Sebastian Cela1, Quirine Ketterings1, Karl Czymmek1,2, Melanie Soberon1, Caroline Rasmussen1
1Cornell University Nutrient Management Spear Program, 2PRODAIRY
Nutrient mass balances for New York dairies
A whole-farm nutrient mass balance (NMB) is the difference between the amounts of N, P, and K imported onto dairy farms as feed, fertilizer, animals, and bedding, and exported via milk, animals, crops, and manure. We can express a NMB per tillable acre to indicate the potential for recycling nutrients in the land base, an environmental indicator, or per hundred weight (cwt) of milk, a milk production efficiency indicator.
The importance of measuring nutrient mass balances
Large positive NMBs per acre suggest high risk of nutrient losses to the environment, while large positive NMBs per cwt reflect low nutrient use efficiencies, and potential economic loss for the farm as well. Negative NMBs (resulting from exports exceeding imports) reflect mining of soil P and K resources, and will eventually reduce crop yields. Annual NMB assessments give farmers a chance to compare the farm against peers in the same milk production group, and to evaluate the impact of management changes on nutrient use efficiency and production.
Distribution of nutrient mass balances across New York dairy farms
In 2006, NMBs for 102 dairy farms from 26 different New York counties showed a range from -35 to 211 lbs N/acre, from -7 to 45 lbs P/acre, and from -45 to 132 lbs K/acre (Fig. 1). Also the NMBs per cwt of milk varied widely among New York dairies: from -1.3 to 2.6 lbs N/cwt, from -0.11 to 0.47 lbs P/cwt, and from -0.73 to 1.69 lbs K/cwt. Ranges in NMB were similar when comparing CAFOs and AFOs.
How do nutrient mass balances relate to milk production per cow?
Dairy farms in our database averaged 19,600 lbs milk/cow per year, slightly higher than the average milk production of New York dairies in 2006 (18,900 lbs/cow per year). Dairy production does not depend on large positive balances (Fig. 2); we found high producing dairies (>20,000 lbs milk/cow per year) with negative NMBs per acre as well as high producing dairies with large positive NMBs per acre.
What’s a “feasible” nutrient mass balance?
The data showed large ranges in NMBs among the 102 farms, but this does not tell us what is reasonably achievable, or “feasible”. A feasible NMB should allow dairy farms to be economically profitable, environmentally sustainable, and flexible enough to allow for the many variations among farms. Based on the largest dairy farm database we had for one individual year (2006), we defined “feasible” NMBs per acre as those at or below which 75% of the dairy farms in our database were operating: ≤105 lbs N/acre, ≤12 lbs P/acre, and ≤37 lbs K/acre (Table 1). We also 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 (Table 1).
Combining both indicators, the most efficient farms have balances in the green area in Fig. 3. Although the current assessment of feasible balances for New York can change over time as more farms join the study, evaluations so far have shown that farms that operate outside of the green area (Fig. 3) might have opportunities for improvements in nutrient use.
Drivers of nutrient mass balances
Farms with high animal densities (more cows per acre) tend to have higher NMBs per acre than low density farms, and therefore higher risk of nutrient losses to the environment. However, NMBs per cwt are unrelated to animal density, except at very low density farms (Fig. 4). This suggests that high density farms need to operate with high nutrient use efficiencies to reduce the risk of nutrient losses. Farms that grow a high proportion of the feed in the farm itself tend to have lower NMBs per acre and similar NMBs per cwt than farms that purchase much of the feed (Fig. 4).
Opportunities to improve nutrient mass balances
Experiences with a large number of farms over the past ten years has shown that opportunities exist for some dairy farms to improve NMBs by producing more feed on the farm, implementing precision feeding, adjusting fertilizer use, exporting crops (in farms with low animal densities) and exporting manure (in farms with high animal densities). Farms with less than 1 animal unit per acre (about 2 acres per cow plus her replacement) were typically able to stay below the feasible balances, whereas on higher density farms, export of manure and/or crops was needed to lower balances.
- 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. Journal of Dairy Science 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. Natural Sciences Education 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/.