Speciation of Phosphorus in Manure-Amended Soils Using Advanced Spectroscopic Characterization.

Confined animal feeding operations (CAFOs) create excess phosphorus loading to soils, contributing to ongoing nutrient loading problems in surface waters. The long-term fate of manure-based P applied to alkaline soils is not known. In the alkaline soils in Southern Idaho, one of the Nation’s most productive dairy regions, added P should react within the soil to form low-solubility Ca-phosphate minerals. In this study, soils were collected from a new long-term manure amendment study located in the Idaho dairy region. Phosphorus speciation in the soils was investigated using extraction-based and molecular speciation methods. Selective extraction results showed that greater than 70% of the soil P is removed in the acid extraction step, suggesting that the soil P is primarily Ca-P minerals. P K-edge XANES and NMR spectroscopy are also being used to elucidate P speciation in the soils. Results from this work will provide mechanistic information on the fate of P in alkaline soils, and will create baseline knowledge needed to evaluate the fate of P in the long-term research site.