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United States Department of Agriculture

Agricultural Research Service

Title: Hydrochloric Acid Fractions in Hedley Sequential Fractionation of Soil and Animal Manure May Contain Both Inorganic and Organic Phosphates

Authors
item He, Zhongqi
item Fortuna, Ann Marie
item Senwo, Z - ALABAMA A&M UNIV
item Tazison, I - ALABAMA A&M UNIV
item Honeycutt, Charles
item Griffin, Timothy

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2005
Publication Date: April 29, 2006
Citation: He, Z., Fortuna, A., Senwo, Z.N., Tazison, I.A., Honeycutt, C.W., Griffin, T.S. 2006. Hydrochloric acid fractions in Hedley sequential fractionation of soil and animal manure may contain both inorganic and organic phosphates. Soil Science Society of America Journal. 70:893-899

Interpretive Summary: Accurately characterizing phosphorus (P) forms in the environment is needed to develop strategies that minimize the adverse environmental impacts of agriculture. A sequential fractionation procedure developed nearly two decades ago has been widely used for characterizing P forms in soil, animal manure, and biosolids. The assumption that hydrochloric acid (HCl) fractions in this procedure contain only inorganic P has long been accepted. In this study, we measured the concentrations of inorganic P and organic P in sequentially-extracted HCl fractions of 15 soils and eight manures. Our data indicated that the exclusion of organic P in HCl fractions without any measurement was a misconception because there were significant amounts of organic P in the HCl fractions of some samples. We recommend that it should be determined experimentally whether the HCl fraction of a sample contains inorganic P only or both inorganic and organic P. Without considering HCl organic P species, data derrived from sequential fractionation schemes might be incomplete. Correcting this methodological misconception would enable researchers to more accurately and comprehensively investigate the fate and interchange of P species in soil and animal manure under various environmental conditions.

Technical Abstract: Accurately characterizing phosphorus (P) forms in the environment is a prerequisite to develop strategies that minimize the adverse environmental impacts of agriculture. Hedley sequential fractionation procedures have been widely used for characterizing P forms in soil and animal manure. Hydrochloric acid (HCl) fractions in these procedures have been assumed to contain only inorganic P. This assumption has been accepted for nearly two decades without any challenge. In this study, we measured concentrations of inorganic P in untreated (control) HCl fractions, after either 3-phytase incubation or oxidative autoclaving. Increased P concentration from 3-phytase or autoclaving, compared to the controls, was attributed to organic P. Our data with 15 soils and eight manures indicated that whereas HCl fractions of some samples contained little or no amounts of organic P, other samples contained significant amounts of organic P in the HC1 fractions. The exclusion of organic P in HCl fractions without any measurement seemed a misconception. We recommend that it should be determined experimentally whether the HCl fraction of a sample contains inorganic P only or both inorganic and organic P. Without condidering HCl organic P species any data derrived from the Hedley sequential fractionation scheme might be incomplete. Inclusion of HCl extractable organic P with other sequentially extracted P forms would provide more accurate and comprehensive knowledge on the fate and interchange of P forms in soil and animal manure under various environmental conditions.

Last Modified: 7/28/2014
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