You can call it manure, guano or dung, but most farmers call the excreta from livestock ‘money in the bank’ for its significant value as a fertilizer. As long as humans have practiced agriculture, livestock manure has been used to improve crop production. In fact, Webster’s defines manure as “material that fertilizes the land” first, followed by a secondary definition referring to livestock excreta. Well-managed land application of the high value fertilizer nutrients in manure can increase crop yields. Additionally, organic matter applied to fields will assist with moisture and nutrient retention and can also reduce soil erosion.

Primary nutrients contained in manure include nitrogen, phosphorous, and potassium, as well as micronutrients. The composition of available nutrients will vary according to several factors including but not limited to:

• Animal species and age
• Feed and dietary supplements
• Housing and bedding systems
• Liquid and solids content
• Storage methods
• The age of the manure
• Land application systems

According to the USDA’s 2009 report “Manure Use for Fertilizer and for Energy – Report to Congress”, there is an increased use of manure to supplement commercial fertilizers in modern agriculture. This is mostly due to rising prices of nitrogenous and phosphatic commercial fertilizers. The report also indicates the economic value of the manure will vary due to local supply and demand factors. In some cases, livestock facility operators are paid for their manure by other users. In other cases, farmers are paying others to get rid of it or paying for use of land to apply it.

This article is primarily focused on use of manure from dairy farm cows, but the concepts discussed also apply to manure from other animals. Dave Tollberg, an agronomist and owner of Northland Crop Consulting, says, “Available nutrients from the manure produced on any farm will vary, so I recommend sampling the manure to get accurate amounts.”

Manure management systems at dairy farms will vary based upon many factors, including housing and bedding systems, available space for storage, value of land, value of the manure as fertilizer, local weather patterns, and numbers of animal units. Large concentrated animal feeding operations (CAFOS) have significant requirements around manure management operations, emergency spill response, monitoring, and comprehensive nutrient management plans for agricultural application of manure.

Generally, the manure being used for agricultural purposes is “raw”. But Dan Hedrington and Mark Broses, waste management specialists at SEH (Short, Elliott, Hendrickson, Inc.), note there is an increased interest in composting and renewable energy applications, so it is likely the manure management options employed at dairy farms may result in a variety of manure resources including:

• Raw Manure
• Composted Manure
• Anaerobically Digested Manure
• Manure BioChar (Terra Preta)
• Manure Combustion Ash

The USDA NRCS has an informative memo “ Manure Chemistry –Nitrogen, Phosphorous, & Carbon”, that provides a summary of various nutrient values related to raw and treated manures. A link is provided further down in this document.

Raw Manure
Tollberg works with many dairy farmers in the Midwest. He says a thousand gallons of liquid dairy manure has approximately 12 lbs nitrogen, 6 lbs P2O5, and 18 lbs K2O available over a 2 year period. Most of this is available the first year. Similarly one ton of daily hauled manure has 5 lbs nitrogen, 4 lbs P2O5, and 8 Lbs K2O.

“With current fertilizer prices, the value of liquid manure is around $13.50 per 1000 gallons and daily hauled manure at $6.75 per ton. It is easy to realize at least $200.00 per acre or more worth of fertilizer with manure applications per year,” Tollberg observes.

This is important when owners are evaluating potential uses for their manure such as renewable energy opportunities or waste disposal methods. When quantifying the actual value of waste, consider the offset of expenditures that might be incurred if other fertilizers need to be purchased. This can be done by testing existing soils in fields considered to determine the existing nutrient status. The nutrient status needs to be compared to the nutrient needs of the proposed crops. These two items compared to the nutrient value of the manure can help to associate a dollar value to the manure.

While offering multiple benefits, there are costs associated with manure spreading. Manure storage, tank agitation, hauling and applying are potential expenditures. Each facility needs to complete research to determine the actual dollar value of their manure.

Tollberg adds, “Of course along with the value of manure comes the expense of getting it to the fields. I work with many farmers who will say that some of their fields will not get any manure because it is too far to haul. It takes too much time and cost too much. This is a logistical problem for many large producers.” He says custom hauling has helped with this problem. The ability to move large quantities of manure using big equipment and a large fleet has helped the dairy producer with the time aspect. The distance to the field will still add expense to the application.

Large livestock facilities can be faced with the problem of securing land to make applications of manure. The rates and timing of manure applications are regulated for CAFO’s to address environmental concerns such as groundwater and surface contamination from over application of nutrients.

