Code of Maine Rules
01 - DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY
001 - MAINE MILK COMMISSION
Chapter 560 - STANDARDS FOR COMPOST PRODUCTS
Section 001-560-5 - COMPOST QUALITY INFORMATION
Current through 2024-13, March 27, 2024
Several quality measures are suggested in the sections describing materials for particular purposes. Some of these quality measures are described here for the convenience of anyone using these standards.
5.A. Compost Stability Levels
Three compost stability levels are recognized. These are:
Mature - Highly stabilized, generally will not reheat to 20 degrees C above ambient, reduction of organic matter greater than 60 percent by weight.
Semimature - In the mesophilic stage (has passed through thermophilic stage but has not completed the mesophilic stage). Generally will reheat to 20 degrees C above ambient temperature. Reduction of organic matter by 40-60 percent by weight.
Fresh - Through thermophilic stage but still in the early part of the mesophilic stage, partial decomposition. Material will easily reheat to 20 degrees C above ambient level. Reduction of organic matter by 20-40 percent by weight.
5.B. Measuring Stability
Stability may be determined by checking for reheating and measuring the reduction in organic matter content. An alternative approach that may be used is to have a laboratory perform an oxidation/reduction test or other test that would measure the level of respiration that is taking place.
To determine if the material will reheat to 20 degrees C above the ambient temperature, follow the following procedure:
Re-pile compost into a pile at least six feet in diameter and four feet high. Provide aeration to this pile. Moisture content of the material in this pile must be between 35 and 60% in order for this test to be valid. Three days after the pile has been formed, the temperature of the compost should be measured at a point about two feet into the pile. This temperature should be compared to the ambient temperature.
The percent reduction of organic matter is a measure of the loss of decomposable material in comparison to the amount present prior to composting. To make this comparison, use the following procedure:
Prior to composting and again following composting, have material tested for the percent organic matter on a dry weight basis. Use these before and after figures to calculate the percent reduction in organic matter using the following formula:
percentage reduction = [1- % A (100-% B)/% B (100-% A)] x 100
Where A is organic matter percentage after composting and % B is organic matter percentage before composting. E.g. using this formula we have calculated the percent of organic matter in the final product necessary to meet various levels of reduction if we started out with 65 percent organic matter.
| % organic matterin original mix (before composting) | % reduction in organic matter | % organic matter in final product (after composting) |
| 65% | 20% | 59.8% |
| 65% | 40% | 52.7% |
| 65% | 60% | 42.6 |
5.C. pH and CaCO3 Equivalency
For most applications, a pH near neutral is desirable so it is important to know the acidity or basicity of the amendment being used. In cases where the pH of the compost material is not close to neutral, ( <6.1 or >7.8 ) the supplier should provide data on either its Liming value or the amount of lime needed to neutralize the product both on a calcium carbonate equivalency basis. For example, if the pH of the material was 5.5, the supplier would be required to indicate how many pounds (CaCO3 equivalents) of liming materials would be needed to bring 100 lbs. of this product to a pH of 7.0. If. on the other hand, the pH was reported to be 8.5, the supplier should indicate how many pounds of CaCO3 equivalents would be provided by 100 pounds of the product.
Measurement of pH. When measuring the pH on compost products, it to test them on an "as is" basis rather than drying them first, since this may affect the results. Given the sample "as is", the pH should be tested by the saturated paste extract method.
5.D. Contaminants
The contaminants that must be measured are those regulated by D.E.P. These are listed in the table below. Acceptable levels of other contaminants will be determined by the use for the product and are discussed in the sections covering specific uses.
D.E.P. ALLOWABLE CONCENTRATIONS OF HEAVY METALS AND ORGANIC CHEMICAL POLLUTANTS
Maximum Permissible Concentrations (mg/kg dry weight)
Cadmium (Cd).......................................................................................................... 10
Chromium (Cr)..................................................................................................... 1,000
Copper (Cu)......................................................................................................... 1,000
Lead (Pb)............................................................................................................... 700
Mercury (Hg)........................................................................................................... 10
Nickel (Ni)............................................................................................................. 200
Zinc (Zn)............................................................................................................. 2,000
Maximum Permissible Concentrations of Organic Chemical Pollutants
Polychlorinated Biphenyls (PCB's)...................................................................... 10 ppm
Dioxin Equivalent
Food Chain Crops.................................................................................... 27 ppt
Non-Food Chain............................................................................. 27 - 250 ppt
* See DEP Landspreading Rules (Chapter 567) for restrictions on the use of land on which this material has been spread.
5.E. Foreign Matter
In many cases, the acceptability of compost based on its foreign matter content can be determined by visually inspecting representative samples of the product. In cases where a more precise approach is needed to determine foreign matter content, the following method, developed by the Florida Department of Environmental Regulations, may be used:
Foreign matter content may be determined by passing a dried, weighed sample of the compost product through a one-quarter inch or six millimeter screen. The material remaining on the screen is visually inspected, and the foreign matter that can be clearly identified is separated and weighed. The weight of the separated foreign matter divided by the weight of the total sample multiplied by 100 is the percentage dry weight of the foreign matter content.
5.F. Reporting Nutrient Content
Section 6 of these rules includes requirements that suppliers provide information on nutrient content of their compost product. Maine fertilizer law, however, requires that products labeled with a nutrient analysis or advertised based on nutrient content must be registered as a fertilizer. This registration requires both the provision of guarantees for the nutrient analysis and the payment of a tonnage tax. It is not the intent of these rules to force compost suppliers to register their product as a fertilizer if, in fact, they are selling it as a soil amendment.
The following standard will be used to determine if a product must be registered as a fertilizer:
