Abstract: Forms and contents of solid-phase phosphorus in pig and dairy cow manures before and after subjection to anaerobic digestion were analyzed, using the sequential extraction method with H₂O, NaHCO₃, NaOH and HCl. Results show that in the effluent slurry from pig dung digesters, HCl-P accounted for 85.50% of the total solid-phased phosphorus (TSP), significantly higher than that in the influent material (P<0.05);.whereas NaHCO₃-P, residual P, H₂O-P and NaOH-P did for 5.83%, 4.71%, 2.15% and 1.81%, respectively, all lower than their corresponding one in the influence to a varying extent; and in the effluent slurry from dairy cow manure digesters,. HCl-P, NaHCO₃-P, H₂O-P, residual P and NaOH-P accounted for 53.73%, 19.62%, 12.66 %, 8.60% and 5.39%, respectively, which did not differed much from that in the influent manure. The inorganic phosphorus in the slurry accounted for 60.98% - 100.00% of TSP. After anaerobic digestion, solid-phased phosphorus of various forms in the digestion sludge from the pig dung digesters displayed an order of HCl-P > NaHCO₃-P > residual P > H₂O-P > NaOH-P in content, each accounting for 87.43%, 5.17%, 4.33%, 1.79% and 1.28%, respectively, in percentage of TSP, respectively; while a different order was found in the digestion sludge from the dairy cow manure digesters, that is, HCl-P > NaHCO₃-P > H₂O-P > residual P > NaOH-P, each accounting for 69.74%, 9.91%, 8.75%, 8.30% and 3.30%, respectively. After anaerobic digestion of pig dung, liquid-phased phosphorus was transformed into solid-phased one and water-soluble P in the latter turned into insoluble P. However, phosphorus in digested dairy cow slurry was less available to plants than that in digested dairy cowpig dung slurry.

Key words: pig manure, dairy manure, anaerobic digestion, phosphorus form