|Rotz, Clarence - Al|
Submitted to: Agricultural Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/23/2012
Publication Date: 2/28/2012
Citation: Belflower, J.B., Bernard, J.K., Gattie, D.K., Hancock, D.W., Risse, L.M., Rotz, C.A. 2012. A case study of the potential environmental impacts of different dairy production systems in Georgia. Agricultural Systems. 108:84-93. DOI: 10.1016/j.agsy.2012.01.005. Interpretive Summary: A rotational pasture-based dairy was compared to a confinement-fed dairy in the southeastern United States to determine the environmental impacts of various on-farm management decisions. The Integrated Farm System Model was used to simulate (25 yr of weather data) various impacts, including carbon sequestration, greenhouse gas emissions, nitrate leaching, phosphorus runoff, sediment losses, and others. The carbon footprint for the pasture-based dairy was about 5% greater than the confinement-fed dairy, without considering the carbon sequestration potential of the perennial pasture system. If considering soil carbon sequestration, the 30-yr (or so) transition period of increasing soil organic carbon that occurs when cropland is converted to pasture resulted in a carbon footprint that is 12% less for the pasture-based dairy compared to the confinement-fed dairy. Nitrate leaching was greater on the pasture-based dairy, a consequence of sandier soils and concentrated deposits of urine and feces; while sediment and phosphorus erosion were greater on the confinement-fed dairy, which were a consequence of soils with greater clay content and the use of tillage. Management strategies are available and were considered that would reduce the carbon footprint for either dairy.
Technical Abstract: The biological and physical processes of an intensively-managed rotational pasture-based dairy and a confinement fed dairy in the southeastern United States were simulated with the Integrated Farm System Model (IFSM) to evaluate management effects on greenhouse gas emissions, soil carbon sequestration, carbon footprint, nitrate leaching, ammonia volatilization, erosion, phosphorus runoff, and phosphorus accumulation in the soil. Erosion and phosphorus runoff were less but nitrate leaching was greater for the pasture-based dairy. Ammonia emissions were greater from the confinement dairy due to the greater handling of manure. Greenhouse gas emissions per cow were greater on the confined dairy, but with greater milk production per cow the carbon footprint was slightly less. However, when the potential for soil carbon sequestration was considered, the carbon footprint of the pasture-based dairy was slightly less than that of the confinement dairy. The results of this study were generally consistent with similar simulation studies done in the northeastern U.S. with variations due to regional differences in climate, soil type, and agronomic practices. Simulated changes in management predicted that increasing milk production through improved genetics or feeding more corn decreased the carbon footprint of the pasture-based dairy, while decreasing the inorganic nitrogen fertilizer application rate and raising replacement heifers on the farm had little effect. On the confinement dairy, covering the manure storage and flaring the resulting biogas decreased the carbon footprint, while eliminating free-stall barns and placing all cattle on pasture had little effect on the footprint. The carbon footprint of this farm was increased by using higher producing, pure-bred Holsteins or producing less forage on the farm. The IFSM was capable of adapting to the climate and production practices of the southeastern U.S., but further improvements could be made to better represent the cropping practices used in this region.