Organic matter stability — why is it so important?

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Organic matter stability is one of the basic markers of a quality compost product.  It is an essential delivery mechanism for compost’s many benefits.

Biodegradation is nature’s way of recycling all plants and animals, breaking down organic matter (OM).  Complex molecular structures become simple compounds and, finally, chemical elements.  These the basic building blocks of life form the planet.

Complete biodegradation takes a long, long time.  But between the death of the organism and its eventual disorganization into atomic parts exists a phase where the degradation process becomes resistant or stabilizes.

While it can take centuries to reach this stage naturally,  composting can speed up stabilization.  Composting is a manufacturing process based on the application and control of nature’s recycling system.  It can achieve OM stabilization in a matter of days or weeks, depending on the  process employed.

Use a stable compost

Using a stable compost adds stable organic matter to the soil.  Stable organic matter can absorb many times its weight in water and hold more nutrients.  Organic matter in the form of living microbial biomass and detritus contribute to soil fertility.  But the stable fraction – humus – is responsible for the soil’s structure, tilth and cation exchange capacity (nutrient-holding capabilities).

Stable organic matter gives compost many of its unique properties.  Compared to compost, the organic matter content in fresh manure is of low stability.  As for peat moss, one study even suggests it may reduce overall soil stability. (Apart from the negative environmental impacts associated with peat, it is generally regarded as too expensive for large-scale projects.)

“Stability” isn’t necessarily something one can see.  But there are tests which can determine if organic matter (like compost) has reached a stable state.  Stability is a standard testing parameter for manufacturers participating in the U.S. Composting Council’s(USCC) Seal of Testing Assurance (STA) program.  As participants in the program, McGill’s U.S. facilities test every month.

Ask for the STA

The STA is a compost testing, labeling and information disclosure program designed for consumers.  It provides the information needed to get the maximum benefit from the use of compost. The program was created in 2000, and the tests were compiled by leading compost research scientists.  When purchasing from a producer with the STA seal, consumers know the product has passed rigorous testing.  It offers assurance related to compost quality.

When shopping for compost, ask for the STA.  Set a minimum target of five percent stable organic matter to improve soil performance.  Combine the STA with soil testing to determine compost application rates.

When it comes to economy, ease of use, and efficacy, a stable compost is the better amendment choice. More information on the STA and what the program entails can be found on the U.S. Composting Council‘s webpage.

SOURCES:  Cornell Cooperative Extension’s Agronomy Fact Sheet #41, University of Minnesota Extension, Organic-matter effects on soil strength properties