Manure hauling, application, and cropping methods are all accounted for in the “Feed Emissions” bucket. The “Feed Production” emissions category uses emissions factors developed following LCA methods and using USDA data. The model makes assumption about average manure hauling / application methods.
The 5% solids cut-off is a good rule of thumb for many situations. However, it is correct that the best distinction of an anaerobic lagoon is one where there is some treatment and deliberate water addition (ie. If we flush the manure out of the barns, if we add water to vacuum it, if we do SLS, etc.). In a case where the only water added is rainwater and maybe wash water (not flush water), the manure pit is likely best described as a slurry.
FARM ES does not currently account for GHG offsets from connecting to a gas pipeline.
If manure solids are used as bedding, they should be categorized as “solid storage” in the FARM ES evaluation, not as “deep bedding”.
We only have the option to specify 2 management strategies for the solid fraction after SLS, so there isn’t a perfect answer to match the farm’s situation. If we could enter more than 2 strategies, we could capture all 4 of the above and weight them by the amount of time (in-vessel composting, windrow composting, sold off-farm, and bedding) – but since we can only do 2, I would focus on those where the manure spends the most ‘time’ of the year, e.g. bedding and sold off farm.
If a farm is using a manure management system not included in FARM ES, the recommendation is to determine the best proxy system that is included in the model.
We would recommend using ‘deep bedding with storage > 1 month’ as a proxy for a compost barn system. The FARM ES model does not list ‘compost barn’ as an option because there is currently insufficient research available on the GHG emissions from compost barn systems.
The Supplementary Data from the Asselin-Balencon paper (https://www.sciencedirect.com/science/article/pii/S0958694612001999) contains a table of manure management emissions factors used in FARM ES (Table S3). The factors are derived from IPCC (2006).
The boundary of the ‘manure’ section of FARM ES is storage and handling. The emissions factor for manure management therefore does not cover emissions after the manure is applied. Because daily spread does not involve manure storage, it has a lower manure emissions factor. Emissions after land application (including daily spread) are incorporated in the feed production emissions category.
The feed production emissions category, which includes an estimate of emissions from land application, is based on LCA research using USDA and other datasets. It is not specific to the farm’s individual field practices.
For additional context, see the following straightforward explanation of the emissions tradeoffs between daily spread and other manure storage. There are many considerations that go into manure management decisions beyond GHGs (e.g. water quality, soil health, etc.). UW Extension has fact sheets on the topic of GHGs and manure.