Phosphorus sorption and desorption properties of the spodic horizon from selected Florida Spodosols

The chemistry of P in the spodic (Bh) horizon of Florida Spodosols has generated considerable interest in recent years, particularly where water quality problems have been reported. Early studies suggested that the Bh horizon can function as a sorption sink for P moving through nonretentive sands. However, the conditions under which P can be retained in or released from the Bh horizon have not been adequately investigated, This study evaluated the P sorption and desorption properties of the Bh horizon h om 16 Florida Spodosols, The samples exhibited P sorption capacities that were reflective of their citrate-dithionite-bicarbonate (CDB)-extractable Al contents. Mean Langmuir sorption maximum (S-max) values of 7.55, 11.08, and 17.49 mmol P kg(-1) were obtained for low-, medium-, and high-Al soils, respectively. The CuCl2-extractable Al (organic matter bound) was the single most important chemical property contributing to P retention, accounting for > 60% of the variability in P sorption. Though anaerobic incubation altered P sorption and release, the effect was generally small and inconsistent. Such treatment reduced P sorption by low-Al soils and slightly increased that of high-Al soils. The tack of response to anaerobic incubation was attributed to generally low levels of reducible Fe in the soils. The samples also exhibited varying degrees of P sorption-desorption hysteresis. Irreversibility was most pronounced for high-Al soils, where > 70% of the added P remained sorbed after nine successive extractions. The relationships between Al contents and P sorption capacities should be useful in Formulating site criteria for control and management of wastewater from dairy and other agricultural operations located on Florida Spodosols.