A great time to begin planning for corn silage harvest is when Minnesota corn crop reaches the milk stage (Figures 1 and 2).
Proper harvest management is critical for high-quality silage, and it starts with harvest timing. This ensures the harvested crop is at the optimum moisture for packing and fermentation.
Silage that’s too wet may not ferment properly and can lose nutrients through seepage.
If silage is too dry when harvested, it will have lower digestibility because of harder kernels and more lignified stover. In addition, dry silage does not pack as well, increasing the potential for air pockets and mold.
Optimum moisture levels
The optimum silage moisture at harvest ranges from:
50 to 60 percent for upright oxygen-limiting silos.
60 to 65 percent for upright stave silos.
60 to 70 percent for bags.
65 to 70 percent for bunkers.
Measuring silage moisture
Due to variability among hybrids and growing conditions, measure silage moisture using a commercial forage moisture tester or microwave oven rather than simply estimating it from the kernel milkline.
Instead, treat kernel milkline as an indicator of when to collect the first silage samples for moisture testing.
A general guideline is to begin moisture testing when the milkline is 25 percent of the way down the kernel for horizontal silos, and 40 percent of the way down the kernel for vertical silos. Then, assume a constant drydown rate of approximately 0.6 percent per day, and measure moisture again prior to harvest, according to a presentation given at the 2003 4 State Forage Conference.
Cutting length and crop processing
Cutting length and crop processing are also important for obtaining high-quality corn silage. Breaking cobs and kernels increases surface area, which improves digestibility, reduces cob sorting and leads to higher density silage that packs better.
Although crop processors are expensive, they can produce a high-quality silage. This, in turn, can increase milk production up to 300 pounds per cow per year, according to previous research at North Dakota State University. The benefit to crop processors is greatest when there are harder kernels resulting from delayed harvest or drought.
When using a crop processor, you can increase chopper cut length, which reduces horsepower requirements while maintaining optimum particle size.
For example, ideal chop length is 0.375-inch theoretical length of cut for unprocessed corn. Recommended settings for processed corn are 0.75-inch theoretical length of cut with 0.08- to 0.12-inch roll clearance.
A 4- to 6-inch cutting height is generally recommended for corn silage, as it maximizes silage yield and milk per acre.
However, drought-stressed corn can accumulate nitrate in the lower part of the stalk, increasing the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high-nitrate silage can worsen if growers harvest drought-stressed silage within 10 days of rainfall, since rainfall increases crop uptake of soil nitrogen.
Managing high nitrate levels
You can manage silage with high nitrate levels by dilution with other sources of feed or by increasing the cutting height to 12 inches.
Research from NDSU shows silage cut at this higher height has 8 percent less silage yield and 2 percent less milk per acre. This same study found that, compared to a 6-inch cutting height, an 18-inch cutting height resulted in 15 percent lower silage yield, 12 percent higher milk per ton and 4 percent lower milk per acre.
Increased silage quality with high cutting is due to a higher ratio of grain to stover. However, corn stalks are a good source of fiber and the lower tonnage with high-chop silage typically makes it hard to justify, unless you suspect high levels of nitrate.
When harvest begins, rapidly fill silos to reduce silage exposure to oxygen and reduce fungal growth.
For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6 inches or less.
Roth, G., Undersander, D., Allen, M., Ford, S., Harrison, J., Hunt, J., Lauer, C., Muck, R., & Soderlund, S. (1995). Corn silage production, management, and feeding (pp. 42). Madison, Wis.: American Society of Agronomy.
Reviewed in 2018