Improvements in Whole Farm Nitrogen and Phosphorus Balances on Dairy Farms in New York.

In an attempt to achieve water quality goals for 2025, each of the states in the Chesapeake Bay Watershed (CBW) has to reduce N and P loads from agriculture. Analyses of trends in whole farm N and P mass balances (NMB) between 2004 and 2013 can aid in evaluation of improvements over time, as well as analyses of feasibility for further reductions. Between 2004 and 2013, 570 NMBs were conducted for 189 dairy farms in New York, including 91 farms and 293 NMBs in the Upper Susquehanna Watershed (USW), headwaters of the CBW. The analyses showed a decline in NMBs per ha over the 10 year period that ranged from 29 to 42% (statewide) and from 29 to 51% (for the USW dairies), depending on the nutrient. Milk production remained constant in both regions. Reductions in NMBs reflected primarily reduced nutrient imports, particularly feed imports. These source reductions reflect increased efficiency of production and reduced risk of N and P loss to watersheds. Extrapolation of data to all dairy farms in the state and CBW suggest that dairies in the USW reduced total N and P imports by 30 and 20%, respectively, contributing to a 29 to 50% decrease in total N pool and 51% decrease in P pool. Evaluation of delivery factors showed that USW dairy farms can deliver up to 49% of their 2013 N balance and up to 72% of their 2013 P balance and still meet the TMDLs set for 2025 for New York agriculture. Farm balances showed that nutrient source reduction is a significant contributor to reduced risk of N and P loss to the environment.