Composting animal manure has long been used as a soil amendment to improve soil health. Composting has increased use as a tool to manage animal manure in recent years for livestock producers. In addition to the soil health benefits associated with applying animal manure compost, other advantages include improved storage options, reduced volume of material to be transported and spread on fields, and it is more suitable to be spread on hay and pastures during the growing season than raw manure.
Composting is a biological process in which aerobic microorganisms decay organic materials such as manure and bedding into a soil like substance. Good composting requires a mix of ingredients that allow the microbial population to consume carbon and nitrogen. A carbon to nitrogen ratio of 25-30:1 is ideal while a ratio of 20-40:1 is acceptable. Moisture content also must fall into a certain range. The ideal range falls between 50-60 percent with 40-65 percent being reasonable. Most well bedded manure pack falls into an acceptable range for both carbon to nitrogen ratio and moisture content. Michigan State University Extension educators recommend On-Farm Composting Handbook, NRAES-54 Natural Resource, Agriculture and Engineering Servic,. 1992. as a reference for composting management practices.
Pure manure is frequently too high in nitrogen and moisture content to be properly composted. However, manure can be mixed with other carbon sources such as straw, corn stover, wood residue, or leaves to balance the carbon to nitrogen ratio and moisture content. Piles of compost are formed and allowed to begin the composting process. During the process aerobic organisms consume the nitrogenous and carbon compounds with oxygen and generate organic matter, carbon dioxide and heat. As heat builds up within the pile and oxygen is depleted a mixing or stirring process is required to release heat and replenish oxygen within the pile. The stirring process can be conducted by special windrow turners or by tractor or end loader with a bucket. Microbe populations within unturned piles will quickly die from the excessive heat of from oxygen starvation.
The composting process of well managed piles can be mostly completed within 4-8 months. High quality compost requires additional time for curing of 2-4 months. High quality compost will be thoroughly decomposed, be more soil like and contain more humus. Unfortunately that time frame may not allow for the composting process to be completed and then spread before winter. Unfinished compost can be spread during the fall months but will be limited in its benefits of fully composted material. The compost material will reduce in volume through the process by about 30 percent. Compost material will be more thoroughly reduced if the process is completed and require less time for spreading.
Compost can be spread on hay fields and pastures without the disadvantages of spreading manure directly. The soil like structure of compost frequently falls to the ground and allows grass to more easily grow through the material than manure pack. Animals are more likely to efficiently graze after compost spreading as opposed to spreading raw manure.
Composting can be an effective manure management practice for livestock operations. For more information on composting animal manure and its use on forage fields contact Frank Wardynski, Ruminant Extension Educator with Michigan State University at email@example.com or 906-884-4386.