Evaluating Alfalfa: The Whys and Hows

Published on Fri, 03/29/2019 - 8:13am

 Evaluating Alfalfa: The Whys and Hows

 By Margaret Smith, PhD - Forage Agronomist, Albert Lea Seed
and Victoria Kemmits - Operations Specialist, Albert Lea Seed

This winter has not been kind in many parts of the Midwest, and alfalfa stands are likely to have some damage. Damage is most likely in older stands, areas of low pH, K and S levels and 2018 seedings. Many new seedings last year in high rainfall areas were already under stress going into winter. Rains in December and bitter cold followed by freeze-thaw cycles in January triggered frost heaving and ice-sheeting, which are detrimental to alfalfa health. Assessing that damage, and deciding how to remedy it, will be crucial in making the most of your hay harvest this year.

Assessing Your Stand
There are two major issues to consider when evaluating your alfalfa stand this spring:
• Plant viability: Is it dead or alive?
• Plant vigor: Is it likely to produce a profitable yield this growing season?

Plant Viability
Plant viability can be determined as soon as the ground begins thawing. Dig a sampling of plants throughout your field and inspect the outer surface of the roots as well as cutting through them to analyze the interior tissue.
A completely healthy alfalfa plant should have a large crown with symmetrical growth, and a large taproot. The root should be a white or off-white color with no discoloration, and the bark should not flake off easily when handled. The stems should be springy and have bright green leaves with no yellowing or browning.
Plants that have been damaged slightly may have a little browning at the crown and slight yellowing of the root but will still grow well. Plants that are severely damaged will have dead crowns and yellow-brown, sometimes hollow and spongy roots. If the great majority of your alfalfa plants are dead, your decision is straightforward. Stands with some damaged and dead plants need further evaluation.

What Should a Healthy Alfalfa Plant Look Like?
A completely healthy alfalfa plant should have these characteristics:
• Large crown with symmetrical growth
• Large taproot, white or off-white with no discoloration
• Bark should not flake off easily when handled
• Stems should be springy and have bright green leaves with no yellowing or browning

Plant Vigor
Don’t fire up the tractor too soon and work up a stand that may be viable. The final decision to keep your stand or not should be based on stem counts after green-up. When stems reach minimum cutting height (2 inches to 4 inches), count stems per square foot to assess plant vigor and potential yield. You can use a 17-inch by 17-inch square, or a hoop/ring 19 inches in diameter. Either of these contains two square feet.
Walk your fields in a random pattern, toss your square or ring in areas of the field representative of your field, then count the stems inside your frame. When counting stems, only count stems from crowns that appear healthy enough to produce all season long.
Stems that are small, spindly, or off-color should not be counted. Count only those taller than two inches: shorter stems won’t grow as fast and won’t contribute to your yield as much as larger ones growing in the same space.

Divide your stem counts by two for the number of stems per square foot count. This will give you a fair estimate of your entire field

Stand Criteria
• If you count 55 or more stems per square foot, your stand is in good shape, and you can expect normal yields for the age of the stand.
• If you find a range of 40 to 55 stems per square foot, then you have some damage and yield will be likely be reduced, though not severely.
• Fewer than 40 stems per square foot means a sizable portion of the alfalfa plants have been affected, and yield will be significantly impacted. You should take action to make this hay stand profitable in 2019.

Taking Action
Even with fewer than 40 alfalfa stems per square foot, you do have options to make the most of your existing stand in 2019
If you seeded alfalfa in 2018, you may consider re-seeding alfalfa directly into the existing plot, but there is some risk. Although many farmers have reported successfully interseeding alfalfa into the previous year’s seeding, avoid planting into older alfalfa stands. Alfalfa is naturally self-allelopathic, or autotoxic, exuding chemicals from its roots that create a toxic environment for new alfalfa seedlings. The longer a stand has been established, the more toxicity exists in the soil.
It is possible to drill in a grass mix to add tonnage and reduce weed pressure while still benefiting from the high nutritional value of the alfalfa. Interseeding with another legume, such as red clover, is another option that can produce hay comparable to straight alfalfa if harvested at the proper time.