Compost: Production, Analysis, & Regulation
Compost producers and users have many goals; sanitation (e.g. killing pathogens, insect larvae, human parasites, or weed seed), bioremediation (e.g. pesticides, petroleum contamination, sewage sludge), building soil organic matter, improving soil structure and moisture holding capacity, enhancing soil microbial activity, or fertilizing crops. Many growers have access to organic waste materials such as manure, horse bedding, lawn clippings, or leaves and are producing compost on their own farm to achieve these goals. Others are purchasing compost from off-farm. If you are applying compost to your fields, you should know: (1) whether the decomposition process is complete, (2) what the nutritional composition of your finished compost is, and (3) how to comply with current nutrient application regulations.
The decomposition process begins with insects breaking down the “parent material” in your compost into smaller pieces, after which bacteria and fungi take over. The first stage of decomposition is called the mesophilic (“middle-loving”) stage, and it takes place when compost temperatures are 40-100°F. During this stage, proteins, sugars, and starches are oxidized and microbial populations increase rapidly as the compost begins heating up.
The second stage of decomposition is called the thermophilic (“heat-loving”) stage, during which temperatures are between 100 and 140°F. Decomposition rates are fastest and microbial activity is at its highest during this stage. At this stage, active actinomycetes produce the compound geosmin, which smells like fresh earth. If your compost smells like earth at this point, you’re on the right track; if your compost smells like sulfur, that means the pile has become anaerobic and sulfur-producing bacteria are active.
After the parent material has fully decomposed, the resulting compost has to cure. It is ready for use once it reaches 86°F. At this point, the energy- and nutrient-containing materials have been combined into a stable organic mass and the compost is considered mature or finished. The compost should be dark-brown and the parent material should not be recognizable. Further degradation should not be noticeable. The length of the time needed to achieve finished compost will vary with many factors and can take anywhere from a couple of weeks to over a year.
Making sure that a compost is finished before adding it to the soil is very important. Application of an unfinished, carbonaceous compost could adversely affect plant growth since the compost may have its own demand for nutrients as the breakdown to maturity continues in the soil. In addition, immature composts made from nitrogen-rich feedstocks are often high in ammonium, which can be toxic to plant growth. Because of the risks with use of immature composts, farmers would be wise to allow a period of at least a week between application of any compost to land and planting or seeding of crops. Finished compost is a dilute fertilizer, having an analysis of about 1-1-1 (N-P2O5-K2O), but varying with regard to the original materials that were incorporated into the pile and how they were composted.
Compost Composition and Analysis
Many farmers are more knowledgeable about how to make compost than they are about the nutrient availability from compost in production agriculture. In most cases, finished compost is classified as a soil conditioner rather than a fertilizer due to the relatively low levels of nitrogen, potassium, and phosphorus, however federal and state regulations consider compost a fertilizer and it is regulated as such (see following section). Finished compost adds nutrients to the soil but releases them over a longer period of time than chemical fertilizers.
Compost Analysis and Interpretation
For information on interpreting compost analysis results and nutrient application implications, click here.
In Massachusetts, several regulations impact the way that compost is made and used. If producing biosolids compost for commercial use, the EPA (40 CFR Part 503) requirements are:
- Compost produced in vessels or using the static aerated pile method must remain at 131°F for 3 days
- Windrow compost must remain at 131°F for 15 days or longer being turned a minimum of 5 times.
Both federal and state regulations also govern the heavy metal content of composts. In 2014, Massachusetts placed a ban on the disposal of commercial organic wastes into landfills by businesses and institutions producing one ton or more of these materials per week. Also, no leaves or yard waste are allowed in landfills. This regulation has increased the amount of municipal and institutional composts being produced and used across the state, especially in municipalities such as Worcester and Boston which require soil for growing food crops to be built on top of existing soils due to frequent historical lead contamination.
Finally, the 330 CMR 31.00 Plant Nutrient Application Regulations went into effect in 2015 requiring that all applications of plant nutrients, including plant nutrients in composts, be based on soil tests and UMass Guidelines (with some exceptions where guidelines do not exist), and that records of each application be kept by the applicator. Nutrient management plans are required for application of plant nutrients to 10 or more acres of agricultural land.
If you are interested in learning more about making compost on your farm, you can order hands-on manuals from the Natural Resource, Agriculture, and Engineering Service (NRAES) located at Cornell University. Two manuals available are On-Farm Composting Handbook (print copies available for $25 here) and Field Guide to On-Farm Composting.
NRAES, Cooperative Extension, PO Box 4557, Ithaca, NY 14852-4557, phone: (607) 255-7654, email: firstname.lastname@example.org
--compiled by G. Higgins, October 2016, from Get Your Compost Analyzed by Frank Mangan, Allen Barker, and Steve Bodine, 2002, and Compost Analysis and Interpretation by Katie Campbell-Nelson, 2015