Well aged, composted horse manure offers numerous benefits to the garden. It supplies not only valuable nutrients but also works as an indispensable soil additive. The manure contains all the primary nutrients that a plant needs to survive such as nitrogen, phosphorus and potassium. It also provides the necessary secondary elements to make a plant thrive such as sulphur, magnesium, calcium, iron, copper, zinc and boron, according to Washington State University.
Horse manure works to hold the particles within the soil together, which can greatly benefit sandy soil conditions by helping it hold much-needed nutrients for plants that would otherwise seep away in a rainstorm or during heavy irrigation. The manure contains a negative electrical charge. The electrical charge helps particles of soil nutrients to bind with the manure. Nutrients have a positive electrical charge which is naturally attracted to the negative charge. Sandy soil contains a neutral charge which renders it incapable of holding nutrients for plants, so when heavy water is applied the nutrients wash away. The horse manure helps hold the beneficial nutrients in place for plants to utilize.
Horse manure contains valuable microorganisms. When applied to soil, the microorganisms work to break down heavy soil, such as clay, into fine particles. This produces aeration into the soil and makes it easier for the plants' roots to work their way through. The soil retains both water and oxygen when horse manure is added.
Chemical fertilizers supply nutrients when watered into the soil. If the plant does not quickly absorb the nutrients they wash away with irrigation. Horse manure stays within the soil even after watering. It slowly releases nutrients into the soil over time. When adding ample horse manure to the soil, the manure can reside in the soil for years slowly feeding the plants as it breaks down.
Earthworms aerate soil with their tunneling and provide nutrients with their fecal matter to plants. They are a valuable addition to any garden because they naturally enrich the soil. Adding horse manure to the soil invites earthworms to reside in the garden because earthworms enjoy consuming the horse manure, according to Washington State University.
Fresh horse manure often contains unwanted weed seeds. Rapid composting helps to eliminate the problem prior to applying the manure to the garden. Horse manure composts easily in a large pile or bin with additions of water and by mixing the manure to supply air. The addition of horse bedding helps the composition to occur. As the horse manure begins to break down it becomes crumbly and rich looking. It appears more like good quality soil and less like manure. Once the manure is crumbly to the touch it can be applied to the garden.