NITRIC-OXIDE AND NITROUS-OXIDE PRODUCTION FROM SOIL - WATER AND OXYGEN EFFECTS

This study was designed to determine the effects of water and O2 on the speciation of denitrification gases (NO and N2O). Nitric oxide was found to be the principal end product from soil incubated under low-moisture conditions, whereas the relative amount of N2O increased under wetter moisture regimes. The total amount of NO plus N2O produced increased with increasing water content for the Brookston clay loam (fine-loamy, mixed, mesic Typic Argiaguoll), whereas it peaked at 150 g kg-1 (15%) water content with the Fox sandy loam (fine-loamy over sandy or sandy or sandy-skeletal, mixed, mesic, Typic Hapludalf). The decrease in NO plus N2O at higher water contents was probably the result of the subsequent reduction of N2O to N2 in the Fox sandy loam soil. The residence time of the denitrification gases in the soil increased with increasing water content, hence facilitating the subsequent conversions of NO to N2O and N2. The thickness of the water film surrounding the microbes affected both the diffusion of O2 through the water and into the microbes as well as the diffusion of denitrification gases (NO, N2O, and N2) from the microbes into the atmosphere. In the sandy loam soil, O2 content and soil water affected both the amount and species of evolved denitrification gases. Oxygen was more effective in decreasing NO production at lower than at higher water contents.