As corn silage harvest season starts in the south and works its way north, it is a good time to review the rules surrounding leachate, the odorous fluid that escapes storage structures holding newly chopped feed.
In a Penn State Extension online article, agricultural engineer John Tyson explained that the main concern about leachate is its impact on the environment. Leachate is a threat to both surface and groundwater because of its high biochemical oxygen demand and low pH.
Biochemical oxygen demand (BOD) is the amount of oxygen needed to break down the leachate. Tyson wrote that silage leachate can have a BOD of 50,000 milligrams of oxygen per liter, compared to 500 milligrams per liter for raw sewage. “Silage leachate is about 100 times as strong as raw sewage,” he noted. Just one gallon of leachate in 10,000 gallons of freshwater can lower the oxygen content to a level that threatens fish survival.
To reduce leachate problems, Tyson said to minimize leachate production. This is done by harvesting and ensiling crops at the proper moisture. The flow of leachate is substantially reduced when silage is harvested at a dry matter content of 30% or greater. He added that covering horizontal silos and piles also helps reduce the prolonged flow of leachate.
Location of the silo or pile also influences the risk of leachate runoff. If selecting a site for a new silage pile, remember that it should be located away from open waterways and wells. Tyson wrote to choose a location that is at least 5 feet above the seasonal high-water table and on a slope of less than 2%. Clean water should be diverted away from the site, and runoff should be directed to a common point for collection and treatment.
Methods of treatment, Tyson explained, are determined on a case-by-case basis. He noted that the most common treatment is to incorporate leachate into a liquid manure system. Tyson offered a note of caution that hydrogen sulfide and other poisonous gases can be created when leachate is mixed with manure, so this treatment option should not be used in covered or underground manure storages.
Land application to a growing crop is another opportunity for distributing leachate. The leachate must first be diluted with water, Tyson explained, in a 1-1 ratio. Otherwise, leachate can be applied directly to fields with nongrowing crops.
The bottom line is that all leachate should be collected and treated properly. “Don’t ignore the problem; it’s not going to go away!” wrote Tyson.