Assessing and improving the sustainability of dairy production is essential to secure future food production. Implementation of Beneficial Management Practices (BMPs) can reduce carbon and reactive nitrogen footprints of dairy farms. BMPs can and have been developed for different farm components, including feed, manure management and field cultivation practices. It is practically and economically infeasible to empirically test all combinations of BMPs at a whole farm scale. We therefore use whole-farm process-based models to assess the impact of several Beneficial Management Practices (BMPs) on carbon and reactive nitrogen footprints of dairy farms in the Great Lakes region. Specifically the aim of this study is to evaluate the influence of Beneficial Management Practices (BMPs) on carbon, reactive nitrogen and phosphorus footprints of dairy farms in the Great Lakes region.
1. Baseline farms
We developed two baseline model farms, a small 150 cow herd farm and a large 1500 cow herd farm, that are thought to be representative for current dairy farming practices in the Great Lakes region, particularly Wisconsin and New York State (Table 1). The two baseline dairy farms were developed based on individual team members’ expertise and a consultation with external experts (Dane County Conservationists, Madison, Wisconsin). For the 1500 cow farm, the baseline scenario was partly based on a previously-studied commercial dairy farm in NY state. Since this commercial dairy farm already employs some BMPs (e.g. anaerobic digestion as BMP in manure management), the farm was ‘downgraded’ to derive the baseline.
2. Beneficial Management Practices
Farm-specific BMPs were developed for three farm components, i.e. “Feed”, “Manure Management & Storage” and “Field management”. These BMPS were developed based on expert judgement and are expected or known to reduce whole-farm GWPs.
To ensure a meaningful integration of BMPs and a consistent comparison of whole-farm BMPs to the baseline and to each other, we used the following set of rules (per farm type): i) Total cultivated area was fixed (areas of individual crops can vary per scenario); ii) Herd size was fixed; iii) Milk production was allowed to float, however, only if the production increased (no decreases in milk production); iv) Purchases of crops and protein mixes were minimized as far as possible.
3. Process model simulation
The Integrated Farm System Model (IFSM4.3) was used to simulate the two baseline farms (i.e. 1500 cow farm in NY and 150 cow farm in WI) and all the individual BMPs. IFSM was used as a baseline model. The other process-based models, that is DNDC, APEX and CNCPS, were used to check IFSM predictions.
4.Whole-farm mitigation strategy
The individual BMPs were analyzed in terms of potential reduction in carbon and reactive nitrogen footprint. The best performing individual BMPs were combined into a whole-farm mitigation strategy and this whole-farm mitigation strategy was subsequently modeled in IFSM.
A comparison of model simulations of feed BMPs to the baseline shows that an integrated feed BMP (low forage, corn silage:alfalfa 3:1, ~2% NDF digestibility, reduced protein 14%, added fat, increased feed efficiency) can potentially reduce carbon and reactive nitrogen footprints with ~20% and ~24%, respectively, while remaining cost effective (18% increase in net return in $/cow), for both farm sizes.
For the small farm, replacing the bedded-pack barn with a free stall barn for the heifers, substantially reduces the carbon and the reactive nitrogen footprint with 12% and 11%, respectively. The manure management BMP 'sealed with flare' provides the largest potential reduction in carbon footprint for both farms (11% - 20%), primarily through a mitigation of CH4 emissions from manure storage.
Field management BMPs only provide a minimal reduction in carbon footprint (~3%), however, the field BMP 'no-till with injection' substantially reduces the reactive N footprint (~16%) for both farm sizes. This reduction is primarily achieved by a reduction in ammonia volatilization.
Based on the results for the individual BMPs, two combined whole-farm mitigation strategies were developed per farm and simulated in IFSM (Figure 1). For both the large farm and the small farm, the integrated whole-farm BMPs show an overall potential to reduce carbon and reactive nitrogen footprints with 33% to 37% and 15% to 42% respectively, simultaneously increasing milk production and the net return per cow with 10% to 12% and 20% to 42%, respectively.
This analysis suggests that BMPs can be applied to reduce greenhouse gas emissions and reactive nitrogen losses without sacrificing productivity or profit to the farmer.
Future research plans include a further comparison and analysis of IFSM predictions with predictions from other process models, including CNCPS, APEX, and ManureDNDC. In addition, we will assess the impact of climate change on the reactive nitrogen and carbon footprint of the baseline farms and the developed whole-farm mitigation strategies.
Karin Veltman, PhD, University of Michigan, Ann Arbor
Alan Rotz, Joyce Cooper, Larry Chase, Richard Gaillard, Pete Ingraham, R. César Izaurralde, Curtis D. Jones, William Salas, Nick Stoddart, Greg Thoma, Peter Vadas, Olivier Jolliet
Veltman et al. (2017) Comparison of process-based models to quantify nutrient flows and greenhouse gas emissions associated with milk production. Agricultural Ecosystems and Environment, 237, 31–44
DairyCAP project, www.sustainabledairy.org, aims to reduce the life cycle environmental impact of dairy production systems in the US.
This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2013-68002-20525. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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