A Chemical Analysis of Worm Castings
I’ve always been curious about the content of worm castings. I have seen and experienced anecdotal evidence that the castings I pull from the bottom of my bin are extremely good for the plants to which I apply it.
There are a number of pages with the mineral content of worm castings, including this one, this one and this one, but I wanted to know what my own castings contained. I don’t doubt that the contents of your bin are going to depend on what you put in it. For example, I’d expect eggshells in the feedstock to increase the calcium content, and crushing those eggshells would probably increase that further.
I decided to contact my local soil testing lab and see what their analysis found. I dug a worm castings from the bottom of my bin and sifted them to remove any large chunks of wood and undecomposed material. I let them dry for a night, placed them in a labeled plastic bag, and filled out a form specifying tests I wanted. I mailed the whole package off to the lab.
Six weeks later, after a phone call to remind the lab I was waiting for results, I received the analysis. Here are the comments from the soil lab:
pH, which was 7.9, was “sufficient for a soil amendment.” Most plants have a pH range they prefer.
Electrical conductivity or salts: “The salts are elevated, however this material can be safely used as a soil amendment if it is used at the recommended application rates.” They didn’t give me recommended application rates, however.
Lime estimate: low, which “indicates less than 1% CaCO3.”
Sodium adsorption ratio (SAR): “Low; sodium is not a problem.”
Everything else tested had “high” levels, including O.M. (Organic Matter), NO3-N (Nitrate-Nitrogen), P (Available Phosphorus), K (Available Potassium), Zn (Available Zinc), Fe (Available Iron), Mn (Available Manganese), and Cu (Available Copper).
Numbers (ppm) and such available in the Full Worm Casting Analysis Report.
6 comments November 12th, 2008
