Agustin J. Olivo¹, Olivia F. Godber¹, Kristan F. Reed¹, Daryl V. Nydam², Michel A. Wattiaux³ and Quirine M. Ketterings¹
¹Department of Animal Science, Cornell University, Ithaca, NY United States ²Department of Public and Ecosystem Health, Cornell University, Ithaca, NY United States, ³Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, Wisconsin, United States.
Introduction
Improving nutrient use efficiency and reducing greenhouse gas (GHG) emissions are important environmental priorities for organic-certified dairy operations. Regular assessment of key performance indicators (KPIs) via decision-support tools can help monitor farm performance and identify opportunities for improvement in these areas. Multiple decision-support tools have recently emerged to evaluate these indicators. However, these tools vary in complexity, required data inputs, scope and aggregation. A study was recently conducted at Cornell University to evaluate nutrient use efficiency and GHG emissions in six organic dairies, and to analyze the impact of alternative farm management practices on GHG emissions. Three decision support tools were used: Cornell nutrient mass balance (NMB) calculator, for whole-farm nutrient use efficiency, and Cool Farm Tool (CFT) and COMET, for GHG emissions. Farms had between 30 and 138 cows, 76 and 266 acres, and were certified organic (Farms 1-6) and grass-fed (Farms 3 and 4). Evaluations were done for two years.
Key findings
Farms showed high whole-farm nutrient use efficiency, primarily driven by low nutrient imports.
Farm-gate NMBs ranged from -5 to 17 lbs N/acre for nitrogen (N), and -2 to 7 lbs P/acre for phosphorus (P). Of the six farms, four met the feasible levels for N per hundredweight (cwt) of milk and per acre of cropland, versus two farms for P and five farms for K (Figure 1). Feasible levels are NMB performance ranges that previous research has shown farms in New York can operate within. Balances were generally low, explained by low animal densities and low nutrient imports. For N, inputs from legume fixation were equivalent to or larger than nutrients imported with feed and organic fertilizer purchases for all farms. Legume stands in sod and pasture fields played an important role in the sustainability of the farms when it comes to N management. For P, low inputs resulted in negative P balances in three of the six farms. Continuously operating under negative P balances may compromise the long-term sustainability of farms by reducing soil test P levels and ultimately crop yields. It is therefore relevant that farms continue tracking farm-gate NMBs, as well as changes in soil test P and plan fertility programs accordingly.
Whole-farm GHG emissions intensity showed variability and were directionally in agreement between CFT and COMET.
Estimations from CFT for GHG emissions intensity, a common way to report farm GHG emissions, ranged from 0.98 to 2.10 lbs of CO2-equivalent (CO2-eq, a common unit to aggregate all GHGs generated in the farm), per lbs of fat and protein corrected milk (FPCM). This value did not include carbon sequestration in soils (Figure 2). Baseline estimations from COMET (that consider different farm GHG sources to CFT) ranged from 0.69 to 2.48 lbs CO2-eq/lbs FPCM. Ranking of farms was similar between the two tools, suggesting that both tools can help identify, among multiple farms, those with the greatest emissions and need for implementing GHG mitigation measures. Enteric fermentation was the single largest source of GHG emissions, followed by energy and fuel use, and feed production or cropland emissions. Manure management emissions were larger for farms with liquid manure storages (Farms 4 & 5), compared to farms with solid manure handling (Figure 2).
Cow milk productivity and manure management strategies showed opportunities to reduce farm GHG emissions.
Milk production per cow ranged from 4,400 (Farm 3) to 22,000 (Farm 5) lbs/cow per year and was negatively associated with GHG emissions intensity. The greater the milk production per cow, the lower the whole-farm GHG emissions intensity (Figure 3). Statistical analysis showed that, for farms with similar characteristics, increasing milk production from 4,000 lbs/cow/year to 11,000 lbs/cow/year could decrease GHG emissions intensity by almost 1 lbs CO2-eq/lbs FPCM.
Analysis of alternative management strategies in the areas of crop management, manure management and farm energy use showed changes in GHG emissions intensity ranging from -8% to +8% compared to current management, when considered alone. For example, theoretical implementation of solid-liquid manure separation and/or anaerobic digestors in farms with liquid slurry storages resulted in an average reduction between 6 and 8% in whole-farm GHG emissions intensity (Figure 4). Implementing strategies such as composting or piling of manure resulted in an increase in GHG emissions intensity for most farms, given the starting practice of daily spread is associated with low GHG emissions (Figure 4). Other strategies such as replacing 50% of the farms’ grid energy use with a solar source and reducing 20% the farm fuel use resulted in a 2% decrease in whole-farm GHG emissions intensity.
Conclusions
Farm-gate NMBs were low or negative, particularly for P. Additional nutrient imports, coupled with nutrient management planning, adequate legume stands, and diet balancing may help improve nutrient balances. GHG emissions varied largely across farms, with enteric fermentation, feed production, fuel and energy use, and manure management representing the largest sources. Management changes that resulted in the greatest GHG emissions intensity reductions included increasing milk production per cow and implementing manure treatment systems in farms with liquid slurry storages.
Full citation
This article is summarized from our peer-reviewed publication: Olivo, A.J., O.F. Godber, K. Reed, D.V. Nydam, M. Wattiaux, and Q.M. Ketterings (2024). Greenhouse gas emissions and nutrient use efficiency assessment of six New York organic dairies. Journal of Dairy Science https://doi.org/10.3168/jds.2024-25004.
Acknowledgements
We thank the participating farmers, Cornell Cooperative Extension (CCE) Educators Janice Degni, April Lucas, Paul Cerosaletti, Dale Dewing, and CCE intern Mikala Anderson for sharing, collecting and processing data, and giving feedback on findings. We appreciate the support of the COMET outreach team at Colorado State University. This project was funded by The Sustainability Foundation at Cornell University, a gift from Chobani, and the Department of Animal Science at Cornell University. For questions about these results, contact Quirine M. Ketterings at qmk2@cornell.edu, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/.
