Nutrient Mass Balances Trends for Dairy Farms in New York and in the Upper Susquehanna Watershed.

Reducing nitrogen (N) and phosphorus (P) loads from agriculture is needed to improve water quality of the Chesapeake Bay Watershed. Annual assessments of whole-farm N, P, and potassium (K) mass balances (NMBs) allow dairy farmers to monitor changes in nutrient use efficiency and potential environmental losses over time. A total of 570 NMBs were conducted for 189 dairy farms in New York (NY) between 2004 and 2013, including 293 NMBs from 91 farms in the Upper Susquehanna Watershed (USW), headwaters of the Chesapeake Bay. On average, NMBs per ha and per Mg of milk were lower for the USW farms than statewide. At both geographic regions, NMBs declined over the study period (by 39 to 42% in NY farms, and by 50 to 59% in the USW), while milk production remained constant at 9,111 kg milk/cow per year (NY farms) and 8,452 kg milk/cow per yr (USW farms). Farmers in the databases reduced the total imports (especially feed imports) and increased the percentage of homegrown feed. Assuming all NY and USW dairies achieved similar reductions in total imports as farms in these databases, this study implies a potential reduction in total nutrient loading from dairy farms over the last 10 years of 29,944 Mg N, 2,994 Mg P, and 10,809 Mg K (statewide), and 4,246 Mg N, 425 Mg P, and 1,377 Mg K (for the USW).