If your field corn maturity is behind schedule, the silage corn certainly will be late.

“We are now at the time of the year that frost often determines when to begin chopping,” says J.W. Schroeder, North Dakota State University Extension Service dairy specialist. “But without a frost forcing the decision, producers may be looking to begin chopping now.”

One of the most important steps in producing high-quality corn silage is to harvest at the proper moisture for the structure in which you’ll be storing the silage, according to Schroeder. Desired moisture levels for different structures are as follows:

• Sealed, airtight silos - 60 percent to 65 percent
• Upright silos - 63 percent to 68 percent
• Trench silos - 65 percent to 72 percent.

Ideally, moisture levels in the silage should be monitored at harvest to prevent harvesting the crop outside the desired range. If moisture testing is not feasible, then you can estimate crop moisture by the stage of crop development.

As kernels start to dent, you can see a separation between kernel starch and milk. The firm starch is deposited in the crown (outer) area of the kernel and the milk occupies the basal area of the kernel. A whitish line appears, separating the two areas. As the crop matures, this kernel milk line moves down the kernel and whole-plant moisture declines. When the milk line reaches the base of the kernel, a black layer forms and the crop is physiologically mature.

Recent research has shown the kernel milk line to be only a rough indicator of corn silage moisture levels. On average, silage moisture levels will be about 70 percent at full dent when the milk line first appears and will fall to 60 percent at physiological maturity (black layer).

Considerable variation occurs between years, however, and when conditions have been particularly dry or wet for several weeks prior to harvest, the moisture can be as much as 5 percentage units different from that predicted by the milk line. When this line reaches the midpoint of the kernel (half milk line), silage yields reach a maximum and the crop moisture level should be near 65 percent. At this point, the stover part of the plant has good digestibility and the moisture is at the desired level for storage in airtight silos.

“One strategy for timing corn silage harvest is to chop a sample at the full dent stage, just as the milk line appears, and determine the moisture content,” Schroeder says. “Then estimate the harvest date for the field using a typical dry-down rate of 0.50 to 0.75 percentage unit per day.”

Another strategy is to determine moisture content using a microwave or commercial moisture tester, such as a Koster tester.

Those of you accustomed to making silage are pretty handy at estimating the percent dry matter, so you can use the grab test, Schroeder says. Squeeze a handful of chopped material as tightly as possible for 90 seconds, then release your grip. If the ball of material expands slowly and no dampness appears on your hand, the material contains 30 percent to 40 percent dry matter.

Silage that is too dry will result in poor packing and air exclusion, poor fermentation and heat production. If haylage becomes too dry, cut fresh material and continue to fill the silo by alternating fresh and dry loads. The addition of water will not increase the moisture of dry silage. The silage does not absorb the water, so the water can run off easily. Also, a garden hose does not deliver enough water to make an appreciable difference in moisture content.

Silage harvested at moisture percentages greater than 70 percent can result in seepage and an undesirable clostridia fermentation, which leads to butyric acid formation; high dry-matter losses; and poor feed quality, palatability and intake potential.

For more information on making corn silage, visit http://www.ag.ndsu.edu/pubs/ansci/dairy/as1253w.htm.

NDSU Agriculture Communication