Compared to nitrogen (N), relatively little is known about the availability of phosphorus (P) from manure to crops. Many state extension bulletins recommend that 50-80% of total P in manure is available to crops the first year after application. This number is likely based on the fact that 35-90% of P in manures is in the inorganic form (Peperzak, et al., 1959; Barnett, 1994), which is immediately available to crops. The remaining P that is not credited in the first year is usually never credited. In addition, the same availability coefficient/index is usually given to all manure types, regardless of species, diets, or storage. Understanding manure P chemistry in soil and trying to predict P availability is an important component for making nutrient management plans that maximize economic benefits and minimize environmental risks.