Pennsylvania Turfgrass – Max Schlossberg, Ph.D., and Nate Leiby, MS Graduate Student (BS TURF ’18), Center for Turfgrass Science, The Pennsylvania State University
Well, to the satisfaction of article browsers, more easily and often than most realize. But the best answer remains; ‘it depends.’ Turfgrass requires greater quantities of N than any other mineral nutrient, and N sufficiency is promptly supported, or N deficiency is promptly reversed, by application of soluble N fertilizer(s) containing urea, NH4, and/or NO3.
There are four N-rich gases that arise from N fertilizers; dinitrogen (N2), nitrous oxide (N2O), nitric oxide (NO), and ammonia (NH3). In fact, every plant-available N-form (urea, NO3, NH4), or intermediate (NO2), serves as soil feedstock for at least one of the above gases. Evolution of these gases from originally plant available N-forms is undesirable. But once emitted, N2 and NO are the most innocuous.
N2O Emissions
Agricultural soil is the greatest source of anthropogenic N2O emission on earth, accounting for nearly 70% of annual totals. Industry and combustion (fossil/other fuels) are the next greatest contributors. Nitrous oxide is a tenacious greenhouse gas that reduces protective ozone and claims very few opportunities for transformation or sequestration.
Incomplete soil denitrification of nitrate
Denitrification is the microbiologically mediated reduction of NO2 and/or NO3 following incorporation of soluble N fertilizer into warm, saturated soil. Under such conditions, the nitrate fraction of a soluble fertilizer application relates directly to early denitrification severity (Figure 1).  Turfgrass systems maintained on highly porous rootzones underlain by functional drainage are unlikely to lose N via denitrification. While systems maintained on native soils having high organic matter content and/or water-retention are more likely, especially in mid- to late-summer.
This is the part of the article where we considered introducing complete vs. incomplete denitrification, and describing the more benign product (N2) of the former and all the a/biotic factors identified by research as comparative facilitators of it. But in the context of modern cultural techniques developed and/or adopted by the most effective turfgrass managers worldwide, it’s a non-starter. No turfgrass manager should maximize water-filled pore space in efforts toward favoring the N2 denitrification product.
Incomplete soil nitrification of ammonium
Nitrification is the microbiologically mediated oxidation of soil ammonium (NH4) and a notoriously prolific generator of soil acidity. Nitrification is a two-stage process, each depending on a separate genus of chemolithoautrophic microbes. Regrettably the second stage, oxidation of NO2 to NO3, is often limited by success of the first; oxidation of NH4 to NO2. Which constitutes feedback inhibition, but by no means incites greater risk to the product of the first stage, right? Wrong. Local oxygen depletion incites electron acceptance by the freshly oxidized NO2, catastrophically reducing it to NO or N2O. Most readers will recognize ‘…fate, it seems, is not without a sense of irony…’ as a quote by Morpheus in The Matrix (1999). But how many know Morpheus was referring to nitrogen? Hmmmm, Danny?
 
NH3 Emissions
Most atmospheric ammonia in North America originates from livestock operations and fertilizer application. In the presence of nitrate or sulfate, NH3 constitutes the most significant and influential precursor to smog formation, i.e., particulate matter <2.5 micrometers in diameter (PM2.5). Elevated PM2.5 levels are monitored in numerous non-attainment regions along the US Eastern Seaboard and are statistically correlated to adverse health effects. Furthermore, ammonia deposition to surfaces, the primary atmospheric removal mechanism, is considered a significant threat to terrestrial and aquatic ecosyst...