Potential for Nitrogen Groundwater Contamination from Animal Confinement Areas in Central Wisconsin
Bowen, Bryan Daniel
University of Wisconsin-Stevens Point, College of Natural Resources
MetadataShow full item record
Soil nitrogen (N) distributions with respect to species and depth were determined beneath five cattle confinement facilities and a single irrigated field location in Portage county, Wisconsin. Cattle barnyards studied ranged in size from 0.04 to 0.97 hectares and in stocking density from 11 to 277 square meters per animal (m2/animal), respectively. The five barnyard sites were separated into two groups: 1.) heavily stocked yards (<80 m2/animal), with residual manure accumulations on their surface; and 2.) those which were stocked at a lower rate (>80 m2/animal), or had minimal organic carbon (O.C.) accumulations. Data obtained from seven barnyard soils indicate that organic matter combined with soil compaction at a barnyard surface restricts water infiltration and soil-atmosphere oxygen transfer and controls the soil N forms. The presence of O.C. greater than 2% combined with stocking densities greater than 80 m2/animal resulted in an average nitrate concentration of 1.7 mg/kg at depths below 30 cm beneath five of seven barnyard soils studied. Beneath the same five barnyard soils 83% to 97% of inorganic N measured was in the ammonium form (NH4-N). A positive correlation of NH4-N to surface O.C. was identified (r=0.879). Factors of manure loading and animal density are thought to contribute to this relationship. Potassium was also positively correlated to NH4-N and found to be an indicator as to the depth of manure loading beneath sandy barnyards where NH4-N was the predominent form of inorganic N present. Within two barnyards where manure sealing of the surface did not occur, 72% to 84% of all inorganic N was found in the NO3-N form. Surface infiltration data suggested that leaching of NO3-N occurred under these conditions. Feedlot management that insured an intact manure surface did not result in rapid vertical NO3-N leaching beneath confinement areas; runoff beyond the confinement areas with subsequent leaching may have posed a groundwater problem in these cases. Uncompacted perimeter zones near fences were also areas that may have contributed NO3-N to groundwater from mineralization of manure Nat the barnyard edges. Low stocking densities or manure removal practices yielded lower total Non barnyard surfaces, but the majority of inorganic N was in the mobile NO3-N form.