Effect of biochar amendment on soil enzymatic activities, carboxylate secretions and upland rice performance in a sandy clay loam Alfisol of Southwest Nigeria

Field studies were conducted over two years to determine changes in soil biochemical properties and rain-fed upland rice yield as influenced by biochar amendment. Treatments consisted of incorporation of rice husk biochar at different rates (B-1 = 0, B-2 = 3 t ha(-1), B 3 = 6 t ha(-1), and B-4 = 12 t ha(-1)). Soil enzymes viz invertase, alkaline phosphatase, urease, and catalase, were significantly (P < 0.05) higher under the highest application rate of biochar (12 t ha(-1)). Higher rates of enzyme activities were recorded within the top soil layer (0-0.1 m). Soil organic carbon, available nitrogen, Bray 1 phosphorus, total nitrogen and soil moisture content were significantly (P. 0.05) increased upon the application of biochar at a rate of 12 t ha(-1) in the top 0-0.1 m layer. Similarly, application of biochar at 12 t ha(-1) significantly (P < 0.05) increased rice rhizospheric carboxylate secretions in the top 0-0.1 m layer. Carboxylate exudates were increased in the order of citrate. malate. acetate. oxalate, while increasing soil layer reduced carboxylate secretions. In general, biochar application improved soil enzyme activities, rhizospheric secretions involved in C, N, P cycling and nutrient solubilization which influence soil nutrient retention, availability and crop performance. Biochar application at 3-6 t ha(-1) significantly (P < 0.05) increased rice grain yield by 46% and straw yield by 47%. (C) 2019 The Author. Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative.