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United States Department of Agriculture

Agricultural Research Service

Research Project: NUTRIENT CYCLING AND UTILIZATION ON ORGANIC DAIRY FARMS Title: Lability of Humic-Bound Phosphorus

Authors
item He, Zhongqi
item Honeycutt, Charles
item Olk, Daniel

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 27, 2008
Publication Date: April 2, 2008
Citation: He, Z., Honeycutt, C.W., Olk, D.C. 2008. Lability of Humic-Bound Phosphorus. Humic Science and Technology Conference Abstract. p. 52.

Technical Abstract: Phosphorus (P) has long been known to be present in humic substances from various sources. However, information on the lability of humic-bound P is very limited although such information is critical for understanding the role of humic substances in P cycling and nutrition. In this presentation, we demonstrate that biotic and abiotic release of humic-bound P can be investigated by phosphatase hydrolysis and UV irradiation, respectively. With this method, we classified humic-bound P into four groups. Labile inorganic P was the portion of inorganic P (Pi) determined without any treatment. Labile organic P was calculated as the increase in Pi determined after enzymatic incubation. UV labile P was calculated as the difference in Pi determined after enzymatic incubation with and without UV irradiation. Less-labile P was calculated as the difference between total P and the sum of the identified P forms as described above. Our data indicated that the form of humic fractions (i.e. mobile humic acid, calcium humate, or fulvic acid) and the management practices (such as inorganic fertilizer or dairy manure application) did not significantly affect the liability of humic-bound P. Lability, however, varied greatly with the source of humic substances. This work represents a method for evaluating lability (i.e. availability for plant uptake) of humic-bound P as enzymatic incubation releases hydrolyzable organic P and UV irradiation abiotically releases P mainly by breaking-down orthophosphate-humic substance complexes.

Last Modified: 11/28/2014
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