Establishing a linkage between phosphorus forms in dairy diets, feces, and manures.
Effective manure management to efficiently utilize organic wastes without causing environmental degradation requires a clear understanding of the transformation of P forms from diet to manure. Thus, the objective of this study was to establish quantitative relationships between P forms in diets, feces, and manures collected from U.S. Northeastern and Mid-Atlantic commercial dairy farms. Total P in diets ranged from 3.6 to 5.3 g kg(-1) dry matter, while the feces had higher P than diets (5.7-9.5 g kg(-1)) and manures had lower P (2.5-8.9 g kg(-1)) than feces. The farms with total dietary P of 4.8 to 5.3 g P kg(-1) had twofold higher concentrations of phytic acid (1647-2300 mg P kg(-1)) than farms with 3.6 to 4.0 g dietary P kg(-1) (844-1100 mg P kg(-1)). Much of the phytic acid in diets was converted to inorganic orthophosphate in the rumen as indicated by a reduction in phytic acid percentage from diets (32%) to feces (18%). The proportion of orthophosphate diesters (phospholipids, deoxyribonucleic acid [DNA]) was twice as high in feces (6.2-10%) as diets (2.4-5.3%) suggesting the excretion of microbial residues in feces. Phosphonates (aminoethyl phosphonates and phosphonolipids) were not seen in diets but were detected in feces and persisted in manures, which suggests a microbial origin. These organic compounds (phytic acid, phospholipids, DNA) were decomposed on storage of feces in slurry pits, increasing orthophosphate in manures by 9 to 12% of total P. These results suggest that reducing dietary P and typically storing feces in dairy farms will result in manure with similar chemical forms (primarily orthophosphate: 63-77%) that will be land applied. Thus, both the reduction of dietary P and storage of manure on farm are important for controlling solubility and bioavailability of P forms in soils and waters.
Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA. gurpal@udel.edu
Gurpal S
GS
Toor
Barbara J
BJ
Cade-Menun
J Thomas
JT
Sims
D000821:Animal Feed; D000822:Animal Husbandry; D000818:Animals; D001682:Biological Availability; D005243:Feces / Q000737:chemistry*; D008372:Manure; D010758:Phosphorus / Q000032:analysis* / Q000378:metabolism*; D012037:Refuse Disposal; D012989:Soil Pollutants / Q000032:analysis; D014873:Water Pollutants / Q000032:analysis
D008372:Manure; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus