Influence of Tithonia diversifolia biochar on selected soil physicochemical properties, leaf nutrient concentrations and broccoli growth

A screen house experiment was conducted to evaluate the effects of Tithonia diversifolia biochar on selected soil physicochemical properties. The study included five treatments with Tithonia diversifolia biochar applied at rates of 0, 10, 20, 30, and 40 t ha^{- 1}, arranged in a completely randomised design with three replicates. Surface soil (0-15 cm depth) from the Iwo soil series (sandy loam) was collected from the Teaching and Research Farm of Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. Each 10 kg soil sample was thoroughly mixed with the respective biochar rate and maintained at field moisture capacity for four weeks in the screen house before sowing broccoli seeds. Soil samples were analyzed for particle size distribution, bulk density, porosity, moisture content, pH, organic carbon, total nitrogen, available phosphorus, exchangeable potassium, calcium, and magnesium. Agronomic parameters measured included broccoli height, number of leaves, leaf area, stem girth, and fresh weight of broccoli biomass. Leaf nutrient concentrations of broccoli were also determined. Data were subjected to analysis of variance, and significant means were separated using Duncan's multiple range test at p = 0.05. Results indicated that biochar-amended plots significantly improved soil physicochemical properties compared to the control. Biochar application also significantly increased broccoli height, number of leaves, leaf area, stem girth, leaf nutrient concentrations, and fresh weight of broccoli biomass. The application of tithonia biochar at rates of 10, 20, 30, and 40 t ha^{- 1} increased the fresh weight of broccoli biomass by 13%, 38%, 26%, and 23%, respectively, compared to the control. The application rate of 20 t ha^{- 1} was found to be the most beneficial, enhancing leaf nutrient concentrations and growth parameters. This study recommends the use of Tithonia diversifolia biochar as a soil amendment to improve soil quality of sandy loam and enhance broccoli productivity and quality.