Dairy Focus: The Basics of Corn Silage

Now is the time for final preparations for the corn silage harvest.

Years ago, experts recommended that corn silage be harvested at the black-layer stage of maturity. In recent years, research and field experience have shown that this practice usually results in silage that is too dry to be well-utilized by dairy cows.

Positioning of the kernel milk line is another method of maturity staging that has been used as an indicator of when to harvest whole-plant corn for silage. The best lactation performance by dairy cows has been shown to occur at roughly the one-half milk line stage of maturity.

But recent research and field experience have shown considerable variation in the relationship between whole-plant moisture content and positioning of the kernel milk line. This variation is related to differences in hybrids and their dry-down characteristics and differences in growing conditions. Blindly harvesting whole-plant corn for silage at the one-half milk line sometimes will result in silage without the right moisture content for good preservation and utilization.

The best use of kernel milk line positioning is as an indicator of when to start monitoring whole-plant moisture content. Once most of the kernels are dented and the milk line is visible, this is the time to chop some whole plants for measurement of moisture content. Whole-plant moisture content should be your trigger for when to harvest corn silage.

You must pay special attention to making an accurate determination of moisture content. Most years, corn takes 55 to 60 days to go from three-fourths silking to the black layer. The chopping time for corn silage is about 10 to 15 days before the corn reaches the black layer. Be sure to check the whole-plant moisture to fine-tune timing.

Another useful tool is U2U Decision Support Tools. The Corn Growing Degree Day (GDD) decision support tool puts current conditions into a 30-year historical perspective and offers trend projections (based on climatology) through the end of the calendar year. You can find it here.

While this tool is not meant to be a crystal ball, data and information derived from the tool can be used to make helpful inferences about your current conditions, especially when combined with personal experience and localized knowledge. Note that data is limited to states within the U2U project area, which include North and South Dakota and Minnesota. It is really quite simple to use. Zoom in on the map, find your area and click on “create a graph.”

Your ideal silage moisture depends on the storage structures you have.

The cutter bar setting is another important element in making high-quality corn silage. If you are using a kernel processor (all kernels are crushed), then set the theoretical length of cut at 3/4 inch and the processor silage roller at 1 to 2 millimeters. For unprocessed corn silage, set the theoretical length of cut at 1/4 inch, but make sure some pieces of stalk are about 1/2 to 3/4 inch long to help maintain effective fiber in the ration. The dryer the silage, the higher the value of the kernel processing.

Packing silage, especially in bags, bunkers and piles, also is very important. With bags, set the tension as tight as possible. The goal is 14 pounds of dry matter or more per square foot of silage. Bunkers and piles should be filled using the wedge method, which is filling at a 40-degree angle. Com silage should be spread into layers no thicker than 6 to 8 inches and then packed completely before the next load is delivered.

With the speed at which commercial harvesters can deliver forage to the yard, packing can be a challenge. A common question is how many tractors are needed to accomplish the task of packing.

Brian Holmes, University of Wisconsin Extension agricultural engineer, developed a spreadsheet to determine the amount of tractor weight needed depending on the tons of silage delivered per hour. You can find it on the University of Wisconsin Extension forage Web page.

Tower silage will pack because of the head pressure created, but it will pack much more uniformly if you have distribution through the silage delivery spout that will layer the silage rather than form a pile.

Finally, all bunkers and piles should be covered with plastic within 12 hours of finishing chopping. Remember that deterioration penetrates well beyond the color difference at the top.

With no cover, Kansas State University researchers measured 80 percent dry-matter loss in the top 10 inches. Covering with plastic reduced dry-matter losses to 20 percent in the top 12 inches. Don’t waste that amount of forage or sacrifice its quality.

Harvesting whole-plant corn at the right moisture content and particle size is crucial to making high-quality corn silage that is well-utilized by dairy cows. Whole-plant moisture content rather than kernel milk line positioning should be your trigger for when to harvest corn silage. Monitor particle size and kernel and cob breakage to ensure that the forage harvester-crop processor is doing the job.

Remember, if you use additives, apply them properly, pack thoroughly and cover securely to minimize storage losses.

Visit for more information on creating corn silage.

Source: North Dakota State University


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