75 cmol/kg) and cation exchange capacity (5.18 and 5.23 cmol/kg) increased with soil depth. Biochar at the rate of 12 tons/ha showed consistently the highest values of soil properties over other rates. The results also showed that biochar at the rate of 8 tons/ha recorded significantly (p<0.05) the tallest soybean plant height at 8 weeks (40.4 and 42.7 cm) and 10 (43. 0 and 49.2 cm) after planting in 2018 and 2019 cropping seasons respectively while the highest number of branches (4.5 and 4.5) was recorded in 2018 cropping season only. The results further revealed that biochar at the rate of 8 tons/ha recorded the highest weight per 100 seed (16.9 and 14.9 g) and seed yield (1304.0 and 1316.7 kg) per hectare in both cropping seasons. From the results of this study, it can be concluded that biochar at the rates of 12 and 8 tons/ha positively influenced soil and soybean plant parameters evaluated. Therefore, biochar at the rate of 8 tons/ha is considered as the optimum rate for sustainable soybean production in the study area.