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• One of the concerns with green chopping would be the potential for nitrates, particularly if the layby or side-dress nitrogen application already has been made.• You need to leave 12 to 15 inches worth of stubble height if you’re going to green-chop. 

Paul L. Hollis

July 15, 2011

6 Min Read

When drought becomes severe, the decision sometimes must be made to salvage the value from a corn crop by cutting it as forage. When this time comes, there are several options for producers, says Dennis Hancock, University of Georgia Extension forage specialist.

“We can look at, for example, trying to green-chop a field, where you actually chop it in the field and feed it to the animals,” says Hancock.

One of the concerns with that would be the potential for nitrates, particularly if the layby or side-dress nitrogen application already has been made, he says. “You need to leave 12 to 15 inches worth of stubble height if you’re going to green-chop. In some of these plants, more nitrates are concentrated in the lower part of the stem. So we want reduce the overall nitrate concentration by increasing the stubble height. We’ll cut it higher than we normally would, say for a corn silage field,” he says.

A second option is to make a hay crop from the field, says Hancock. “Again, we have the same restriction regarding nitrates. Nitrates will not dissipate in the hay. We need to increase the cutting height so that we’re reducing the total nitrate concentration. But with hay production, the cattle actually do pick through the hay more. They generally select more leaf material out of the hay. As a result, their actual intake of nitrates will be lower, and as a consequence, we can lower our cutting height, making it easier. Still, we need to leave about 8 to 12 inches of stubble. That’s a lot if we’re trying to make hay,” he says.

One of the strategies for dealing with that situation, says Hancock, is to windrow the crop as you’re cutting it with a mower conditioner.

No need for raking

“A mower conditioner can allow us to windrow that right in behind the crop as we’re cutting the crop and it’ll eliminate the need for going back and raking. The problem with doing that with hay is getting it to dry down. We want to avoid trying to rake the hay because of the stubble height, which will make it very difficult. So our objective is to try and let it cure out in the windrow. That will take a lot of time. Of course, if drought continues, drying weather will allow for that, but making hay out of that is a little more difficult.”

It’s important to use a conditioner not only because it will allow the producer to windrow the crop, but it also will break up the stems more and allow the moisture to evaporate from those stems more readily, notes Hancock.

A third option is to try and graze the crop, he says. This can be challenging, especially if you’re trying to move animals around.

“There are two key rules: never turn them in hungry, and don’t graze it so tightly that we remove the growth down to below 6 to 8 inches. In both of those cases, grazing animals can eat so much, that if you graze it too closely, it can increase the nitrate intake, and it can be such a high level of intake at one time, that we end up with a flush of nitrates getting into the animal’s system.”

The grazing preference for these animals as they go into the field is that they will take on ears and leaf material first, says Hancock. Then they’ll start with the tops of the plants and work their way down.

“One strategy we can think about is using a technique called frontal grazing. We begin at the far part of the field where we have water resources, and we begin to graze progressively away from the water resource. All we need to do then is move one hot wire or one fence further down the pasture. We don’t necessarily need to worry about a back fence in that case.”

Fourth option

A fourth option, says Hancock, is making silage out of the crop — probably one of the best options available.

“Silage is such a superior way of handling this because it reduces the nitrate concentration in the crop. It retains more of the quality and reduces the amount of time we’re required to handle the crop. In the process of fermentation, we could end up with a reduction in nitrates of up to 50 to 60 percent. So it’s important that we create conditions where the fermentation is well-supported.”

One of the challenges of putting up silage from a crop like this is that it still needs to be wilted, says Hancock.

“Even though this crop is drought-stressed, the moisture level is still going to be 85 to 90 percent, even if it’s beginning to turn brown and die back. We still need to wilt it to get down to an optimum of 64 to 70 percent moisture. That can be easily done with a mower conditioner, and windrowing behind the mower-conditioner. Usually, it’ll take a few hours for it to wilt down from 85 to 90 percent down to 65 to 70 percent.”

One option, he says, instead of chopping it for silage, is to make bale silage from it. This will make it easier to handle the crop. After windrowing behind a mower-conditioner, you can follow in behind with a baler and wrap it with plastic to create silage.

“In this system, we still advise that you raise the cutter bar. You still want to leave about 6 to 8 inches of stubble height. We’re trying to reduce nitrate levels as much as possible, especially if we’re feeding this into a dairy ration.”

Regardless of the silage system, it’s important to allow the crop to ferment for three to four weeks before you start feeding the crop if you suspect nitrates will be high.

“Regardless of how the crop is harvested, we still need to test the nitrates. Nitrates can cause some major animal problems, so what we need to do is to assess the nitrate level. There are field kits for doing this, but it’s important that we quantify exactly how many nitrates are there. That can be accomplished usually by taking it to a lab and running a nitrate analysis. When we develop a ration, we can dilute the forage down to a point to where it’s safe to feed to the animals.”

It’s important, says Hancock, to use a hay corer to take those samples as well. “The hay corer will give us a good random sample into the bale so that we get a good cross-section of stem, leaf and other material within that bale itself. It’s also important that we get a good representative sample throughout the entire field. Some areas of the field may be elevated in terms of nitrates whereas other areas may be low.”

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About the Author(s)

Paul L. Hollis

Auburn University College of Agriculture

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