Measurement of greenhouse gas (GHG) emissions is a challenge to the animal industry as it is difficult to accurately measure enteric emissions from ruminants. Enclosed chambers and tracer-ratio techniques are common measurement approaches, but their use can alter animal diet, behavior and stress levels and soil emission processes. Non-interfering techniques which do not impact soil or air transport processes, or the animal or its surroundings, provide a more appropriate approach to determine absolute emissions. While micrometeorological integrated horizontal flux and mass difference techniques have been used to study animal emissions in paddocks, they require substantial instrumentation and are practical only for small paddocks. Classical micrometeorological methods such as flux-gradient, eddy covariance, relaxed eddy accumulation and boundary layer budgeting have been used to evaluate emissions from larger source areas. This review focuses on a new technique, inverse dispersion analysis, which is a more flexible approach to measure emissions from small paddocks or whole farms as it allows fluxes to be calculated from gas concentration measurements of interest at a point upwind and a point downwind, along with statistical information on wind turbulence measured using a three dimensional sonic anemometer. Our purpose is to discuss advantages and disadvantages of these various techniques to determine absolute amounts of enteric emissions from ruminants, and provide examples of their application.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. (C) 2011 Elsevier B.V. All rights reserved.

Ammonia is the primary basic gas in the atmosphere and has the most important role in the neutralization of atmospheric acids generated by fossil fuel combustion. The reaction product forms a NH(4)(+) aerosol, which is a major component of atmospheric particulates. These NH(4)(+) particulates are part of atmospheric haze and may be transported long distances from the production site before returning to the surface by dry deposition or scavenged by precipitation. Animal production produces a significant component of anthropogenic NH(3) emissions and the National Academy of Sciences concluded that NH(3) emissions estimates from animal feeding operations have not been characterized sufficiently, leading the US Environmental Protection Agency to institute studies in the United States to obtain NH(3) emissions from animal feeding operations under the US Environmental Protection Agency Air Consent Agreement. The objective of this study is to obtain additional broiler NH(3) emissions estimates using a backward Lagrangian stochastic technique. This technique uses NH(3) concentrations measured upwind and downwind of the farm, wind observations, and atmospheric dispersion model calculations to obtain whole-farm emissions. Ammonia emissions were low at bird placement and increased steadily after about the third week of growth. At the end of the flock (47 d, ~297,000 birds), cumulative emissions for the flock cycle period were 0.016 kg of NH(3).bird(-1).flock(-1). Between-flock emissions, including bird harvest, cleanout, temporary storage of litter outside of the buildings, and downtime (buildings closed), added another 0.003 kg of NH(3).bird(-1).flock(-1). Emissions from this broiler farm were less than from some eastern US broiler farms but were comparable to broiler farms in Europe. Based on the results of this study and a similar winter study at this same farm, total flock wintertime and summertime (flock cycle plus between-flock) NH(3) emissions from this farm represented 7.8 and 8.3% of feed N as NH(3)-N, respectively, or an annual average of 8.1%.

Accurately measuring NH3 produced from poultry litter and emitted from mechanically ventilated broiler houses continues to be a challenge. Many technologies and methods are available to measure NH3, with costs ranging from inexpensive (but rather inaccurate, such as colorimetric tubes) to expensive (for precision analytical equipment such as laser spectrometers). This study investigated the variability among selected low, midrange, and high-cost instruments. Inter-instrument and intra-instrument comparisons were made using colorimetric pull tubes and dosimeter tubes, electrochemical sensors, and tunable-diode open-path laser spectrometers (OPL). This study consisted of inside and outside broiler house studies to evaluate instrument performance under different environmental conditions and NH3 concentrations. The OPL showed the least variation during the in-house and outside comparisons. The electrochemical sensors and colorimetric tubes performed well at NH3 levels typically found in a properly ventilated broiler house. With no ventilation, variation among instruments increased as NH3 concentrations increased. With the exception of the OPL, concentrations on the outside were too low and environmental elements were too harsh for these instruments to perform well.

Ammonia gas is the only significant basic gas that neutralizes atmospheric acid gases produced from combustion of fossil fuels. This reaction produces an aerosol that is a component of atmospheric haze, is implicated in nitrogen (N) deposition, and may be a potential human health hazard. Because of the potential impact of NH3 emissions, environmentally and economically, the objective of this study was to obtain representative and accurate NH3 emissions data from large dairy farms (>800 cows) in Wisconsin. Ammonia concentrations and climatic measurements were made on 3 dairy farms during winter, summer, and autumn to calculate emissions using an inverse-dispersion analysis technique. These study farms were confinement systems utilizing freestall housing with nearby sand separators and lagoons for waste management. Emissions were calculated from the whole farm including the barns and any waste management components (lagoons and sand separators), and from these components alone when possible. During winter, the lagoons’ NH3 emissions were very low and not measurable. During autumn and summer, whole-farm emissions were significantly larger than during winter, with about two-thirds of the total emissions originating from the waste management systems. The mean whole-farm NH3 emissions in winter, autumn, and summer were 1.5, 7.5, and 13.7% of feed N inputs emitted as NH3-N, respectively. Average annual emission comparisons on a unit basis between the 3 farms were similar at 7.0, 7.5, and 8.4% of input feed N emitted as NH3-N, with an annual average for all 3 farms of 7.6 ± 1.5%. These winter, summer, autumn, and average annual NH3 emissions are considerably smaller than currently used estimates for dairy farms, and smaller than emissions from other types of animalfeeding operations.

