INSOLUBLE Fe-RELATED INORGANIC AND ORGANIC PHOSPHATES IN ANIMAL MANURE AND SOIL

Authors: He, Zhongqi; Dao, Thanh; Honeycutt, Charles

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2005
Publication Date: 3/5/2006
Citation: He, Z., Dao, T.H., Honeycutt, C.W. 2006. Insoluble fe-related inorganic and organic phosphates in animal manure and soil. Soil Science. 171:117-126

Interpretive Summary: Environmental conditions have significant impacts on the solubility and thus bioavailability, of plant nutrient phosphorus (P). For example, insoluble iron-P compounds can become soluble under reducing conditions, such as during flooding. In this study, we investigated insoluble inorganic and organic P species in animal manure and soil with the combining actions of an inorganic P-releasing enzyme and a reducing agent. Our data indicate that poultry litter, dairy manure, and a sandy loam soil contained different species and amounts of reducible iron-related phosphorus. Therefore, changes in the chemical and biological environments of manure in storage and/or after application to soil can influence the bioavailability and runoff of these P compounds. Findings in this study enhance our understanding of manure and soil P chemistry, providing insight into improving management of manure P under various environments.

Technical Abstract: Identifying and quantifying insoluble and reducible P species in animal manure and soil are important issues in environmental P chemistry. We applied a joint dithionite-3-phytase incubation at pH 5.0 (100 mM acetate buffer) to investigate reducible P in animal manure and soil. After removal of soluble phosphate by 100 mM acetate (pH 5.0), poultry litter and dairy manure solids were incubated with the reducing agent sodium dithionite and/or 3-phytase to identify insoluble manure P species. Poultry litter contained most (spontaneous) labile P (9.7% of insoluble P), reducible inorganic P (3.2% of insoluble P), non-Fe-related (reducible-irrelevant) organic P (5.7% of insoluble P), and Fe-related (reducible) organic P (16.2% of insoluble P). In dairy manure, 51.5% of insoluble P was most labile P, 28.1% non-Fe-related organic P, and 20.4% Fe-related organic P, but no reducible inorganic P. In a sandy loam soil, only Fe-related inorganic P (682 mg kg-1dry soil) was observed, compared to the original 2 mg soluble P kg-1 dry soil). These data indicate that changes in the chemical and biological environments of manure and soil, such as anaerobic conditions and enzymatic activity, can influence manure P solubility and therefore bioavailability.