Labor Day is in the rearview mirror. It’s no longer possible to change the hybrid, plant density, pest management, fertilizer strategies, or the summer weather. For farmers across the northern tier of states, all that’s left is to harvest the corn silage crop as it stands in the field.

Whether things went amazingly well or horribly wrong this growing season, harvesting corn silage that will store and feed to its maximum potential really comes down to two things: moisture and processing. Miss the mark on either account and you’ll pay the price for months to come.


“Dry matter content of whole-plant corn varies with maturity,” says Joe Lauer, University of Wisconsin extension corn specialist. “The position of the kernel milkline is not a reliable indicator for determining harvest timing. Geographic location, planting date, hybrid selection, and weather conditions affect the relationship between kernel milkline position and whole-plant dry matter content,” he adds.

Total silage yield escalates up to the point where kernel black layer is reached and the plant begins to desiccate, which is generally around 60 percent whole-plant moisture. However, delaying harvest until maximum dry matter yield is achieved reduces nutrient availability, though starch content is higher.

Researchers often cite 65 to 68 percent moisture as the optimum level for maximizing corn silage quality and storability in a horizontal silo. That doesn't leave a lot of room for error. Most feeding and storage problems come from silage that is over 70 or under 60 percent moisture.

Though the kernel milkline is not a reliable moisture meter, Lauer suggests it can be used to indicate when to start sampling whole plants.

“Corn should be first sampled to measure dry matter shortly after full dent stage (80 percent kernel milk) for bunker silos and bags, at 60 percent kernel milk for conventional tower silos, and at 40 percent kernel milk for sealed (oxygen-limited) tower silos,” Lauer says. “It is important to begin sampling early as a precaution against variation in dry down. You will likely be too wet, but you will have an indication of how quickly dry down is occurring when the next sampling date takes place.”

Here’s how Lauer suggests fields be sampled and tested:

1. Sample three to five plants in a row that are well bordered and representative.

2. Put the sample in a large plastic bag.

3. Keep plants cool, and chop as quickly as possible.

4. Measure moisture using NIR spectroscopy and/or by drying using a Koster Tester, microwave, or convection oven.

Lauer notes that the average whole-plant moisture loss per day is about 0.5 percent during September; however, this can vary with environmental conditions.


Though it took a number of years to figure out, we now know that not all processed silage is created equal or translates to improved livestock performance.

Dave Mertens, retired dairy scientist at the USDA Dairy Forage Research Center in Madison, Wis., developed a laboratory test to quantify corn silage processing. Most silage producers and nutritionists are familiar with the test and the kernel processing score (KPS) that it yields. The problem, of course, is that tests take time, and when results are finally known the silage harvest is often completed — too late to make any adjustments.

Though KPS remains the current gold standard of evaluation, quick on-farm tests that allow for immediate harvester adjustments have also been developed. These include:

1. Fill a 32-ounce cup with corn silage, dump its contents, and look at the corn kernels. If two or less whole or half kernels are observed, this is considered ideal; two to four whole or half kernels are considered adequate.

2. Agricultural engineers at the University of Wisconsin suggest a float method.

3. Use the Penn State shaker box and look at the kernels in the pan. Again, there should be few whole kernels in the sample.

Some level of processing quality control needs to be a routine part of the corn silage harvest. Check it, then check again as whole-plant moisture and hybrids change. No system or test is perfect, but they all will help in the avoidance of feeding an underprocessed crop.

At this point, two things make for great corn silage: correct whole-plant moisture and proper processing. Attention to both will translate to maximum livestock performance.