Estimating Denitrification Rates in Soil from Field Nitrous Oxide Emission Monitoring: A Meta-Analysis from Agricultural Settings.

Denitrification is a significant component of the agricultural soil nitrogen balance and can result in yield loss in some cases, particularly under waterlogged conditions. Rates of denitrification vary greatly over time and space due to a large number of factors that affect them, including nitrate concentrations, dissolved oxygen, soil water, organic carbon, pH and temperature. Reliable field estimates of denitrification are relatively scarce, owing to high spatio-temporal variability and the expense of achieving a precise field measurement when it occurs. In contrast, measurements of nitrous oxide (N₂O) fluxes are more abundant and may be useful for inferring denitrification rates. This study analyzed 405 site-years of data with co-located cumulative N₂O and N₂ observations from 297 previous studies in an attempt to assess how reliably denitrification rates can be estimated when only N₂O emissions data is present. The study also explored whether statistical modeling using site characteristics and other auxiliary information can help constrain the relationship. Results suggest that using N₂O emissions data to estimate denitrification, without local training data, can constrain denitrification rates to within approximately one order of magnitude, but not much better. The relationship was applied to a database of agricultural N₂O measurements in order to estimate cumulative denitrification losses. Future work could apply a similar methodology to unaggregated measurements N₂ and N₂O in an attempt to better quantify the factors driving changes in the ratio of N₂O to denitrification.