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Soil Science:
doi: 10.1097/SS.0b013e31823782da
Technical Article

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

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

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Abstract

Abstract: 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.

© 2012 Lippincott Williams & Wilkins, Inc.

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