Characteristics and Availability of Different Forms of Phosphorus in Animal Manures

The rapid development of intensive livestock industry has greatly increased the discharge of animal manure. Reasonable utilization of large amounts of phosphorus(P)in animal manure can not only save the fertilizer resource, but also avoid water pollution from manure due to direct discharge or excess application in farmland. In this study, P contents and fractionation in 76 animal manures were analyzed using Hedley P fractionation method based on the survey for 52 livestock farms, and P mobility and environmental risks in different manures were evaluated as the reference for manure P management. The results showed that there were significant differences in total P content of animal manures. The mean P contents were 22.5, 13.7, 12.9, 9.6 g P·kg-1 and 7.5 g P·kg-1, in which the proportion of organic P in total P were 33.1%, 41.5%, 66.4%, 28.1%and 36.8%in pig, chicken, duck, cattle and sheep manures, respectively. The contents of total and organic P in non-ruminant animal manure(pig, chicken and duck manures)were 1.7~3.0 times and 2.1~3.0 times greater than that in ruminant manure (cattle and sheep manures)and the proportion of organic P in total P in poultry manure was higher than that in other manures. P mineraliza-tion was easier in non-ruminant animal manure with lower C/P ratio(19~29), compared with that in ruminant manure with C/P ratio of 38~45. Manure P was sequentially extracted by deionized water(H2O-P), NaHCO3(NaHCO3-P), NaOH(NaOH-P)and HCl(HCl-P). The pro-portion of H2O-P, NaHCO3-P, NaOH-P, HCl-P and residual-P in total P in ruminant animal manure were 27.8%, 32.8%, 18.1%, 15.2%and 6.1%, respectively, while that were 24.6%, 19.4%, 12.7%, 34.4% and 8.9% in non-ruminant animal manure. The significant differences were in NaHCO3-P and HCl-P between ruminant and non-ruminant animal manures. Ruminant manure had greater proportion of liable P (H2O-P and NaHCO3-P)in total P(>60%), but the characteristics of higher mineralization rate might result in fast release of liable P in nonruminant animal manure. Both ruminant and non-ruminant animals have high availability of P in manures. Therefore, the contribution of long-term application non-ruminant animal manure to environmental risk is similar to application of ruminant animal manure with applica-tion of the same amount of P. However, due to the higher P content, the former may contribute to higher environmental risk, compared with latter based on application of the same amount of manure.