Landscape-scale estimation of denitrification rates and nitrous oxide to dinitrogen ratio at Georgia and Pennsylvania LTAR sites

Abstract:

Denitrification results in a significant loss of plant-available nitrogen from agricultural systems and contributes to climate change, due to the emissions of both the potent greenhouse gas nitrous oxide (N₂O) and environmentally benign dinitrogen (N₂). However total quantities of the gases emitted and the ratio of N₂:N₂O are often not clearly understood, because N₂ emissions cannot be directly measured in the field because of the high background level of N₂ in the atmosphere. While variability in soil conditions across landscapes, especially water content and aeration, is believed to greatly impact both total denitrification rates and N₂:N₂O, the measurement limitations have prevented a clear understanding of landscape-scale emissions of denitrification products. The Cary Institute has developed an approach where soil core are maintained in a sealed system with an N₂-free airstream, allowing emitted N₂ and N₂O emissions to be measured without interference from atmospheric N₂. Emissions of the gases are measured under a range of oxygen concentrations and soil water contents. Laboratory responses can then be correlated with measured field conditions at the sampling points and resulting emission estimates extrapolated to the field-scale. Measurements are currently being conducted on peanut/cotton rotations, dairy forage rotations (silage corn/alfalfa), and bioenergy crops (switchgrass and miscanthus) at Long Term Agricultural Research (LTAR) sites at Tifton, GA and University Park, PA.