Nitrous oxide production in grassland soils: assessing the contribution of nitrifier denitrification

Abstract

Nitrifier denitrification is the reduction of NO 2 − to N 2 by nitrifiers. It leads to the production of the greenhouse gas nitrous oxide (N 2O) as an intermediate and possible end product. It is not known how important nitrifier denitrification is for the production of N 2O in soils. We explored N 2O production by nitrifier denitrification in relation to other N 2O producing processes such as nitrification and denitrification under different soil conditions. The influence of aeration of the soil, different N sources, and pH were tested in four experiments. To differentiate between sources of N 2O, an incubation method with inhibitors was used [Biol. Fertil. Soils 22 (1996) 331]. Sets of four incubations included controls without addition of inhibitors, incubations with addition of small concentrations of C 2H 2 (0.01–0.1 kPa), large concentrations of O 2 (100 kPa), or a combination of C 2H 2 and O 2. The results indicate that the availability of NO 2 − stimulated the apparent N 2O production by nitrifier denitrification. A decreasing O 2 content increased the total N 2O production, but decreased N 2O production by nitrifier denitrification. No significant effect of pH could be found. The study revealed problems concerning the use of the inhibitors C 2H 2 and O 2. Almost one-third of all incubations with inhibitors produced more N 2O than the controls. Possible reasons for the problems are discussed. The inhibitors C 2H 2 and O 2 need to be tested thoroughly for their effects on different N 2O producing processes before further application.