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.

Fertilization of crops with liquid swine (Sus scrofa domesticus) manure (LSM) is a common practice throughout the world. In the Ebro Valley (northeast Spain) intensive swine production is very important and generates high quantities of LSM. Fertilizing maize (Zea mays L.) with LSM is a common waste disposal option. Nevertheless, continuous LSM application could have negative effects as heavy metal soil contamination could lead to plant toxicity. We assessed the effects of applying 29 and 51 m3 LSM ha−1 yr−1 to a field of maize during 6 yr. We measured the accumulation of total and extractable (EDTA) Cu and Zn in the soil and the concentration of these nutrients in maize plants and grain. During the 6 yr of the experiment a total of 6.6 to 11.9 kg Cu ha−1 and 12.8 to 22.5 kg Zn ha−1 (29 and 51 m3 LSM ha−1 yr−1, respectively) were applied to the soil. Total Cu and Zn soil concentrations increased by 32 and 11%, respectively, after 6 yr of LSM application. Extractable Cu and Zn soil concentrations increased more than 60% after 6 yr of consecutive LSM applications. It would take at least two to three centuries of regular LSM application to reach phytotoxic soil concentrations for Cu and Zn. Maize grain yields were about 13 to 14 Mg ha−1 over the 6 yr period, which also seems to confirm the absence of phytotoxicity. Copper and Zn concentrations in whole maize plants and grain during the last 2 yr of the experiment were lower than threshold values for animal and human ingestion (30 mg Cu kg−1 and 500–1300 mg Zn kg−1).

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.

State phosphorus indices (PIs) are being evaluated across the United States due to variability in phosphorus (P) management recommendations and questions about the lack of water quality improvement in some watersheds. Nutrient management planners in New York (NY) and Pennsylvania (PA) were surveyed via two separate "but related" questionnaires to document perspectives on the current NY-PI and PA-PI and to obtain recommendations for improvements. Many planners were content with the current versions of the PIs but felt improvements could be made to more strongly discourage application of manure under conditions of high P loss potential and better promote certain best management practices. The NY planners felt that the NY-PI should discourage manure application during winter and to fields near streams, and should more strongly promote manure incorporation or injection, establishment of cover crops, ground coverage with crop residues, and implementation of setbacks and vegetated buffers. Similarly, the PA planners felt that the PA-PI should more strongly discourage manure application to fields with insufficient ground cover, near subsurface drainage and surface inlets, and during winter. In addition, the PA planners said the PA-PI should more strongly encourage soil conservation practices such as no-till, use of cover crops, and vegetated buffers. Results of the survey suggest common experiences and viewpoints among planners in NY and PA, resulting in a valuable on-theground assessment of the PIs as a nutrient management planning tool in both states, and the potential for development of a single, physiographic region PI.

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