The authors are a research ecologist with the U.S. Dairy Forage Research Center, an assistant professor with Cornell University, and a national program leader for land and air with USDA Agricultural Research Service, respectively.

Climate change is a growing risk for the agricultural sector, and livestock producers are looking for ways to improve the resilience of their operations while reducing greenhouse gas (GHG) emissions. The U.S. Dairy Net Zero Initiative has pledged to achieve net-zero dairy by 2050, which will require that GHG emissions generated by dairy production are offset by carbon dioxide (CO2) that is removed from the atmosphere.

At the same time, the federal government is investing in a nationwide strategy for measurement, monitoring, reporting, and verification (MMRV) of GHGs and carbon storage in the agriculture and forestry sectors. In order to track progress toward net zero agriculture, we need to understand farm carbon balance and how new innovations and alternative management practices will affect emissions and carbon storage.

The complete picture

Farm carbon balance provides a snapshot of a farm’s GHG emissions after subtracting carbon storage in soil and plants. In dairy operations, major GHG emissions include methane (CH4) from enteric fermentation and manure management, nitrous oxide (N2O) from field emissions and manure management, and CO2 from farm energy and fertilizer use. Permanent perennial cover (grasslands, woodlands, and wetlands) provides long-term carbon storage in agricultural landscapes, while integrating pasture or perennial forages into the farm system may add opportunities for soil carbon accumulation.

Significant research investment has been directed at reducing enteric CH4 emissions from ruminant livestock. Promising strategies include herd genetic selection, new feed additives, precision feeding for animal age classes, and management practices that enhance herd health and longevity.

A growing number of dairy producers are transitioning their replacement heifers to pasture to reduce feed costs and improve animal health. Although grazing may elevate herd enteric CH4 emissions, conversion of underperforming croplands to well-managed pasture elevates soil organic carbon while reducing the contributions of young stock to manure storage facilities.

Manure management is a major challenge for livestock operators who want to reduce their GHG emissions while faced with the constraints of manure storage infrastructure and spreadable acres. For confinement dairies, manure emissions are second only to enteric methane as a source of farm GHGs and may be greater on farms with large storage lagoons. At the same time, managing manure as a valuable nutrient resource can bolster farm profitability while improving farm carbon balance.

From livestock to crops

In the best-case scenario, livestock operations are circular systems, where nutrients are removed from the field as biomass (forage) at harvest, and these nutrients are later returned via manure application. A 2005 review documented notable benefits of manure application, including improvements in soil structure, increases in soil organic carbon and microbial activity, and greater aggregate stability. This is in addition to the climate and economic benefits of substituting manure for expensive fossil fuel-derived fertilizers. Technologies that will better predict manure nutrient content and allow for precision application are in development and have potential to make the substitution of manure for synthetic fertilizers less risky for crop production.

Ensuring that nutrient applications are aligned with crop need is a key strategy for reducing field GHG emissions and other losses to the environment. Large confinement operations may require spreadable acres that extend beyond the footprint of their land base. In this scenario, the manure generated by the herd exceeds the nutrient requirements of the operator’s croplands.

To achieve nutrient mass balance, it is necessary to transport manure to more distant croplands in need of nutrient applications. The USDA Agricultural Research Service’s Manureshed Working Group is developing innovative, cost-effective solutions for processing and redistributing manure to locations with nutrient deficits to achieve both agronomic and environmental benefits.

Effective strategies for reducing GHG emissions from manure handling vary with farm size. Composting is relatively inexpensive and can significantly reduce CH4 emissions from manure storage. Solid-liquid separation allows for handling of solid and liquid fractions that can be managed more effectively for land application. For large farms or networks of farms, it may be economically feasible to install lagoon covers or digesters.

Crunching the numbers

A number of decision support tools have been developed to process farm data and predict how new or improved practices are likely to affect farm economic and environmental outcomes. Unfortunately, they typically lack transparency and are limited in their capacity for capturing the complex dynamics of dairy farm systems.

The Ruminant Farm System (RuFaS) model was developed to address these limitations and inform sustainable decision-making on dairy farms. The model is transparent, allows the user to add variables that are relevant to an operation’s climate, soil, and production system context, and accounts for the interactions between farm subsystems.

The vision of the development team is that RuFaS will advance research and be an applied tool for the dairy industry. Thus, the envisioned path to impact for the model is illustrated in these steps:

1. Footprinting — RuFaS calculates baseline estimates of current farm outputs and environmental outcomes.
2. Planning — RuFaS identifies practices that will generate progress toward farm sustainability goals.
3. Implementation — RuFaS informs decisions to implement practices, track progress, and facilitate continuous improvement.
4. Impact — RuFaS applications support industry-wide progress toward sustainable production.

Manure-livestock systems are complex, and there is no one-size-fits-all solution for improving farm carbon balance. Strategies to achieve net zero, as well as other environmental and economic goals, should be adapted to the farm operation in its regional context.

This begins with an accurate accounting of a farm’s baseline performance and requires effective tools for tracking farm emissions, crop and animal production, and economic and environmental outcomes. Best management practices that promote manure from waste stream to valuable nutrient resource are a key strategy for improving both farm carbon balance and profitability.