Boulder Vermicomposting

Vermicomposting Horse Manure

July 18th, 2009

Via the Manure Management articles section of the Equine Extension department of Colorado State University, I found this interesting article on vermicomposting horse manure.  It references another article about composting horse manure quite a bit.

These articles are quite explicit about methods to create the compost, and have good information about the processes of vermicomposting or composting.  They also do a good job of explaining some of the decisions a someone with horse manure will need to take (what kind of worms, how to set up windrows).

Here’s a great quote about the profligacy of E. foetida:

50 pounds of Eisenia will reproduce to 1,000 pounds of worms shortly after four doubling
periods (in just over 16 months). In two years, that initial 50 pounds of Eisenia will be more than enough (3200 pounds) to vermicompost the manure from 30 horses.

And the article also answers a very important question about horse dewormers and redworms:

Will horse dewormers kill red worms?

The most common wormer used is known by the brand name Ivermectin® made by the Merial Company. Merial’s research shows that the active chemicals in Ivermectin® are deactivated when manure is exposed to sunlight. Equine studies show that 95 percent of the active chemicals in Ivermectin® are deactivated in the horse before being passed in the feces. Leading experts in vermicomposting believe that the concentration of Ivermectin® in the horse manure is not high enough to seriously injure Eisenia.

Apparently the Ivermectin used for horses has been rebranded Zimecterin; it might be worth asking the vet about this situation because I couldn’t find anything.

These articles don’t, however, give much advice about what to do with the presumably vast amount of vermicompost your worms will be generating.  Assuming the worms reduce the weight of the manure by 20%, that’s still over 4 tons of vermicompost a week when your operation is fully going (assuming 30 horses).  This is about all the advice you get on what to do with castings:

Castings can be tilled into the soil directly from the windrow or screened for adding to greenhouse soil mixes, potted plants, lawns, and gardens.

Vermicomposting at this scale is an economic decision.  50 pounds of red wrigglers will probably cost you 500-700 bucks, and you have labor, land and equipment costs.  On the other hand, you have to get rid of your manure somehow and beyond castings, you might be able to start a business selling redworms to home wormkeepers like me.

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