Date of Award
Master of Science
James R. Russell
Because congregation of cattle near surface waters may result in sediment, nutrient, and pathogen loading of water resources, management practices to alter distribution or limit grazing may enhance water quality of a stream within a grazed pasture. Objectives of this study were to relate pasture physical characteristics, shade distribution, and tall fescue prevalence in cool-season grass pastures to the temporal and spatial distribution of grazing cattle; and to quantify stocking rate effects on forage sward height, proportions of bare and manure-covered ground, and bank erosion adjacent to streams. During a 3-year period, an on-farm research study was conducted in the Lake Rathbun watershed located in southern Iowa to evaluate factors that may affect nonpoint source (NPS) pollution occurring from grazed Midwestern pastures. In one study, Global Positioning System (GPS) collars recorded location of 2 to 3 cows per pasture at 10 min intervals for 5 to 14 d in the spring, summer, and fall of each year on five producer farms. For determination of temporal and spatial distribution of the cattle, position coordinates of each GPS measurement were located on aerial maps using ArcGIS 9.2 software (ESRI, Redlands, CA) and categorized as being located in the Water Source (directly within stream and/or ponds), Waterside Zone (within 30.5 m of a Water Source), or Upland Zone (greater than 30.5 m from a Water Source). In a second study, thirteen producer farms that ranged from 2 to 107 ha with stream reaches of 306 to 1778 m that drained watersheds of 253 to 5660 ha were also utilized to quantify stocking rate effects on proportions of bare and manure-covered ground, forage sward height, botanical composition, and stream bank erosion within 15.2 m of a stream in riparian areas of grazed pastures. Stream bank erosion was measured by fiberglass pins (1.6 x 76.2 cm) at 1 m intervals from the streambed to the top of the bank at 10 equidistant transect locations on each side to measure bank erosion during winter/early spring, late spring/early summer, and late summer/fall grazing seasons on each of the thirteen pastures. Proportions of GPS cow observations within the Waterside Zone increased with decreasing pasture area (r2 = 0.61) and with increasing proportions of total area (r2 = 0.62) and shade (r2 = 0.42) within the Waterside Zone in similar-sized pastures. Management that increases stocking rates per unit of stream length was found to increase manure-covered ground and decrease forage sward height, but not affect proportions of bare ground or stream bank erosion rates adjacent to pasture streams. The proportion of bare ground and stream bank erosion that occurred was likely a result of stream hydrology and overland flow factors from above-normal precipitation during the study, as well as naturally occurring freeze/thaw cycles. Results infer management practices to minimize the NPS pollution of pasture streams will be most effective on small or narrow pastures or both rather than in large, wide pastures and altering cattle distribution will influence factors continually transporting nutrients from grazed pastures.
Douglas Allen Bear
Bear, Douglas Allen, "Pasture management effects on nonpoint source pollution of Midwestern watersheds" (2011). Graduate Theses and Dissertations. 11983.