Difficult challenges in the dairy industry such as those resulting from COVID-19 result in times when a market is not available for milk.  When those occur, using milk as a crop fertilizer may provide a short-term option for gaining some value from milk.  Below are some questions and answers for using milk as a fertilizer.

What Is Milk’s Value as a Fertilizer?

Nearly all protein is readily degradable providing a source of nitrogen to a crop.  In fact, one can assume that 100% of the nutrient in milk will be plant available during the cropping season immediately following application.  Here is a quick comparison of milk and dairy manure nutrient value.

Table 1. Typical nutrient concentrations for milk and dairy manure (pounds per 1,000 gallons). Reference: Carrie Laboski, University of Wisconsin webinar, https://youtu.be/Gk2aeVl4EoU

Are there Environmental Concerns with Milk?

Yes, there are two issues which should be considered in planning.

• Milk has a very high “Biological Oxygen Demand”, many times higher than manure.  That means, when it is breaking down in soil or water, it consumes a lot of oxygen.  The oxygen demand for degrading 1 Pint of Milk will consume all the oxygen from 1,600 gallons of surface water.  Milk cannot be allowed to get into fresh water!
• The degradation process for milk will produce significant and powerful odors.  Injecting or disking milk into the soil will minimize those odors.  The soil is a good filter for odors.  If this is not possible, chose a site with no downwind neighbors.  Check the weather forecast for the 48 hours after milk is to be land applied.  Note wind direction during the evening and nighttime hours, when odors often concentrate near the ground.  Select a site with no neighbors in this direction. See Timing Manure Application to Avoid Neighbor Nuisances for additional information. Discussions with neighbors about your plans for milk disposal are also encouraged.

If applied to a Nebraska corn field, what might be a reasonable rate?

If no fertilizer or manure has been applied, milk can be used to supply the primary nitrogen requirement of the crop as a pre-plant fertilizer. Scenario’s #1, #2, and #3 illustrate examples of applying milk to corn fields which have not received fall or spring applied fertilizer or manure.  Between 3,000 and 4,000 gallons of milk should meet the nitrogen requirements of these crops. The resulting application of 78 to 104 lbs of P₂O₅/acre should only slightly exceed the corn crop’s phosphorus removal (75 to 90 lbs of P₂O₅/acre).

If a base rate of nitrogen fertilizer has been applied, milk should only be used to offset the planned fertilizer used at planting or post-planting.  Scenario 4 suggests that 100 lbs N/acre has been applied pre-planting and only 1,100 gallons should be applied to offset the originally planned 51 lbs N/acre at or following planting.

Table 2. University of Nebraska nitrogen recommendations for corn for four scenarios.¹

¹ Spreadsheet used for these estimates. https://go.unl.edu/milkasfertilizer

² If post-planting fertilizer applications are planned, reduced milk application to match those split fertilizer applications.                                                                                                                                   

Are There Alternative Application Sites Besides Corn?

If corn fields are not available, here are a few options to be considered:

• Alfalfa fields, immediately after harvest. Legume crops such as alfalfa can be options for utilizing a lot of milk nitrogen.
• Field going into wheat or other small grain production.  Milk should not exceed the crops N requirement!  Excess N can lead to lodging.
• Fields harvested for forage production (apply soon after harvest).  Milk may affect forage palatability or quality. Maximizing time between milk application and the next harvest is desirable.
• Post-harvest fields are an option. If several months are to lapse between milk application and planting the next crop, a cover crop would be recommended.
• Application on pastures to be grazed is suggested as only a last resort. If necessary, apply milk shortly after grazing or harvest. 

Visit with your agronomist or crop consultant about desirable rates.

Are There Additional Considerations in Selecting a Milk Application Site?

Milk is likely to be spread on only a few acres.  If spread at 3,000 gallons per acre, a 1000 cow lactating herd dumping milk producing 8,000 gallons per day will need access to less than 3 acres of land per day that milk is dumped. Choose locations in a field that are:

• Removed from surface water.
• Removed from neighbors.
• Unlikely to experience runoff.
• NOT tile drained or connected to a shallow water table.
• NOT manured or fertilized since last fall (unless milk is to replace planting and post-planting fertilizer application).

Can I Add Milk to My Manure Storage?

Yes.  However, give some thoughts to two issues:

• Milk fats will coat mechanical systems and result in clogging. Add milk to the manure stream after all pumps and separation equipment.
• Do I have enough storage volume? 1000 lactation cows producing 8 gallons of milk per cow per day will add 1,100 cubic feet (or 0.3 acre-inches) to the stored volume.  A 2000 cow lactating herd dumping milk for 5 days will need sufficient storage space for about 11,000 cubic feet (2 thousand cows X 5 days X 1,100 ft³)  or 3 acre-inches (2 thousand cows X 5 days X 0.3 ac-in). In this situation, a one acre pond would need to hold 3 additional inches of depth.

Reference:  Carrie Laboski and Becky Larson, University of Wisconsin faculty. Land Spreading of Milk webinar (https://youtu.be/Gk2aeVl4EoU) sponsored by University of Wisconsin. April 7, 2020