Ammonia (NH3) emissions were determined from three commercial dairy farms in the north-central U.S. The dairies employed similar management, having naturally ventilated free-stall barns where bat-it waste is scraped and transferred to outdoor lagoons. Three potential emission sources were distinguished at each farm: barns, lagoons, and sand separators. A backward Lagrangian stochastic (bLS) inverse-dispersion technique was used to measure emissions. Total farm emission varied from 15 to 330 kg NH3 d(-1) depending on the farm and season. Inter-farm variability was largely explained by farm size (animal population). Emissions showed variability on seasonal and daily scales: summer rates were roughly ten times those of the winter; and mid-day rates were approximately three times those at night. The lagoons emitted 37% to 63% of the farm total during summer and fall, but they were frozen in winter and their emissions were immeasurably small. The yearly per-animal emissions front the three dairies were estimated at 20, 19, and 20 kg NH3 animal(-1) year(-1). Regarding the measurement technique, US proved well-suited to our study. With modest resources we were able to measure emissions front the variety of sources at each farm and quickly move between farms. Overall agreement in measured emissions at the three farms, together with a general harmony of our measurements with those front previous studies, provides a measure of confidence in the measurement strategy.

Within broiler production facilities, NH3 concentrations have always been of concern from a bird performance and worker health standpoint. However, NH3 emitted from poultry houses is receiving increased attention from the environmental and community nuisance perspectives. Studies on NH3 emissions from poultry operations found within the literature do not address how NH3 disperses or the actual concentrations observed at varying distances downwind from poultry houses. The objective of this study was to measure downwind NH3 concentrations emitted from broiler houses when ventilation rates would be at a maximum. Open-path laser spectrometers were utilized for this study and for period 1 were placed 100, 200, and 300 ft from the houses from 28 to 49 d and in period 2 were placed at 100, 200, and 500 ft from 50 to 56 d. Data were collected during the last 4 wk of a 56-d grow-out cycle in 2 periods during a summer flock on a 4-house broiler farm located in northeastern Georgia. Ammonia concentrations were lower as distance from the houses increased, with NH3 levels at 100, 200, 300, and 500 ft being less than 1 ppm in approximately 60, 75, 85, and 90% of the observations, respectively. Ammonia concentrations extending to 100 ft from the houses were influenced by the tunnel fans themselves. Wind direction and wind speed were the factors that significantly influenced downstream NH3 concentrations beyond 100 ft. At no time did measured NH3 levels meet or exceed established Occupational Safety and Health Administration-US Environmental Protection Agency NH3 odor-detection threshold values during this study.

D3 20 57.8 63.0 1.55b 1.03 D3 37.5 58.4 62.5 1.53 1.04 D3 87.5 58.2 63.6 1.54 1.01 D3 137.5 59.1 63.3 1.49 1.01 Mean D3 58.4 63.1b 1.53 1.023b 25(OH)D3 20 59.3 63.3 1.48a 1.01 25(OH)D3 37.5 59.0 64.5 1.54 1.01 25(OH)D3 87.5 59.0 64.4 1.50 0.98 25(OH)D3 137.5 59.0 64.6 1.51 0.98 Mean 25(OH)D3 59.1 64.2a 1.51 0.995a D3+25(OH)D3 50+37.5 58.8b 64.2 1.535b 1.00 D3+25(OH)D3 50+70 60.8a 65.7 1.465a 0.97 Mean D3+25(OH)D3 59.8a 64.9a 1.500 0.985a Mean Factorial 58.7b 63.6b 1.518 1.009b

