Nutrient accumulation below cattle feedlot pens in Kansas
Received for publication April 30, 2008. Waste excreted on cattle (Bos taurus) feedlot pens is a source of N and other nutrients that could potentially leach into soil and negatively impact local groundwater quality. Analyses of soil chemical and physical properties beneath active open air feedlot pens were conducted at four Kansas locations to determine nutrient accumulation. Results were compared to estimated nutrient deposition, and remediation implications were considered. The surface concentrations of NH4–N, organic N, organic C, Cl–, and extractable P were elevated at the surface and rapidly decreased with depth to 1.0 m. Ammonium N in the top 0.25 m ranged from 8000 to 375 mg kg–1 but decreased below background (5.6 mg kg–1) at 1.0 to 1.3 m. Organic N in the top 0.25 m ranged from 22,000 to 500 mg kg–1 and was the largest N source. At three of four feedlots, NO3–N was below background concentration (4.1 mg kg–1) for the entire profile whereas one feedlot had a >75 mg kg–1 increase from the background concentration in the top 1.0 m. Considering expected nutrient deposition onto the pen surface only a fraction of the nutrients were found beneath feedlot pen surfaces. While in use, these feedlots do not appear to have a high potential for groundwater contamination from NO3–N leaching. However, if they were to become inactive NO3–N may increase and could leach into groundwater. Upon closing of the feedlots, the land could be largely remediated by removing the top 0.25 m of pen surface, a zone holding 48% of total profile N.