How well do we understand nitrous oxide emissions from open-lot cattle systems?

Authors: Waldrip, Heidi; CASEY, KENNETH - Texas A&M Agrilife; Todd, Richard; Parker, David; Rotz, Clarence - Al; COLE, NOEL - Retired ARS Employee

Submitted to: Waste to Worth Conference
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2017
Publication Date: 4/10/2017
Citation: Waldrip, H., Casey, K., Todd, R.W., Parker, D.B., Rotz, C.A., Cole, N.A. 2017. How well do we understand nitrous oxide emissions from open-lot cattle systems?. Waste to Worth Conference. Pg. 74413. Available at https://articles.extension.org/pages/74413/how-well-do-we-understand-nitrous-oxide-emissions-from-open-lot-cattle-systems.

Interpretive Summary: Nitrous oxide emissions from concentrated animal feeding operations, such as open-lot beef and dairy cattle systems, is currently a hot research topic due to potential regulation of emissions. In addition, understanding both nitrous oxide production and loss are important to ensure sustainable nitrogen management in open-lot cattle systems for both the producer and the environment. However, there are limitations to current measurement techniques, uncertainty in the magnitude of feedyard nitrous oxide fluxes, and a lack of effective mitigation methods. Scientists from ARS (Bushland, TX. and University Park, PA.) and Texas A&M AgriLife Research assessed nitrous oxide emissions from open-lot cattle pens, including comparison of measured and modeled emission rates, discussion of measurement methods, evaluation of mitigation options, and pinpoint areas that require further research. Published annual flux rates for open-lot feedyards and dairies were highly variable and ranged from 0.002 to 4.3 kg of nitrous oxide per animal. Overall, the magnitude and dynamics of nitrous oxide emissions from open-lot cattle systems are not well understood. Further research is required to quantify feedyard nitrous oxide fluxes, standardize measurement methods, and develop cost-effective mitigation methods.

Technical Abstract: Nitrous oxide is an important greenhouse gas that is produced in manure. Open lot beef cattle feedyards emit nitrous oxide but little information is available about exactly how much is produced. This has become an important research topic because of environmental concerns. Only a few methods are available to measure feedyard nitrous oxide and it is unclear which methods are appropriate. We need a better understanding of how nitrous oxide is produced and how it can be controlled cost-effectively. In addition, improved understanding of manure nitrogen transformations is needed to see how gaseous losses differ with changes in weather and management. Researchers at the USDA-ARS Conservation and Production Research Laboratory in Bushland, Texas looked at the current understanding of nitrous oxide losses from beef cattle feedyards. We wanted to compare measured and modeled nitrous oxide emission rates and compare different measurement methods. Another goal was to assess potential methods to reduce feedyard nitrous oxide losses. In laboratory and field studies, we measured nitrous oxide emission rates from manure. Then we developed new mathematical models to predict rates of feedyard nitrous oxide loss. Temperature and manure water and nitrate content were important for accurate prediction of nitrous oxide from manure. Nitrous oxide is produced by microbes that use soluble carbon as a growth substrate. These studies showed that the stability of the carbon in manure was important in predicting emissions. Nitrous oxide losses were lower when the carbon was less available to microbes. We found that published nitrous oxide emission rates were highly variable. They ranged from almost zero to 4.3 kg of nitrous oxide per animal each year. This variability was due to differences in manure management practices and animal diets among open lot cattle systems. However, other major causes of variation were the use of different measurement methods and changes in nitrous oxide production due to weather. In 15 experiments, nitrous oxide was measure from chambers placed in pens at commercial Texas feedyards. Measured nitrous oxide losses ranged from below detection to 101 mg of nitrous oxide per square meter per hour. Manure was then analyzed to determine what characteristics were related to these nitrous oxide losses. From there, two mathematical models were developed. Predictions made with both models agreed by 52 to 61% to measured nitrous oxide emission rates. Inclusion of organic matter data tended to improve model prediction accuracy, but more work is needed to make these models useful for feedyard conditions. This work showed that neither the amount of nitrous oxide lost from feedyards nor how it was produced were well understood. Five primary knowledge gaps were identified for further research. These were: (1) improved and somewhat standardized nitrous oxide measurement methods; (2) better understanding of manure microbiology and chemistry; (3) better understanding of factors that influence feedyard nitrous oxide emissions; (4) cost-effective and practical methods strategies to reduce nitrous oxide emissions from different manure storages on feedyards; and (5) improved mechanistic models for forecasting feedyard nitrous oxide losses. It is likely that nitrous oxide emissions will be regulated in the future. It will be important to manage manure nitrogen to limit nitrous oxide losses to balance the economics of beef production with environmental concerns.