Which Manure is right for your garden?

Posted by: Carol O'Meara, Boulder County Extension

Set aside your coffee and breakfast, gentle reader; the following is not fit for mealtime conversation.  Fall is approaching, and with it a ritual of the garden: manuring.  We pile it on to improve the soil, enhancing tilth, microbes, and fertility.  Enfolding it into the ground sets us up for a wonderful bounty next year.

(Photo from Washing State University)

Before you go out and get just any manure, take a trip with me through the wonderful world of the ruminant digestive system, where we’ll ponder that age-old question of “which is better – cow, sheep, chicken, or horse?” 

“That depends on what you want in your soil.  Chicken has hardly any fiber, but lots of nitrogen.  Horses have a lot of long fibers that add tilth to the soil,” says Frank Garry, Veterinarian and Professor of Clinical Sciences at Colorado State University.  “Monogastric systems are simple.  We’re monogastric, so are pigs, dogs, or cats.  We have enzymes and acids in the stomach to break down food to a certain point,” he says. “Our intestines absorb nutrients but some things won’t break down, like fiber.  So what goes in comes out.”

Poultry poo has a lot of nitrogen (photo by Fred McClanahan, Jr.)

Ruminants, such as cows, sheep, goats, deer, elk, bison, moose, and yaks have a multi-compartment stomach where they use the power of microbes to ferment their food.  In combination with ruminating, - chewing their cud - ruminants very efficiently break down what they’ve eaten. 

“Ruminants are designed to eat fast, then hide in the woods; they’ll walk away to find a safe spot where they rechew what they ate to break it down further. We only get one chance at macerating our food, but ruminants spit it up over and over, chewing it to bits so it can be fermented further, releasing nutrients.  It’s a cool dance that the lowly monogastric doesn’t have,” said Garry. 

This fermentation-based system allows ruminants to be excellent recyclers of food waste produced by humans.  Able to adapt to a wide range of food, the discards from breweries, sugar beet pulp, wheat mids, French fry manufacturing, cotton, or corn ethanol production are being fed to livestock.  Known as commodity feeds, they’re taken and blended based on nutrient contents to create customized combinations targeted at individual herd needs.

Material only passes once it’s broken into tiny particles, so cow pies are comprised of small bits; this is useful as building blocks for soil fertility and organic matter.  Most of the ruminant manure has more phosphorus than people want, because it’s present in high quantities in plants that they eat.

Rabbits and horses aren’t set up the same way, so aren’t as efficient at breaking down the plants they eat.  “They have a similar system of fermentation, but it’s in the hind gut (with no rumination).  As a result their waste has more long-stem fiber.  But it really depends on the plants they eat,” said Garry.  Horse manure is an excellent source for building organic matter and improving tilth.

Horse manure as far as the eye can see (Photo from University of Minnesota Extension)

Weed seeds can slip past the process occasionally, but the relative amounts of weeds you’ll get from the different poo depends largely on what the animal eats.  Goats and sheep are browsers, chomping down more weeds.  Elk and deer browse too, but prefer more leafy fare.  Horses and cows graze grass, typically, but might nosh on a few weeds in the process.

Should you just want to boost the nitrogen amount in your soil, chicken manure is an excellent choice.  Younger gardens, which need more organic matter to improve the soil, benefit from horse dung.  For all-around good maintenance, cow, sheep, goat, yak, and other ruminant manure works well.  Follow your nose to the manure that’s perfect for your garden, and you’ll set yourself up this fall for success next spring.