Corn Silage Harvest and Storage Tips for 2024

Recent cooler nights are hinting that fall is just around the corner. That also means corn silage harvest will be starting very soon. 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, a corn plant reaches maximum yield and quality at nearly the same time 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: http://www.midwestforage.org/pdf/592.pdf.pdf. Directions for using a microwave oven are included in the following publication:  https://store.extension.iastate.edu/Product/Livestock-Determining-Moisture-of-Immature-Corn-Silage-Disaster-Recovery-Series.

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: https://www.iowabeefcenter.org/information/IBC50.pdf. For assistance on how to sample a corn field for Nitrate levels, the Iowa Beef Center also has this article: https://www.iowabeefcenter.org/information/NitrateSamplingInCorn.pdf.

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.

In addition to focusing on silage quality, keep a few safety considerations in mind. One safety concern is silo gases, especially in upright silos, though they can also be a concern in bags or bunkers. The fermentation process produces nitrogen dioxide, which converts to nitric acid when contacting moisture in the lung. At low levels, nitrogen dioxide causes a burning sensation in the nose, throat and chest, while at high levels it causes death within seconds. Fermentation also produces carbon dioxide, which is odorless, colorless and heavier than air so it settles in low spots. It displaces oxygen and can cause death from asphyxiation (lack of oxygen.)  The biggest risk from silo gases is in the first two to three weeks after filling. It is recommended to stay clear of the silo for at least three weeks, then run the silo blower for 15 to 20 minutes with the door closest to the top of the silo open, before entering the silo. Do not enter the silo during or after filling for at least three weeks, and keep children and visitors away from the silo area during the danger period. If you must enter a silo during the three-week danger period or even when opening the silo, wear an approved, self-contained breathing apparatus and ventilate the silo for 20 minutes before entering.

Safety risks around bunkers also include machinery accidents during filling and avalanches during feedout. Extra caution should be used by pack tractors, especially when operating above the solid side walls of the bunker to prevent rollover accidents. Trucks delivering forage should unload at the base of the ramp and not operate above the sidewalls of the bunker. When feedout starts, falls when uncovering bunkers or taking feed samples, avalanche of the pile or collapsing silage could happen. Take feed samples from the loader bucket after moving a safe distance away from the bunker face. Try to stay a distance of at least three times the height of the pile away from the face. Always remove silage from the top of the pile first to prevent undercuts which may collapse.

When it comes to pricing corn silage, there are a few options available to provide some assistance. For a ballpark estimate of pricing silage based on corn grain value see the ISU Extension publication “Pricing Forage in the Field” http://www.extension.iastate.edu/agdm/crops/pdf/a1-65.pdf. For a more detailed approach to pricing corn silage, there is an Excel spreadsheet from ISU Extension called “Silage Pricer”. It is on the following Ag Decision Maker website at the bottom of the page under Analysis: https://www.extension.iastate.edu/agdm/cdcostsreturns.html. There is also a mobile app from the University of Wisconsin for pricing corn silage. For details and the app links go to: https://fyi.uwex.edu/forage/new-extension-mobile-app-for-pricing-standing-corn-silage/.