Field evaluation of vegetative filter effectiveness and runoff quality from unstocked feedlots

ABSTRACT:

Smaller beef cattle feedlots—less than 1,000 head—are often used for only a part of each year, but little is known about the pollution potential caused by feedlot residual manure when cattle are not present or about the effectiveness of vegetative filter strips under these conditions. This study quantified beef cattle feedlot runoff quality, particularly during unstocked conditions, evaluated reductions of fecal bacteria and nutrients in vegetative filter strips treating feedlot runoff, and assessed the relative importance of site characteristics on observed reductions. Established vegetative filter strips on four commercial feedlots located across central and eastern Kansas were instrumented with automated samplers at vegetative filter strip inlets and outlets, and 22 feedlot runoff events were analyzed for reductions in fecal coliform, Escherichia coli, fecal streptococci, total nitrogen and total phosphorus. Events when few or no cattle were present averaged one-sixth the total nitrogen (20 mg L⁻¹), one-seventh the total phosphorus (6 mg L⁻¹), and one-fortieth the fecal coliforms (2.1 × 10⁴ cfu 100 mL⁻¹) of events with cattle present. Measured concentration reductions from all events and vegetative filter strips averaged 77 percent (fecal coliforms), 83 percent (E. coli), 83 percent (fecal streptococci), 66 percent (total nitrogen), and 66 percent (total phosphorus). Vegetative filter strips allowed no discharges for 92 and 93 percent of feedlot runoff events at the sites with the ratio of vegetative filter strip:drainage area greater than 0.5. Constituent reductions were positively correlated to vegetative filter strip:drainage area ratio and negatively correlated to event rainfall depth. This study provides general support for the use of vegetative filter strip:drainage area ratio as a design guideline.