Deciding when to green chop drought-stressed corn or turn into silage


COLUMBIA, Mo. — Many Missouri corn growers are unsure about when to green chop and/or ensile their drought-stressed crops. There are key points to take into consideration on both the crop and livestock side, according to University of Missouri Extension specialists.

Agronomy recommendations (MU Extension state agronomy specialist Kelly Nelson):

  • Evaluate pollination and do a yield estimation on the field based on current pollination. This could be helpful to the farmer when it gets close to harvesting the crop for silage. There are several yield estimation calculators available for corn. Count the ears (the number in 17.5 feet of row), the number of rows of pollinated corn on the cob and the number of kernels that are pollinated in the row. Multiply these together and divide by 90. This will provide an estimated yield of the pollinated corn in the field, assuming it fills out throughout the rest of the season.
  • Count if there is tip back. If there is pollination of the ear, kernels are typically lost at the tip of the ear first, called “tip back,” caused by abortion. Precipitation can help fill out kernels that are present, but once the kernel is aborted, precipitation won’t help fill out that seed. Evaluate the number of kernels per ear even if there is tip back to get an estimated grain yield. This helps make an informed decision on the value of the silage vs. value of the grain harvested.
  • Consider stalk nitrates. With droughty corn, you can get high stalk nitrate levels. Nitrate toxicity is a concern in drought conditions. This will affect the height at which the corn is chopped. (See nitrate management recommendations below.)
  • Use guidelines on corn moisture levels for chopping for silage. According to a University of Wisconsin guide to harvest timing, silage harvest usually begins around 50% kernel milk, which is approximately 42-47 days after silking, so silking must occur by Aug. 15-20 to mature before typical killing frost dates, but remember the timing of silage harvest depends on achieving the proper moisture for the storage structure.
  • Be aware of aflatoxin issues. The presence of aflatoxin could affect the price farmers receive at the grain elevator. This can’t be determined yet, but it can be a factor.
  • Crop insurance considerations. Communicating with your crop insurance adjuster is important so you know what you need to leave in the field to allow the adjuster to evaluate yield.

Nitrate management recommendations (MU Extension livestock field specialist Zachary Erwin):

  • Be aware of highest nitrate accumulations. They are generally in the bottom 8-12 inches of the stalk, so cutting higher will help lower nitrates in the forage. Spot testing would be a minimum safety consideration, but if someone needs to green chop now and it was fertilized heavily with nitrogen, consider sending a sample off to a lab for a quantitative test. Samples can be variable within any field, so caution should be taken on how much is fed at one time.
  • Never chop and let it sit overnight or during the day. Nitrates will accumulate and can convert to nitrites, becoming extremely toxic when left in a wagon for prolonged periods. Only chop what will be fed right after chopping and in amounts that will be cleaned up within two hours of feeding. Producers should cut a sample and feed a very low amount for a few days until the sample can be submitted and results received before increasing the amount fed. However, once green chopping starts, cows will expect daily feed delivery and can be difficult to keep satisfied if it continues to stay dry. Farmers must be committed to daily feeding once they start.
  • Feeding rates. Recommendations for feeding levels all depend on nitrate levels and the class of animals being fed. Bred cows are the most susceptible to nitrates, and abortions are the first sign. If they are stocker cattle, death will generally be the first sign. Neither is ideal, so caution is always recommended.
  • Give it a full 30 days if possible. Nitrates will drop after a 30-day ensiling period. The minimum is 21 days, but try to give it a full 30 days to get the maximum reduction before re-testing. The range of nitrate reduction is variable as well – 25% to 50% – and proper harvest timing is key to getting the maximum reduction. Silage that is too dry may not have as significant of a drop in total nitrate levels. The good news is that if the nitrate levels do drop, even silage without much corn makes great stock cow feed.

Herbicide considerations (MU Extension weed scientist Kevin Bradley):

In a press release, Bradley said, “One of the most important considerations is the forage and feeding restrictions of the herbicides that have already been sprayed for weed control in these fields. Fortunately, most herbicides that are commonly applied in corn allow for some type of grazing or forage use following application, typically ranging from as little as zero to as many as 60 days after application. But it is critical for producers to consult the specific product label of the herbicide(s) applied before deciding to utilize their corn crop for forage.”

Bradley said there are many more herbicide restrictions for green chopping soybeans.

The question of when (MU extension soil and cropping systems specialist Justin Calhoun):

“It’s a judgment call on what yield potential is on a particular field,” said Justin Calhoun, at the Fisher Delta Center in southeastern Missouri. “If growers have a historically high-yielding field and booked some corn at high prices, they can still turn a profit on roughly 20% loss and might consider keeping the corn for grain. But if lower yields are already expected, it might be in the grower’s best interests to consider pulling the plug.”

There are few cattle in southeastern Missouri, Calhoun said, and so letting what little dryland corn they have keep going in drought is often their best choice because the only other option is to bury it.

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