- Milk production efficiency has significantly improved, with 30% fewer cows producing twice the amount today.
- Increases in crop yields, fuel efficiency of farm equipment, and efficiency in producing most resources have led to changes in environmental impact.
- Simulations of dairy farms in 1971 and 2020 revealed changes in nutrient losses and farmgate life cycle assessments of greenhouse gas emissions, fossil energy use, and blue water use.
- The national average intensity of GHG emissions decreased by 42%, but total GHG emissions increased by 14% over the 50-year period.
- Fossil energy use intensity decreased by 54%, but total blue water use increased 42% due to increased dairy production in dry western regions.
- Major pathways of nitrogen loss include ammonia volatilization, leaching, and denitrification.
- Simulated nitrogen and phosphorus runoff losses decreased 27 to 51% through more efficient fertilizer use, reduced tillage, and greater use of cover crops.
- Emissions of methane and reactive non-methane volatile organic compounds increased due to greater use of long-term manure storage and silage stored in bunkers and piles.
Dairy farms in the United States (US) have altered significantly during the last 50 years. Milk production efficiency has skyrocketed, with around 30% fewer cows producing about double the quantity of milk today. Other advantages include increased crop yields, fuel economy of farm equipment, and efficiency in the production of the majority of agricultural resources (electricity, fuel, fertilizer, etc.). These enhancements have resulted in changes in the environmental effects of farms. Through modelling of typical dairy farms in 1971 and 2020, variations in nutrient losses and farmgate life cycle evaluations of greenhouse gas (GHG) emissions, fossil energy consumption, and blue (ground and surface) water use were found for six regions and the US. For all environmental measures analyzed, intensities expressed per unit of fat and protein-adjusted milk produced decreased, while overall effects across all farms or milk produced rose for 5 of the 13 environmental metrics. Reductions in the consequences of dairy farms in the eastern United States were compensated by big increases in western areas as cow numbers increased significantly. The national average intensity of GHG emissions was reduced by 42%, resulting in just a 14% rise in total GHG emissions from all dairy farms throughout the 50-year period. The intensity of fossil energy usage declined by 54%, while the total number of farms decreased by 9%. Water consumption for milk production declined by 28%, but owing to the substantial rise in dairy production in the arid western areas, which rely more on irrigated feed crops, overall blue water use grew by 42%. Ammonia volatilization, leaching, and denitrification were the major mechanisms of nitrogen loss. Total ammonia emissions from US dairy farms climbed 29%, whereas leaching losses were reduced by 39%, with no change in nitrous oxide emissions. Simulated nitrogen and phosphorus runoff losses for all dairy farms fell by 27 to 51% due to more effective fertilizer usage, less tillage, and increased use of cover crops. Methane and reactive non-methane volatile organic compound emissions rose by 32% and 53%, respectively, as long-term manure storage and silage kept in bunkers and piles were used more extensively. Although great success has been achieved in increasing production efficiency, more improvement with new techniques and technology is required to fulfill dairy product demand while decreasing overall environmental consequences, especially in light of expected climatic unpredictability.
