Methane, nitrogen monoxide, and nitrous oxide fluxes in an organic soil

Field and laboratory studies were performed to estimate fluxes of the a-ace gases nitrogen monoxide (NO), nitrous oxide (N2O), and methane (CH4) in an organic soil, to determine the microbial processes involved, and to assess how soil water and nitrogen controlled flux rates. Metabolic inhibitors showed microbial nitrification to be the major NO source, regardless of the soil moisture content. Nitrification also produced N 2O, but denitrification losses of this gas from flooded, anaerobic soil were much higher. Up to 26% of nitrified N was converted to NO, but most of this (95%) was consumed microbially before it could escape across the soil surface. The NO-consuming process appeared to be co-oxidation by soil heterotrophs, not coupled to energy production. Organic matter content and CO2 production were therefore good predictors of NO oxidation rates across soil types, and NO oxidation was stimulated by manure addition.; Soil water and nitrogen had nonlinear effects on trace gas fluxes, acting on both production and consumption. Kinetic analysis showed that nitrate was a weak noncompetitive inhibitor, but ammonium a strong competitive inhibitor of soil CH4 oxidation at field fertilization rates. However, spatial and temporal factors complicated fertilization effects on CH4 oxidation in situ. Ammonium was immobilized in surface soil and rapidly nitrified, limiting its inhibitory effect on CH 4 oxidation. Fertilizer N stimulated nitrification and denitrification and therefore gaseous N-oxide production, but other, unexpected fertilizer effects were also observed. Ammonium fertilizer decreased NO oxidation rates. Nitrate and other salts stimulated NO and N2O losses during nitrification, an effect apparently related to soil nitrite accumulation.; The controls exerted on trace gas fluxes by soil water were mediated primarily through diffusion rates. Oxygen diffusion controlled the balance of anaerobic (methanogenesis and denitrification) versus aerobic (CH 4 oxidation and nitrification) processes. Soil moisture content also controlled the diffusion rate of atmospheric CH4 to soil methanotrophs, and the escape of gaseous N-oxides from production sites across the soil surface.