Nitrous Oxide Emissions and Carbon Sequestration in Turfgrass: Effects of Irrigation and Nitrogen Fertilization (Year 1)

In this study, annual nitrous oxide (N2O) emissions were greatest in urea and least in untreated (no N) among treatments. Differences were negligible due to irrigation treatment. Irrigation levels may be decreased further in the final year to induce slight stress on the low irrigation treatment. All fertilizer treatments maintained acceptable quality, however the controlled-release fertilizer resulted in more consistent visual quality ratings compared to urea and untreated. Urea fertilizer had higher peak fluxes after fertilization and overall annual emissions than polymer-coated N-fertilizer. Thus, controlled released N fertilizers, such as polymer-coated urea, in turfgrass systems could potentially help mitigate N2O emissions.

Ross C. Braun, Dale J. Bremer, and Jack D. Fry Summary.In this study, annual nitrous oxide (N 2 O) emissions were greatest in urea and least in untreated (no N) among treatments.Differences were negligible due to irrigation treatment.Irrigation levels may be decreased further in the final year to induce slight stress on the low irrigation treatment.All fertilizer treatments main-tained acceptable quality, however the controlled-release fertilizer resulted in more consistent visual quality ratings compared to urea and untreated.Urea fertilizer had higher peak fluxes after fertilization and overall annual emissions than polymer-coat-ed N-fertilizer.Thus, controlled released N fertilizers, such as polymer-coated urea, in turfgrass systems could potentially help mitigate N 2 O emissions.
Rationale.Nitrous oxide (N 2 O) is an important greenhouse gas implicated in global climate change.Turfgrass is typically fertilized with nitrogen (N) and irrigated while having the potential to emit N 2 O at similar rates as other agricultural soils and thus, play an important role in atmospheric N 2 O budgets.The development of manage-ment practices, such as slow-release N fertilizer and/or deficit irrigation, may miti-gate N 2 O emissions.
Objectives.To quantify the magnitude and patterns of N 2 O emissions in turfgrass and determine how irrigation and N fertilization may be managed to reduce N 2 O emissions.
Study Description.The study is being conducted under an automated rainout shelter near Manhattan, KS (Figure 1).By shielding rainfall from turfgrass, research-ers can control the amount of water applied to plots.'Meyer' zoysiagrass was sodded June 4, 2013, and maintained at a 1-inch mowing height.During the summer (June -August) of 2014 and 2015, two irrigation treatments were applied including medium (72% reference evapotranspiration [ET o ] replacement) and medium-low (54% ET o replacement) (Figure 2).Three N-fertilization treatments included urea and polymer-coated N, both at 2 lb/1000 ft 2 , and a control with no N applied.Because little drought stress was observed in the 54% ET o treatment in 2014, irrigation amounts in both treatments were reduced, specifically from 72 to 68% ET o replacement in the medium and from 54 to 33% ET o replacement in the medium-low treatment in 2015.
Nitrous oxide emissions were measured with static chambers placed over the turfgrass surface and then analyzed with gas chromatography (Figure 3).Measurements began on October 29, 2014 (DOY 302) and continued weekly-to-monthly until October 5, 2015 (DOY 278), concluding the first year of data.Irrigation and fertilization treatments will be repeated in 2016 for a second year of measurements through October 30, 2016.Carbon sequestration in the upper soil profile (0 to 12 inches) will be measured by sampling soil C at the end of the 3-year study; initial soil C was measured on August 28 2013.Ancillary measurements included soil moisture, temperature, nitrate, ammonium, visual quality, mowing frequency, and percent green cover using digital image analysis.
Results.Cumulative annual emissions of N 2 O were significantly greatest in urea and least in untreated (no N) zoysiagrass among treatments.Annual emissions were 1.82, 2.09, 2.77 kg N 2 O-N ha -1 yr -1 for untreated, polymer-coated urea, and urea, respectively (Figure 4).Annual emissions were similar to those reported in other turfgrass studies, which ranged from 1 to 3.85 kg N 2 O-N ha -1 yr -1 across various turfgrass species and under different fertilization regimes (Bremer, 2006;Kaye et al., 2004;Lewis and Bremer, 2013).The percentage of applied N fertilizer emitted as N 2 O in this study was 2.2% from poly and 2.9% from urea fertilizer.The highest fluxes and majority of emissions occurred in the summer because of the fertilization events and, presumably, higher soil temperatures.There were spikes after applications of urea fertilizer, but increases were much smaller with application of controlled release (poly) N fertilizer.Both urea and controlled release N fertilizer treatments resulted in higher turfgrass quality than the control; however, all three treatments maintained acceptable turfgrass quality during deficit irrigation treatments (Figure 5).).Any points below yellow horizontal dashed line at rating of 6 would be below acceptable quality.Means followed by the same letter on a date are not significantly different according to Fisher's protected least significant difference test (P ≤ 0.05).
research reports online at: http://newprairiepress.org/kaesrr July 2016 Nitrous Oxide Emissions and Carbon Sequestration in Turfgrass: Effects of Irrigation and Nitrogen Fertilization (Year 1)

Figure 1 .
Figure 1.Automated rainout shelter moving across plots activated by 0.01 inch of rain.

Figure 2 .
Figure 2. Plots received precise irrigation amounts based on daily ET during summer period.

Figure 3 .
Figure 3. Close-up of one of twelve static chambers used for sampling N 2 O.

Figure 4 .
Figure 4. Cumulative fluxes of N 2 O-N from plots treated with urea, polymer-coated urea, and untreated.Vertical dashed lines represent fertilization dates.

Figure 5 .
Figure5.Visual ratings (9 = best quality) of 'Meyer' zoysiagrass prior to and following the summer period under the automated rainout shelter.Plots were fertilized with urea and poly on DOY 153 (2 June) and only urea fertilizer again on DOY 197 (July 16).Any points below yellow horizontal dashed line at rating of 6 would be below acceptable quality.Means followed by the same letter on a date are not significantly different according to Fisher's protected least significant difference test (P ≤ 0.05).