Ssj50152 893..899

Accurately characterizing phosphorus (P) forms is a prerequisite to developing effective remediation strategies to minimize the adverse environmental impact of agricultural expansion. Modified or unmodified Hedley sequential fractionation procedures have been widely used for characterizing P forms in soil, animal manure, and biosolids. Hydrochloric acid (HCl) fractions in these procedures have often been assumed to contain no organic P. As a result, many researchers for the last two decades have measured concentrations of inorganic P in HCl fractions without measuring organic P. In this study, we measured colorimetrically concentrations of inorganic P in untreated (control) HCl fractions after 3-phytase incubation or oxidative autoclaving of these fractions. Phosphorus concentrations in some samples were also determined by inductively coupled plasma optical emission spectroscopy. The increases in measured P concentrations, compared with the controls, were attributed to organic P in these fractions. Data for 15 soil and eight manure samples indicated that, although HCl fractions of some samples contained negligible amounts of organic P, others contained significant amounts of organic P. The concentrations of organic P were greater than inorganic P in one soil sample and two manure samples. We recommend that organic P in HCl fractions be measured experimentally to determine whether the HCl fraction contains inorganic and organic P. Identification of possible organic P species contained in HCl fractions of the Hedley sequential fractionation schemes would provide more accurate and comprehensive knowledge of the fates and interchanges of P forms in soil and animal manure under various environmental conditions. PHOSPHORUS is an essential nutrient for plant growth and development. It is added to cropland in the form of fertilizers or animal manures to maintain its availability for profitable crop production. However, P runoff from agricultural land has been identified as a nonpoint source of pollution and the cause of accelerated eutrophication in surface waters (Sharpley et al., 1999). It is expected that the first 50 years of the 21st century may be the final period of rapid global agricultural expansion accompanied by a 2.4to 2.7-fold increase in nitrogenand P-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems (Tilman et al., 2001). Thus, minimizing eutrophication will be a great challenge. Because P exists in nature in various forms with different degrees of solubility and bioavailability, accurately characterizing these P forms and their transformations in soil/water environments is a prerequisite to developing effective remediation strategies to minimize adverse environmental impacts. Sequential fractionation with dilute bases, acids, and organic solvents has been long used to characterize P in soil and animal manure (Barnett, 1994; Bowman and Cole, 1978; Chang and Jackson, 1957; Hedley et al., 1982b; Peperzak et al., 1959). The Hedley et al. (1982b) fractionation scheme has been widely used for investigating the forms and transformations of soil P under various environmental conditions (Cross and Schlesinger, 1995; Schoenau et al., 1989; Tiessen et al., 1984; TrasarCepeda et al., 1990). This procedure separates soil P into anion exchange resin, 0.5MNaHCO3, 0.1MNaOH, 1 M HCl, and residual fractions. An additional step of 0.1 M NaOH with sonication following 0.1 M NaOH extraction is occasionally included to explore the P held at the internal surfaces of soil aggregates (Beck and Sanchez, 1994; Hedley et al., 1982a; Schmidt et al., 1996; Zheng et al., 2002). Alternatively, the anion exchange resin fraction has been replaced by a H2O extraction to investigate P distributions in biosolids (Ajiboye et al., 2004; Sui et al., 1999), animal manure and composts (Ajiboye et al., 2004; Dou et al., 2000; Dou et al., 2003; He and Honeycutt, 2001; He et al., 2004; Sharpley and Moyer, 2000; Wienhold and Miller, 2004), and relevant amendments or soils. Hedley et al. (1982b) measured inorganic and organic P (difference between total P and inorganic P) present in water, 0.5M NaHCO3, and 0.1M NaOH fractions. They, however, assumed that only inorganic P exists in the 1 M HCl fraction, which has led many researchers to measure only inorganic P in HCl fractions without considering any organic P (e.g., Cross and Schlesinger [1995]; Schoenau et al. [1989]; Sharpley and Moyer [2000]; Sui et al. [1999]; Tiessen et al. [1984]; Trasar-Cepeda et al. [1990]). There are only a few reports (Dou et al., 2000; Dou et al., 2003; He and Honeycutt, 2001; He et al., 2003;Wienhold andMiller, 2004) in which the concentration of total P in all four fractions were measured. He et al. (2003) reported a difference in inorganic P and total P of 29% in the HCl fraction of swine manure. Dou et al. (2003) reported significant amounts of organic P in the HCl fractions of swine and broiler samples, but they presented no specific quantitative data. Furthermore, none of the five publications have raised the issue that organic P should not be presumably excluded from HCl fractions; rather, it should be Z. He, A.-M. Fortuna, W. Honeycutt, and T.S. Griffin, USDA-ARS, New England Plant, Soil, and Water Lab., Orono, ME 04469; Z. N. Senwo and I.A. Tazisong, Dep. of Plant and Soil Science, Alabama A&M Univ., Normal, AL 35762. Trade or manufacturers’ names mentioned in the paper are for information only and do not constitute endorsement, recommendation, or exclusion by the USDA-ARS. Received 12May 2005. *Corresponding author ([email protected].