Grazing can reduce the environmental impact of dairy production systems

Authors: Rotz, Clarence - Al; Soder, Kathy; Skinner, Robert; Dell, Curtis; Kleinman, Peter; Schmidt, John; Bryant, Ray

Submitted to: Forage and Grazinglands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2009
Publication Date: 9/17/2009
Citation: Rotz, C.A., Soder, K.J., Skinner, R.H., Dell, C.J., Kleinman, P.J., Schmidt, J.P., Bryant, R.B. 2009. Grazing can reduce the environmental impact of dairy production systems. Forage and Grazinglands. Available: www.plantmanagementnetwork.org/sub/fg/research/2009/impact/

Interpretive Summary: Dairy production, like other livestock production systems, has various environmental impacts involving both water and air quality issues. The use of well-managed rotational grazing as a production strategy provides benefits to the producer and society for many, but not necessarily all, environmental concerns. An experimental comparison of the diverse environmental impacts among dairy production strategies is not feasible; there are too many factors to be considered, and these factors are highly interrelated and influenced by soil type, weather, and management decisions. Computer simulation offers the only practical means of systematically comparing farming systems. A comprehensive simulation analysis illustrated the environmental impacts of four diverse dairy production systems in Pennsylvania that used confinement feeding and managed rotational grazing strategies. Grazing systems greatly reduced soil erosion and sediment-bound phosphorus runoff. Runoff of soluble phosphorus and volatilization of ammonia were also reduced, but nitrate leaching loss was increased. The net greenhouse gas emission or carbon footprint of milk production was reduced just a little through the use of grazing, but during the transition of row cropland to perennial grassland, soil carbon sequestration greatly reduced the carbon footprint of grass-based systems. These environmental benefits should be used to encourage greater adoption of managed rotational grazing in regions where this technology is well adapted.

Technical Abstract: Incorporating managed rotational grazing into a dairy farm can result in an array of environmental consequences. A comprehensive assessment of the environmental impacts of four management scenarios was conducted by simulating a 250 acre dairy farm typical of Pennsylvania with: (1) a confinement fed herd producing 22,000 lb of milk per cow per year; (2) a confinement fed herd producing 18,500 lb; (3) a confinement fed herd with summer grazing producing 18,500 lb; and, (4) a seasonal herd maintained outdoors producing 13,000 lb. Converting 75 acres of cropland to perennial grassland reduced erosion 24%, and sediment-bound and soluble phosphorus runoff by 23 and 11%, respectively. Conversion to all perennial grassland reduced erosion 87% with sediment-bound and soluble phosphorus losses reduced 80% and 23%. Ammonia volatilization was reduced about 30% through grazing, but nitrate leaching loss increased up to 65%. Grazing systems reduced the net greenhouse gas emission by 8 to 14%, and the carbon footprint, expressed per unit of energy corrected milk, decreased 9 to 20%. Greater carbon sequestration in perennial grassland relative to row cropland, reduced the carbon footprint of an all grassland farm up to 80%. The environmental benefits of grass-based dairy production should be used to encourage greater adoption of managed rotational grazing in regions where this technology is well adapted.