An inverse-dispersion technique is used to calculate ammonia (NH3) gas emissions from a cattle feedlot. The technique relies on a simple backward Lagrangian stochastic (bLS) dispersion model to relate atmospheric NH3 concentration to the emission rate QbLS. Because the wind and the source configuration are complicated, the optimal implementation of the technique is unclear. Two categorically different measurement locations (for concentration and winds) are considered: within the feedlot and downwind. The in-feedlot location proved superior, giving a nearly continuous QbLS timeseries. We found average emissions of 0.15 kg NH3 animal−1 day−1 in both 2004 and 2005, representing a loss of 63% (2004) or 65% (2005) of the dietary nitrogen in the animal feed. Downwind measurement locations were less useful for several reasons: a narrow range of useable wind directions; ambiguity in the choice of wind statistics to use in the calculations; low NH3 concentrations; and downwind deposition of NH3. When addressing a large source (like a feedlot) that modifies the ambient wind flow, we recommend in-source measurements for use in inverse-dispersion applications.

where Z is the height above ground, L is the Obukhov length, and b is value of O'w/u* in neutral stratification. The bLS model is fully defined with a single measurement of windspeed S and direction (3 at an arbiopen-path lasers measured line-average methane concentration (Cd above and (up to 100 m) downwind of the source (Fig.2); beam height Zb ~ 1m. Measurements were made over five days in May and June 2001; each day gas was released over two to three hours, CL being averaged over 15 minute intervals. Data shown here cover four daytime releases, and one nighttimeearly morning release. Our bLS model was based on Thomson's (1987) well-mixed 3d model for Gaussian inhomogeneous turbulence, implemented with standard Monin-Obukhov (MO) formulae for surface layer wind statistics: the profiles of mean windspeed (S), of standard deviations of the velocity fluctuations (O'u, O'v, O'w),and of a Lagrangian timescale (TL ). We chose TL to ensure the turbulent Schmidt number Se = 0.6 (as is implied by Project Prairie Grass; Wilson et aI., 2001). To parame. terisation of O'w we used Figure 2: Tracer source is shown by the center square, (1) laser paths (not all used simultaneously) are given by lines. Meteorological tower is indicated by the symbol. Grid spacing is 12 m.

Concentrated animal production can have a significant effect on the atomospheric environment. Methane (CH4) emissions from two swine waste holding lagoons were determined periodically in 1997 and 1998. Emission rates from the lagoons were measured under ambient conditions with little disturbance to the natural environment. One farm (NC10) used a periodic ‘flush’ to remove wastes (8h cycle). The second farm (NC20) used a ‘pull-plug’ system with a 1 week cycle time. In general, flux rates followed a diurnal pattern with greater fluxes during the day when both temperature and windspeed were greatest. Methane emissions from the lagoons were related to windspeed, effluent temperature and volatile solid loading into the system. Average emissions from NC10 ranged from 20 to 115kgCH4ha−1 per day. Greatest emissions were during the spring period when the sludge depth was deepest. Emissions from NC20 were much less (5.3–10.7kgCH4ha−1 per day) due primarily to fewer number of animals and type of manure handling system. Emissions followed a diurnal pattern with greatest emissions during the day when effluent temperature was greatest. The average flux for the year from the two lagoons were 62 and 8kgCH4ha−1 per day which corresponded to 6.0 and 1.6kgCH4 per animal per year, respectively.

Gaseous methane (CH4) emissions were determined during the winter and summer from `farrow-to-finish' (FF) swine production houses and during the summer from a `farrow-to-wean' (FW) house in 1998 in the coastal plains of North Carolina. The houses were instrumented with sensors to determine cycling of the individual forced-ventilation fans. Laser spectrometry was used to measure CH4 concentration differences between the intake and exhaust points of the houses. Differences in CH4 concentrations were combined with fan operation data to calculate CH4 fluxes from the houses. During the cold winter measurement period, CH4 fluxes averaged 6.9 g CH4animal−1d−1 in the FF house. During summer measurement periods, CH4 fluxes were much greater and averaged 33 and 46 g CH4animal−1d−1 from the FF and FW houses, respectively. The much larger emissions during the summer than winter, indicate that CH4 house emissions were primarily from fresh feces and the underground storage/wash pits containing lagoon effluent; and not directly from the animals since temperature would have little affect on direct animal emission. Emission factors based on animal units (au) of 454 kg animal−1 were much greater at the FW farm with a pull-plug waste management system (7–8 day wash cycle) than at the FF farm with a periodic flush system (8 h wash cycle).

