Horse manure is a voluminous, inexpensive, and commonly available composting material. Horse manure contains a useful balance of nitrogen, phosphorus and potassium, and usually is pre-mixed with bedding material which provides carbon matter to facilitate rapid composting. Composted horse manure adds organic matter and micronutrients to garden soil, as well as improving soil structure and fertility.
According to the Maryland Department of Agriculture Horse Outreach Workgroup, a single 1,000-pound horse creates 40 to 50 pounds of manure ever day--about a ton each month. Many horse owners are happy to make this excess of compostable material available free or inexpensively to anyone who can transport it.
The benefit of the large quantity of available horse manure is that it facilitates constructing a compost pile large enough to reach temperatures sufficient to kill weed seeds as well as fly larvae or pathogens contained in the material. The significant quantities of compost produced can be used as an invaluable soil addition as well as filling for raised beds and mulch for vegetables, perennials, trees and shrubs.
Livestock manures including horse manure are often spread fresh on farm pastures and fields. However, much of the high nutrient content, particularly nitrogen, contained in fresh manure is in a highly soluble form which washes out quickly in the rain, which loses the benefit of nutrients to the growing plants but also pollutes rivers and streams, damaging aquatic ecosystems.
By composting horse manure, either alone or in combination with other yard waste, the nitrogen in it is converted to a more stable form. In the garden soil, composted manure releases its nutrients slowly over time, adding to long-term soil fertility and strong healthy plant growth.
The ideal carbon-to-nitrogen ration for fast, odor-free composting is about 25 to 1. Horse manure with an ordinary amount of bedding comprises a carbon-to-nitrogen ration of about 15 to 1. This means that the addition of just a modest quantity of dry brown carbon matter, such as dead leaves, wood chips, or wood shavings, will result in the perfect carbon-to-nitrogen ratio for the most rapid, efficient composting.
Moisture content and oxygen are also necessary to a composting operation. Horse bedding materials along with added brown carbon matter also ensure that the compost pile will have sufficient quantities of incorporated oxygen, while horse-urine saturated bedding, and the moisture content of fresh manure, help to ensure that the compost pile remains sufficiently wet to facilitate rapid, thorough composting.