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Early season frost is challenging for corn silage producers, according to Karl Hoppe, Extension livestock systems specialist at NDSU’s Carrington Research Extension Center.

Frost makes an abrupt end to the corn-growing season. This begins the dry-down period for the corn plants.

“Good corn silage fermentation requires adequate moisture to reduce dry-matter loss and spoilage,” Hoppe says. “When the moisture of corn silage is too low, it’s difficult to pack the silage pile and exclude air.”

Once oxygen has been used up, the microbes begin to ferment and make organic acids. When the pH is low enough, the microbes stop and the silage pile has completed the fermentation process.

If corn silage is too dry, the fermentation process is difficult to complete. Evidence of this is corn silage that is brown, lacks a strong fermentation odor and is warm. Silage that heats months after being placed in the pile indicates poor packing and poor fermentation.

Making silage when the corn is too wet also has problems. Kevin Sedivec, NDSU Extension rangeland management specialist, says that corn should be harvested for silage at a moisture content of 65% to 70% when using a horizontal bunker. If too wet – above 70% – yield potential is reduced and seepage will occur, resulting in the undesirable occurrence of clostridia bacteria fermentation.

Clostridia bacteria are very inefficient, converting forage sugars and organic acids into butyric acid, carbon dioxide and ammonia. Silage with these bacteria loses dry matter, creates a foul smell due to the butyric acid, and has a higher pH, resulting in poor forage quality and palatability.

The challenge is chopping a corn field at the best moisture. This becomes a bigger challenge when a killing frost makes everyone’s corn fields ready to harvest at the same time and corn chopping equipment is limited.

Producers can estimate the water content of the corn visually. Research at NDSU’s Central Grassland Research Extension Center found:

• Corn with the entire plant still green, tasseled and having two cobs in the R2 kernel stage (early kernel, no denting and no milk) was at 77.4% water content.
• Drought-stressed corn with the bottom three to four leaves that were brown tested at 76.5% water content. The plants had one cob in the R2 kernel stage.
• Drought-stressed corn with the bottom four to seven leaves that had turned brown and no cobs had a water content of 67.9%.

A rule of thumb for determining when corn silage is ready is when the corn is at dent kernel and about the 75% milk stage. However, silage corn varieties may retain moisture longer, compared with quick dry-down corn grain varieties. This stay-green trait can make fields variable in actual moisture content, Sedivec says.

Hoppe notes that the best way to determine moisture content of the plant is to take a whole plant sample. In other words, chop a load of silage and do a dry-matter test. A moisture tester can provide a quick result.

Using the microwave method of drying a sample is relatively quick, too.

“Just don’t use the household microwave because the smell of corn silage will hang with that microwave oven,” Hoppe cautions.

When harvesting conditions are not ideal, using a silage inoculant may help the fermentation process advance more quickly and make a better silage when moisture levels are too high or too low.

For more information on testing for feed quality or how to dry samples in the microwave oven, contact an NDSU Extension agent in your county.