The phosphorus cycle in pig slurry measured from 32PO4 distribution rates

Abstract

SUMMARY: The rate of isotopic distribution of labelled phosphorus, added as H₃³²PO₄, between inorganic and organic phosphates and phosphates contained in micro-organisms was measured in pig slurry. Incorporation of ³²P in all these phosphates occurred quickly in both aerated and non-aerated pig slurry. On the basis of a simplified model, turnover times for phosphorus were calculated to be of the order of 10–20 weeks for both non-aerated and aerated pig slurry.Pig slurry contains 1–2% P (of dry matter) of which 10–30% is in organic molecules and 2–3% is in micro-organisms. About 10–20% of the organic phosphates is in solution, amounting to 10–20 mg P/l. The concentration of inorganic P in solution is of the order of 10–100 mg/1 though, at low Ca/P ratios in the feed, can be as high as 1000 mg/1.Organic phosphates in solution in pig slurry are of high molecular weight and probably consist of DNA complexes with polyphosphates, Ca and (if used in the feed) Cu.It is concluded that all organic phosphates in pig slurry are of microbial origin and that the feed composition has little influence on the organic phosphate content of the slurry.Arguments for application of the results to pig slurry in general and to wastes from other animals are given.