ABSTRACT Title of Dissertation: WATER QUALITY IN MANAGEMENT INTENSIVE GRAZING AND CONFINED FEEDING DAIRY FARM WATERSHEDS Rachel Esther Gilker, Ph.D., 2005 Dissertation Directed By: Professor Ray R. Weil, Natural Resource Sciences and Landscape Architecture Dairy farm size has increased in the United States, while the profit margin has decreased. An alternative to confined feeding dairy farming is management intensive grazing (MIG), a grass-based system relying on rotational grazing for most of the herd’s dietary requirements. Previous research has measured high levels of nitrate leaching under MIG, citing the liquid nature and high nitrogen (N) content of urine. However, this research included heavy N fertilizer applications or was conducted on monolith lysimeters with artificial leaching processes and did not accurately represent mid-Atlantic MIG dairy farms. Phosphorus (P) losses have typically been attributed to runoff and erosion but are now being ascribed to leaching as well. To measure the magnitude of N and P losses to groundwater, we sampled shallow groundwater and pore water on one confined feeding and two MIG-based Maryland dairy farms between 2001 and 2004. Transects of nested piezometers and ceramic-tipped suction lysimeters were installed in two watersheds on each farm. Two streams running through two of the grazed watersheds were also sampled to measure the effects of grazing on surface water. For three years, groundwater and surface water samples