The environmental impacts of grazing in dairy production

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

Submitted to: American Forage and Grassland Council Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2009
Publication Date: 6/21/2009
Citation: Rotz, C.A., Soder, K.J., Skinner, R.H., Dell, C.J., Kleinman, P.J., Schmidt, J.P., Bryant, R.B. 2009. The environmental impacts of grazing in dairy production. American Forage and Grassland Council Conference Proceedings, June 21-23, 2009, Grand Rapids, MI. 2009 CDROM.

Interpretive Summary: An interpretive summary is not required.

Technical Abstract: Dairy farms impact the environment in a number of ways, all of which are influenced by the choice of including grassland and managed rotational grazing. Because of the diverse environmental impacts of farming and the interactions of these impacts, an experimental comparison of production strategies is not feasible. A more practical approach is to use process-level simulation of farming systems. The Integrated Farm System Model was used to conduct a comprehensive assessment of the environmental impacts of grazing and confinement dairy production strategies. Four systems producing the same amount of fat corrected milk were compared on 250 acres of a clay loam soil in central Pennsylvania: 1) a confinement-fed herd of 90 Holstein cows plus replacements producing 22,000 lb of milk per cow per year (3.4 % milk fat), housed in free stall barns, and fed total mixed rations including alfalfa (100 acres), corn silage and high moisture grain (150 acres) grown on the farm; 2) a confinement-fed herd of 100 Holstein cows plus replacements producing 18,500 lb of milk (3.5% milk fat), housed in free stalls, and fed alfalfa (50 acres), perennial grass hay (75 acres), corn silage and high moisture grain (125 acres) produced on the farm; 3) the same as system 2 except that the 75 acres of perennial grassland was used for rotational grazing of cows and heifers during half of the year; and 4) a spring-calving herd of 125 Holstein/Jersey cows maintained outdoors all year producing 13,000 lb of milk (3.9% milk fat) with all of the land in perennial grassland and rotational grazing for up to 7 months of the year. Simulations of the four production systems illustrated a number of environmental benefits for the use of perennial grassland and managed rotational grazing. Converting 75 acres of cropland to perennial grassland reduced eroded sediment loss by 24%, and both sediment-bound and soluble phosphorus runoff by about 22% (Systems 2 and 3 vs. 1). Conversion to all perennial grassland reduced sediment erosion 87% with sediment-bound and soluble phosphorus losses reduced 80% and 23%, respectively (System 4 vs. 1). Ammonia volatilization was reduced about 30% through rotational grazing, but nitrate leaching loss increased up to 55% (Systems 3 and 4 vs. 1 and 2). Grazing systems lowered the net greenhouse gas emission by 10 to 20%. The carbon footprint (net greenhouse gas emission per unit of milk produced) was not consistently improved through grazing, but when expressed per unit of fat corrected milk, the footprint was reduced 14 to 20% (Systems 3 and 4 vs. 1 and 2). Soil carbon sequestration provided additional benefit during the transition from row crops to perennial grassland, reducing the carbon footprint of an all grassland farm by up to 80% during this transition period (System 4). 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.