Phosphorus Retention Capacity of the Spodic Horizon under Varying Environmental Conditions

The spodic (Bh) horizon of Spodosols with Al, Fe, and C accumulations usually has a high P sorption capacity. However, the Bh horizon of prevalent Spodosols in the Lake Okeechobee basin of Florida is subject to a fluctuating watertable that could change the dynamics of P in these soils under alternating aerobic and anaerobic conditions. Further, the Bh horizon of this basin is often impacted by P moving vertically following heavy surface application of dairy manure. Our objectives were to relate the P retention capacity of the Bh horizons of the Lake Okeechobee basin to other soil parameters, and to evaluate P retention of manure‐impacted Bh horizons under aerobic and anaerobic conditions. High watertable decreased the P retention capacity for the majority of the soils in this study. High manure‐impacted areas have Bh horizons with high P concentrations as a result of P movement from the surface A horizon through the eluted E horizon. The P appeared to be temporarily retained and could be released upon prolonged contact with water. This P is likely to move horizontally above the Bh horizon to drainage ditches and eventually into the lake, causing eutrophication. The equilibrium P concentrations and water soluble P concentrations of Bh horizon soils that did not receive high rates of manure application (native soils and pasture soils) are low and it is unlikely that P would move laterally out of such systems, above the Bh horizon.