By Bill Weiss, Mark Sulc, Ohio State University Extension
For corn silage ideal moisture concentrations are between about 62 and 70%. They can be harvested a little wetter (maybe up to 72%) if it goes into a bunker. The wetter it gets the more seepage you get (loss of nutrients and potential environmental issues if seepage gets into a water source, example: fish kill). Wet corn silage also produces an acetic acid-based fermentation which means a loss of energy (1 mole of glucose is fermented to lactic acid and acetic and 1 mole of carbon dioxide is lost, which is energy). Clostridia is not a major risk for corn silage because pH drops quickly but it can be a major concern for wet grass or alfalfa silage.
Fires are caused when silage is chopped too dry. The silage doesn’t pack well, trapping oxygen which allows aerobic metabolism which produces a lot of heat. Wet hay is also a major risk factor for fire for the same reason, the wet hay allows aerobic metabolism (molds and yeast) which produce heat. For more details please refer to the Penn State Factsheet, https://extension.psu.edu/silo-fires.