Purpose
Methane emissions from manure storages significantly contribute to the livestock industry’s carbon footprint. While various manure management strategies are used to reduce greenhouse gas (GHG) emissions on farms, such as anaerobic digestion and composting, many of these strategies are cost-prohibitive for small-to-medium-sized farms. Strategic manure application timing to limit GHG emissions is a practical, scalable option to reduce methane production in manure storages.
Carbon credits are financial incentives for farmers who adopt practices that reduce greenhouse gas emissions, such as cover crops or methane emissions abatement. These credits can then be sold to companies seeking to offset their emissions. This study evaluates the impact of manure application timing on methane emissions from storages and explores how carbon credits could act as an incentive for farms to employ climate-smart manure management practices. By comparing different manure application strategies (fall, spring, in-season sidedress, and split applications), we assess the methane reductions and improved economics of optimized timing.
What Did We Do?
Methane emissions were estimated using data from a lab-based study conducted by Andersen et al. (2015), who measured methane emissions from deep-pit swine manure at various temperatures. From this data, we created a model incorporating manure production rates and ambient temperature dynamics to predict daily methane emissions from a 4800-head slurry storage and 4800-head deep-pit swine production facility.
Seven application scenarios were compared: fall (November 1), spring (April 15), sidedress (June 1), fall-spring, fall-sidedress, spring-sidedress, and fall-spring-sidedress split applications. Total methane emissions were calculated for each scenario, allowing us to determine the GHG emissions abated by shifting from a fall application to an alternate strategy. An economic assessment was conducted using a $30/metric ton carbon dioxide equivalent (MT CO2e) carbon credit valuation to determine the financial implications of these methane mitigation strategies.
What Have We Learned?
For our swine slurry store model, methane emissions were highest in the single fall application scenario due to the full storage attained during peak summer temperatures, with annual emissions totaling nearly 0.5 MT CO2e/pig-space (Figure 1). Shifting application to spring or sidedress reduced emissions by approximately 50%. Split applications showed a further reduction in emissions by maintaining lower storage volumes throughout the year.
From an economic perspective, carbon credits significantly enhanced the financial viability of the new application strategies. Carbon credits from abated emissions are projected to bring a maximum of $10/pig-space, or about $74/acre, to the farm annually in the F-S-SD scenario (Table 1). The improved manure application timing can also benefit crop yield, making a spring or sidedress manure application even more economically favorable.
Table 1: Projected carbon credit income for a 4800-head wean to finish swine farm with a slurry storage for fall, spring, sidedress, fall-spring split (F-S), fall-sidedress split (F-SD), spring-sidedress split (S-SD), and fall-spring-sidedress split (F-S-SD) applications.
| Fall | Spring | Sidedress | F-S | F-SD | S-SD | F-S-SD | |
| Carbon Credit Income
($/acre) |
$ – | $ 33.63 | $ 33.71 | $ 41.95 | $ 45.82 | $ 45.69 | $ 52.06 |
| Carbon Credit Income
($/pig-space) |
$ – | $ 6.50 | $ 6.51 | $ 8.10 | $ 8.85 | $ 8.83 | $ 10.06 |
Future Plans
Further research should be conducted to refine the temperature aspect of the model. In the slurry store model, we assume that the manure temperature equals the 10-day average temperature. A study to verify the true manure temperature throughout the year would improve the confidence level of the current model. For deep pit barns, we use measured temperature data from 58 barns over 13 months, but manure temperatures were collected from the manure pump out access port and may not represent average manure temperatures in the barn. Future models to assess differences between deep pit and slurry store emissions will highlight the optimal manure management strategies for limiting GHG emissions.
Using specialized high-clearance irrigation equipment, like the 360 RAIN from 360 Yield Center, could enhance the feasibility of more frequent manure applications, reducing methane emissions while maintaining crop nitrogen availability. Additionally, developing standardized carbon credit protocols for manure management could create opportunities for more producers to monetize methane reduction efforts, further incentivizing climate-smart manure application strategies.
Authors
Presenting author
Jacob R. Willsea, Graduate Research Assistant, Iowa State University Department of Agricultural and Biosystems Engineering
Corresponding author
Daniel S. Andersen, Associate Professor, Iowa State University Department of Agricultural and Biosystems Engineering, dsa@isatate.edu
Additional Information
Andersen, D.S., Van Weelden, M.B., Trabue, S.L., & Pepple, L. M. (2015). Lab-assay for estimating methane emissions from deep-pit swine manure storages. Journal of Environmental Management, 159, 18-26. https://doi.org/10.1016/j.jenvman.2015.05.003
Talkin’ Crap Podcast Episode:
Andersen Lab Poster Repository:
https://iastate.box.com/s/3kkzdzcjlk9qcfrgbv6mj9x7vdk1v0fp
Acknowledgements
USDA-NRCS
Brent Renner
360 Yield Center
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