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JenREES 10-25-20

Black nightshade in wind-damaged corn fields.
Berries turn from green to black when they ripen.

Grazing Corn Residue: Have received some questions on corn residue management. Cattle grazing can be a beneficial way of residue management if one has access to cattle. Note: I’ve been seeing quite a bit of black nightshade and some horsenettle, particularly in corn fields that had wind damage. Both species have poisonous leaves (increase concentration as plants age) and berries (decrease concentration as berries ripen). Frost doesn’t change toxin levels. UNL forage specialists say when cattle graze corn fields containing nightshade species, there’s enough dilution with the grain, leaf, and husk that poisoning shouldn’t be an issue. We’d recommend watching the cattle as some may prefer grazing the nightshade. I’ve also seen cattle prefer weeds after herbicide applications, so also watch that if fall herbicides are applied. Ultimately, would just recommend don’t turn cattle empty into stalks with significant amounts of nightshade, watch cattle, and don’t graze past the point of 50% of leaf/husk removal. Dr. Jerry Volesky shares more here: https://twitter.com/jenreesources/status/1320513145941692418?s=20.

So, how does one calculate 50% leaf/husk removal and the grazing days for cattle on corn residue? The following is information from my beef Extension colleague, Brad Schick.

  • “There are 8 lbs of grazable dry matter per bushel of corn.
  • Leaf and husk make up 39.6% of the dry matter in corn residue.
  • Intake on corn residue fields will be close to 2% of bodyweight.

Having corn stalks to graze is a great resource for livestock producers. For dry cows, it is a relatively inexpensive feed that can typically meet or come very close to meeting nutritional needs. Grazing can also help get rid of corn remaining in the field and potentially reduce volunteer corn the following year. But are cattle really grazing stalks?

Yes and no. In everyday conversation, grazing corn stalks is said, but the stalk is the last thing cattle eat. Cattle do eat stalks, particularly if they are left on a field too long, but they are primarily consuming leaf, husk, and leftover corn. The stem or stalk makes up about 48.5% of the residue, while the leaf blade and husk make up 39.6%. Cattle will consume leaf and husk if available. That diet will consist of 52 to 55% TDN (total digestible nutrients) and 5 to 5.5% crude protein.

When thinking about how long to graze corn residue, the calculation to follow is that for every bushel of corn produced, there is 16 lbs of dry leaf and husk. The recommended grazing plan should be to remove 50% of the leaf and husk. This assumes that portions of the forage will also be lost to trampling, defecation, and other considerations such as wind. That leaves 8 lbs (16 lbs X 50%) of good forage on a dry matter basis that is available for consumption for every bushel of corn.

For example, say the field produced 200 bu/ac corn. By the calculations, there is 1600 lbs of dry matter per acre available (8 lbs X 200 bu = 1600 lbs). A 1000 lb animal will consume about 26 lbs of dried forage per day which means a 1300 lb animal will consume about 34 lbs per day. However, with lower quality forage such as corn residue, intake will be closer to 2% of bodyweight. In this example, that means closer to 26 lbs for the 1300 lb animal. So, how many days of grazing is that? By the calculations, there are 61 days of grazing for one cow grazing one acre (1600 lbs DM ÷ 26 lbs = 61 days). A general rule is about 30 cow days per 100 bushels/acre of corn produced.

Calves and replacement heifers can be also be a great option but will need a protein source in order to meet their growing requirements. Not only is grazing corn residue good for the cattle producer, but it is also good for the crop producer. Studies from the University of Nebraska-Lincoln have shown that grazing corn residue increases or at least maintains crop yields. (Grazing Corn Residue: A Win-Win for Crop and Cattle Producers).” More info. can be found at: https://go.unl.edu/fsa9.

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