Sequence of Products Formed During Denitrification in Some Diverse Western Soils

Abstract

Abstract The sequential products of anaerobic denitrification were determined on seven Western soils (four alkaline, two acid, and one neutral) by soil and gas analysis. The soils with 1% alfalfa and added KNO 3 were incubated at moistures slightly greater than field capacity and with an atmosphere of He. The soils and gases were periodically analyzed and balance sheets prepared. The sequence of NO 3 ‐ → NO 2 ‐ → N 2 O → N 2 operated in all soils. The N 2 O and N 2 were determined on a gas chromatograph. The rates of nitrogen interchanges and maximal amounts of nitrite, N 2 O, and N 2 were determined. From this data it was postulated that the rate‐limiting process for denitrification in acid soils is the reduction of nitrate, while in alkaline soils it is the reduction of nitrite. The reduction of N 2 O was rapid in all instances. The total time for complete reduction of 300 ppm. N as nitrate to N 2 at 30°C. varied only from 28 to 96 hours for the 7 soils. Lowering the temperature to 25° or 20°C. influenced all rates for 3 alkaline soils and resulted in a twofold increase in denitrification time for the 10°C. drop. Decreases in initial concentration of added KNO 3 to 150, 75, and 37.5 ppm. did not change the overall rate of dentrification. There was, however, a marked reduction in the maximal amounts of N 2 O found in the gaseous atmosphere when the initial KNO 3 concentration was reduced.