Manure management tackles climate change on the farm

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Dairy farming is New York’s most important agricultural sector, accounting for $2.5 billion in annual sales by nearly 4,000 farms, or 47 percent of the state’s agriculture sales in 2017.

The number of dairy farms in New York has fallen by half over the last two decades, the U.S. Department of Agriculture reports, and there are 11 percent fewer cows (roughly 625,000). Yet while there are fewer farms, the average herd size has grown and production per cow is up 45 percent, increasing total output to about 15 billion pounds annually. That’s a lot of milk.

Cows produce more than milk, however. Overall, agriculture contributes 11 percent of global greenhouse gas emissions and 8.4 percent of the U.S. total.

The estimated GHG emissions attributable to dairy farming is 83.5 metric tons of carbon dioxide equivalent, 1.3 percent of the U.S. total. That may not seem like a lot, but tackling the problem of climate change requires innovation across a range of industries, including agriculture. 

Among the innovative ideas that have emerged: putting worms to work.

Methane makers

The largest source of GHG emissions from dairy herds is “enteric fermentation”—cow belches and burps. Cows are “ruminants.” They create energy from their feed by fermenting it in their stomachs prior to digestion. Fermentation without the presence of oxygen produces methane, which the animal belches out during the fermentation process. Methane is a greenhouse gas that is 26 times as powerful as carbon dioxide. 

What can be done? The Zero Emissions Livestock Project, a startup at the Royal College of Art in London, recently introduced a mask to capture cow belches and burps. The firm reports a 53 percent reduction in methane released to the atmosphere. 

It has also been shown that the composition of a ruminant’s diet influences the volume of methane produced. Careful management of feed can help reduce a cow’s GHG emissions. As sheep and goats are also ruminants, their contribution to climate change may also be reduced by changing what they eat. 

The next largest contributor to climate change from dairy comes out the other end of the cow. 

The Livestock and Poultry Environmental Learning Community reports that a mature dairy cow produces roughly 120 pounds of manure each day, which translates to about 27 billion pounds of feces and urine every year in New York alone. 

In a day, the average milk cow generates about 14 gallons of manure while producing 8 gallons of milk. 

All of this manure can have a significant impact on GHG emissions if it isn’t managed effectively. A traditional dairy farm contains enough cropland to grow feed for the cows. And that cropland needs the fertilizer provided by the manure. By maintaining a balance between the dairy herd’s manure supply and the adjacent cropland’s fertilizer demand, long-term storage of manure is unnecessary and the GHG impact of manure is modest.

Peter Wright, an agricultural engineer with Cornell’s Department of Animal Science, notes that daily spreading of manure isn’t always feasible as the ground may be wet or frozen soil or the crops aren’t able to benefit. Spreading manure under these conditions can impair water quality, prompting a need for storage. This is required for large farms.

If the supply of manure exceeds the demand for fertilizer, the excess must be stored. Just as in the cow’s gut, stored manure that ferments without oxygen will produce methane. 

If the supply of manure exceeds the demand for fertilizer, however, the excess is often stored in large lagoons. Just as in the cow’s gut, manure in lagoons ferments without oxygen and produces methane. 

Manure management is more challenging as the size of the herd grows. The share of total dairy production in large farms has been increasing steadily. In 1997, there were only 21 dairy farms in New York with 1,000 cows or more (0.2 percent). These farms accounted for 4 percent of milk production. By 2017, 3 percent of all New York dairy farms had herds over 1,000 and they were producing 35 percent of total output.

Better management of manure is needed if dairy farming’s contribution to climate change is to be reduced. 

One option is to processing the manure through an anaerobic digester. A closed system, the digester allows the capture and use of the resulting methane (the principal component of natural gas). While burning natural gas still has an impact on climate, it is a far cleaner fuel than coal or oil and can contribute to a slowing of climate change by displacing dirtier fuels.

Wright notes that the net GHG impact is zero, as the plants that are the feedstock for the digester removed carbon dioxide from the atmosphere as they grew.


