Phosphorus transport in Spodosols impacted by dairy waste

Deposition of P-laden dairy waste onto acid, sandy Spodosols located in the Lake Ocheechobee Basin in south Florida is commonly recognized to increase levels of P in soil profiles, groundwater, and local streamflow. In the soil profile, P accumulations occur in the surface A horizon, to a lesser extent in the E horizon, and to a much greater extent in the reactive Bh or spodic horizon. A one-dimensional mathematical model was used to demonstrate sorption and transport of P vertically through a 90-cm profile of an initially P-free Spodosol with A (0-15 cm), E (15-75 cm), and Bh (75-90 cm) horizons for conditions of steady, saturated water flow. Ten pore volumes (equivalent of 2.5 years of rainfall) of P-laden influent was applied before applying 40 volumes (equivalent of 10 years of rainfall) of P-free water. The loading of P in the influent was shown to greatly impact P transport during water flow in the soil. As expected, nonlinear sorption resulted in much greater retardation of P breakthrough in the soil effluent for the lowest influent concentration of 10 g m(-3) than for either 100 or 1000 g m(-3) concentrations. An underlying assumption in the model was that multi-dimensional water flow could be ignored. However, multi-dimensional flow under field conditions may well result in partial bypass of flow around highly consolidated Bh horizons.