MANURE SOURCE EFFECTS ON SOIL PHOSPHORUS FRACTIONS AND THEIR DISTRIBUTION.

Manure can be applied to soils as a major source of nutrients such as phosphorus (P). The environmental chemistry and plant availability of applied soil P are influenced by the chemical forms of P in the solid phase. The objectives of this study were to determine the amounts, availability, and chemical forms of P in a Hord silt loam soil (fine-silty, mixed, mesic Pachic Haplustoll) amended with beef and sheep feedlot, turkey house, and composted paunch manures. Manures were applied in alternate years from 1991 to 1997. In 1996, after three manure applications, total P in the manured 0-15-cm soil depth increased up to 14%and inorganic P up to 25% compared with nonmanured. Bray and Kurtz 1-P in 0-15-cm soil depth was almost 4 times greater in manured soil than in nonmanured (47.2 mg P kg^-1 soil versus 12.7 mg P kg^-1 soil).Soluble P was more than 4 times higher in the 0-15-cm depth of manured soils (13.9 mg P kg^-1 soil) compared with nonmanured soil (3.2 mg P kg^-1 soil). Nonoccluded P was more than 1.5 times higher in manureamended soils (78.4 mg P kg^-1 soil) than in nonmanured (46.8 mg P kg^-1 soil) in the 0-15-cm soil depth. Occluded P in 0-15-cm soil depth was greatest in turkey manure-amended soil (45.2 mg P kg^-1 soil), followed by beef manure-amended soil (36.7 mg P kg^-1 soil). In 1997, all P fractions were higher in 0-7.5-cm depth than any other amended soil depth, and the same general trends among fractions held as in 1996. Although animal source of applied manure does have some influence on P fractionation and depth distribution, most P remains in the zone of application, emphasizing the need for conservation of the surface soil.