Compost has been a staple for the organic gardener and farmer for centuries. Scientific studies, along with years of anecdotal evidence, attest to the value that compost can bring to your growing environment. Even farmers who rely on chemically-managed crop production techniques are increasingly adding compost to their practices.
Compost provides organic matter, a broad range of nutrients and active biology – all important elements of a rich, healthy organic soil. However, the quality and safety of composts vary dramatically based on the source of composted material and the composting process itself.
Organic materials used in industrial and commercial composting include yard debris, livestock waste, human food waste, industrial waste (such as unused carrot tops) and agricultural field waste – specific materials are primarily based on what is available to a local composter. These organizations will use aerobic methods (high temperature), anaerobic methods (low temperature) or a combination to decompose their raw materials in to a compost product.
These sources of organic inputs have potential harmful qualities: pesticide residue (debris from chemically-treated environment, pesticide-treated food sources, manures), weed seeds (discarded weed material), pathogens (most manures) and natural toxins (debris from black walnut trees).
Proper composting techniques using low-risk organic inputs can eliminate many of these potential hazards although some composters will ‘over process’ their product in order to minimize this risk, destroying many of the nutrients and microorganisms that are the foundation of effective compost.
As you can imagine, this wide range of inputs and production techniques result in composts whose quality and risks range widely as well. Examples of compost quality:
- % nitrogen ranges from 0.27% to 7%
- pH ranges from 5.7 to 9.2
- ppm arsenic ranges from 6 to 15 (the EPA considers .43 ppm in soil a cancer risk, the average US soil contains 5 ppm)
I am a huge advocate of using compost as part of an organic program. However, I strongly recommend that you know your supplier, their input materials and their composting processes, particularly when using compost on food crops. Find a supplier who is willing to share this information with you. If you want consistent, high-quality results from your compost, stick with your trusted source.
Compost Research – due to the focus on chemical management practices in the past century, as is true of many organic growing methods, limited research has been performed on the subject of compost.