Consider replacing old, low-yielding alfalfa stands after this year’s first cutting, suggests Rory Lewandowski, Ohio State University Extension educator.
"The 2012 growing season is providing an opportunity to evaluate marginal alfalfa stands now following a harvest,” he says. “If the stand doesn’t meet good production criteria, planting it to an annual crop like corn is still an option.”
To evaluate a stand’s productivity, he says to count plants or stems per square foot. Older stands have fewer plants per square foot than younger ones, but more stems per plant if they’re healthy. Sample at least four to six random areas within the field.
Alfalfa stands over three years old should have a minimum of six plants per square foot to remain in production. Dig up the plants in some of the sampled areas and split the roots lengthwise to evaluate plant health. In healthy stands, fewer than 30% of plants show significant discoloration and rot in the crown and taproot. Healthy plants have vigorous crown shoots distributed evenly around the crown. If over 50% 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, wait for at least 6” of regrowth, Lewandowski advises. The guidelines for stand evaluation based on square-foot stem counts are: greater than 54 stems, no yield reduction; 40-54 stems, keep the stand but expect some yield reduction; less than 40 stems, consider replacing the stand because yield reduction is significant.
Silage corn or another annual forage crop are good replacement options this time of year. But planting alfalfa back into old alfalfa fields generally isn’t recommended because of the threat of autotoxicity, he says.