Sorption of diuron by wheat straw, its ash arising from burning, ashbased black carbon and ashamended soil was studied. The sorption of diuron on ashfree soil and wheat straw occurred via partitioning behavior with log Koc values of 2.33 and 2.07, respectively. The ash adsorbed 9.7 times more diuron than wheat straw when leaving them unburned in the field. Black carbon was 7~45 times more effective than ash and ashamended soil was 3 times more effective than ashfree soil in sorbing diuron over the range of the experimental concentrations. Aging of the ash for 1 year in the soil did not influence ash sorptivity. The biodegradation of diuron in the soil in the presence and absence of the ash was fitted to firstorder kinetics. The rate constant reduced by 45% and the half life increased by 66% when 0.5% ash was amended to the soil.