Phosphorus Composition of Sheep Feces and Changes in the Field Determined by ~(31)P NMR Spectroscopy and XRPD

摘要

Information on the P species in sheep feces is lacking.Such information is required to understand P-cycling in grazed ecosystems.The P composition of feces from sheep grazing grass in Scotland was assessed on freeze-dried samples by ~(31)P MAS(magic angle spinning)NMR(nuclear magnetic resonance)spectroscopy and XRPD(X-ray powder diffraction).The ~(31)P MAS NMR spectrum showed resonances and sidebands consistent with dicalcium phosphate dihydrate(brushite)and ammonium magnesium phosphate hexahydrate(struvite).XRPD confirmed the result and allowed quantification of these minerals,which accounted for 63% of the P.To determine transformations in the field,sheep feces were collected and reapplied to sheep-free pasture in synthetic patches during late summer.The dry weight decreased with time and the feces disappeared between 84 and 112 days following heavy rainfall.The concentration of P in the feces recovered at intervals up to 84 days changed little with time but the contribution from brushite and struvite decreased and within 1 week <50% remained indicating conversion into other forms.Solution-phase ~(31)P NMR spectra of NaOH/EDTA extracts of thefeces were dominated by the inorganic orthophosphate with minor amounts of organic P that were attributed to phosphate esters and polyphosphates.