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Establishing a Linkage between Phosphorus Forms in Dairy Diets, Feces, and Manures
Author(s) -
Toor Gurpal S.,
CadeMenun Barbara J.,
Sims J. Thomas
Publication year - 2005
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2004.0232
Subject(s) - feces , phytic acid , manure , phosphorus , zoology , dry matter , food science , biology , organic matter , slurry , excretion , chemistry , agronomy , biochemistry , microbiology and biotechnology , ecology , materials science , organic chemistry , composite material
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.