Leaching Characteristics of Repacked Soil Columns as Influenced by Subsurface Flow Barriers
Reducing the leaching of NO−3-N is of great interest. The effects of different types of subsurface barriers on delaying and reducing anion leaching and the effect of barrier size on anion leaching were investigated. Three repacked soil columns filled with soil from a Sparta loamy fine sand (sandy, mixed, mesic Entic Hapludoll) mapping unit were used to run Cl−breakthrough experiments under saturated, steady-flow conditions. Subsurface barriers used were no barrier (NB), a polyethylene disk placed above the Cl−, the same disk placed below the Cl−, a compacted soil layer created outside of the column and placed above the Cl− (CA), and a compacted layer formed in situ above the Cl−. Compared with NB, all barriers tested delayed initial breakthrough of Cl− and reduced peak Cl− concentration. Subsurface barriers delayed occurrence of the peak concentration, indicating that harriers prolonged residence time of Cl− in the soil column. Among subsurface barriers used, the CA was most effective in delaying and reducing Cl− leaching. Initial breakthrough of Cl− was delayed by 0.9 relative pore volumes, and peak concentration was reduced by >50% with the CA treatment compared with the NB treatment. The occurrence of the peak concentration was also delayed by 1.2 relative pore volumes. Compared with the NB treatment, a 3-cm plastic disk, just large enough to cover the applied Cl−, reduced peak concentration of Cl−. A 5-cm-diam. barrier also delayed initial breakthrough of Cl−, reduced peak concentration by 40%, and delayed occurrence of the peak by 0.6 pore volumes.