Marty B. Rhoades

Daily, monthly, seasonal, and annual ammonia emissions from Southern High Plains cattle feedyards.

Ammonia emitted from beef cattle feedyards adds excess reactive N to the environment, contributes to degraded air quality as a precursor to secondary particulate matter, and represents a significant loss of N from beef cattle feedyards. We used open path laser spectroscopy and an inverse dispersion model to quantify daily, monthly, seasonal, and annual NH emissions during 2 yr from two commercial cattle feedyards in the Panhandle High Plains of Texas. Annual patterns of NH fluxes correlated with air temperature, with the greatest fluxes (>100 kg ha d) during the summer and the lowest fluxes (<15 kg ha d) during the winter. Mean monthly per capita emission rate (PCER) of NH-N at one feedyard ranged from 31 g NH-N head d (January) to 207 g NH-N head d (October), when increased dietary crude protein from wet distillers grains elevated emissions. Ammonia N emissions at the other feedyard ranged from 36 g NH-N head d (January) to 121 g NH-N head d (September). Monthly fractional NH-N loss ranged from a low of 19 to 24% to a high of 80 to 85% of fed N at the two feedyards. Seasonal PCER at the two feedyards averaged 60 to 71 g NH-N head d during winter and 103 to 158 g NH-N head d during summer. Annually, PCER was 115 and 80 g NH-N head d at the two feedyards, which represented 59 and 52% of N fed to the cattle. Detailed studies are needed to determine the effect of management and environmental variables such as diet, temperature, precipitation, and manure water content on NH emissions.

EFFECT OF WIND TUNNEL AIR VELOCITY ON VOC FLUX FROM STANDARD SOLUTIONS AND CAFO MANURE/WASTEWATER

Researchers and practitioners have used wind tunnels and flux chambers to quantify the flux of volatile organic compounds (VOCs), ammonia, and hydrogen sulfide and estimate emission factors from animal feeding operations (AFOs) without accounting for effects of air velocity or sweep air flow rate. Laboratory experiments were conducted using a small rectangular wind tunnel (30.5 cm length, 15.2 cm width, 5.1 cm height). The objectives of the research were to (1) quantify the effect of wind velocity on VOC flux rates, (2) compare and contrast a two-film model with different wind speed corrections, and (3) provide insight into methods for either selecting appropriate wind tunnel velocities or conducting post-sampling wind velocity corrections to simulate field emission rates. Fluxes were measured on standard solutions and on manure/wastewater from beef cattle and dairy AFOs. Volumetric air exchange rates were varied between 0.6 and 44 exchanges per minute, corresponding to calculated longitudinal air velocities of 0.003 to 0.23 m s-1. Exhaust air was sampled using stainless steel sorbent tubes and analyzed for eleven volatile organic compounds comprised of seven volatile fatty acids (VFAs: acetic, propionic, isobutyric, butyric, isovaleric, valeric, and hexanoic) and four heavier molecular weight semivolatile organic compounds (sVOCs: phenol, p-cresol, indole, and skatole) using gas chromatography/mass spectrometry. Sulfur-containing VOCs were quantified using a portable total reduced sulfur meter. Flux rates for VOCs with small dimensionless Henrys law constants (i.e., those found at AFOs) increased with increasing air velocity. The two-film model with an experimentally derived reference gas-film transfer coefficient was found to reliably predict VOC flux at velocities between 0.003 and 0.23 m s-1. However, the two-film model did not reliably predict VOC flux with other air velocity correction formulae, an indication that flux is a function of wind tunnel geometry and turbulence factors, and not just average air velocity or sweep air flow rate. These results corroborate other studies that show that air velocity is a major factor affecting VOC fluxes from AFOs, verifying that an air velocity correction factor is required for estimating accurate VOC emission factors using wind tunnels and flux chambers.

RATE AND FREQUENCY OF UREASE INHIBITOR APPLICATION FOR MINIMIZING AMMONIA EMISSIONS FROM BEEF CATTLE FEEDYARDS

Reduction of ammonia emissions from animal feeding operations is important from the perspective of environmental policy and its impact on agriculture. A laboratory study was conducted to evaluate how rate and frequency of urease inhibitor application affect ammonia emissions from simulated beef cattle feedyard manure surfaces. The urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) was applied at rates of 0, 1, and 2 kg ha-1, at 8, 16, and 32 day frequencies, and with or without simulated rainfall. Synthetic urine was added every two days to the manure surface. Gaseous ammonia was trapped by bubbling through a sulfuric acid solution using a vacuum system and analyzed for nitrogen using automated procedures. NBPT applied every 8 days was most effective, with the 1 and 2 kg NBPT ha-1 treatments resulting in 49% to 69% reduction in ammonia emission rates, respectively. The 8-day, 1 kg NBPT ha-1 treatments had the most promising benefit/cost ratios of 0.48 to 0.60. Simulated rainfall reduced the ammonia emission rates from 1% to 25% as compared to the non-rainfall treatments, although the differences were not statistically different. The use of NBPT for reducing ammonia emissions looks promising; however, possible buildup of urea in the pen surface may require a higher NBPT application rate with time.

