Soil Nitric Oxide Emissions from Nitrification and Denitrification

A silty loam soil treated with 1-allyl-2-thiourea as an inhibitor of autotrophic nitrification, and sulfide as an inhibitor of nitric oxide reductase in respiratory denitrification, was studied to evaluate the respective contribution of these two microbial processes to the nitric oxide (NO) flux from the soil. Soil samples were either unamended or amended with ammoniated fertilizer or biosolids from a wastewater treatment plant at an application rate of 100 lb-nitrogen/acre. Water-filled pore space and temperature were maintained within respective ranges of 22 ± 2% and 22 ± 1°C. NO fluxes from unamended, chemically fertilized, and biosolids-amended soil samples increase in that order, and autotrophic nitrification accounts for 80, 84, and 92% of the NO flux, respectively. The suggested Jousset-Peirce index (psi), which shows the contribution of respiratory denitrification with respect to heterotrophic nitrification and chemodenitrification, decreases by a factor of 3.3 and 5.6 from unamended to chemically fertilized soil samples and from unamended to biosolids-amended soil samples, respectively. An ancillary finding reveals the dramatic sensitivity of denitrification to the presence of sulfide.