An alfalfa stand good enough to keep?
Focus on Forages by Dan Undersander,
Now, before the snow accumulates, is a good time to walk alfalfa fields and decide whether they are good enough to keep for next year or should be replaced. Generally, speaking alfalfa stands begin to decline in the Midwest after the second production year. We usually see that yields after the second production year are down about 17% from the previous two years.
Realizing that most input costs are the same regardless of yield, economic analyses suggest that it is not profitable to keep an alfalfa stand that would yield 17% less than optimum. (Would you plant a corn hybrid that yielded 17% less than some other hybrids?)
Some fields will last longer and some decline more rapidly. The best is to evaluate individual fields for stand density and plant health to get an idea of what the field might yield next year.
The evaluation is a simple two-step process:
Step 1. Estimate existing stand condition by stem density and then dig a few plants to determine plant health and likelihood of winter survival.
Estimating stand density is simple: Just visually assess the field for at least 55 stems per square foot. This is generally easy to do now. When alfalfa has been harvested in the fall, you can look at the number of cut ends. Or, if the alfalfa was allowed to regrow, stems are often short and have lost leaves from frost, so individual stems are easy to see.
If you are unsure of what 55 stems per square foot looks like, then you can count 1 or 2 square feet to get a visual image of the required stem density of optimum yield. Some seed companies make square foot measures available to customers. Once you have a visual idea of what stand density is desired, it is easy to check fields to determine their stand density.
Stands with an average stem density of more than 55 stems per square foot are in good shape and have potential for continued high production. As the graph here shows, stands with between 40 and 55 stems per square foot will have reduced yield and are probably in their last year of production. Stands with less than 40 stems per square foot should be replaced or interseeded.
Step 2. Dig a few plants and examine the top 4 to 6 inches of taproot. Healthy roots are colored similar to the inside of a potato. Areas of the taproot with brown or black discoloration are rotted.
All alfalfa plants will get some browning and blackening as they age and all plants will gradually develop some amount of crown rot (black area in the crown). A small amount is tolerable, but as the rot covers more than 50% of the crown diameter, winter survival is reduced and growth the following year is reduced.
If you dig eight or 10 plants, you can quickly get an idea of the stand plant health and, based on the number of plants, can determine if the stand will be the same next year or worse. If you are slightly less than 55 stems per square foot, but the plants are healthy, yield next year will likely be similar to this year. On the other hand, to the extent plants show crown and root rot or worse, you can expect the stand to decline and yield less next year than this year. Such stands should be targeted for replacement.
A more detailed description of this stand evaluation process with pictures is available in a University of Wisconsin Extension publication you can download from