Upper Susquehanna watershed and New York State improvements in nitrogen and phosphorus mass balances of dairy farms

Abstract

States in the Chesapeake Bay watershed (CBW) are required to reduce nitrogen (N) and phosphorus (P) loads from agriculture to achieve water quality goals for 2025. Assessing nutrient mass balances (NMBs) on farms over multiple years allows for evaluation of trends in nutrient accumulation and potential losses in geographic regions. Between 2004 and 2013, 570 NMBs were conducted for 189 dairy farms in New York, including 91 farms (293 NMBs) in the Upper Susquehanna watershed (USW), headwaters of the CBW. The average NMBs per hectare and per megagram of milk were lower for farms in the USW than statewide. Data showed a decline in NMBs per hectare over 10 years that ranged from 29% to 42% (statewide) and from 29% to 51% (for the USW dairies), depending on the nutrient, while milk production remained constant in both regions. Reductions in NMBs resulted primarily from reductions in nutrient imports, particularly through feed management. These source reductions reflect increased efficiency of production and reduced risk of N and P loss to the CBW. Extrapolation of comparisons in NMBs between 2004 and 2013 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. We conclude that USW dairy farms can deliver up to 49% of their 2013 N pool and up to 72% of their 2013 P pool at the edge of the farms (their NMB) and still meet the total maximum daily load (TMDL) for N and P set for 2025 for New York agriculture. This study illustrates that significant nutrient source reduction can be obtained by implementing nutrient conservation practices, such as precision feeding and fertilizer management, combined with annual assessment of whole farm balances. Such a reduction in nutrient imports onto farms results in a reduction of the pool of nutrients available for accumulation in the soil or direct loss to water bodies and the atmosphere.