Location: Livestock Nutrient Management ResearchTitle: Nitrous oxide emissions from southern high plains beef cattle feedyards: Measurement and Modeling
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2017
Publication Date: 9/30/2017
Citation: Waldrip, H., Todd, R.W., Parker, D.B., Casey, K.D. 2017. Nitrous oxide emissions from southern high plains beef cattle feedyards: Measurement and modeling. Transactions of the ASABE. 60: 1209-1221. doi: 10.13031/trans.12085.
Interpretive Summary: Nitrous oxide is potent greenhouse gas, and current methods to estimate nitrous oxide losses from beef cattle produce inaccurate results. Researchers with USDA-ARS at Bushland and Texas A&M AgriLife in Amarillo measured nitrous oxide on commercial feedyards. Nitrous oxide losses were very variable and ranged from zero to 216 pounds per acre each day. Greater emissions occurred when manure was wet, and temperature and nitrate concentrations were high. Lower emissions were seen when manure organic matter was stable. Mathematical models were developed and were 52 to 61% accurate at predicting feedyard nitrous oxide losses. It was concluded that valid estimates will require additional information.
Technical Abstract: Predictive models for nitrous oxide emission are crucial for assessing the greenhouse gas footprint of beef cattle production. The Texas Panhandle produces approximately 42% of finished beef in the U.S. and cattle production is estimated to contribute 8 Tg carbon dioxide equivalents from nitrous oxide. However, nitrous oxide production from manure is a biochemical process that is not static and depends on numerous environmental and chemical factors. Process-based models that estimate nitrous oxide emissions from manure in open-lot cattle production systems typically rely on information derived from studies of soil biochemistry. Limited study has been conducted on manure-derived nitrous oxide in open-lot beef production systems; therefore, little is known about specific factors involved in nitrous oxide emission from feedyards. The objectives of this study were to determine variables related to nitrous oxide losses from Texas Panhandle feedyards and develop empirical models to predict their emissions. Nitrous oxide flux data were collected from a series of 15 non-flow-through non-steady-state (NFT-NSS) chamber studies (10 chambers per study) conducted from 2012 to 2014 on two commercial beef cattle feedyards. Manure samples (loose surface manure and the underlying manure pack) were analyzed for basic physicochemical properties, soluble carbon and nitrogen, and Ultraviolet-visible (UV-vis) spectral characteristics related to degree of organic matter (OM) stability and humification. Measured nitrous oxide emissions ranged from below detection to 101 mg per square meter per hour (average 4.8 + 12 mg per square meter per hour) and were positively related to manure water content, temperature, and nitrate concentration (P less than 0.01). Emissions were negatively related to manure OM, ammonia/ammonium, dissolved carbon and dissolved nitrogen concentrations, and UV-vis parameters related to OM humification (P less than 0.05). Based on these data, empirical models were developed and evaluated to predict manure-derived nitrous oxide emissions. Model predictions were not significantly different from observed emissions (P less than 0.05). The unbounded Index of Agreement (IA) indicated that model predictions were within 52 to 61% agreement with observations. Inclusion of OM characteristics improved model predictions of high nitrous oxide emissions but tended to overestimate low level emission rates. This finding provides evidence for the importance of carbon stability in limiting manure nitrous oxide production. These models may improve parameterization of existing process-based models and are novel methods for predicting feedyard nitrous oxide emissions.