U.S. livestock produces $10 billion worth of fertilizer annually. Treated as waste, much of this manure is discarded or runs off to pollute waterways. Of this "waste," chicken manure is valuable because of its nitrogen content. Plants require nitrogen to grow but drain soil of this essential nutrient over time. Replacing nitrogen is a primary motive behind fertilization, and the organic movement has encouraged natural ways to revitalize soil. Chicken manure is one answer.
Nitrogen is an essential nutrient for plant growth, and although it is available in the atmosphere, most plants cannot "fix" atmospheric nitrogen in a usable form. Nitrogen provides an essential element for protein formation, keeping plants strong, and helps plants to use energy efficiently. Chicken manure is one of the highest animal manures in terms of nitrogen content, leading the University of Florida Extension to call it the best natural fertilizer.
The second ingredient found in most chemical fertilizer cocktails, phosphorus aids plants with photosynthesis, water uptake and energy usage. Because phosphorus must normally be mined from rock, it is a challenging--and inefficient--nutrient to provide to plants. However, like nitrogen, chicken manure has one of the highest phosphorus contents of any livestock manure, so high that the U.S. Department of Agriculture's Agricultural Research Service has developed methods to isolate the phosphorus in poultry manure in order to eliminate the need to acquire it through mining operations.
Plants need potassium to drive many of their metabolic processes, which allow them to undertake photosynthesis and control the release of gas and water vapor from their leaves. Although chicken manure doesn't outshine other manures in potassium content the way that it does for nitrogen and phosphorus, it contains about the same amount of potassium as most other manures.
According to the University of Florida Extension, organic matter is a final soil amendment provided by poultry manure. Organic matter refers to living and dead plant and animal material that, when added to soil, confers a variety of benefits, including improved water and nutrient retention, better aeration, more fruitful soil microorganisms and an environment more conducive to earthworms. "Rodale's Ultimate Encyclopedia of Organic Gardening" recommends that soil consist of 5 to 6 percent organic matter and recommends composted manure as one method of boosting organic matter in your garden soil.