Phosphorus (P) runoff from agroecosystems in the northeast United States is a well known environmental concern for surface waters, particularly in areas where poultry and dairy manure are abundant. More recent studies have concluded that P leaching can also significantly contribute to environmental degradation under P-saturated soil conditions. Laboratory studies were conducted to gain a greater understanding of P forms in leachate extracted from soils subjected to heavy annual dairy and poultry manure applications for between 1 and 40 years. The soils ranged from 60 to 2167 mg Mehlich-3 extractable P per kg soil (7.5 to 1146 mg Morgan extractable P/kg soil). Intact soil cores (0-15 cm) were taken in stainless steel cylinders and fitted with airtight stainless steel caps. Three cores were taken per field. The stainless steel units were saturated with water and attached to a peristaltic pump using chemically inert tubing. Water was slowly pumped through the soil profile and recycled until equilibrium concentrations were reached after many cycles. The concentration of P in the soil water was measured at daily intervals. Initial concentrations of P in leachate differed greatly from P concentrations in leachate that was recycled until equilibrium was achieved in terms of both inorganic P and organic P content and proportion, yielding valuable information concerning P mobility in agroecosystems. Equilibrium concentrations of total dissolved P in leachate ranged from 0.11 mg L-1 in soil subjected to short-term manure additions and to 7.64 mg L-1 in soil subjected to long-term manure additions. The percentage of total P in leachate that was organic P ranged from 90% in soil subjected to short-term manure additions and 2% in soil subjected to long-term manure additions. While the proportion of organic P to inorganic P decreased, the organic P content in leachate remained unchanged. Manure additions increased inorganic P leachate concentrations, but did not affect organic P concentrations. After determining this, the hydrophobic and hydrophilic properties of the organic P were investigated to see if the leaching process affected the properties of organic P in soil, which could have implications for the mobility of organic P in the subsoil. A resin fractionation procedure was developed and employed to distinguish between leachate hydrophobic and hydrophilic organic P forms using Amberlite XAD-7 and MSC-1H. It was determined that there was no systematic difference in the proportion of hydrophobic and hydrophilic organic P as a function of duration of manure amendments. The property and therefore most likely the mobility of organic P in the subsoil remained the same regardless of duration of manure amendments.