It's been said that with 9 million acres of corn and 1.8 million beef cows in Nebraska, there are more than twice the number of cornstalk acres needed to graze all of Nebraska's beef cows.
With harvest right around the corner, and as growers prepare to stock cornstalk fields for the fall and winter, here are a few tips to keep in mind for grazing corn residue.
Reasons to scout
It's a good idea to start by scouting fields before grazing — for a couple of reasons, explains Mary Drewnoski, Nebraska Extension beef systems specialist.
Too much corn on the ground can cause acidosis or death in cattle. If there are more than 8 to 10 bushels of corn per acre on the ground, a grazing strategy to control corn intake should be used.
The other factor is variability in feed value in cornstalk fields, Drewnoski says.
"Right now, we're trying to identify the major causal factors, so we can come up with adaptive management strategies," Drewnoski says. "We don't really know what those factors are, but we have some ideas. One thing is in winter, it's not exactly calm in Nebraska. We get wind. Anytime you drive on the interstate, you notice all the husks in the fencerows — and the husk has the most feed value of the corn residue left in the field.
"If you graze the field later, or it's a field where stalks are chopped low or don't have windbreaks around them, we may be losing a lot of feed value — not because of weathering, but because those husks disappear."
Deciding stocking rate
Of course, scouting early can help determine a stocking rate for cornstalk fields.
A general rule of thumb is for every 100 bushels of corn per acre, you can stock one 1,200-pound cow for one month. Another quick way to estimate grazing days per acre available for a 1,200-pound nonlactating cow is to take corn bushel yield and divide by 3.5. For example, 180-bushel yield divided by 3.5 would equal 51 grazing days per acre if stocked at one cow per acre.
The Corn Stalk Grazing Calculator can be used to calculate a more definitive stocking rate based on corn yield per acre and average weight of cattle grazing. The calculator, an Excel spreadsheet, is available for download or as a mobile app.
However, determining when to destock should account for the loss of leaf and husk material as the grazing period progresses. It's typically recommended to remove only 50% of the leaf and husk. However, Drewnoski notes it may be better to think of target rates as 80% of the husk.
"In my mind, we can predict fairly well what you should be grazing, but as you start losing husk whether to wind loss or trampling, to me that's a great indicator of when to leave the field," Drewnoski says. "When you see limited amounts of husk in the field, that's time to go."
The quality of grazing starts as high as 70% total digestible nutrients, which Drewnoski notes is because of kernels and husk left on the ground. The overall quality of grazing can drop as low as 45% TDN, depending on stocking rate and how much feed material is left in the field — often, when TDN declines, it's because there's nothing left but leaf, cob and stalk.
Mature nonlactating, spring-calving cows with a body condition score (BCS) of 5 or better won't need protein supplemented when grazing at the recommended stocking rates. If the field is stocked too high for too long, however, supplementation will be needed later in the grazing period.
Drewnoski notes first-calf heifers will need protein and energy supplementation — and feeding 2 pounds of dried distillers grains per day in early winter and 2.5 pounds in late winter will meet this need.
"The other is fall pairs," Drewnoski says. "I do know some people in eastern Nebraska that put out late summer-calving cows and, of course, they have to supplement."
Lactating fall-calving cows also need protein and energy supplementation. If cows are in good condition, 5.5 or greater going into the winter, feeding 5 pounds per head per day of dried distillers grains will result in some loss of condition over the winter, but does result in acceptable breed up.
If cows have a BCS of 5 or less, feeding 7 pounds of distillers during early lactation — and reducing it to 5 pounds after breeding — will help maintain condition.
Drewnoski notes a free choice mineral with at least 145,000 international units per pound of vitamin A, assuming an intake of 4 ounces per day, is needed for all classes of cattle. If distillers isn't being fed, 5% phosphorus also is probably needed in the mineral as well.
Connecting cattle and cornstalks
Last year, Nebraska Extension developed the Crop Residue Exchange at cropresidueexchange.unl.edu, an online platform that allows cattle producers to find crop producers willing to lease crop residue acres for cattle grazing — ultimately providing a mutually beneficial agreement for both parties involved.
"For most situations in Nebraska, fall grazing at our recommended stocking rate is not going to have any negative impacts on the crop, and in fact, you will see some positive impacts," Drewnoski says. "Especially in high-yielding fields in no-till systems, the increase in cycling of nutrients due to grazing can improve soybean yields by a couple of bushels an acre, and it's a couple of bushels somebody paid you for."