Manure and The Shell Game
Posted: February 5, 2005
Everything has to be someplace – land, air or water. So where does that leave manure? It gets spread on the land, runs into the water or volatilizes into the air. Too much manure in the wrong place causes problems and under the right conditions air, land and water can all be the wrong place!
Sometimes our efforts are like trying to guess which shell the carnival huckster has the pea under. Is the manure going to end up under the land shell, the water shell or the air shell?
Historically, manure was put on the land to help grow crops. Livestock farms were at an advantage over earlier grain farms because they could return manure to the land to aid in crop production. However, putting too much manure on the land just leads to more in the surface and ground water. When manure is lying on floors or in gutters, open storages or on top of the ground harmful components can escape to the air. Up until recently manure and air quality meant odor. Now it can also mean degradation of air quality from volatilized ammonia, escaping hydrogen sulfide and even precursors for fine particulate matter. It can be complicated and confusing evaluating animal housing systems and manure handling, storing, treating and spreading methods for nutrient flows and air emissions.
Some feel that adding a treatment process can solve the problem. In reality whether it’s a biogas unit, treatment lagoon, a solids separator or just a manure pile, none of these shells are automatic solutions. They may change the form or offer storage for the nutrients but they don’t destroy N, P or K. Gaseous forms of nitrogen can be driven off but, depending on the form, it may cause more problems in the air. Nitrogen lost to the air as nitrogen gas, a common constituent of air, is OK; but nitrogen released as ammonia, nitrous oxide or other nitrogen components are not desirable. Phosphorus and potassium may settle to the bottom of large lagoons or ponds giving the impression that their amounts have been reduced. When the lagoon fills up or is better agitated during clean out the P and K magically reappear. Add to this conundrum that there is competition beyond animal manure for use of the land, air and water shells. Municipalities and industries are interested in the land shell as a receptor for nutrients (NPK) removed from their waste streams by treatment plants. Homeowners, highway builders, developers and commercial enterprises are also interested in land for other uses. Wastewater treatment plants also want to discharge N under the water shell. All of us want to have high quality air under the air shell to breathe while adding emissions from our cars, homes, and factories. In many places the amount of nutrients that can be safely handled under the three shells has already been exceeded.
What’s a cow to do? Eat right, make efficient use of nutrients and handle manure correctly and responsibly. When evaluating and selecting a manure handling strategy it is important to expand the boundaries of the system beyond just the barn, treatment unit or field. It starts at the selection of the location of the animal unit, not only on the farm but also where the farm itself is located. What are existing conditions of land, air and water and their ability to absorb more materials? Feed ration, animal housing, management, manure handling and cropping methods all should be evaluated based on where the manure and its constituents eventually end up. When comparing manure strategies check under all the shells to assure that you aren’t just moving the problem under a different shell rather than solving it. Also, before expanding or establishing a dairy facility check out what’s already under the land, air and water shells from existing agricultural, municipal, transportation and commercial sources.
Robert E. Graves, Agricultural and Biological Engineering Extension