State, Regional and Farm-Scale Nutrient Balances: Tools for Enhanced Efficiency of Whole-Farm Nutrient Use.

Efficient management of nutrients requires implementation of an approach that allows farmers to safely and confidently reduce nutrient imports onto and/or increase exports from farms over time. Adaptive management (AM) was recently approved as a valid approach to nutrient management, and recognized by the Natural Resources Conservation Service (NRCS) in its new national NRCS590 nutrient management standard. Many states are currently discussing approaches for implementation of an AM process, primarily at the field level. While State-level nutrient balances for nitrogen (N) and phosphorus (P) and potassium (K) are important for evaluating the potential impact of State and Regional level policies and documenting impact of implementation of policies, farm-scale whole farm nutrient mass balances (NMBs) are more effective for a farm-level AM approach; knowing a farm's NMB is one step toward improving our understanding and management of nutrient movement onto, within, and away from any particular farm. Annual assessments of NMBs on 102 New York farms show that NMBs are mainly driven by total N, P, and K imports (R² ranged from 0.75 to 0.87); total imports in turn are mainly driven by feed imports (R² ranged from 0.70 to 0.93); and feed imports are driven by the animal density and the percentage of feed produced in the farm (R² ranged from 0.67 to 0.80). A subset of farms that conducted an annual NMB for 4 years or more showed 30-50% reduction in N,  P, and K balances over the 4 year period. These results illustrate the effectiveness of use of annual NMBs for end-of-season evaluations and for achieving impact as part of an AM process.