Effects of biochar and nitrogen fertilizer on soil physicochemical properties, nitrogen use efficiency and upland rice ( Oryza sativa) yield grown on an Alfisol in Southwestern Nigeria

Purpose Biochar and inorganic fertilizer when co-applied have been reported to increase crop yield and enhance soil fertility. However, studies on this complementary effect on soil properties and rain-fed upland rice performance in Sub-Saharan Africa are still scanty. Methods Field factorial studies conducted over 2 years was set up to investigate the interactions between rice husk biochar and inorganic nitrogen (N) fertilizer on a sandy clay loam Alfisol. A two-factor (4 × 4) in RCBD where rice husk biochar was incorporated at four doses, 0, 3, 6, and 12 t/ha −1 , inorganic N fertilizer (urea) at four rates, 0, 30, 60 and 90 N kg/ha −1 , and their combinations was adopted. Results Results showed that combination of biochar and N fertilizer exerted significant ( P > 0.05) interactive effect on rice harvest index, grain and straw yield and N-use efficiency. Interaction between biochar and N fertilizer increased agronomic efficiency by 140% and grain nutrient recovery by 191% over 2 years. Combination of biochar and N fertilizer reduced soil bulk density, increased water holding capacity and soil chemical status such as pH, N, P, K, Corg, Ca, ECEC and base saturation, all within the top 10 cm depth of the soil. Conclusions Overall, the results established that rice husk biochar can be used as a soil conditioner to enhance upland rice yield on an Alfisol. The combined dose of 3–6 t/ha −1 biochar and 30 kg/ha −1 of N fertilizer is thus recommended for upland rice farmers in the study area.