Odor Characterization at Open-Lot Beef Cattle Feedyards Using Triangular Forced-Choice Olfactometry

Odor is a growing concern at concentrated animal feeding operations as residential houses encroach upon rural areas once occupied only by agriculture. A research project was conducted to determine baseline ambient odor characteristics at large open-lot beef cattle feedyards and to develop a better understanding of when and why odors occur at feedyards. Ambient odor samples were collected two to four times per month over a 12-month period in 2002-2003 at three large commercial open-lot beef cattle feedyards in the Texas panhandle. Ambient odor samples were collected upwind of the feedyard, downwind of the pens, and downwind of the runoff storage pond. Odor samples were also collected on five separate days covering four months in 2004 from a surface isolation flux chamber to estimate odor emission rates from the feedyard surface. All odor samples were collected in 10 L Tedlar bags and analyzed with trained human odor panelists for odor concentration (detection threshold, DT) by dynamic dilution forced-choice olfactometry, intensity by reference scaling, and hedonic tone. Manure moisture content and weather data were collected on-site at each of the feedyards. At two of the feedyards, mean DTs downwind of the pens and storage pond were statistically similar to upwind DTs, ranging from 33 to 45 OU m-3. At the third feedyard, mean DTs downwind of the pens (69 OU m-3) and pond (124 OU m-3) were statistically higher than the mean upwind DT (36 OU m-3) (p < 0.05). Odor emission rates ranged from 0.3 to 3.2 OU m-2 s-1 during a period when downwind DTs ranged from 17 to 132 OU m-3. A number of elevated DTs were explained by elevated manure moisture contents from recent precipitation. These results demonstrate that odor production from open-lot beef cattle feedyards is a complex phenomenon that depends at least partially on weather conditions. Thus, odor prediction and control will likely be difficult at these facilities.

CONTINUOUS AMMONIA EMISSION MEASUREMENTS FROM A COMMERCIAL BEEF FEEDYARD IN TEXAS

Ammonia emissions from cattle feedlots pose the potential to react with other compounds such as oxides of nitrogen and sulfur, which lead to detrimental environmental effects. Ambient ammonia (NH3) concentrations were measured continuously at a beef cattle feedyard for 12 months beginning in March 2007. Concentrations were measured every 5 min, 24 hours per day, at a sample intake height of 3.3 m using a chemiluminescence analyzer. On-site weather data were collected concurrently. Modeled emissions of NH3 were compared with the mass balance of N for the feedyard. Mean annual NH3 concentrations were 0.57 ppm, with a monthly average low of 0.37 ppm in December 2007 and a monthly average high of 0.77 ppm in August 2007. Flux densities were calculated using a backward Lagrangian stochastic model (WindTrax 2.0.7.8). Mean annual flux density was 70.7 µg m-2 s-1 (2.2 kg m-2 year-1). Mean monthly flux density ranged from 42.7 to 123.1 µg m-2 s-1 (0.11 to 0.32 kg m-2 month-1) in November and April 2007, respectively. Both concentration and flux density had a diel distribution with minima during the nighttime hours and maxima during the early afternoon. On an annual basis, 48.8% of fed N was volatilized as NH3. The inverse modeled daily ammonia production per head was 85.3 g NH3-N (head fed)-1 d-1.

Chemical Composition of Pen Surface Layers of Beef Cattle Feedyards1

The biological, physical, and chemical characteristics of beef cattle feedyard pen surfaces may affect nutrient transformations and losses to the atmosphere, ground water, or surface water. Feedyard pen surfaces can typically segregate into 3 or 4 layers. The purpose of this study was to determine if there were seasonal, within-pen location, days-on-feed, or urine effects on the chemical composition of the pen surface layers of feedyards. Samples were collected from 5 locations in 9 pens at 3 feedyards in each season and were analyzed for gravimetric water, pH, electrical conductivity (EC), nitrate + nitrite-N (NOx-N), ammonia + ammonium-N (NHx-N), N, C, and P. The percentage of water increased (P < 0.01) with depth among the manure layers and decreased in the soil. The pH of the manure layers increased with depth (P < 0.01) from approximately 7.6 to 8.2. The EC of the manure layers was greater (P < 0.01) than the EC of the soil layer, whereas the NOx-N concentration was greater (P < 0.01) in the soil layer. The NHx-N concentrations were lowest in the soil layer (P < 0.01). Total C and N concentrations decreased (P < 0.01) with sample depth. The composition of the layers was affected by season and location within the pen. Recent urine deposition did not affect the lower layers. The NHx-N concentration of the layers increased with days on feed. The differences in the chemical and physical properties of the layers in a feedlot pen may potentially affect nutrient losses to the atmosphere and to groundwater.

