The eutrophic state of adjacent Lake Okeechobee and recently reported increases of phosphorus levels in Everglades National Park have led to efforts to reduce the phosphorus content of agricultural drainage originating in the Everglades Agricultural Area. In order to better understand the movement of phosphorus from agricultural fields to surface water, phosphorus sorption by Histosols was studied by measuring the amount of inorganic phosphorus removed from solution by known amounts of soil (quantity/intensity experiments) for Histosols representing a variety of cultural histories and soil classifications. The experiments were summarized with phosphorus sorption indices and by fitting to sorption models. A sorption index formed by the ratio of the amount phosphorus sorbed and the log of the equilibrium P concentration for a solution initially having 100 mg L−1 added phosphorus varied widely even among Histosols with the same classification and similar cultural histories. Among 18 Histosols typical of the Everglades Agricultural Area, the phosphorus sorption index ranged from 37 to 210; the amount of P sorbed at 10 mg L−1 equilibrium P, after adjusting for initial labile P, ranged from 20 to 1800 mg kg−1; and the slope of QI plots at 10 mg L−1 P concentration ranged from 6 to 840 L kg−1. There was a significant correlation among phosphorus sorption index, ash, pH, total Ca, and free carbonates. When two or three parameter linear models were considered, oxalate extractable Fe and Al, and total Fe became important.
ASJC Scopus subject areas
- Soil Science