Marked changes in herbicide sorption-desorption upon ageing of biochars in soil

► Fresh biochars undergo rapid ageing process with contact time in soil. ► Fresh biochars in soils exhibited high sorption and non-singular sorption-desorption isotherms. ► Aged biochars in soil showed singular sorption-desorption isotherms for atrazine. ► At 10 t ha−1, biochars in a Ferrosol lost their high sorption capacity in three years. ► Herbicide application rates may need to be frequently adjusted after biochar addition to soils.