Where phosphorous levels are too high, some fields can not be used for land spreading until the levels fall within the guidelines. Nutrient Management Plans will restrict the application rates of manure in winter as well as prohibit manure applications on slopes are too steep. In developing a manure management plan, both the value of the manure and the management concerns need to be considered to best optimize the resource.

Treated Manure
Other environmental concerns associated with storage, handling, and application of raw manure include odor control and pathogen exposure. This, along with the continual expansion of residential homes in agricultural areas has limited many farm expansions and caused farmers to reconsider areas that they have historically spread manure. Complaints by neighbors, or alternate higher economic values of land can have a significant impact. Use of treatment technologies such as composting, anaerobic digestion, or thermal treatment may provide some options to address these issues.
Composting occurs naturally through the biological decomposition of organic materials. During the process, odors are reduced and heat is produced, (usually between 122 and 140 degrees F). The heat kills pathogens and plant seeds and ultimately produces a stable product. The final compost material is valuable as fertilizer but can also be used for animal bedding or sold to consumers.

In addition, the process generally reduces the volume to about one third of the original mass, so if it is field applied it can be less costly to transport.

Thermal treatment technologies (pyrolysis, gasification, and/or combustion) may also prove to be feasible manure management options in locations where:

• Land values are high
• Significant nutrient restrictions are in place
• Value of manure is low
• The value of renewable energy is high

Anaerobic digestion of manure is increasingly being used at dairy farms to create biogas as a fuel source for heat, electrical power generation, and natural gas replacement. While anaerobic digestion does not significantly decrease the nutrient value or the volume of waste, it can effectively destroy pathogens and reduce odors. The modification of odors to a more palatable scent could potentially give the producer opportunities to spread manure over a longer season or in areas that they might have needed to bypass because of pressures from local residents. Separation of solids from digested manure may provide a supplemental product for retail sale as a soil amendment, provided that the USEPA Class A standards for biosolids are met.

The use of pyrolysis is being evaluated in Wisconsin, Australia, and Europe to determine the economic value of creating biochar from waste manure. The thermal process results in a large reduction in overall waste volume and transport costs. Biochar, similar to Terra Preta, can be utilized as a soil amendment to increase nutrient retention and soil moisture, and absorb herbicides and pesticides. The Wisconsin Department of Agriculture, Trade and Consumer Protection published a 2006 report “Market Feasibility for Products Developed at the Cashtons Green Energy Park” with a comprehensive summary of this technology.

Another thermal technology being employed in Wisconsin is the EcoCombustion Energy System. This system uses gasification and combustion technology to effectively burn manure for heat and power production. More information on this system can be found at www.burnmanure.com. Paul Schneider, CEO of EcoCombustion reports the resultant ash is less than 3 percent of the original manure volume and can be used as a soil amendment. Nitrogen values in thermally treated manure are typically very low, but phosphorous and potassium remain with significant fertilizer value.

Closing
SEH’s Hedrington says engineers who specialize in agriculture waste can help farmers develop and implement customized manure management solutions.

“So many options exist that it can be beneficial to have a consultant help identify the optimal approach, based on an individual farmer’s situation,” he says.

Like the old saying goes...”Money is like manure. It’s not worth a thing unless you spread it around, encouraging young things to grow.” For farmers, using manure and spreading it around often are the best ways to spread the wealth.

For additional information:

• Manure Use for Fertilizer and for Energy – USDA Report to Congress, June 2009 (http://www.ers.usda.gov/Publications/AP/AP037/AP037.pdf)
• How much fertilizer do your animals produce? (http://learningstore.uwex.edu/assets/pdfs/a3601.pdf )
• Manure Chemistry –Nitrogen, Phosphorous, & Carbon, USDA Natural Resources Conservation Services, August 2007, Manure Management Information Sheet No. 7 (http://www.or.nrcs.usda.gov/technical/engineering/environmental_engineering/Compost_Netmeeting/Manure_Chemistry_Info_Sheet.pdf)
• Building Soil Organic Matter with Organic Amendment, University of Wisconsin 2002 (http://www.cias.wisc.edu/wp-content/uploads/2008/07/soilorgmtr.pdf )
• Comprehensive Nutrient Management Planning – USDA Natural Resources Conservation Services website (http://www.wi.nrcs.usda.gov/technical/cnmp.html)