Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/25/2002
Publication Date: 10/1/2002
Citation: Interpretive Summary: There are many forms of phosphorus (P) in animal manures, both inorganic and organic. The P that is land applied as manure has the potential to be lost from soils and enter waterways where it can lead to water quality problems. It has been stated in the past that organic forms of P, found in manures, are held less tightly by the soil than inorganic P and therefore pose a greater threat to water quality. We examined several organic P compounds typically found in animal manures to determine the ability of the soil to hold these compounds and prevent them from being lost to nearby watercourses. In two of the three soils analyzed, all of the organic P compounds were retained more tightly by the soil than the inorganic P. On the remaining soil, one organic P compound was held more tightly than the inorganic P, but the other organic P compounds were held less tightly. This data suggests that organic P found in manures may actually be held more tightly by soils and therefore pose less of a threat to water quality than inorganic sources of P.
Technical Abstract: Organic phosphorus (P) can comprise a significant amount of the total P in animal wastes, yet there is little information on the potential for organic P to be transferred from soils to watercourses. We examined the adsorption of organic P compounds to soils typical of the Southeastern U.S., i.e. Blanton Sand (loamy, siliceous, thermic, Grossarenic Paleudult), Cecil sandy clay loam (fine, kaolinitic, thermic, Typic Kanhapludult), and a Belhaven sandy loam (loamy, mixed, dysic, thermic, Terric Medisaprist). The behavior of four organic P compounds was studied: adenosine 5' triphosphate (ATP), adensosine 5' diphosphate (ADP), adenosine 5' monophosphate (AMP) and inositol hexaphosphate (IHP); while inorganic P was used as an inorganic reference. Laboratory studies were conducted to determine the effects of concentration (0-130 mg P/L), pH (4.6 to 7.6), and soil properties on P adsorption. All the organic P compounds had greater adsorption than inorganic P on the Blanton and Cecil soils at all concentrations and ranges of pH. In the Belhaven soil, IHP had the greatest sorption followed by inorganic P and the nucleotides (ATP, ADP, and AMP respectively). Adsorption of organic P was positively correlated with soil organic matter and Fe and Al contents. The greater sorption of some organic P compounds over that of ortho-P suggests that these compounds may pose less of a threat to water quality, although this preferential sorption may increase soluble P in situations where there is displacement of ortho-P by organic P added in manures.