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Silage runoff – also known as leachate, effluent or juice – occurs when crops have a higher-than-ideal moisture content. The majority of runoff occurs within two weeks after filling. High packing densities, which are especially common with larger piles, squish the juice out of the silage.

Oftentimes, when a crop is in the structure and water comes in contact with the crop (such as during a rain event), runoff occurs. Anyone who has made silage is familiar with silage runoff, and it can come from all types of storage structures.

Silage runoff is not a good thing. Not only does it mean you harvested your crop too wet, but it also represents a loss of valuable nutrients, such as sugars and soluble protein.

These soluble nutrients are especially valuable because they can be immediately used in the rumen during fermentation. This also means your ensiled crop is losing value.

Silage runoff also means dry matter (DM) loss, or what some may call “shrink,” is occurring. In a worst-case scenario, runoff can represent more than a 5-percent loss in DM tons.

Silage effluent needs to be contained, especially in CAFOs, because it is a very strong pollutant of surface and groundwater and can result in massive kills of aquatic life. 

Runoff has a very high biological oxygen demand, and, when it mixes with streams, rivers, or bodies of water, it can significantly decrease the oxygen content of the water, which the fish rely on for survival. It is estimated that one gallon of runoff can lower the oxygen content of 10,000 gallons of water, enough to kill fish.

Silage runoff has also demonstrated the ability to cause algae blooms, which also deplete oxygen and kill fish. 

Silage runoff can also increase groundwater acidity, and it can smell bad. Michigan State University Extension suggests that any wells located within 150 feet of the silage storage should be checked routinely for contaminants, such as nitrates and E. coli.

Fortunately, runoff can be prevented by following these steps:  

  • Ensile at the proper DM content. The proper DM content for corn silage is 32 to 35 percent, and the proper DM content for alfalfa silage is 40 to 45 percent. 
  • Minimize contact between silage and rain water by using a quality silo plastic. 
  • Slope the plastic to divert water off the silage area.  Slope the pad and design the layout so rain does not run into other storage structures. 
  • Lastly, many operations choose to control effluent in a runoff collection facility.  In the case of CAFOs, they are required to have a runoff collection facility.

Dr. Der Bedrosian is a forage products and dairy technical specialist with VitaPlus

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