Excessive phosphorus (P) fertilization can lead to eutrophication of surface water. Compositional differences between Alaquod E and Bh, and Paleudult E and Bt horizons are factors affecting sub-surface P transport in these soils. The objective of this study was to relate P sorption characteristics to compositional differences in Alaquod and Paleudult sub-surface horizons and to evaluate implications for risk of P loss via sub-surface flow in these soils. Soils were sampled by horizon from six sites located in Florida. Iron (Fe) and aluminum (Al) were extracted by sodium citrate-bicarbonate-dithionite, ammonium oxalate, and sodium pyrophosphate. The P retention characteristics were determined for all samples using single-point (1,000 mg P kg−1) isotherms and the traditional Langmuir isotherms for 33 Bh and 45 Bt samples. Eluvial horizons of Alaquods have no measurable P retentive capacity, whereas E horizons of Paleudults can retain P because of presence of metal oxides as indicated by oxalate, pyrophosphate, and citrate-bicarbonate-dithionite extractions. The P retention capacities of Bh and Bt horizons are highest among horizons studied. Greater resistance to P desorption for Bt relative to Bh horizons likely relates to the greater abundance of Fe oxides and kaolinite clay in the Bt and to the predominance of organically over inorganically complexed Al in the Bh. Compositional differences between Alaquod and Paleudult sub-surface horizons explain differences in tendencies of P retention and release within Alaquod and Paleudult profiles and within the landscape-hydrologic settings associated with these soils.
Soil and Water Science Department, Institute of Food and Agricultural Sciences, Gainesville, Florida, USA.
Address for correspondence: Dr. Vimala D. Nair, Soil and Water Science Department, 106 Newell Hall, P.O. Box 110510, Institute of Food and Agricultural Sciences, Gainesville, FL 32611, USA. E-mail: email@example.com
Received March 16, 2011.
Accepted for publication November 21, 2011.
Financial Disclosures/Conflicts of Interest: This study was supported in part by a grant from the Florida Department of Agriculture and Consumer Services.