Issue No. 1, Article 6/March 26, 2010
Time to Evaluate Alfalfa Stands
It will soon be time to assess the overwintering condition of alfalfa fields. Stand density at the beginning of the growing season is one estimate of a field's potential productivity. In pure alfalfa fields two methods are commonly used to evaluate stand density: plant count and stem count.
The traditional approach, especially in the early spring, has been to count plants within a square foot area. As a general guide, the suggested number of plants per square foot is as follows:
- More than 12 in the spring of the first production year
- More than 8 in the spring of the second production year
- More than 5 in the spring of the third production year
A similar guideline for spring evaluation is that a two-year-old stand with 6 or fewer plants per square foot or a three-year-old stand with 3 or fewer plants per square foot will not produce well.
The preferred method of stand evaluation is to count stems per square foot, an approach shown to be a good indicator of potential yield. Stem counts can be taken when the plants are 4 to 6 inches or taller. Count any stem that would be cut at harvest. If there are fewer than 39 robust stems per square foot, consider tearing up the stand.
Whether you count plants or stems, make several counts across the field to achieve a representative sampling. Assess plant health by digging up a number of plants from different areas of the field and splitting them lengthwise to determine crown and root vigor. Roots that exhibit disease or severe discoloration in the crown or more than a couple of inches below the crown may not produce well. Healthy roots will have firm, white tissue on the inside.
Alfalfa plants experiencing winter injury will be slow to green up, have shoots on only one side of the crown (asymmetrical growth), or show uneven growth and root damage.
Many factors, including forage inventory, cash flow, and available land, need to be considered when deciding whether to keep an alfalfa field, but assessing stand density is an important factor, and perhaps the starting point.--Jim Morrison