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Soil Phosphorus Forms Related to Extractable Phosphorus in the Everglades Agricultural Area

McCray, James Mabry; Wright, Alan L.; Luo, Yigang; Ji, Shangning

doi: 10.1097/SS.0b013e31823782da
Technical Article

Optimizing P fertilizer recommendations with proper soil testing will reduce overapplication and is vital for reducing P discharge into the Everglades. Soil samples from five Histosols in the Everglades Agricultural Area were analyzed with the objectives of (i) quantifying the forms of soil P and (ii) relating extractable P using water, acetic acid, Bray 2, and Mehlich 3 extractants to these P fractions. The percentages of five P fractions generally increased with increasing recalcitrance in the order of labile P (KCl-Pi), Fe-Al–bound P (NaOH-Pi), humic-fulvic–bound P (NaOH-Po), Ca-Mg–bound P (HCl-Pi), and residual P with the exceptions of two acid soils in which the highest percentage of total P was in the humic-fulvic fraction. Water-extractable P was strongly (P < 0.001, r = 0.97) correlated with labile P, with each measuring greater P with decreasing pH. Acetic acid–extractable P was correlated (P < 0.05) with residual P (r = 0.47) and negatively correlated with Fe-Al–bound P (r = −0.53). This suggests that this extractant recovers more recalcitrant forms of soil P associated with residual P yet is unable to remove P associated with hydroxides of Fe and Al. Bray 2–extractable P included labile P, humic-fulvic P, and some residual P, with possible contribution from Fe-Al–bound P. Mehlich 3 was the only extractant tested that included labile and nonlabile (primarily Fe-Al–bound ) P while excluding residual P, thus deemed to best indicate the plant-available P pool.

Everglades Research and Education Center, University of Florida, 3200 E. Palm Beach Rd., Belle Glade, FL 33430. Dr. James Mabry McCray is corresponding author. E-mail:

Received March 23, 2011.

Accepted for publication September 13, 2011.

Financial Disclosures/Conflicts of Interest: The study was supported by a grant from the Florida Department of Agriculture and Consumer Services and by donations from the Florida Sugar Cane League, Inc. Sugarcane IndustryResearch Committee. Fertilizer for some of the tests was donated by Wedgworth’s, Inc. The authors have no conflicts of interest to report.

© 2012 Lippincott Williams & Wilkins, Inc.