Valuable plant nutrients and organic by-products make up the bulk of cow manure. As a fertilizer, cow manure offers an eco-friendly alternative to processed chemical fertilizers. Using manure to fertilize lawns, gardens, flowerbeds, trees and shrubs offers the gardener a chance to recycle a natural product. Throughout history the farmer has realized the value of cow manure to fertilize fields and produce healthy crops. In early days virtually every farm housed a dairy cow and even a few oxen so an abundant supply of cow manure was readily available.
Cow manure contains varying amounts of phosphorus, nitrogen, potassium and other nutrients. The ratios vary depending upon the animals' feed, health and environment. Adding aged manure to the garden adds organic matter to the soil, which helps the soil absorb water and hold it during the heat of the day. It also adds aeration around the plant's root system.
Nitrogen and Water
Cow manure offers abundant nitrogen plus other nutrients when incorporated into garden soil. Fresh cow manure holds 70 to 85 percent moisture, according to the University of California. As time passes and the manure ages, the moisture evaporates. Well-aged manure holds around 9 to 15 percent water. The evaporation causes the nutrients to concentrate within the manure. Dried, aged manure offers a slow release of nitrogen, which greatly benefits the soil and the plants growing in it.
The abundant supply of manure makes it readily available to the home gardener. Manure is sold at garden supply and home improvement stores. Many farms also sell aged manure to the public. Purchasing cow manure helps the environment by recycling an overabundance of a natural product. Within the state of Oklahoma, 10 million tons of manure produced annually is available for use in fertilizer, according to Oklahoma State University.
Using cow manure as an organic soil and fertilizer additive does hold disadvantages. Cows often consume weed seeds that survive through the animals' digestive tract to emerge viable. Placing the manure into the garden plants the weed seeds. Manure can also be high in salt content, depending on the cows' diet. When using cow manure in sandy soil, a zinc deficiency can result, according to Ecochem. Dairy cow manure tends to contain a lower salt and weed content then steer manure due to the dairy cows' diet and environment.
Ideally, cow manure should be aged at least 60 days before garden application. Using fresh manure can be dangerous because it often contains protozoa and bacteria. It is advised to apply aged manure at least 120 days before harvesting any vegetables that have come into contact with the manure to lessen the danger of contamination.