Another approach to the methane problem is composting, an aerobic process (i.e. with oxygen) that breaks down the manure without creating significant levels of methane. The rate of return from an investment in composting is not compelling for farmers, however. Bulk compost sells for $25 to $35 per cubic yard.

But that’s ordinary compost. Vermicomposting is another thing altogether. Once a colony of hungry worms feasts on manure, what gets excreted by the worms is transformed into supercompost. Vermicompost can be sold for up to $600 per cubic yard.

Rhonda Sherman

Rhonda Sherman, a leading authority on vermicomposting at North Carolina State University, notes that “vermicompost is just teaming with microorganisms that are beneficial to plants. It also contains nutrients that are readily taken up by plants, as they are fully stabilized by having (been) ingested and passed through a living being. Nor will it ‘burn’ plants like compost that hasn’t matured.”

Sherman says a little vermicompost goes a long way—mixing 10 to 20 percent of vermicompost with other soil amendments is very effective. Vermicompost “increases the rate of germination of flowers and fruit, (and) improves crop yields, root development and stress tolerance.” She also notes there’s some evidence that vermicompost reduces attacks from plant pathogens and insect pests.

Cornell University also conducts vermicomposting research—including early work with Worm Power, a Rochester-area venture. 

Worm Power

Established by ag engineer Tom Herlihy in 2003 and initially supported by a series of federal grants, Worm Power was a pioneer in the commercial application of vermiculture. 

Located in Avon, the operation has a longstanding relationship with the adjacent Coyne Farms.

Coyne has been an innovator since its founding in 1922. In 2019, it was nominated as one of the most influential breeders of the previous 25 years by Holstein International. It currently milks about 1,000 registered Holsteins. 

Brian Coyne is enthusiastic about the partnership with Worm Power. “I get to sell cow manure. Not many guys get to say that!” Without Worm Power as an outlet for his manure, he would spread more on his fields, “but that heavier dose wouldn’t be good for the crops as it would add too much phosphorous, which is particularly bad for legumes.” 

Worm Power begins its production process by composting de-watered manure and silage for 40 days with temperatures running from 140 to 170 degrees. This kills pathogens and weed seeds and begins the growth of microorganism. 

The finished compost is spread on three continuous-flow beds, already populated by millions of eager worms. Popularly called “red wigglers,” the Latin name is Eisenia fetida. These worms can eat 25 to 35 percent of their body weight each day.Herlihy used to joke that Worm Power was Livingston County’s largest employer: “Our worms are our workers. My job is to create the maximum environment for them and to keep them fat, dumb and happy.”

The worm castings and excrement slowly move to the bottom of the bed while the worms stay on the top with the unconsumed compost. The product is harvested from the bottom of the bin and carried by conveyor to an adjacent building for further processing.

Worm Power sells both dry worm castings ($27 for 15 pounds) and a liquid extract ($35 for a gallon), although its principal focus is the extract. Both products are certified organic. 

Pat Burke

Worm Power has been successfully marketing to golf courses and greenhouses and is exploring the growing cannabis market. Acquired by an investor group led by Pat Burke of Burke Group Inc. in 2013, the firm reports sales of about 1 million gallons over the previous five years and plans to increase the pace of sales to 1 million gallons annually over the next five years. Currently, Worm Power purchases all its manure from Coyne. Its planned expansion can be accomplished with additional Coyne supply.

General Manager Ted Miller holding bag use for creating the worm casting extract

Sherman says commercial vermicomposting is experiencing rapid global expansion, not only in agriculture but also among expanding urban food waste collection programs. Moreover, the size of dairy herds continues to grow, particularly in western states. Nationwide, 55 percent of all milk production comes from farms with 1,000 cows or more (compared to 18 percent in 1997). Vermicomposting can help these mega-dairies reduce the impact of their herds’ waste output and help the planet slow the pace of climate change. 

Kent Gardner is Rochester Beacon opinion editor. He holds a Ph.D. from the Department of Agricultural and Applied Economics at the University of Wisconsin-Madison.

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