Simultaneous enhancement of carbon sequestration and crop productivity through excessive biochar application in root vegetable (Raphanus raphanistrum L.) cultivation

Abstract Biochar, a soil amendment, is gaining attention for its potential in enhancing carbon sequestration and improving soil fertility. The conventional application rate for biochar is 2 t ha − 1 ; however, achieving maximum carbon sequestration requires higher inputs, necessitating investigation into optimal application methods to sustain crop productivity. This study evaluated the impact of a 10-times higher biochar application (20 t ha − 1 ) on root vegetable ( Raphanus raphanistrum L.) cultivation and soil carbon sequestration, focusing on two methods broadcasting (O-BC) and band application (B-BC). The O-BC treatment improved root growth in Raphanus raphanistrum L. by increasing biomass and enhancing the uptake of P and K, thereby boosting productivity and nutrient assimilation. This demonstrates the key functions of P in energy transfer and root development, and K in osmoregulation and carbohydrate transport, which are crucial for root growth and development. The O-BC treatment offers the most balanced and robust enhancement of Raphanus raphanistrum L. growth and nutrient acquisition across plant parts. In contrast, the B-BC treatment provided only modest benefits, likely due to localized, high concentrations of biochar creating temporary imbalances in soil physicochemical properties (e.g., pH, EC) that limited optimal root development. The O-BC treatment resulted in greater biomass accumulation and enhanced P, K uptake in root tissue, leading to the highest yield (4.67 t ha⁻¹), followed by B-BC (4.51 t ha⁻¹) and the control treatment (4.28 t ha⁻¹). Biochar application at 20 t ha⁻¹ enhanced soil carbon sequestration, reaching 43.75 t ha⁻¹, which is 10 times the conventional amount. These findings demonstrate that a high amount of biochar applications with the optimal application method, can effectively overcome the potential risks of high-rate application and improve root vegetable productivity while simultaneously contributing to long-term climate mitigation through increased carbon sequestration.