Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: March 29, 2002
Publication Date: N/A
Information is needed on the contribution of organic polyphosphate phytate to the sources and sinks of dissolved phosphorus in the soil-manure-water system that is often associated with water quality degradation in watersheds with confined animal feeding operations. Effects of Na+, Ca2+, Al3+, and Fe3+ and three cation to phytate-P mole ratios on phytate enzymatic dephosphorylation were determined in dairy manure containing from 1 to 100 g L-1 of total solids. Phytate dephosphorylation by Aspergillus ficuum phytase EC 184.108.40.206 followed first-order decay kinetics at 20 oC. As counterion concentration increased and Ca2+ to phytate-P mole ratios reached 6:6, dephosphorylation decreased by 50 (± 3.6) and 40 (± 4)% at pH 4.5 and 6, respectively. Polyanionic phytate had high affinity for Al3+ and Fe3+ and reduction in dephosphorylation averaged 27 and 32% at a mole ratio of 1:6 and reaching over 99% at mole ratio of 6:6, for Al3+ and Fe3+, respectively. In dairy manure, a phytase-hydrolyzable P fraction was native and proportional to manure solid concentration. The differential protective effects of cations influenced the accuracy of estimates of the PHP fraction in manure. Low Ca2+ concentrations did not interfere with IP6 net dephosphorylation in manure while Ca2+ at 6:6 Ca to IP6-P mole ratio, Al3+ and Fe3+ severely inhibited the reaction. Increased manure TSS also decreased IP6 susceptibility to dephosphorylation. Therefore, the nature of the counterion and its mole ratio to P control phytate physical state in solution and its susceptibility to enzymatic hydrolysis that may lead to phytate persistence in manure and potentially where manure is land applied.