Location: Livestock Nutrient Management Research2020 Annual Report
Objective 1: Characterize and improve prediction of ammonia and greenhouse gas emissions from cattle production systems. Subobjective 1A. Characterize methane (CH4) emissions from southern Great Plains grazing systems. Subobjective 1B. Assess the impact of environmental conditions and management practices and their interactions on emissions of NH3 and GHG from open lot cattle production systems. Subobjective 1C. Improve NH3 and GHG emissions measurements for feedyards and dairies. Objective 2: Improve feed nutrient use in cattle to maintain animal productivity, reduce emissions of ammonia and greenhouse gases, and mitigate pathogens and antibiotic resistant bacteria. Subobjective 2A. Determine effects of cattle diet on enteric CH4 production. Subobjective 2B: Evaluate and improve models to predict enteric CH4 emissions from grazing and feedyard cattle. Subobjective 2C. Identify and quantify sources of enteric nitrous oxide (N20) emissions from cattle in respiration calorimetry chambers. (NEW 2019) Subobjective 2D: Develop alternative strategies that reduce methane emissions while maintaining production. Research Goal 2D.1: Quantifying the impact of supplements in animal diets, such as fungal based probiotics, seaweed and condensed tannins, on enteric methane emissions, and establishing the biochemical and/or physiological mechanisms responsible for emission reductions. Research Goal 2D.2. Quantifying the impact of new technologies and animal management systems on enteric methane emissions. Objective 3: Manage soil and manure reactive nitrogen, phosphorus and carbon to improve soil properties, reduce nutrient loss and mitigate pathogens and antibiotic resistant bacteria. Subobjective 3A. Evaluate the effectiveness, practicality and economics of chemical inhibitors and manure amendments to reduce N20 and NH3 emissions from beef cattle feedyards, dairies, and manure-amended soils. Subobjective 3B. Quantify field-scale emissions of N20 from manure-amended soils. Subobjective 3C. Establish protocols for examining AR in agroecosystems. Subobjective 3D. Characterize forms of P in manure-amended soils. Subobjective 3E: Evaluate soil C/N change with land use on the southern High Plains.
Beef and dairy cattle production provide vital human nutrition and important economic activity. Cattle production, like all human endeavors, also contains environmental risks. This multidisciplinary research will help us to better understand and mitigate the environmental risks from cattle production systems on the Southern Great Plains. We will quantify and improve predictions of emissions of ammonia (NH3) and greenhouse gases (GHG) from cattle production systems. The research will focus on the predominant agricultural GHG emissions of methane (CH4) and nitrous oxide (N20). Sources of these emissions include grazing animals (enteric emissions), emissions from cattle, pen and lagoon surfaces at beef feedyards and dairies, and emissions from soils following land application of manure. We will determine the effects of cattle diet on enteric GHG emissions on scales that range from single animal to whole pastures, feedyards or dairies. We will test potential mitigation methods to reduce emissions from manure surfaces and cropped fields using controlled laboratory experiments followed by pilot-scale and field-scale experiments. We will quantify the changes in soil carbon (C), nitrogen (N), and phosphorus (P) from application of manure or land use change. A collaboration of ARS laboratories will test methods to characterize antibiotic resistant (AR) bacteria and genes from manure-impacted soil. Research results will provide science-based information and technologies for livestock producers, extension specialists, and regulators to protect air quality, manage feedyard and dairy manure, enhance production efficiency, and improve sustainability of livestock production.
Research at Bushland, Texas, in fiscal year 2020 was conducted during the fourth year of the project plan "Improved Practices to Conserve Air Quality, Maintain Animal Productivity, and Enhance Use of Manure and Soil Nutrients of Cattle Production Systems for the Southern Great Plains." Objective 1: Scientists from Bushland, Texas, and El Reno, Oklahoma, conducted studies to quantify greenhouse gas emissions from grazing cow-calf pairs. Live-animal methane emissions were lower from automated head chambers than from fully enclosed animal respiration chambers. In manure land application studies, researchers discovered that incorporation of manure, a common practice to reduce ammonia emissions, actually increased nitrous oxide emissions. Effects were more pronounced after rainfall events. Researchers studied the effects of large rainfall events on greenhouse gas emissions at commercial beef cattle feedyards. Measured greenhouse gas emissions were suppressed for five to 10 days following large rainfall events. These results are being used to modify a new empirical model of greenhouse gas emissions from open-lot cattle systems. In other laboratory work, ARS scientists showed the complexity of nitrous oxide production and changes in microbial community structure based on temperature and rainfall. This work will help develop novel methods and evaluate existing methods to mitigate emissions: understanding the source and underlying driving factors for gas production is the first step towards effective greenhouse gas mitigation from cattle production systems. Objective 2: Although uncommonly known, cattle emit small quantities of enteric nitrous oxide. Bushland, Texas, researchers evaluated enteric nitrous oxide and its relationship to the rumen microbiome. Plant tannins can modify ruminal fermentation and scientists tested two tannin types to see if there were any effects on gaseous emissions. Quebracho tannin reduced methane emissions by as much as 68 percent. Other tannins were not so promising for methane, but all reduced nitrous oxide emissions. Grain processing and specific grain type, cause differences in its digestibility. Researchers conducted studies to see how substituting steam-flaked corn for steam-flaked wheat affected rumen function. Overall, the wheat diet led to higher enteric greenhouse gas emissions than corn. Steam-flaked wheat had no substantial environmental value (in terms of greenhouse gas emissions) or animal productivity value over steam-flaked corn. Newer studies are investigating manure effects on soil nutrients, pathogens, and antimicrobial resistant bacteria in the Southern High Plains. The transfer of antibiotic resistance genes (ARG) are a large concern for the agricultural and general