Effects of SO2 and NO2 on Nitrification in Soil

Abstract Nitrification in Lima loam, pH 7.2, was not affected by continuous exposure of the soil to 0.5 ppm of SO2 or to brief exposures to higher SO2 levels. Such treatment did not increase the levels of soluble K, Mg, Ca, Mn, Fe, and Al. Intermittent exposure of Hudson silty clay loam, pH 5.0, to SO2 reduced the rate of nitrate formation. Continuous fumigation of the acid soil with 10 ppm of SO2 decreased the rate of nitrification, and continuous fumigation with as little as 1.0 ppm increased the quantity of soluble Mn and Fe. Continuous fumigation of Lima loam with 5 ppm NO2 inhibited the rate of ammonium disappearance, led to greater rates of nitrate formation, and resulted in nitrite accumulation. Nitrite at a level of 30 µg N/g of soil also reduced the rate of ammonium disappearance. The results demonstrate that nitrification in certain soils could be inhibited in areas acutely polluted with SO2 and NO2.