Garden Gold From Digested Cow Pies
This summer, I received a load of crap that made me very, very happy. I’ve been using aged cow manure in the garden for years, especially appreciating its soil conditioning qualities. Cow manure is weed free, thanks to cow’s multi-chambered tummies and the tiny seed-eating aphids that live in manure piles. It’s also the best top dressing I’ve ever found, looking (if not smelling) like chocolate frosting, a most handsome effect.
My newly prepped front entry beds are looking exquisitely prepped just now, thickly coated with digested cow manure. This is the ‘new’ form of poo I’ve been experimenting with and so far, it’s fabulous. Digested cow manure is what’s left over after manure is mined for energy. Here’s how it works: Dairy farmers collect cow manure in pits when they wash down their barns. The liquids are sprayed back on the grazing fields and the solids (often mixed with field crop waste) are trucked to an anaerobic digester facility, where the methane is stripped out and converted to electricity, which gets sold to local power companies, partly offsetting trucking costs.
Turning Poop Into Power
Anaerobic digestion produces biogas (mainly methane and carbon dioxide) by composting organic materials in an oxygen-free environment. When manure breaks down outside, the biogas becomes a ‘greenhouse gas’, but when it’s captured in an anaerobic digester, the result is clean power and a big pile of digested poo. It’s not exactly like aged, composted manure, but it has similar nutrient levels, low pathogen levels, and is an excellent soil conditioner. Because it is not as aged, it does smell more ripe, as holiday visitors to my home have noted.
Anaerobic digesters are hardly new, but today’s technology makes them far more efficient. In Washington State, dairy coops share local digesters to create energy and manage their mounds of manure. It took time to figure out how to get that end product into gardens, but today, you can buy it as bags of Magic Dirt, USDA certified, biobased potting soil that has been approved for organic growers by the Idaho Department of Agriculture and the Mulch and Soil Council (bet you didn’t know there was one!).
A Great Bulk Buy
You can also, as I did, get large loads of digested manure delivered by the same folks who sell composted dairy manure. In the soil, the digested stuff works like a more nutritious form of peat moss, opeing tight soils and absorbing and holding up to three times its weight in water, but without the environmental damage caused by peat moss extraction. (Besides harming the peat bogs, peat moss harvesting releases 2,400 tons of methane per acre. Seriously.) In contrast, each cubic yard of digested cow manure has generated over 100 kWh of green, renewable energy.
Also known as ‘digestate’, digested manure brings a lot of nutrients to the soil, including nitrogen, phosphorous, potassium and sulfur, as well as absorbent cellulose fibers. Lots of folks are trying to figure out how to manage these digestates, some of which contain ingredients other than manure and field crop residues. For gardeners, the answer is very simple; stick to manure-and-crop-waste based digestates and spread them far and wide. You can rake this yummy stuff into a struggling lawn, spreading it about an inch deep, and see better growth within a season. Spread over beds and borders, it helps nurture hungry roots and looks tidy to boot.
OK For Edibles?
Digestate is low in pathogens and is starting to be more widely used on farm fields, golf courses, and some parks as a fertilizer and soil conditioner. As more gardeners learn about the value of digested poo, that market will grow as well, especially among those of us who value green, renewable resources. By using manure and promoting its use, we can help to reduce America’s massive accumulations of manure and other organic leftovers, keeping them out of waterways and turning them into an asset.
To find out who might deliver digested poo to you, contact your local Agricultural Extension Agent or ask a Master Gardener. In the meantime, here are some cool links if you want to learn more.