Drought-stressed corn: Should you high-chop?

Posted on August 17, 2021 in Forage Foundations
By Dr. Michelle Chang-Der Bedrosian, Vita Plus forage products and dairy technical services

The Midwest has had quite the smattering of weather and corn-growing conditions this year.  Parts of eastern Michigan are seeing one of their best years, but, as we move further west, drought has led to a not-quite-so-bright crop outlook.

Due to the severity and timing of this drought, multiple conditions are occurring simultaneously:

  • The plant’s growth is stunted during the grain-fill stage, leading to low starch content.
  • Dry conditions have led to plants that are at the right dry matter (DM) for harvesting.
  • The bottoms of corn stalks are accumulating nitrates.

If producers wait for the corn kernels to fill (which may never actually come to fruition), the plants may dry too much in the field, potentially leading to lodging, stunted fermentation, and spoilage upon feedout.  Even with drought-stressed corn, the key to ensiling is a proper moisture content.  The ideal moisture content to ensile corn for silage is 65% to 68% moisture (32% to 35% DM).

With drought-stressed corn, looks can be deceptive:  The plant may look dry, but, because the stalk holds most of the moisture, it can actually be much wetter than it looks.  The only way to be sure is to chop the plant and measure the moisture content either with a Koster tester, microwave, air fryer or SCiO cup.

Nitrate gases
Under stressed conditions, such as drought, nitrates may accumulate in the plant because the plant is not growing.  During the initial stages of fermentation, these nitrates can turn into the poisonous gas nitrous oxide, which is also known as silo gas.

Silo gas, while often a brown or yellow color, can also be clear and invisible.  Even in a silo that appears normal, silo gas may be present and deadly.  If you see this gas, or if you smell a bleach aroma from the silage, leave the area immediately, alert anyone else who may work with the silage, and seek immediate medical attention.

Fortunately, there are management methods that can help you avoid this gas:

  • Do not harvest for at least three days after a soaking rain. When it rains, nitrates travel up the stalk and are used by the plant.
  • Ensure the crop undergoes a thorough fermentation as this can destroy 30% to 60% of silo gases.
  • Raise the cutter bar for stressed crops since nitrates accumulate in the bottom of the plant.

Should I high-cut my drought-stressed corn?
Typically, high-cutting corn for silage results in a drier plant that has more digestible fiber and more starch than a normal cutting scenario.  As mentioned above, it also helps mitigate the risk of silo gas.  However, drought-stressed corn usually has a higher fiber digestibility already, which may negate the benefits of high-cutting in drought situations.  Furthermore, high-cutting may not be a good idea in scenarios where forage inventories are low.  Penn State researcher Dr. Greg Roth reported that corn silage yield dropped 7.4% when cutting height was raised to 19 inches, a difference that would be magnified with the already-stunted, drought-stressed plants.

Ultimately, you must weigh the potential benefit of keeping nitrates out of the silo against the small concentration of starch and the drawbacks of a yield drag.  To make an informed decision, hand-chop five to 10 plants – both at a normal and a high-chop height – and submit the samples to a lab to be analyzed for nutrient content and nitrates.  If you do choose to high-chop corn, segregate that feed to ensure that it can be targeted to high-producing cows to get the most value from the crop.

Contact your Vita Plus consultant for help in making this decision.

Category: Drought
Feed quality and nutrition
Forage Foundations
Forage harvesting
Silages