– Rory Lewandowski, Extension Educator Wayne County and Crossroads EERA
Should I keep this alfalfa stand or rotate it to a different crop? This question comes up at this time of the year because often the farmer plans to harvest a first cutting and then, if the stand is questionable, there is still time to plant corn for silage. There are two basic methods that can be used 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.
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. Determine the number of plants per square foot immediately after a harvest or any time before a harvest. To evaluate a stand based on stems per square foot, the recommendation is to wait until there is at least 6 inches of growth. Regardless of the method used, sample at least 4-6 random areas within the field to arrive at a decision. Both of these methods assume that the objective is a pure or nearly pure stand of alfalfa.
Alfalfa stands that are over 3 years old should have a minimum of 6 plants per square foot to remain in production. In addition, it is a good idea to actually 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% of plants will show significant discoloration and rot in the crown and taproot. Healthy plants will 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.
The guidelines for alfalfa stand evaluation based on counting the stems per square foot are: 1) greater than 54 stems: no yield reduction 2) 40 to 54 stems: keep the stand but expect some yield reduction and 3) less than 40 stems: consider replacing the stand because yield reduction is significant.
As noted earlier in this article, alfalfa is typically rotated into corn. 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. This is not a recommended agronomic practice due to autotoxicity potential. Autotoxicity of alfalfa is defined as an allelopathic effect that inhibits the germination of new alfalfa seedings and/or inhibits the root growth of new seedlings. The general recommendation is to rotate out of alfalfa for one growing season.
The 2012 growing season is providing an opportunity to evaluate marginal alfalfa stands now following a harvest. If the stand doesn’t meet good production criteria, planting it to an annual crop like corn is still an option.