SUMMARYThe formation of CH3ONO in 11 soils treated with HNO2or NaNO2in a closed system, was studied by measuring the concentration in the gas space above the soil and by absorbing CH3ONO in HI. The gaseous concentration of CH3ONO increased and then decreased following additions of HNO2or NaNO2, and the production of CH3ONO increased with increasing concentrations of HNO2or NaNO2added to soils.The amounts of CH3ONO trapped in HI were 13.5 to 20.4 times higher than those determined by integrating under the net production curves. The evolved CH3ONO amounted to 0.4 to 3.5% of added NO2−, and 4.2 to 50% of the gaseous forms of N absorbed by acidic KMnO4solution. The CH3ONO evolved from soils was positively correlated with the methoxy content of the soils, and inversely related to soil pH, with negligible amounts being evolved from alkaline soils. The results show that CH3ONO is a product of NO2−decomposition in soils, and indicate that small concentrations of the gas may be produced in N–fertilized soils in which NO2−accu