Saturday, December 8, 2012

N-P-K Value of Vermicompost

One question I often get concerns the N-P-K of worm castings.

The first thing I want to discuss is the difference between worm castings and vermicompost.

Worm castings are literally worm poop. The processed material that has been eaten by worms and been excreted. If you have worm castings then you have worm poop. This is nearly virtually impossible to achieve in a home vermicompost system since the worms will run out of food and die before you achieve this. 

Vermicompost is more accurate. Vermicompost is what I produce (and most other vermicomposters produce). Vermicompost is a mixture of worm castings, partially composted wastes, and any resistant materials that won’t readily break down. Really high quality vermicompost should have a high percentage of worm castings, but will also contain some other material (my vermicompost often has some egg shells, coffee grounds, and some small pieces of bedding). These are not contaminants, as they don't harm anything when used to make tea, start seeds, or as top dressing (things I commonly do with my vermicompost.
So, I will use the term vermicompost in this discussion to be accurate. 

When I've had my vermicompost tested the results have sometime come back high (once as 2-1-1), but more commonly much lower (1-0.5-0 or 0.5-0-0) typically with high calcium (these probably differ depending on what I've fed the worms).

Do these numbers seem low to you? They would if you were to compare them with commercial fertilizer. However, the value of vermicompost (or worm castings) is more significant than a standard N-P-K fertilizer scale would suggest.

The N-P-K fertilizer scale was developed to give consumers information about hat hey were purchasing in commercially bagged fertilizer-- it tells you what's in the bag so you know how to apply it.

Vermicompost is far more complex than chemical fertilizer, and it contains many other substances (biological and chemical that improve soil and support healthy plants. Some of these include humus, worm mucus, and plant growth promoters like cytokinins.  In addition, vermicompost commonly contains ten times as much microorganism activity as plain soil (microscopic bacteria and fungi). 

All of these support a healthy soil food web. The microorganisms in the soil are able to provide the plant with everything it needs to be healthy. Because the soil is a living system there is no excess fertilizer to run off. Healthy soil makes for healthy plants.

The humus and worm mucus in the vermicompost helps the soil hold more water, retain its structure (or tilth), and stay aerated, while also providing binding sites for micronutrients that would otherwise wash out of soil during heavy rains. 

So, as you tend to your worm bin this winter think about the great soil amendment that your worms are making and how wonderful your garden will be next year...



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