Soil Gas Diffusivity Controls N 2 O and N 2 Emissions and their Ratio

Abstract

© 2016 Soil Science Society of America. Knowledge of soil biological and physical interactions with respect to N2O and N2fluxes is essential to ensure that agricultural land management is environmentally and economically sustainable. This study determined how varying soil relative gas diffusivity (Dp/Do) affected cumulative N2O and N2fluxes under simulated ruminant urinary-N deposition. Using repacked soil cores, the effects of varying soil bulk density (ρb; from 1.1 to 1.5 Mg m-3) and soil matric potential (φ; -10 to -0.2 kPa) on Dp/Dowere examined in a Templeton silt loam soil (Udic Haplustept) following the application of simulated ruminant urine (700 kg N ha-1). Fluxes of N2O and N2, soil inorganic N, pH, and dissolved organic C (DOC) dynamics were monitored over 35 d. Soil Dp/Dodeclined as soil bulk density and soil moisture increased. Soil N2O emissions increased exponentially as Dp/Dodecreased until Dp/Doequaled 0.005, where upon N2O fluxes decreased rapidly due to complete denitrification, such that N2fluxes reached a maximum of 60% of N applied at a Dp/Doof <0.005. Regression analysis showed that Dp/Dowas better able to explain the variation in N2O and N2fluxes than water-filled pore space (WFPS) because it accounted for the interaction of soil rb and y. This study demonstrates that soil Dp/Docan explain cumulative N2O and N2emissions from agricultural soils. Under grazed pasture systems, potential exists to reduce the emissions of the greenhouse gas N2O and significant economic losses of N as N2if soil management and irrigation can be maintained to maximize Dp/Do.