What is the manure module and what does it do?
The manure module is one of the biophysical modules within RuFaS. After the animal module has modeled animal excretion, the manure passes to the manure module where it is removed from the housing area by a manure handler, digested and/or separated if appropriate, and stored.
The manure module tracks nitrogen, phosphorus, carbon, volatile and total solids excreted by the animals as the manure moves throughout every step of the manure management process. It tracks losses of these components to emissions and leaching and holds manure until it is either exported off the farm or spread on fields in the crop and soil module. Climatic factors (temperature and humidity) as well as the type and quantity of bedding mixed into the manure impact the losses and composition of manure as time progresses.
The manure module is linked to the animal module through the pen designation in the animal module. At a minimum, each animal category must have a pen and that pen must be linked to a manure management scenario. The same scenario can be repeated for multiple pens, or each pen could have its own manure management scenario. A manure management scenario consists of bedding type, manure handler, separation and/or digestion, and storage.
The manure module is also connected to the crop and soil module through the manure field connector. Through this connection, the crop and soil module requests manure from the manure module based on the application information provided by the user. For more information on manure field application check out the description in the crop and soil module!
What can the user change in the manure module?
Bedding
Bedding quantity, dry matter, and nutrient composition can be edited in the manure module. There are 4 main types of bedding (sand, sawdust, straw, and manure solids) but no bedding is also an option.
Manure handlers
Manure handlers can be edited in RuFaS to clean at different frequencies and use differing amounts of water (recycled or fresh) for cleaning.
Separators
Mechanical manure separators can be configured in RuFaS to have varying amounts of separation efficiency on components including total and volatile solids, and nutrients (N, P, and K).
Digesters
The default digester in RuFaS is modeled as a complete mix digester with 25 days of retention time. Aspects of the digestor can be configured including accumulation period and volume, temperature set points, and methane leakage (default 1%).
Manure storage
There are many options for manure storage in RuFaS including composting, compost bedded pack barns, open lots, slurry storage underfloor or outdoor, and anaerobic lagoons. Storage time period is one of the biggest factors impacting emissions from storage and can be edited to meet user specifications. On liquid manure storage the addition of covers, crusts, or cap and flare systems can also be modeled.
What are the inputs of the manure module?
As alluded to above, each pen from the animal module must be linked to a manure management scenario and these manure scenarios can be repeated across pens or uniquely defined for each pen. Scenario inputs include:
Bedding: type, quantity, and nutrient content
Handler: type, water usage, frequency
Separation: type, separation efficiency
Anaerobic digestion
Storage: length of time, cover/crust/cap and flare on liquid manure storage
What are the outputs of the manure module?
While the total list of manure module outputs can be accessed through use of the model, a few key outputs of interest that are available by pen or animal class include:
Manure storage emissions (N2O, NH3, CH4)
Biogas capture from anaerobic digestion and avoided CH4 emissions through use of a cover and flare system
Manure composition (N, P, K, volatile solids, total solids)
Quantity of manure
What is the future of the manure module?
Non-mechanical separators: Mechanical separation was the first undertaking in separation by the RuFaS team due to its feasibility and the knowledge base surrounding its function. We recognize that other separation systems including weeping walls, gravity lanes, vermifiltration, and more exist. Given the amount of time manure spends in these systems, they are more complex to model as losses (emissions) will occur in these systems, but they have not been forgotten by the team and will be integrated.
Digesters: Complete mix anaerobic digesters are not the only type of digester that is in use on dairy farms today, others include plug flow and covered lagoons. In the future, these digester types will be options in the manure module.
Daily spread: The current workaround in RuFaS with daily spread is to set manure storage time to 1 day. In the future, we plan to integrate this more closely with field application.
Pasture: Grazing and pasture management (and associated manure deposition on pasture) is not a current feature of RuFaS and can only be approximated with daily surface manure application. The intent of a future submodule on this topic is to capture the different ways pastures can be managed and reflect the impact of grazing animals on pastured soils and crops.