Chopping silage corn at the right moisture will bring higher milk yields per ton of silage fed, says J.W. Schroeder, North Dakota State University Extension dairy specialist.

He quotes University of Wisconsin research showing that dairy cows perform best when whole-plant moistures are in the 60-75% range at harvest.

"That range also works well for achieving good packing and fermentation in the horizontal silos. Increased seepage losses, increased acidity and lower dry-matter intakes are common problems when whole-plant moisture is greater than 70%," Schroeder says.

If storing in upright silos, plan for whole-plant moistures in the 62-65% range. Corn silage harvested at 60% moisture or less consistently results in reduced fiber and starch digestibility.

Silage harvest usually begins 42-47 days after silking, or at about 50% kernel milk. However, kernel milk is not a good indicator of whole-plant moisture. Schroeder recommends sampling plants from the field and testing for moisture to determine whole-plant moisture accurately. Hybrids, soil moisture, soil fertility, weed control and sample location in the field all impact the whole-plant moisture and drydown rate.

Rarely are fields to be harvested uniform, he says. University of Wisconsin research conducted in 2003 found that knoll areas of a field were as much as 20% drier than its lower areas. Keep in mind, significant rainfall will rehydrate moisture-stressed corn plants by as much as 6-8% within a day or two.

Mike Ballweg, University of Wisconsin Extension Sheboygan County crops and soils agent, offers these sampling recommendations:

  • Sample two or more locations for each representative area in the field. If sampling more than once, sample the same locations to determine the rate of drydown.
  • Sample three to five plants in a row. These plants should be well-bordered and representative.
  • Chop samples as quickly as possible and put them in a plastic bag.
  • Use near-infrared spectroscopy for most accurate moisture results. When using a Koster oven or microwave, add 2-4% moisture onto test results to account for residual moisture.

Use 0.5%/day as an average drydown rate during September. Depending on the year, the average drydown rates for that month range from 0.4% to 0.7% per day. On the other hand, daily drydown rates during September can vary greatly from near 0%/day to as much as 1%/day.