Whole Farm Mass Nutrient Balances as Assessment Tool for Dairy Farms.

Nutrients imported onto livestock farms, in excess of nutrients exported, contribute to nutrient accumulation and potential environmental degradation. Mass nutrient balances (MNBs) have been used to addess nutrient loadings and potential losses on farms. Our objectives are to: (1) increase awareness of individual farm MNBs; (2) document balances for a wide range of dairy farms; (3) identify options for more efficient nutrient use; (4) identify implementation opportunities /challenges; and (5) measure individual farm and industry progress over time. In 2003 we initiated a statewide MNB assessment project, which to date has generated 390 annual MNBs (150 New York State dairy farms). Annual MNBs were calculated as the difference between nutrients in imported feed, fertilizer, animals, and bedding, and nutrients in exports such as milk, animal and crop sales, and manure or compost exported of the farm. This difference was expressed on a per ha cropland or per kg milk basis. Additional data collected included farm production characteristics such as cropland area, animal numbers, and crop yields. Over the four years, N balances ranged from -60 to +347 kg N/ha; P balances ranged from -11 to +51 kg P/ha. There was a large range of MNBs, also within farms with similar size. Nutrient balances increased with production intensity (milk produced per tillable ha cropland) and animal density (animal units per tillable ha cropland). Benchmarks, developed from a systematic mass nutrient balance data collection process, provide producers with a useful tool to measure their nutrient management progress over time. This project increased farmer awareness of nutrient use efficiency, specifically through the delivery of farm-specific reports that placed farm measures into the larger database (peer to peer comparisons). However, within-farm evaluations are needed to identify practical management alternatives with a potential to lower balances.