Background Odors in Tedlar® Bags Used for CAFO Odor Sampling

Tedlar® film is manufactured in a wet solvent process and continues to emit organic compounds after manufacturing. Tedlar® bags are used for odor sampling at concentrated animal feeding operations (CAFOs). Odor regulations for CAFOs vary widely, but maximum detection thresholds (DT) of 2 to 15 have been proposed downwind of feeding operations. Results at the WTAMU Olfactometry Laboratory have shown that both commercially available Tedlar® bags and homemade Tedlar® bags have a detectable background odor (DTs of 20 to 60 typical) even following standard protocols for purging. Purging the bags before sampling was not effective in reducing DTs to acceptable levels, as verified with SPME analysis. Heating the Tedlar® bags for 24 hrs, when combined with purging immediately after heating and again prior to odor sampling, reduced background DTs to less than 12. This is an acceptable range for odor sampling at open lot beef cattle feedyards or any other locations where DTs are expected to be greater than sixteen.

Characterization of organic matter in beef feedyard manure by ultraviolet-visible and fourier transform infrared spectroscopies.

Manure from beef cattle feedyards is a valuable source of nutrients and assists with maintaining soil quality. However, humification and decomposition processes occurring during feedyard manures on-farm life cycle influence the forms, concentrations, and availability of carbon (C) and nutrients such as nitrogen (N) and phosphorus (P). Improved understanding of manure organic matter (OM) chemistry will provide better estimates of potential fertilizer value of manure from different feedyard sources (e.g., manure accumulated in pens, stockpiled manure after pen scraping) and in settling basin and retention pond sediments. This will also assist with identifying factors related to nutrient loss and environmental degradation via volatilization of ammonia and nitrous oxide and nitrate leaching. We used Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies to characterize structural and functional properties of OM and water-extractable OM (WEOM) from different sources (surface manure, manure pack, settling basin, retention pond) on a typical commercial beef feedyard in the Texas Panhandle. Results showed that as beef manure completes its on-farm life cycle, concentrations of dissolved organic C and N decrease up to 98 and 95%, respectively. The UV-vis analysis of WEOM indicated large differences in molecular weight, lignin content, and proportion of humified OM between manures from different sources. The FTIR spectra of OM and WEOM indicate preferential decomposition of fats, lipids, and proteins over aromatic polysaccharides such as lignin. Further work is warranted to evaluate how application of feedyard manure from different sources influences soil metabolic functioning and fertility.

Factors Affecting Emission Measurements with Surface Isolation Flux Chambers

We conducted field experiments to evaluate how factors such as sweep air flowrate, time since urine deposition, and flux chamber footprint area affect ammonia fluxes from open-lot feedyard and dairy surfaces as measured using three different flux chamber designs. The chambers included a 26.5-cm diameter chamber (North Carolina State University design), a 49-cm diameter chamber (EPA-type design), and a 1.2 m x 2.4 m rectangular chamber (West Texas A&M University design). Clean sweep air collected upwind of the feedyard (<50 ppb NH3-N) was supplied to the chambers using a large compressed air tank, and ammonia concentrations were measured using a Thermo Environmental Instruments 17C chemiluminescence NH3 analyzer. Ammonia fluxes increased up to 10-fold between sweep airflow rates of 0.1 and 1.0 volumetric changes per minute. Ammonia fluxes from urine spots were highly dependent on the time since the urine was excreted. In one instance, the flux decreased at 57 ug/m2/min for every minute elapsed during the first two hours after excretion. Maximum fluxes and variability among individual flux measurements decreased with increasing flux chamber footprint area. A better knowledge of how these factors affect calculated emission rates will be beneficial to future development of emission factors for open-lot feedyards and dairies.

Effect of Urease Inhibitor Application Rate and Rainfall on Ammonia Emissions from Beef Manure

Social, economic, and environmental factors have prompted the desire to reduce global atmospheric ammonia emissions. A research project was conducted to assess the efficacy of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) for reducing ammonia emissions from simulated open-lot beef cattle feedyard surfaces. A mixture of beef cattle feces and urine (manure) was placed into small emission chambers (167 × 167 × 170 mm deep). A urea solution was added every 2 days to simulate continual urine deposition in the feedyard. Clean air (1.4 L min-1) was passed over the manure surface, and ammonia was trapped in an acid solution. The six treatments (three replications per treatment) included combinations of NBPT application rate with or without simulated rainfall. NBPT was applied at zero, steady (5 kg ha-1 every 4 days), or increasing (5 kg ha-1 initially, doubled every 4 days up to 40 kg ha-1) rates. Rainfall treatments received 6 mm every 4 days. For all treatments, mean ammonia emissions from the manure were lower (p < 0.05) when simulated rainfall was added. Mean ammonia emission rates for the NBPT treatments were 26% to 33% of the non-NBPT treatments, demonstrating that NBPT was effective at reducing emissions from the manure surfaces in both wet and dry conditions. There were no statistical differences in mean ammonia emission rates for the steady and increasing NBPT application rates, showing that a steady NBPT application of 5 kg ha-1 every 4 days was effective in reducing ammonia emissions from the manure. The use of NBPT appears promising for reducing ammonia emissions at beef cattle feedyards. Additional research is warranted to study the effectiveness under long-term conditions in an outdoor feedyard setting.