How to manage rejected milk
As a professor in the department of soil science at the University of Wisconsin-Madison, Carrie Laboski was in unchartered territory when she presented to 628 web attendees from across the upper Midwest.
“I have never before given a presentation on landspreading milk,” she says. “In 2017, I assisted the Wisconsin Department of Agriculture, Trade and Consumer Protection to develop a short guidance for farms that were losing their milk contract from one processor, and I’m not sure if any milk from that situation was landspread.”
So Laboski, along with colleagues Jamie Patton and Kevin Shelley, did some digging for her presentation that provided producers, some of whom are facing the issue of dumping loads of milk due to the fallout from the COVID-19 pandemic, with vital information as they navigate issues many have never faced before.
READ MORE: Milk dumping is a coronavirus reality
That’s because there are several issues to consider when a significant amount of milk enters the waste stream. It simply can’t be flushed down the drain, spread in a field, or dumped into the manure pit. There are water quality, agronomic, and nutrient availability concerns that must be addressed. And managing milk in manure storage, handling, and treatment systems requires special attention.
Compared with liquid dairy manure (less than 4% dry matter) milk has six times more available nitrogen, nine times more available phosphorous, and five times more biochemical oxygen demand.
“Biochemical oxygen demand is the amount of oxygen required by microbes to break down organic materials,” Laboski says. “Low dissolved oxygen results in fish kills and destroys aquatic habitat.”
While producers don’t think of milk as a fertilizer, “sometimes you have to make lemonade out of lemons,” Laboski says. “The nitrogen, phosphorous, and potassium fertilizer value of milk is about $32.60 per 1,000 gallons. And nearly 100% of nutrients in milk are plant available.”
Compared with dry manure (less than 4% dry matter), for every 1,000 gallons there are 46 pounds of nitrogen, 26 pounds of phosphorous, and 17 pounds of potassium. That compares with 7 pounds of nitrogen, 3 pounds of phosphorous, and 11 pounds of potassium in dairy manure.
“These nutrients that have been or will be applied must be credited toward the total nutrient application rate,” Laboski says. “Applying milk to meet crop nitrogen needs may oversupply phosphorous. So you should consider a soil test to determine the amount of phosphorous in the soil when selecting an application rate.”
Laboski offers the following guidance when milk is applied to fields:
- Milk should not enter ground or surface water.
- Follow all setbacks in your nutrient management plan.
- Apply milk only to soils that are suitably dry (less than 75% of field capacity in the top 8 inches). A good indicator for most soils is that the soil forms a ball and no moisture appears when squeezed.
- Avoid applying when rain is predicted, eminent, or directly after a rain.
- Milk should not run off or pond during application.
- Apply uniformly across the field. Shallow-inject or incorporate to reduce odor and risk of runoff. If milk must be applied to tiled fields, till the soil 3 inches to 5 inches deep before application, and the tile should not be running.
- Calibrate application equipment.
- Consider multiple applications with less volume per application. “New Zealand research suggests waiting 20 days between applications to allow for microbial degradation,” Laboski says.
“You also need to consider that the fats in milk can clog the pores in some soils,” she says. “That could lead to excess ponding or runoff in a field.”
When selecting a field, avoid:
- fields with steep slopes or long slope length
- fields with phosphorous levels greater than 100 ppm
- fields with an estimated phosphorus index of greater than 6
- fields with estimated erosion rates greater than tolerable soil loss
- nearby streams, rivers, lakes, wetlands, and drainage ditches
- fields with seasonal or permanent high water tables
- fields with high to moderate potential for flooding
- sandy or loamy sand soils, particularly the subsoil
- soils shallow to bedrock
- large drying cracks at the soil surface
- fields that have had manure or fertilizer applied since last summer
- alfalfa or forage legume stands that were terminated last fall or will be terminated this spring
- fields that are tile drained
“Perhaps one of the most important considerations is your neighbors,” Laboski says. “Give your neighbors a call to let them know in advance when, where, and why you are spreading milk.”
Each crop also has its own recommendations. For corn, Laboski says to consider sidedressing to reduce the potential for early-season nitrogen losses and increase utilization on somewhat poorly drained and wetter soils or sandy soils that are somewhat excessively drained.
On moderately and well drained soils, lower temperatures early in the season may limit odor. But milk landspreading may not be ideal on somewhat poorly drained and wetter soils and is discouraged on sandy soils and soils that are excessively drained. “At 4,300 gallons an acre, milk will supply 200 pounds of nitrogen,” Laboski says.
For small grains, a preplant application provides the opportunity for incorporation. However, milk application should not exceed the crop’s nitrogen needs because it could lead to increased lodging and increased vegetative growth. Over-the-top milk applications should be limited to reduce the potential for nutrient loss after rainfall and to reduce odor.
Legume crops will use available nitrogen in the soil over fixing nitrogen. However, applying nitrogen to soybeans may result in lush vegetative growth, increasing the risk of lodging and white mold infections.
“The bottom line is that the nutrients from all sources should not exceed crop nutrient needs,” Laboski says. “And where milk is applied, consider sampling the fields before the next growing season.”
In addition to agronomic concerns, producers also need to be aware of various local or state regulations regarding the spreading of milk on land. Experts advise producers to check with water quality or resource management officials for any rules or regulations that are in place.
Managing Milk in Manure Systems
Producers handling rejected milk loads must also consider the challenges when incorporating into a manure system. Rebecca Larson, associate professor and Extension specialist in the department of biosystems engineering and division of Extension, University of Wisconsin-Madison, says milk has fat, which will coat mechanical systems and result in clogging.
“If adding milk to the manure system, it’s best to put it in as far downstream in the system as possible,” she says. “When adding milk to manure storages, it should be mixed evenly,” she says. “Odor will increase, and will remain for some time. It is important to use management practices to reduce and disperse odors in storage and land application.”
There are also safety factors to consider. “Because milk has sugars and other easily degradable materials that can increase gas production, there is an increase in the production of gases including carbon dioxide and methane, which can both pose risks for asphyxiation. Methane has the added risk of explosion,” she says. “As always, producers should follow recommended manure gas safety procedures, but they must be aware of the added precautions when milk is added.”
For producers with anaerobic digesters, Larson says studies have shown there can be an increase in biogas production with increased milk additions until a threshold is reached and production is reduced.
“It’s important to add milk slowly to allow for microbial communities to adjust and then assess the impacts to biogas and methane,” she says. “And do not exceed permit volumes.”
Information on landspreading of milk can be found at https://fyi.extension.wisc.edu/covid19/2020/04/08/considerations-for-landspreading-millk/. This site includes a webinar on milk landspreading, as well as additional Extension and agency resources.
The University of Wisconsin-Madison has just published a summary factsheet on the agronomic considerations for landspreading milk. It can be accessed at https://ipcm.wisc.edu/download/pubsNM/UW-LandspreadingMilkConsiderations2020.pdf.