Sequential Products of Anaerobic Denitrification in Calcareous and Noncalcareous Soils by Use of the Gas Chromatograph

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 KNO3 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 NO3-->NO2-->N2O-->N2 operated in all soils. The rates of nitrogen interchanges and maximal amounts of nitrate, N2O2 and N2 were determined. From this data it was postulated that the rate-limiting process for denitrification in acid soils is the reduction of nitrate. The reduction of N2O was rapid in all instances. The total time for complete reduction of 300 ppm. N as nitrate to N2 at 30 degrees celsius varied only from 28 to 96 hours for the 7 soils. Lowering the temperature to 25 degrees to 20 degrees celsius influenced all rates for 3 alkaline soils and resulted in a twofold increase in denitrification time for the 10 degee celsius drop. Decreases in initial concentration of added KNO3 to 150, 75, and 37.5 ppm did not change the overall rate of denitrification. There was, however, a marked reduction in the maximal amounts of N2O found in the gaseous atmosphere when the initial KNO3 concentration was reduced.