Phosphorus-31 nuclear magnetic resonance spectroscopy transect study of poultry operations on the Delmarva peninsula

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Nonpoint source phosphorus (P) pollution into the Chesapeake Bay watershed from poultry operations contributes to the algal blooms, hypoxia, anoxia, and fish kill events that occur there most years. A major source of soluble, bioavailable P species is poultry litter, which is used as a crop fertilizer on fields adjacent to the tributaries of the Bay. A potentially significant source of orthophosphate in the litter is the heavily phosphorylated compound myo-inositol hexakisphosphate (phytate), which is indigestible by poultry and thus becomes a major component of their excreta. Phytate evaluation in environmental samples is expensive; hence, its impact is not captured in standard farmer-friendly eutrophication potential guides, like Delaware's Phosphorus Site Index. In this transect study of two poultry operations on the Delmarva Peninsula, we measured the incidence of all P compounds using solution 31P nuclear magnetic resonance (NMR) spectroscopy and extracts, relating them to relevant geochemical properties. The contribution of phytate to the overall pool of P declined from around 50% in manures to between 2 and 13% in down-gradient soils and sediments, corresponding to a rise in the relative proportion of orthophosphate (increasing from 39% to 65–88%). The results show that the large pool of phytate P spread onto croplands during standard operating practice at poultry farms on the Delmarva Peninsula does not appear to accumulate; rather, phytate decreases in down-gradient locations, most likely due to transport off-site and/or through in situ biological activity.

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