The paper examines the strengths and weaknesses of a rangeof meteorological flux measurement techniques that mightbe used to verify predictions of greenhouse gas inventories.Recent research into emissions of methane (CH4)produced by enteric fermentation in grazing cattle and sheepis used to illustrate various methodologies. Quantifying thisimportant source presents special difficulties because the animalsconstitute moving, heterogeneously distributed, intermittent, pointsources. There are two general approaches: one, from the bottom up,involves direct measurements of emissions from a known number ofanimals, and the other, from the top down, infers areal emissions ofCH4 from its atmospheric signature. A mass-balance methodproved successful for bottom-up verification. It permits undisturbedgrazing, has a simple theoretical basis and is appropriate for fluxmeasurements on small plots and where there are scattered pointsources. The top-down methodologies include conventional flux-gradientapproaches and convective and nocturnal boundary-layer (CBL and NBL)budgeting schemes. Particular attention is given to CBL budget methods inboth differential and integral form. All top-down methodologies require ideal weather conditions for their application, and they suffer from the scattered nature of the source, varying wind directions and low instrument resolution. As for mass-balance, flux-gradient micrometeorological measurements were in good agreement with inventory predictions of CH4 production by livestock, but the standard errors associated with both methods were too large to permit detection of changes of a few per cent in emission rate, which might be important for inventory, regulatory or research purposes. Fluxes calculated by CBL and NBL methods were of the same order of magnitude as inventory predictions, but more improvement is needed before their use can be endorsed. Opportunities for improving the precision of both bottom-up and top-down methodologies are discussed.

A mass balance method is described for calculating gas production from a surface or volume source in a small test plot from measurements of differences in the horizontal fluxes of the gas across upwind and downwind boundaries, It employs a square plot, 24 m x 24 m, with measurements of gas concentration at four heights (up to 3.5 m) along each of the four boundaries. Gas concentrations are multiplied by the appropriate vector winds to yield the horizontal fluxes at each height on each boundary. The difference between these fluxes integrated over downwind and upwind boundaries represents production. Illustrations of the method, which involve exchanges of methane and carbon dioxide, are drawn From experiments with landfills, pastures and grazing animals. Tests included calculation of recovery rates from known gas releases and comparisons with a conventional micrometeorological approach and a backward dispersion model. The method performed satisfactorily in all cases. Its sensitivity for measuring exchanges of CO2, CH4 and N2O in various scenarios was examined. As employed by us, the mass balance method can suffer from errors arising from the large number of gas analyses required for a flux determination, and becomes unreliable when there are light winds and variable wind directions. On the other hand, it is non-disturbing, has a simple theoretical basis, is independent of atmospheric stability or the shape of the wind profile, and is appropriate for flux measurement in situations where conventional micrometeorological methods can not be used, e.g, for small plots, elevated point sources, and heterogeneous surface sources. (C) 1998 Published by Elsevier Science Ltd. All right reserved.

Legumes are commonly used to provide nitrogen (N) for succeeding crops, but the net gain in N to the system is rarely measured. This study developed a N budget for a winter legume production system to estimate sources, sinks, and net system gain in N. Crimson clover (Trifolium incarnatum L.) reseeded from the preceding year and was killed with herbicide the following spring. A forage sorghum crop (Sorghum vulgare Pers.) was planted and harvested twice during the summer. Subplots were sampled at frequent intervals throughout the growing seasons for measurements of plant biomass and N content (leaves, stems, seeds, roots, and litter) and soil mineral N. During the clover growing season, soil N mineralization and leaching rates were estimated with an insitu chamber technique, and aerial ammonia (NH3) transport measurements were made biweekly by micrometeorological techniques. Nitrogen in the clover crop increased until anthesis, and then declined slightly prior to desiccation with herbicides. Total N accumulated in the clover at desiccation was 323 kg N ha(-1) (28 In leaves, 81 in stems, 40 in seeds, 44 in surface-layer roots, and 130 in dead leaves and litter). Aerial NH3 absorption by the clover was small during the growing season (0.18 kg N ha(-1)) but NH3 loss from the killed clover was also minimal (0.25 kg N ha(-1)) and occurred during the period shortly after herbicide application. The summer sorghum crop took up 454 kg N ha(-1) over the course of two cuttings from the soil mineral and mineralized organic N resource plus atmospheric NH3 and other atmospheric N inputs such as wet and dry deposition. Total N accumulated by the clover from N fixation, soil mineral N uptake, and NH3 absorption provided the equivalent of 70% of N removed by the sorghum crop.

Gaseous ammonia (NH3) transport is an important pathway in the terrestrial N cycle. In the atmosphere NH3 neutralizes airborne acids and is a major factor determining air quality and acid rain deposition patterns. Redeposition of atmospheric NH3 plays an important role in the N balance of natural ecosystems and has been implicated in forest decline, plant species change and eutrophication of surface water. Much of the N in soil-plant animal systems can be lost to the atmosphere, particularly with surface applied livestock waste, or urea and anhydrous ammonia fertilizers. Plants can have a significant impact on NH3 transport because they can both absorb and desorb atmospheric NH3. Under conditions of low soil N or high atmospheric NH3 concentrations, plants absorb NH3. Under conditions of high soil N or low atmospheric NH3 concentrations, plants volatilize NH3. This article discusses methods for evaluating NH3 transport in the filed, the rate of NH3 volatilized from fertilizer application, and the effects of plants on net NH3 transport.