It is very common for manure storages to not be emptied completely, often because it is difficult to do so. This residual manure is considered aged or inoculated.

The aged manure is primed with methane-producing bacteria, so University of Guelph researchers predicted that pits containing aged manure would release more methane than those that were completely emptied out. In a study comparing manure storages that were filled with half fresh manure and half aged manure versus those with only fresh manure, that proved to be true.

In both warm and cold seasons, fewer methanogen inoculum through complete emptying of a manure storage resulted in a 55% reduction in greenhouse gas emissions. The majority of emissions from stored manure are in the form of methane, so most of this reduction was in methane emissions.

The researchers took it a step further and evaluated whether different levels of leftover manure (0%, 5%, 10%, 15%, 20%, or 25%) made a difference in released emissions. They found that the decline was linear. For example, when aged manure was reduced from 15% to 5%, methane emissions fell by 26% in warm weather and 45% in the cold season.

“Overall, this is a really significant reduction,” Claudia Wagner-Riddle, a professor at the University of Guelph, summarized in a North American Manure Expo presentation. “This is a technique that would be very helpful.”

More complete emptying of storages would require engineering changes to the current design of manure storages, but this could be a worthwhile endeavor for reducing greenhouse gas emissions. Between manure in storage, manure deposited on pastures, and manure applied to fields, emissions from farms related to manure average between 22% and 32%, Wagner-Riddle shared.

This article appeared in the May 2022 issue of Journal of Nutrient Management on page 9.

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