Kinetics of Phosphorus Sorption in Vegetative Treatment Area Soils

Abstract

<p>Vegetative treatment systems have been proposed and are being utilized to treat runoff from animal feeding operations. These systems use soil and vegetation to remove contaminants (solids, phosphorus, and nitrogen) from the feedlot runoff water and limit potential impacts runoff could have on water quality. Research has shown that these systems soils play a key role in retaining the phosphorus. Thus, the purpose of this experiment was to determine the rate of phosphorus sorption by the soil and in so doing evaluate the impact the runoff contact time with the soil has on phosphorus removal from the solution and retention in the soil. In this experiment, a phosphorous solution of 100 mg P/L, taken to approximate concentrations in the feedlot runoff, was added to soil samples obtained from three different locations in Iowa. After adding the phosphorous solution to each soil sample, the sample was continuously mixed and a sample of solution collected at 0, 1, 2, 4, 7, 14, 21 and 28 days to measure the amount of phosphorus remaining in solution. The results indicated that in most cases phosphorus was quickly sorbed as equilibrium was reached within approximately 24-hours. This indicates that relatively short contact times are required to phosphorus removal; however, in several cases phosphorus removal occurred more slowly and might place a limit on appropriate application rates. The results indicated that phosphorus sorption generally occurred more quickly in VTA soils than in the grass soil samples. Based on the measured sorption parameters, VTA areas ranging from 0.5 – 2.25 hectares are required per hectare of feedlot area.</p>