Whole farm management to reduce nutrient losses from dairy farms: A simulation study

Whole-farm simulation provides a tool for evaluating long-term impacts of nutrient conservation technologies and strategies on dairy farms. A farm simulation model was verified to predict the production and nutrient flows of the De Marke experimental dairy farm in the Netherlands. On this farm, technologies such as a low ammonia emission barn floor, enclosed manure storage, manure injection into the soil, and intraseeding of a grass cover crop on corn land were used to reduce nitrogen loss and improve nutrient recycling. This experimental farm was simulated over the 1996 to 2003 weather years where predicted production and use of feeds were within 15% of values measured on the actual farm. Simulated nitrogen and phosphorus flows through the farm and losses from the farm were generally within 10% of actual. After this process-based model was found to accurately represent the nutrient conservation technologies used at De Marke, simulation was used to evaluate the environmental and economic impacts of their use on representative farms in southern Pennsylvania. Total nitrogen loss from the farms, primarily in the form of ammonia emission, was reduced by 24% to 55% with a 7% to 45% reduction in P runoff loss. The highest reductions were obtained on a 1,000-cow farm where initial losses were high due to a greater number of animals per unit of cropland. The cost of this technology was greater than the value of the nutrients saved, causing a reduction in the annual net return of $88/cow for a 100-cow farm and $64/cow for the 1,000-cow farm.