community. However, no study assessed background levels of soil ARG. ARS researchers along with researchers from The University of Pennsylvania, compared feces from an assortment of fowl and livestock to characterize antibiotic residues, ARG and microbial diversity. Overall, tetracycline ARG were very common and tended to be associated with broiler chickens. Cattle and swine manure had highly variable microbial communities. Individual farm management practices and specific animal types impacted ARG presence. Objective 3: Research characterizing the occurrence of antibiotic resistant bacteria continued. Researchers in Bushland, Texas, and Lincoln, Nebraska, evaluated ARG after land application of manure to understand transport of manure-derived antibiotic resistance from agricultural systems. Research examined genes that transmit resistance for b-lactamase, tetracycline, macrolide, sulfonamide and integrase. This work showed potential for temporary ARG "blooms" right after manure application. Interestingly, ARG were unevenly distributed in the soils, which makes it hard to say if they came from manure or were already present as background soil fauna. This work led to a recommendation for normalized quantitative PCR (qPCR) ARG values, expressed as the number of ARG targets per 100,000 16S ribosomal RNA genes. Investigations to characterize soil organic matter continued. Labile soil carbon has been proposed to be a more sensitive indicator of soil carbon stocks than total carbon. Investigations on long-term dryland cropping systems indicated that traditional and conservation-based methods of cropping in water-limited, semi-arid areas may be insufficient to remediate or recover labile soil carbon. This work confirmed that labile carbon is a more sensitive indicator of carbon status in the Southern High Plains than total carbon. An ARS researcher at Lubbock, Texas, collaborating with ARS researchers from Auburn, Alabama, characterized the lability of organic and inorganic forms of phosphorus in high iron and aluminum soils from Alabama that had received poultry manure. All laboratory analyses were completed.
1. Nitrous oxide emissions from Southern High Plains beef cattle feedyards are affected by climate. Nitrous oxide is a potent greenhouse gas that has been linked to climate change. Elevated nutrient concentrations make livestock manure a source for nitrous oxide production. Scientists from Bushland, Texas, Clay Center, Nebraska, and Texas A&M AgriLife Research (Amarillo, Texas) investigated how weather affects nitrous oxide from commercial beef cattle feedyards. They determined that nitrous oxide emissions were greatest under warm temperatures and shortly after rainfall events. It would be useful if producers and regulatory personnel could predict weather-derived nitrous oxide emissions from animal agriculture. Bushland, Texas, researchers developed an empirical model to assess the effect of manure removal frequency on annual nitrous oxide emissions. These data will be useful for updating national greenhouse gas emissions inventories for beef cattle feedyards. In addition, the bottom line for producers, the cost of managing on-farm nutrients, can be improved for increased manure value.
2. Grazing cattle produce less methane when fed high quality forage or hay. Cattle produce methane as a natural byproduct of digestion, but it is challenging to measure, especially from grazing cattle. A team of scientists from Bushland, Texas, Woodward, Oklahoma, El Reno, Oklahoma, and Texas A&M AgriLife Research, Amarillo, Texas, studied how cattle methane emissions were affected by hay nutritional quality and fiber content. Experiments were conducted on groups of grazing cattle in pastures, and from individual cattle in lab-scale respiration chambers. In both field and lab experiments, cattle fed a high-quality hay diet (high crude protein) produced less total methane per unit of digested organic matter than when fed low-quality hay. These results increased understanding of how much methane was produced by grazing cows. This work can guide producers towards higher quality feed to improve performance, as well as precision feeding to meet the energy and protein needs of animals. In addition, regulators can improve inventory estimates. Scientists can use the results to validate computer programs that predict emissions.
3. The addition of tannins to diets containing wet distilled grains plus solubles can reduce enteric methane production by cattle. Some feed additives, such as natural tannins, can manipulate ruminal metabolism and the rumen microbiome to produce lower levels of methane. The effect of methane on global warming, and animal agriculture's contribution is important because methane has a high global warming potential. Reducing cattle-derived methane is a good-faith gesture showing animal producers as environmental stewards. ARS reseaerchers at Bushland, Texas, and Ames, Iowa, investigated how different dietary ingredients affect greenhouse gas emissions and rumen microbial activities in cattle. Using a combination of techniques showed that tannin-rich peanut skin, a common by-product in the region, directly suppressed methanogenesis. These data were encouraging and have prompted investigations on other additives that may provide cost-effective mitigation of enteric methane from beef and dairy cattle.
4. Diet manipulation is an effective way to manage manure nitrogen and phosphorus. Manure provides plants with nutrients necessary for crop production. Manure use as fertilizer holistically recycles nutrients and promotes sustainable food production systems. However, problems arise when manure is applied improperly. In many cases, there is insufficient surplus land on which to safely apply excess nitrogen and phosphorus. This is particularly true in the Southern High Plains, where most cattle producers import rather than grow cattle feed. Diet manipulation, where nutrients are fed to meet, but not exceed, animal requirements help balance farm nutrients. Other alternatives include manure treatment systems, such as anaerobic digestion or microbial remediation, to remove and recycle excess nitrogen and phosphorus from beef and dairy manure. However, regional water availability makes many manure treatment systems impractical, such as anaerobic digestion or fertigation. Research by ARS scientists at Bushland, Texas is ongoing to study cropping systems, manure management and application systems, manure application rate and timing for producers in the Southern High Plains. Improved understanding of the value of manure will enhance its use locally as a crop nutrient.
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