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United States Department of Agriculture

Agricultural Research Service

Research Project: NUTRIENT CYCLING AND UTILIZATION ON ORGANIC DAIRY FARMS Title: Spectral and Chemical Characterization of Phosphates Associated with Humic Substances

Authors
item He, Zhongqi
item Ohno, T - UNIV OF MAINE
item Cade-Menun, B - STANFORD UNIVERSITY
item Erich, M - UNIV OF MAINE
item Honeycutt, Charles

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 26, 2006
Publication Date: June 15, 2006
Citation: He, Z., Ohno, T., Cade-Menun, B.J., Erich, M.S., Honeycutt, C.W. 2006. Spectral and chemical characterization of phosphates associated with humic substances. Soil Science Society of America Journal. 70:1741-1751

Interpretive Summary: Because organic matter (OM) influences many processes in soils and natural waters, characterization of phosphorus (P) associated with OM may shed light on its function in P cycling and nutrition. As the first step in our efforts to better understand the chemistry of P associated with OM, we used advanced instrumental and innovative wet chemical approaches to investigate the chemical nature of P in four OM standard and reference fractions supplied by the International Humic Substances Society. Our results demonstrated that source (soil vs. peat) was a more important factor than organic matter fraction (humic acid vs. fulvic acid) in influencing the properties of P. Our data indicate that a large portion of P in peat OM is not available for plant uptake, but more than half of P in soil OM is potentially bioavailable. This work represents a much more complete characterization of OM (humic substance)-bound P than previously reported in the literature. This research improved the techniques used to investigate P in soil, and provided further information on P cycling in agriculture.

Technical Abstract: As humic substances are involved in many processes in soils and natural waters, characterization of P associated with humic substances may shed light on the function of natural organic matter in P cycling and nutrition. In this study, we investigated the chemical nature of P in the IHSS Elliott Soil humic acid standard (EHa), Elliott soil fulvic acid standard II (EFa), Waskish peat humic acid reference (WHa), and Waskish peat fulvic acid reference (WFa) by fluorescence spectroscopy, FT-IR, solution 31P NMR, 3-phytase incubation and UV irradiation. We observed more similar characteristics between EHa and EFa as well as between WHa and WFa than between the two humic acids or two fulvic acids themselves, indicating that source (soil vs. peat) was a more important factor than fraction (humic acid vs. fulvic acid) with respect to the properties of P in these humic substances. Phosphorus in WHa and WFa was mainly present in the orthophosphate form. However, only about 5% was soluble. After treatment by both UV irradiation and enzymatic hydrolysis, soluble orthophosphate increased to 17% of WHa P, and 10% of WFa P. Thus, it appears that a large portion of P in Waskish peat humic substances is not labile for plant uptake. Treatment by both UV irradiation and enzymatic hydrolysis raised soluble orthophosphate to 67% of EHa P and 52% of EFa P, indicating that more P in Elliott soil humic substances is potentially bioavailable.

Last Modified: 11/23/2014
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