April 14, 2020
Jim Dickrell
The University of Wisconsin (UW) has released detailed recommendations for land spreading milk or milk/manure mixtures.
The document was prepared by Carrie Laboski, Jamie Patton and Kevin Shelley with the UW Nutrient and Pest Management Program.
They say that on average, 1,000 gallons of milk contains 46 lb of nitrogen (N), 26 lb of P₂O₅ and 17 lb of K₂O. “This is approximately 6 times more available N, 9 times more available P₂O₅ and 1.5 times more K₂O than an equivalent volume of liquid dairy manure,” the say.
“If nutrients from milk enter ground or surface water, degradation of water quality will occur,” they add. “Milk also has a biochemical oxygen demand that is about 5 times greater than dairy slurry. Thus, fish kills should be expected if milk enters surface waters.”
The N, P and K in milk also should be considered 100% plant available. There is also very little nitrogen volatilization, so the full N value should be credited whether incorporation occurs or not. Soil incorporation is recommended, though, to reduce odor and potential runoff.
The agronomists recommend a milk/manure sample be taken from lagoons prior to land spreading to get a better idea of nutrient content and appropriate spreading rates. Soil testing after application is also recommended to determine follow-up fertility needs in the growing crop.
“Due to high crop nitrogen need, corn grain, corn silage and warm season grass fields should be potentially prioritized for preplant milk applications,” say the agronomists. Typical recommended nitrogen application rates for corn range from 100 to 200 lb/a. “Milk applied at 4,300 gallons/a would provide 200 lb/a,” they say.
Alfalfa and clover can be top dressed, but applications should occur as soon after harvest as possible to minimize drop damage. Milk application to soybeans can stimulate lush vegetative growth, which can contribute to lodging and increase the risk of white mold pathogens.
The Minnesota Pollution Control Agency also notes that addition of milk to lagoons can create its own set of challenges. Crust formation over the lagoon will likely be affected and odors may be more prevalent. The fat in milk may also plug equipment, so more frequent cleaning might be needed.
Dumping milk down the drain in your milk house is not recommended since milk house waste treatment systems are not designed to handle large volumes of milk. The biological demand of milk will likely overload the treatment system.
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