Corn Silage Harvest and Storage Tips

August 20, 2021 8:10 AM
Blog Post

Historically, corn silage harvest starts within the next two weeks. However, harvest has started early in some droughty areas with light soils. Corn is a high yielding, high energy, low protein forage that is commonly used for growing and finishing beef cattle, in cow-calf production systems, for growing dairy heifers, and for lactating dairy cows. Understanding proper harvest management and timing is critical for producing high-quality corn silage.

Silage that is too wet when harvested may not ferment properly and can lose nutrients through seepage. If silage is too dry, it has 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 silage moisture at harvest ranges from 50-60% for upright oxygen-limiting silos, 60-65% for upright stave silos, 60-70% for bags, and 65-70% for bunkers.

As a forage crop, corn generally reaches maximum yield and quality around 50% kernel milkline development or R5.5. But due to variability among hybrids and growing conditions, it is necessary to measure silage moisture using a commercial forage moisture tester or microwave oven rather than simply estimating it from the kernel milkline.  Instead, kernel milkline should be used 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 1/4 of the way down the kernel for horizontal silos or bunkers, and 1/2 of the way down the kernel for vertical silos. A short article from the University of Wisconsin on whole plant moisture variability in the field, desired moisture for various storage structures, and procedures for moisture determination of corn silage can be found here: Directions for using a microwave oven are included in the following publication:

Generally, a cutting height of 4 to 6 inches is recommended for corn silage, as it maximizes silage yield and quality. However, drought-stressed corn can accumulate nitrates in the lower part of the stalk, thus increasing the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high nitrate silage can be made even worse if drought-stressed silage is harvested within 10 days of a rainfall event, since the rain increases crop uptake of soil nitrogen.  An article on Nitrate Toxicity and Testing from the Iowa Beef Center can be found here: For assistance on how to sample a corn field for nitrate levels, the Iowa Beef Center also has this article:

Silage with high nitrate levels can be managed by dilution with other feeds or by increasing the cutting height up to 12 inches. Cutting at 12 inches leaves the wettest, poorest quality part of the plant in the field. This leads to a decrease in forage moisture by 3-4% and an increase in forage quality by 8-12%. However, it also means a reduction in forage yield by 10-15%. Corn stalks though, are a good source of fiber and the lower tonnage with chopping silage at a higher cutting height typically makes it difficult to justify doing so in the absence of high nitrate levels.

Length of cut and crop processing are also important for obtaining high-quality corn silage. This is because the breakage of cobs and kernels increases surface area, which improves digestibility, reduces cob sorting by cows, and results in higher density silage that packs better. If two or more half or full kernels are present in a 32-ounce cup of silage, then more kernel breakage is needed.

When harvest begins, fill silos rapidly to reduce exposure of silage to oxygen and to reduce fungal growth. For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6 inches or less. Any extra time spent to thoroughly cover bunker silos and obtain a good seal around bunker sidewalls is also a good investment. Additional information about silages and other wet forages from the Iowa Beef Center can also be found here: In summary, producing and storing high-quality silage can be achieved with proper considerations for harvest management and timing.


Angie Rieck-Hinz Field Agronomist in NC Iowa

Angie Rieck-Hinz is a field agronomist in north central Iowa for Iowa State University Extension and Outreach. She has worked for ISU Extension and Outreach for over 30 years, serving in various roles on campus and now in the field.  She works closely with farmers on integrated pes...

Joshua Michel Field Agronomist in NE Iowa

Joshua Michel joins ISU Extension and Outreach as a field agronomist after working at the Muscatine Island Research and Demonstration Farm. While at the farm he was responsible for coordinating corn and soybean field studies that included planting, harvesting, tillage and pest management. Mi...