1 Quart Bag of Fresh All Purpose Horse Manure – Organic Gardening Fertilizer. The best there is from our HAPPY horses. The smell of a stable for those that no longer can make it to their horses. Buy more save more with bulk discount. Water and Aeration Composted horse manure worked into thesoilhelps aerate the soil and allows it to retain more moisture. In clay soil, it helps break up clumps of compacted soil and forms tunnel-like openings that let air and water in. In sandy soils, it has the opposite effect by holding together the sand in larger clumps and letting it retain more water. In any soil type, it helps prevent topsoil erosion. Soil Nutrients Composted manure retains as much as 95 percent of its nitrogen as opposed to raw horse manure, which will lose 50 percent of its nitrogen to rain and erosion if spread on the garden. Composted manure allows nitrogen to break down in a more stable form, making it more accessible toplants. Another soil benefit is that only 50 percent of the available nutrients are used in the first year, with the remaining nutrients being disseminated over the next several years. Annual applications create a buildup of nutrients and make other forms of fertilizer unnecessary. Bacteria, Earthworms and pH Composted horse manure improves the soil for earthworms, a necessary component of healthy soil. It provides food for them, which in turn allows them to multiply. It supports the growth of healthy soil bacteria, and with time can change the pH levels so the soil is neither too acidic nor too alkaline. How to Use Horse Manure Fertilizer After the horse manure has been composted, it can be spread on top of the garden soil just before planting time. Avoid spreading it when heavy or frequent rains are expected to prevent the fertilizer from washing away. If possible, work it into the soil before planting. It can also be used as mulch or as a top dressing for trees, shrubs and in vineyards. Cured horse manure compost, which is compost that has been allowed to sit for an additional one to three months, can be used asseedstarter medium or potting mix.