Ameliorating effects of biochar as a soil amendment vary with its feedstock, properties, application rate, reaction time with the soil, and soil properties. The objective of this study was to investigate the effects of rice husk biochar at different application rates on the physical-chemical properties and nutrient availability of red soil and mustard growth using pot experiment. The biochar prepared at 500℃ was applied at six rates, i.e. 0, 1, 2, 3, 5, and 10% (w/w) (C₀, C₁, C₂, C₃, C₅ and C₁₀). The results indicated that the physical-chemical properties of the red soil were significantly improved due to application of the biochar at C₃, C₅ and C₁₀. The soil bulk density was reduced by 0.11g/cm³, 0.28g/cm³ and 0.42g/cm³, respectively, compared to C₀. Soil CEC for C₃, C₅ and C₁₀ treatments increased by 52.16%, 187.02% and 214.35%, respectively, compared to C₀. Soil pH significantly increased from 4.5 for C₀ to 8.4 for C₁₀. The organic matter content, available P and available potassium of C₃, C₅ and C₁₀ treatments increased significantly, but the alkali-hydrolysable nitrogen content decreased for C₁₀ treatment compared to C₀. Application of the biochar also increased the contents of nutrients in plant leaves and plant biomass yields. Leaf tissue N concentrations increased from 1.63 to 2.44 g/kg, leaf tissue P from 2.32 to 3.09 g/kg and leaf tissue K from 47.1 to 56.7 g/kg. The mustard yields increased significantly from 108.37 g/pot for C₀ to 608.7 g/pot for C₁₀. In conclusion, application of the biochar at 5% (w/w) was appropriate for the red soil with high acidity, low fertility, and poor water holding capacity. The biochar applied at this rate can promote mustard growth and increase uptake of N, P, K nutrients by the plant.