WOOSTER, Ohio – Crop growers wondering if they should keep their alfalfa or rotate to a different crop still have time to switch to corn if they find their alfalfa stands don’t meet production criteria, an Ohio State University Extension educator said.
Thanks to warmer, drier conditions this year, the 2012 growing season is providing a prime opportunity for growers to evaluate marginal alfalfa stands following the first harvest, said Rory Lewandowski, an agricultural and natural resources educator for OSU Extension.
In fact, growers still have time to plant corn for silage if they determine after the first cutting that their alfalfa stands are questionable, he said.
“Last year, we had so much rain that everything was behind and even if growers wanted to rotate out, they couldn’t do that because the fields were just too wet,” Lewandowski said. “This is one of those years that the weather has cooperated enough to open up the opportunity to do this.
“Growers should look and see if the stand is productive enough to meet their production goals. But if not, with the weather we’ve had, they can rotate out and get some more production out of that land.”
Alfalfa is typically rotated into corn, Lewandowski said.
“But occasionally the question comes up regarding whether it is possible to plant alfalfa back into these old alfalfa stands to either thicken up the old stand or to start over with a new seeding,” he said.
This practice is not generally recommended due to autotoxicity potential, which is an allelopathic effect that inhibits the germination of new alfalfa seedings and/or inhibits the root growth of new seedlings, Lewandowski explained.
“The general recommendation is to rotate out of alfalfa for one growing season,” he said. “But growers who do decide to rotate have to also consider what they are going to rotate to?
“Corn silage is good this time of year, or another annual crop for forage.”
Growers can use two basic methods to evaluate stand productivity: evaluate the stand density in terms of plants per square foot; or evaluate by counting the number of stems per square foot, Lewandowski said. Older stands naturally have fewer plants per square foot, but older plants, if they are healthy, produce more stems as compared to a younger plant.
“Regardless of the method used, sample at least 4-6 random areas within the field to arrive at a decision,” he said. “Both of these methods assume that the objective is a pure or nearly pure stand of alfalfa.”
Growers should also determine the number of plants per square foot immediately after a harvest or any time before a harvest.
Criteria to consider when evaluating alfalfa stand productivity based on plants per square foot include:
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Alfalfa stands that are over three years old should have a minimum of six plants per square foot to remain in production.
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Growers should dig up the plants in some of the sampled areas and split the roots lengthwise to evaluate the health of the plants. In healthy stands, fewer than 30 percent of plants will show significant discoloration and rot in the crown and taproot.
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Healthy plants will have vigorous crown shoots distributed evenly around the crown. If over 50 percent of the plants show signs of root and crown rot, the stand should be rotated to another crop.
To evaluate a stand based on stems per square foot, the recommendation is to wait until there are at least six inches of growth. The guidelines for alfalfa stand evaluation based on counting the stems per square foot are:
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Greater than 54 stems: no yield reduction.
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Forty to 54 stems: keep the stand but expect some yield reduction.
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Less than 40 stems: consider replacing the stand because yield reduction is significant.