Surplus milk: dump it or soil-apply as fertilizer?


COVID-19 forced major milk purchase cutbacks by schools, restaurants, hotels, grocery chains and consumers.

Supply management normally keeps the balance, but COVID blasted supply and demand right out of sync.

There are currently more jobless Canadians than usual and an unemployment rate hovering around 10 percent.

According to Statistics Canada young people, women and workers in less secure jobs were first to face mass layoffs due to the pandemic. Milk, once thought to be a necessity, is absent from the grocery list of many shoppers.

In areas where the imbalance has resulted in surplus milk, the consequence has been dumping. In an attempt to find the bright side of the situation, the University of Minnesota reminded dairy producers that milk is rich in protein and fat, both highly sought after components.

They remind farmers that the cash outlay to produce surplus milk has already been made. That value is still in the milk, even if it won’t go into a human mouth. But dumped milk can serve as an excellent source of nutrients for 2021 field crops. After all, it is fertilizer.

Research at the University of Wisconsin says every 1,000 gallons of milk contains the equivalent of 46 pounds nitrogen (N), 26 pounds phosphorus (P2O5) and 17 pounds potassium (K2O). The two options for dumping milk are land spreading or adding to manure storage. Both are good ways to recycle the nutrients in milk.

University of Minnesota manure management specialist Melissa Wilson says applying milk directly to the soil is better than mixing with manure because many of the milk nutrients are in a highly soluble, plant-available form.

Land-applied milk should be put down in a way that protects water quality, same as if it’s manure. Nutrient leaching and runoff are concerns, especially early in the year when there are not yet crops, hay lands are not growing and soil won’t absorb it. Do not apply more nitrogen than the 2021 crop can use.

To help determine that amount, collect a milk sample and send it to a lab for analysis.

Follow the same guidelines established for manure application. Do not apply milk within required setbacks from water bodies, dugouts, ditches, tile intakes, sinkholes or other surface water areas.

Milk has a strong odor as it decomposes in the field. Inject or incorporate it as soon as possible. Avoid applying milk immediately before or after a rain event.

If you have the extra manure storage capacity, adding milk may be a better option. While it still ends up land applied, it gives you more time to plan for proper nutrient management and eliminates a special pass to apply milk only. Although milk should flow better through liquid application equipment compared to liquid slurry, the fats in milk may plug equipment. If this becomes a problem, rinse with water often.

The addition of milk will change the normal nutrient content of your manure. You should collect a sample from your storage and send it to a lab before application to adjust your application rates appropriately.

Milk can be added to anaerobic digesters, although there is some concern this may increase gas production, although not necessarily methane production.

The Wisconsin Department of Agriculture says, “Exercise extreme caution if considering adding milk to anaerobic digesters. Consult the digester company before adding milk to the digester to determine appropriate volumes of milk that can be added without negatively impacting the digester’s microbial communities.”

Do not dump milk down the drain with your milk house wastewater.

These wastewater treatment systems are not designed to handle milk. The biological oxygen demand will overload the treatment system.