April 29, 2020 | by James Giese

Wisconsin researchers offer solution for farms having to dump milk

A row of milk trucks dumping milk in a field

Dairy farmers across the United States have had to withhold milk deliveries due to supply chain disruptions amid the COVID-19 pandemic.

Farmers in Wisconsin, who prefer to remain anonymous because of the sensitivity of the issue, told The Daily Churn that the situation has been brutal; dumping milk, they say, is devastating.

“About two-thirds of fluid milk is consumed in the home and fluid sales are up, reversing a long-standing trend,” Mark Stephenson, UW–Madison Department of Agricultural and Applied Economics, Center for Dairy Profitability, and Division of Extension, said in a recent webinar. But food services and institutional sales are way down, he says, causing overall fluid milk consumption to drop by up to 10%.

Stephenson says that in Wisconsin — which produces roughly 2.61 billion pounds of milk every month — there have been numerous reports of dairy farmers spreading excess milk on their land. Nor is Wisconsin alone. One cooperative estimates that nearly 4 million gallons of milk is dumped across the country every day.


Offering farmers an alternative to dumping milk into manure storage facilities, the University of Wisconsin Division of Extension recommends applying the milk or milk and manure mixtures to croplands — but carefully.

Carrie Laboski, UW–Madison Department of Soil Science, and Division of Extension joined the webinar to address some of the best practices for land-spreading milk to mitigate environmental impact, including understanding soil nutrient availability, agronomics and water quality.

Safely land-spreading milk

Laboski notes that milk has six times more available nitrogen (N) and nine times more available P2O5 (phosphorous) than liquid dairy manure, which means that it has to be applied differently. Raw milk contains an average of roughly 46 pounds of nitrogen per 1,000 gallons, depending on its protein content. Laboski recommends farmers use their component test values to establish an accurate estimation of the nitrogen content in their milk.

The good news? Unlike manure, Laboski says milk has very low concentrations of nitrogen in forms readily susceptible to volatilization, when some forms of nitrogen become ammonia gas (NH3) — leading to losses of nitrogen in the soil. Which means volatilization losses from milk applications are likely limited and the full nitrogen value should be credited whether incorporation occurs or not.

Both phosphorus and potassium in milk are considered 100% available for uptake by plants, though Laboski says manure is a better source of potassium than milk. Like manure, milk contains more available phosphorus than nitrogen relative to crop needs. Applying milk to meet crop nitrogen needs could oversupply phosphorus, potentially increasing the risk of phosphorus loss to surface water.

Large agricultural equipment used to spread nutrients on crops

Manure expo spreading demo; photo courtesy of M. Broeske, University of Wisconsin-Madison.

Decreased fertilizer bills

After land application of milk or milk and manure mixtures, Laboski recommends retesting soils for fertility before the next growing season. Variability in application rates and milk nutrient content will impact soil nutrient levels across the field, she says. Up-to-date soil tests will provide a good estimate of future nutrient application needs.

“The N, P and K fertilizer value is $32.60/1,000 gallons,” she says. So, properly applied, land-spreading milk can help lower a farmer’s fertilizer bills.

Due to the high concentrations of nitrogen and phosphorus in milk, applications should be in fields with low risk for nutrient loss through leaching, runoff and erosion, Laboski adds. She recommends applying as close as possible to when crop nutrient uptake will occur and avoid land applications of milk on fields with sandy or loamy sand soil textures, particularly in the subsoil; seasonal or permanent high water tables; or fields with high to moderate potential for flooding.

“The primary concern with land-spreading milk is that we do not want it to runoff and get into surface water,” says Laboski, “and we do not want it leaching into groundwater.”

Milk has a biochemical oxygen demand (BOD) that is about five times greater than dairy slurry. This is important because the high BOD can lead to low dissolved oxygen if milk enters surface water resulting in fish kills and destruction of aquatic habitat.

Things to keep in mind when land-spreading milk

Laboski says it’s best to avoid applications around streams, rivers, lakes, wetlands, drainage ditches and wells. Other suggestions:

  • Apply only to soils suitably dry for application — soils at approximately 75% field capacity or less in the top 8 inches.
  • Avoid applying milk after or before rainfall.
  • Apply milk uniformly across a field using liquid manure application equipment. Where possible, milk should be shallow-injected or incorporated to reduce odors and the risk of runoff to surface waters.
  • Milk should not be allowed to runoff or pond during application. Properly calibrate field application equipment to ensure delivery of intended rate.

Putting milk into septic systems is not an option, according to Becky Larson, UW–Madison Department of Biological Systems Engineering, and Division of Extension. She says the fat will clog the small pores in drainage systems. Using beneficial management practices, she adds, will also help to reduce and dispense odors.

Despite the challenges, Larson sees an upside for those farmers who own or have access to anaerobic digesters. Citing research studies, she says an increase in milk additions aids biogas production — at least to a certain threshold. She recommends adding milk slowly to allow microorganisms to adjust and to assess impacts to biogas and methane.

As milk supply chain disruptions are addressed, the need to land-spread milk should be eased. In the meantime, the University of Wisconsin Division of Extension says understanding the basics of land-spreading milk will help farmers meet this challenge without undue environmental impact.

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