Advanced manure treatment may become a major system on some dairy farms in the future. Reducing the impacts of excess nitrogen and or phosphorous may be necessary on farms with a limited or remote land base. Additional treatments to recover solids, extract energy, concentrate nutrients, reduce odors, reduce the mass/volume, and/or reduce pathogens may become more of a priority as farms seek to move toward sustainability. Potential systems should be evaluated from many perspectives including on an economic and effectiveness basis. There are many variables to consider in evaluating a manure management system. Potential systems should be selected based on many criteria including: operational history, operational reliability, market penetration, capital cost, O&M cost, value proposition, and vendor information and documentation including case studies and customer reviews.
What did we do?
Manure management formally started in the second half of the 20th century with the development and implementation of the water quality best management practice (BMP) of long-term manure storage. Storage provides farms with the opportunity to recycle manure to cropland when applied nutrients can be more efficiently used by the crop. Many long-term manure storages were built to improve nutrient recycling and minimize risk. In some cases, anaerobic lagoons were built to both reduce the organic matter spread to fields and store manure. Simultaneously as poultry and livestock consolidation escalated, more manure storages were built and their volume increased to reflect the recognized need to store manure longer. Cooperative Extension, Soil and Water Conservation Districts and Natural Resources Conservation Service have assisted in providing planning, design, construction and maintenance of these manure storage systems.
What have we learned?
Many lessons have been learned from storing manure long-term. They include, but are not limited to:
- While storing manure long-term reduces water quality impairment, it also produces and emits methane, a greenhouse gas. Greenhouse gases are reported to contribute to global warming. The US dairy industry is under attack by some because of this, and it is likely that the decline in fluid milk sales has, in some part, been affected by this. The lesson learned here is that the implementation of BMPs can have unintended consequences; therefore, all future BMPs need to be thoroughly vetted before substantial industry uptake happens in order to avoid undesirable unintended consequences.
- Larger long-term storages are better than short-term (smaller) ones. Storages that store manure for a longer period of time provide farms with increased flexibility when it comes to recycling manure to cropland.
- Long-term storages can emit odors that can be offensive to neighbors and communities. Farms have adopted improved manure spreading practices, namely direct incorporation, to reduce odor issues but incorporation doesn’t work well on some crops. Some farms have also adopted anaerobic digestion as a long-term storage pre-treatment step in order to reduce odor emissions from storage and land application.
- Substantial precipitation can accumulate in long-term storages located on farms in humid climates. Increased storage surface area (generally an outcome of building larger storages) results in more precipitation to store and handle as part of the manure slurry. Every acre-foot of net perception results in 325,900 gallons of additional slurry to store and spread. If each manure spreader load is 5,000 gallons, then this means 65 additional loads are required.
- Neighbors of larger farms are more sensitive to intensive truck traffic than regular but low-level truck traffic. Long-term storages require intensive, focused effort to empty and the over the road truck traffic can be offensive in some farm locations.
- Insufficient storage duration results in the need to recycle manure to cropland during inopportune times and thus may not be contributing to the BMP goal. Fall spreading is still required on many farms; however, it also may be unlikely that a sufficient spring planting window exists for farms to spread all their manure in the spring, avoid compacting wet soils and also get spring crops planted in time.
- Where longer term storage duration and or incorporation of the manure to prevent odor emissions is needed to facilitate spring and summer manure spreading, farms may have more manure nutrients than needed to meet crop demand.
The above lessons learned support the need for advanced manure treatment systems on some farms that can also be used as the basis for considerations that should be included when evaluating all manure treatment systems. It is important that the manure treatment equipment/system components and the overall system address the farm need(s) as best as possible. A challenge with evaluating the existing manure treatment equipment available to the farmer is the lack of performance and economic data. Comparatively, advanced manure treatment (we define this as treatment above basic primary solid-liquid separation) is in its infancy stage of adoption and thus little field performance data exists. Our plans are to continue (as funding allows) to perform more on-farm manure treatment system evaluations and to report facts to our US dairy industry stakeholders.
Corresponding author, title, and affiliation
Curt Gooch, Environmental Systems Engineer, PRO-DAIRY Dairy Environmental System Program, Dept. of Animal Science, Cornell University
Peter Wright, Agricultural Engineer, PRO-DAIRY Dairy Environmental System Program, Dept. of Animal Science, Cornell University
Additional project information, including reports about on-farm assessment of manure treatment systems, is available on the Dairy Environmental System Program webpage: www.manuremanagement.cornell.edu
New York State Department of Agriculture and Markets for their continued financial support of the PRO-DAIRY Program, the New York State Energy Research and Development Authority (NYSERDA) for funding many on-farm sponsored projects, and the US dairy farmers who have collaborated with us for over three decades.
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