A whole-farm nutrient mass balance (NMB) is a useful measure of the nutrient status of a dairy farm. Research is needed to define and determine a feasible NMB range for dairy farm systems in New York State (NY). The objectives of this study were to (1) document the distribution of N, P, and K mass balances of 102 NY dairy farms (including 75 small, 15 medium, and 12 large farms); (2) establish initial NMB benchmarks based on what 75% of the farms achieved; (3) determine the maximum animal density that allows an example NY dairy farm to balance cow P excretions and crop P removal without exporting crops or manure; and (4) identify opportunities to improve NMB over time. Nutrient mass balances of the 102 farms ranged from -39 to 237 kg of N/ha for N without including N2 fixation (N1), from -14 to 259 kg of N/ha when N2 fixation was included (N2), from -7 to 51 kg of P/ha, and from -46 to 148 kg of K/ha. Seventy-five percent of the farms were operating at NMB less than 118 kg of N/ha for N1, 146 kg of N/ha for N2, 13 kg of P/ha, and 41 kg of K/ha (75% benchmarks). Farms with the highest nutrient use efficiencies (lowest NMB per unit of milk produced) operated with less than 8.8 kg of N/Mg of milk for N1, 11.8 kg of N/Mg of milk for N2, 1.1 kg of P/Mg of milk, and 3.0 kg of K/Mg of milk. The biggest contributor to the NMB was the amount of imported nutrients, primarily feed purchases. The example farm assessment (assuming no export of crops or manure) suggested that, when 70% of the feed is produced on the farm and P in feed rations does not exceed 4 g of P/kg of DM, cow P excretion and crop P removal were balanced at a maximum animal density of 2.4 animal units (AU)/ha (~0.97 AU/acre). Dairy farms operating with animal densities <2.4 AU/ha typically had NMB below the 75% benchmark, whereas most dairies with more than 2.4 AU/ha needed to export manure or crops to meet the 75% benchmark. Opportunities to reduce NMB on many farms, independent of size and without changes in animal density, are possible by more tightly managing fertilizer and feed imports, increasing the percentage of farm-produced nutrients, implementing precision feeding, and exporting crops or manure.

This two‐part article reports on a process for integrating knowledge to develop and evaluate nutrient management plans for dairy farms. The focus is on accounting for and managing N, P, and K on a commercial farm. The case study farm was a well managed, progressive dairy farm located in central New York with 320 lactating cows (Bos taurus), 290 heifers, and 600 acres of crop land. This farm had the resources and management skills that are a model for dairy fanning in the future. However, mass nutrient balances indicated that 60 to 72% of imported N, P, and K were in excess of nutrient exports from the farm; 60 to 80% of the imported nutrients were from purchased feeds. Evaluation and refinement of animal diets resulted in a reduction in crude protein content of the rations by 2 percentage points while supporting a 13% increase in milk production and a 34% decrease in total N excretion. Partial budgets projected that ration reformulation increased net farm income by $40 200. Implementation of a crop nutrient management plan was expected to decrease fertilizer purchases and application expenses by about $1350, but construction of a remote manure storage pond and custom spreading of manure resulted in a decrease of net farm income of $4000. The vast quantity of data required and the complexity of the analysis indicate that developing computerized decision aid tools will be necessary to apply the process to a large number of farms. Research Question Water quality concerns and proposed or enacted nutrient management regulation have created a heightened awareness of the need for improved nutrient management on dairy farms. Mass nutrient balances indicate about 67% of N, P, and K imported onto dairy farms as purchased feed, fertilizer, and N fixation are not accounted for as products sold. A process is needed that reduces nutrient loading on dairy farms. This process should incorporate (i) an assessment of nutrient imports and exports, (ii) a more accurate system for formulating animal diets, (iii) a system to protect water quality by predicting manure and soil nutrient status and determining agronomically appropriate manure and fertilizer application rates, and (iv) a method to evaluate the impact of proposed changes on farm profitability. Literature Summary Many studies have shown that more nutrients (N, P, and K) are imported onto dairy farms than are exported. There is a need for nutrient management on dairy farms to protect water from contamination from these excess nutrients. When environmental objectives are met by more efficient allocation of resources and better use of information, economic efficiencies may also be realized. Since nutrients constitute a scarce resource, practices designed for economically efficient nutrient use should also be environmentally sound. The need for a multi‐disciplinary approach in sustainable agriculture research has been well documented. The benefits of farmer involvement in sustainable agriculture research have also been noted. However, few studies that use a multidisciplinary ap...

Whole-farm nutrient mass balances (NMB) can assist producers in evaluation and monitoring the nutrient status of dairy farms over time. Most of the previous studies that report NMB for dairy farms were conducted over 1 to 3 yr. In this study, annual N, P, and K mass balances were assessed on 54 dairy farms in New York State for 4 to 6 yr between 2005 and 2010 with the objectives to (1) document changes in NMB over time and drivers for change, and (2) identify nutrient use efficiency parameters that predicted the potential for improvement in NMB. The study farms varied in size (42 small, 12 medium and large) and management practices. Phosphorus, K, and 2 N balances (N1 without N2 fixation, and N2 including N2 fixation) were calculated. In general, farms with high initial NMB levels reduced them over time whereas farms with negative NMB tended to increase their NMB, demonstrating a tendency across all farms to move toward more optimal NMB levels over time. Sixty-three to 76% of farms (depending on the nutrient) reduced their NMB per hectare over the 4 to 6 yr, and 55 to 61% of these farms were able to do so while increasing milk production per cow. Across all farms, the overall reduction in NMB per hectare averaged -22kg of N/ha for N1 (29% reduction), -16kg of N/ha for N2 (15% reduction), -4kg of P/ha (36% reduction), and -10kg of K/ha (29% reduction). Change in feed imports was the most important driver for change in N and P balances across farms, whereas adjustments in both feed and fertilizer imports affected the K balances. Key predictors of potential areas for improvement in NMB over time include total nutrient imports, feed imports, animal density, percentage of farm-produced feed and nutrients, and feed nutrient use efficiency. Overall, this study highlights the opportunities of an adaptive management approach that includes NMB assessments to evaluate and monitor changes in nutrient use efficiency and cost-efficiency over time.

Nutrient loss and accumulation as well as associated environmental degradation have been a concern for animal agriculture for many decades. Federal and New York (NY) regulations apply to Concentrated Animal Feeding Operations and a comprehensive nutrient management plan (CNMP) is required for regulated farms. The whole farm nutrient mass balance (NMB) calculator was created to evaluate the impact of CNMPs and field or herd farm management changes on the whole farms’ nutrient use efficiency. This tool calculates the nitrogen (N), phosphorus (P) and potassium (K) imported onto and exported from the farm, and expresses the difference as N, P, and K balance per acre of cropland and per volume of milk produced. Farmers and their advisors can use the NMB calculator to compare their farm's nutrient balance to those of peers with similar milk production, to identify opportunities to increase nutrient use efficiency, and to monitor progress over time. The NMB calculator is used in a capstone course on whole farm nutrient management at Cornell University to communicate the challenges and opportunities in addressing the long‐term sustainability of the dairy sector and to illustrate the potential for improvement over time. The objectives of this paper are to introduce the NMB calculator, outline the classroom NMB exercise, and describe both producer and agricultural student feedback on the usefulness of whole farm NMB assessment for reaching more sustainable balances.

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