Integration of Biochar with Chemical Fertilizers Improves the Economic Yield, Quality of Holy Basil (Ocimum sanctum L.) and Soil Health

An attempt was made to recycle distillation waste biomass (DWB) of holy basil (Ocimum sanctum Linn) for cultivation of the same crop. The DWB-derived BC was co-applied with chemical fertilizer (CF) to improve the effectiveness of CF in holy basil cultivation. A pot experiment was conducted to evaluate the co-application of DWB derived BC with and without CF on plant growth, yield and soil nutrient availability. The application of BC (5 t ha^− 1) with a 100% recommended dose of CF resulted in the highest fresh herbage (320.5 g plant^− 1), dry herbage (95.0 g plant^− 1) and essential oil yields (0.8 g plant^− 1). BC (5 t ha^− 1) treated with 50% of the recommended dose of CF exhibited the highest total phenol (30.13 mg GAE g^− 1) and total flavonoid (66.63 mg QE g^− 1) contents in dry leaf extract. Significantly greater antioxidant activity was recorded in the treatment receiving co-application of BC with the recommended dose of CF than in the treatment receiving only BC and the recommended dose of CF. Compared with the control and CF treatments, the BC treatment significantly improved the cation exchange capacity and organic carbon in the soil. Furthermore, the co-application of BC with 100% of the recommended dose of CF was the most efficient treatment for improving the soil properties and nutrient availability. Hence, the integration of BC with the recommended dose of CF improved nutrient availability for a longer time, resulting in better economic yield and quality of the medicinal herbs.