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Spot stand issues in the fall.

Agronomy Bulletin 23 ─ Assessing Alfalfa Stands

Situation

As alfalfa stands age and thin, production can drop. Typically fields begin to decline in their third year of production. Field evaluation helps identify less profitable fields that need to be targeted for replacement.

Factors to Consider

  • When to assess fields
  • Stem density
  • Plant density
  • Root health
Minimum plant density for a healthy stand

Action Plan

  1. Assess stands in fall. Fall is the best time to evaluate productivity. It allows time to plan for fall tillage and alternative cropping prior to applying fall fertilizer or spring herbicides. Checking fields in fall also helps you anticipate weed control needs. Spring assessment is still valuable to evaluate winter injury or kill.
  2. Determine plant density. The number of plants in a square foot provides clues to stand health. As population decreases, weeds can invade. Low plant populations also can decrease alfalfa quality. Plant count once was the preferred method for estimating alfalfa yield, but we now know that stem density is a better predictor of yield potential. Older stands may have fewer plants, but the remaining plants are likely to have many stems. It is still important to evaluate plant count to determine if there are enough to maintain the crop.
  3. Determine stem density. Potential yield in alfalfa is determined by counting the number of stems per square foot. Evaluate three or four representative areas of the field. Mark off a 2-square-foot section of each area and count only the stems tall enough to be cut by the mower. Divide your count by two to determine stem density.
  4. Evaluate root health. Look at a few alfalfa plants across several areas of the field. Dig up the entire crown and at least 6 inches of the tap root. The crown and root should be symmetrical with many shoots emerging from the top and sides of the crown. Cut the crown and root lengthwise to look for root rot and discoloration. The more discoloration and rot in the root, the lower the yield potential of the plant.
Alfalfa stem density recommendation and how to rate alfalfa crown and roots

Summary

Consider many factors when making a decision to keep or replace an alfalfa stand. Assessing stem density may be a good starting point. Keep an eye on the number of plants per square foot and evaluate roots to help predict the yield potential of an alfalfa stand. For more information, contact your local Mycogen Seeds commercial agronomist or trusted agronomic adviser.

Published on Thursday, August 15, 2013