Melanie Soberon1, Sebastian Cela1, Quirine Ketterings1, Caroline Rasmussen1, Karl Czymmek1,2
1Cornell University Nutrient Management Spear Program, 2PRODAIRY
A review: The whole farm nutrient mass balance assessment
In an adaptive management approach for whole farm nutrient management, records are kept in such a way that one can assess the nutrient status of the whole farm, pinpoint the areas where improvements can be made, and then track the progress of those improvements from year to year. In a previous issue of What’s Cropping Up? (Soberon et al., 2015), the concept of assessing the nutrient mass balance (NMB) for nitrogen (N), phosphorus (P) and potassium (K) on a whole farm was described. A follow-up study examining feasible whole farm NMBs using data from one year (2006) for 102 dairy farms from 26 different New York counties showed a wide range in farm balances (-35 to 211 lbs N/acre, -7 to 45 lbs P/acre, and from -45 to 132 lbs K/acre) (Cela et al., 2015). This work also resulted in the establishment of feasible balances, based on what 75% of the farmers were able to achieve: ≤105 lbs N/acre, ≤12 lbs P/acre, and ≤37 lbs K/acre and defined a “feasible” NMB per cwt of milk produced as those at or below which 50% of the dairies were operating in 2006: ≤0.88 lbs N/cwt, ≤0.11 lbs P/cwt, and ≤0.30 lbs K/cwt. The “optimum operational zone” was described where farms are operating below the feasible NMBs per acre and per cwt (Cela et al., 2015). To generate a clear understanding of the specific management changes that result in long-term, sustainable solutions over time in a farm’s nutrient status, NMB assessments must be examined over multiple years.
Tracking nutrient mass balances over time on 54 New York dairy farms
In this study, we analyzed data from 54 New York dairy farms that conducted annual NMB assessments for 4 to 6 years between 2005 and 2010. There was a range of farm sizes in the dataset; 42 had less than 200 cows and were classified as animal feeding operations (AFOs), and twelve exceeded 200 cows and were classified as concentrated animal feeding operations (CAFOs) based on New York thresholds at that time. On average over the first two years (initial assessment), AFOs reported lower animal densities than CAFOs (0.53 vs 1.06 AU/acre, respectively), lower milk production per cow (18,609 lbs vs 23,202 lbs/cow/yr, respectively), and a higher percentage of homegrown feed (77 vs 68%, respectively). Whereas, feed use efficiencies were higher for CAFOs (22, 28, and 11% for N, P, and K, respectively) than for AFOs (16, 21, and 7% for N, P, and K, respectively).
Fig. 1. Average N, P, and K balances (lbs/acre) and milk production per cow (1000 lbs/cow/yr) in the beginning and the end of the study, for AFOs and CAFOs.
In the beginning of the study, NMB per acre averaged 67 lbs N/acre, 10 lbs P/acre, and 30 lbs K/acre across the 54 farms. Seventy-four, 76, and 63% of the farms reduced the N, P, and K balances per acre over time, and 55 to 61% of these farms were able to simultaneously increase milk production per cow (Fig. 1). The overall change in NMB per acre averaged -20 lb/acre for N (29% reduction), -3.6 lbs P/acre (36% reduction), and -9 lbs K/acre (29% reduction). After four to six years of annual NMB assessments and monitoring (final assessment), the average balances for the 54 farms decreased to 47 lbs N/acre, 6 lbs P/acre, and 21 lbs K/acre. Over time, farms with the highest initial NMB exhibited the most drastic reductions in NMB, while farms that had low or negative initial NMB tended to increase them over time. Because the ideal NMB is farm-specific, but slightly positive, these results indicate that farms made changes in NMB that were directionally correct.
Comparison with the previously established feasible NMB benchmarks
Initially, 36 of the 42 small farms (86%) and 5 of 12 medium and large farms (42%) operated with N balances per acre below the feasible benchmarks proposed for NY dairies by Cela et al. (2015). The percentage of AFOs versus CAFOs operating below the benchmark values after 4 to 6 years increased to 93 and 50%, respectively. The largest increase in the percentage of farms meeting the feasible P and K balances was observed in the CAFOs, which increased from 42 and 25% in the initial assessment years, to 75 and 50% in the final NMB assessments, respectively (Fig 2).
Fig. 2. Number (and percentage) of AFOs and CAFOs with feasible NMB (lbs/acre) in the initial and final assessment.
What were the main drivers of change?
The single largest driver of change in N and P balances among the 54 farms was a change in imported feed. The largest drivers of change in K balances were the amount of feed and fertilizer purchased (Fig. 3).
Fig. 3. Average reduction in N, P and K imported through feed and fertilizer (lbs/acre) across all farms over the study period.
After 4 to 6 years of NMB assessment, the average nutrients imported through feed changed by -10.4 lb N/acre, -1.7 lb P/acre and -3.8 lb K/acre (Fig. 3). Similarly, the average nutrients imported through fertilizer changed by -3.8 lbs N/acre, -0.9 lbs P/acre and –2.1 lbs K/acre (Fig. 3). Reduced feed imports can be achieved through a variety or combination of different management practices including increasing the amount of homegrown feed and feed use efficiency, and implementation of precision feeding.
New York dairy farms reduced their NMBs over time while maintaining or increasing milk production per cow. While change in feed imports was the most important driver for change in N and P balances across farms, adjustments in both feed and fertilizer imports affected K balances. Farmers were able to improve their farm’s balance by making changes in total nutrient imports, feed imports, animal density, percentage of farm-produced feed and nutrients, and feed nutrient use efficiency, highlighting the opportunities of an adaptive management approach that includes NMB assessments to evaluate and monitor changes in nutrient use efficiency over time.
Soberon, M.A., Q.M. Ketterings, K.J. Czymmek, S. Cela, and C. Rasmussen (2015). Whole farm nutrient balance calculator for New York dairy farms. What’s Cropping Up? 25(2).
Cela, S., Q.M. Ketterings, K.J. Czymmek, M.A. Soberon, C.N. Rasmussen (2015). Feasible whole farm nutrient mass balances for New York dairy farms. What’s Cropping Up? 25(2).
Soberon, M.A., S. Cela, Q.M. Ketterings, C.N. Rasmussen, and K.J. Czymmek. 2015. Changes in Nutrient Mass Balances over time and related drivers for 54 New York dairy farms. J. Dairy Sci. (in press).
Cela, S., Q. Ketterings, K. Czymmek, M. Soberon, and C. Rasmussen. 2014. Characterization of nitrogen, phosphorus, and potassium mass balances of dairy farms in New York State. J. Dairy Sci. 97:1-19.
Soberon, M.A., Q.M. Ketterings, C.N. Rasmussen, and K.J. Czymmek. 2013. Whole Farm Nutrient Balance Calculator for New York Dairy Farms. Nat. Sci. Educ. 42:57–67.
Thanks to all the farmers, consultants, SWCD and NRCS staff, and Cornell Cooperative Extension educators that participated in this study. Thanks also to Françoise Vermeylen from the Cornell University Statistical Consulting Unit for statistical advice. This work was supported by grants from the Northern New York Agricultural Development Program (NNYADP), Northeast Sustainable Agriculture Research and Extension (NESARE), Federal-Formula Funds, and a USDA-NRCS Conservation Innovation Grant. For questions about these results contact Quirine M. Ketterings at 607-255-3061 or firstname.lastname@example.org, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/.