The Use of Phosphorus Sorption Isotherms to Project Vegetative Treatment Life Expectancy

Abstract

<p>Beef feedlots of all sizes are looking for cost-effective solutions to manage feedlot runoff. Vegetative treatment systems (VTSs) have been proposed as a potential option. A vegetative treatment system consists of a solid settling structure followed by additional treatment components, vegetative infiltration basins (VIBs) and vegetative treatment areas (VTAs), which use soil and vegetation to treat and utilize nutrients in the applied runoff. Investigations have shown that VTSs can provide a cost effective means of treating and controlling open feedlot runoff; however, sustainability and life expectancy of these systems have not yet been determined. This study investigated, based on the vegetative treatment area’s ability to absorb and utilize phosphorus, the expected life of four VTSs on beef feedlots in Iowa. For this study, VTA life was defined as the amount of time it took for the top 0.3 meters of the soil profile to become saturated with phosphorus. Soil phosphorus sorption capacity, phosphorus loading rate, and initial soil phosphorus concentration had the largest impacts on VTA life. The impact of phosphorus removal through vegetation growth and harvest varied with the area of the VTA, with larger treatment areas having a larger increase in life than smaller vegetative treatment areas. Expected phosphorus sink life for the top 0.3 m of the soil for the four monitored vegetative treatment areas was calculated to range from 4.5 to 13 years.</p>