NITROGEN MANAGEMENT OF A FEEDLOT RUNOFF CONTROL SYSTEM WITH VEGETATIVE FILTER STRIP

Abstract

Runoff from beef cattle feedlots is usually stored in holding ponds. These ponds can be a concentrated source for contaminating surface and groundwater. Vegetative filter strips (VFS) can be effective in protecting surface and groundwater by reducing diffuse contamination. The objectives of this project were to evaluate the contaminant control, and to determine the sustainability of the VFS for nutrient and runoff water control. A runoff control system for a small feedlot was constructed to utilize a VFS for water and nutrient control. To reduce contamination load, a debris basin was constructed to collect and store suspended solids. The basin provided 5 - 8 minute hydraulic retention, before evenly discharging the water across the VFS. Over a three-year period, the debris basin effectively reduced the mass of total and volatile suspended solids, and chemical oxygen demand by 80, 67, and 59%, respectively. Significant contaminant reductions in the runoff water were measured as it passed through the system for most precipitation events. No measurable water was observed exiting the VFS during the three year study period by either infiltration below the root zone or by direct release from the site; therefore, the discharge water from the basin was effectively used for hay crop production. The estimated total nitrogen load in the discharge water entering the VFS was equivalent to or less than the total nitrogen removed by the crop. Two-dimensional electromagnetic induction maps have been generated beginning before the VFS was put into operation and have continued to the present. These maps were used to illustrate zones within the VFS where salt and nutrient loading are occurring. The apparent electrical conductivity of the VFS in the region of the debris basin discharge tubes have been disproportionably increased due to salt and nutrient loading. Surface soil nitrate-nitrogen levels, particularly closest to the discharge tubes, have also increased.