What is more important for enhancing nutrient bioavailability with biochar application into a sandy soil: Direct or indirect mechanism?

► Direct or indirect mechanisms accounting for the enhancing nutrient bioavailability with biochar application are evaluated in the present study. ► Direct release form biochar is important for cations (e.g. K, Ca, Na, Mg) bioavailability with biochar addition. ► The SEM-EDX analysis indicated that mineral sorption on biochar surface influenced P sorption. ► The direct P release altered soil pH and changes of Fe, Al oxides and accumulation of Ca controlled P bioavailability with biochar application. ► The long term effect of P bioavailability with biochar application deserves further attention.