Agronomy Blog

Spring Alfalfa Stand Assessment

by Logan Vaughn | Apr 6, 2017

Growers are currently preparing for spring seeding of alfalfa throughout the Midwest. A major focus prior to seeding is the evaluation of existing stands for winter injury and assessing the need for replacement.  This technical bulletin will review our current situation, discuss steps to evaluate your stands this spring and provide management suggestions for damaged stands.

Winterkill Potential
It is still a bit early to completely evaluate alfalfa stands for winter injury at the time this article is being written, but we are beginning to receive calls and have evaluated some issues with stand survival. Over the course of the winter, there were several warm ups through January and especially February. This led to complete snow melt throughout the majority of the upper Midwest and the risk of premature break in plant dormancy. Weather Trends 360® reports 9.7°F degrees above average for the month of February for Appleton, WI, with several days in the 50°F high temperature range. This was followed by a return of cold temperatures in March which could be a concern especially for plants that possibly broke dormancy - this could be more concerning as we move further south and experienced even warmer temperatures during this time.

Below are key areas to consider with alfalfa stand survival in relation to this year’s weather:

  • The amount of snow and length of cover can be a great benefit in protecting theLogan Alfalfa 1 cited alfalfa stand. Snow cover is an excellent insulator and can protect the crop from drastic temperature fluctuations. Six inches or more is preferred but as little as 4 inches can contribute to a 10°F difference in temperature. There were several warm ups throughout this winter leaving alfalfa stands without cover for weeks at a time.
  • Soil moisture is a frequent topic when discussing crop growth but is also a factor in alfalfa survival. Alfalfa grown on well drained soils is less likely to have as much winter injury. Fields located in lower areas or on poorly drained soils are more likely to have flooding and ice sheeting which can cause plant death. Ice sheeting could be concern this year due to warmer temperatures melting snow resulting in ponding followed by freezing temperatures.
  • Frost heaving of alfalfa results when repeated freezing and thawing pushes the tap root and crown out of the soil. This can break the taproot and damage the crown. This has been an issue in areas the past few years and if severe enough can lead to stand replacement. Heaving can be difficult to evaluate as plants can appear to be alive and healthy, but could die later or performance can be compromised. I’ve already been hearing reports of growers seeing this in 2017.
  • Temperature is a critical factor in alfalfa winter injury. Temperatures below 15 F can freeze the crown and cause plant injury or death.  This winter did not have the Polar Vortex type temperatures of a few years ago but certainly periods low enough to cause damage especially with lack of snow cover. Additionally the wide range in temperatures isn’t ideal for dormant plants.
  • Early break of dormancy is a concern this year as we had the warm up in February followed by a cold stretch in March. The question is if temperature were high enough in your region to break dormancy. Then how were the plants able to with withstand cold temperatures after breaking dormancy. Also, did the alfalfa plants have enough carbohydrates stored to compensate for these challenges? This will likely be an issue in some fields this spring.

While environmental factors such as weather play a major role in winter survival of alfalfa, several management practices also make a difference in the plants ability to survive:

  • Older stands are more likely to sustain winter injury than newer stands.
  • Selecting varieties with high winter hardiness and disease resistance ratings are less likely to experience winter injury.
  • Maintaining recommended soil pH and fertility also helps limit injury; keep pH levels above 6.6 and potassium at high levels.
  • Harvest frequency and timing of fall cutting can affect alfalfa winter survival- shorter intervals between harvest and fall cutting that doesn’t allow plants to replenish root carbohydrate reserves can reduce winter survival. Keeping at least 6 inches of fall stubble can also help retain more snow and provide additional insulation from temperature fluctuations.

Diagnosing Injury
Logan Alfalfa 2 citedOnce the frost is out of the soil, determining if plants are alive can be done by digging plants and examining the roots.

  • Healthy roots should be firm and white in color with little to no root rot.
  • If roots are browned, dehydrated and stringy then they are most likely winter killed. If over 50% of the root is infected with root rot then the plant will likely die later in the spring. This process can be completed until green up and stand assessments can be utilized.

Uneven growth is a sign of winter injury to alfalfa. Plants form buds in the fall for spring growth, during winter some buds on a plant can be killed while others will survive. If these buds are killed during the winter then the plant must form new buds in the spring which can delay growth and yield. This can result in shoots of different height on the same plant. If this scenario is observed, it is recommended to alter management practices in the future such as more balanced soil fertility and/or selecting more winterhardy varieties.

Logan Alfalfa 3 citedIf winter injury has occurred and there is concern about whether to keep the existing stand, there are stem density guidelines developed by the University of Wisconsin to aid in the decision.  A healthy stand should have at least 55 stems/ft2. Stem counts fewer than 40 per ft2 is severely limiting yield and should be considered for removal.

Logan Alfalfa 4 citedaIf counting stems takes too long, traditional plant density guidelines can also be used as a too l to determine the alfalfa stands future. The Universtiy of Wisconsin recommends that high yielding alfalfa stands should have over 25 plants/ft2 during the seedling year. Densities of 10-20 plants/ft2 are recommended for stands in year 2-3. After year 3, a stand should have at least 6 plants/ft2 to be considered productive.

If the decision is to remove the stand due to winter injury, it is recommended to take caution when seeding alfalfa into a field where alfalfa was previously grown. Alfalfa produces toxins that are released when the plants are killed from plowing, spraying or winterkill. These toxins can reduce germination and growth of a new alfalfa seeding. This occurrence is known as autotoxicity. A variety of factors determine how long it will take for the toxins to degrade and move out of the root zone so its suggested to grow a different crop for at least one growing season after killing an older alfalfa stand. Generally the autotoxin compounds are removed from sandy and lighter textured soils quicker than from heavier soils. Weather also plays a factor in the rate of toxin removal as warm and moist soil conditions helps increase the speed of removal. Autotoxins are more concentrated in stems and leaves than in roots of plants so removal of top growth before plowing can help reduce but not eliminate its presence.

Due to the nitrogen credits from alfalfa, planting corn into a field coming out of alfalfa is recommended. If a field only has patchy stand loss, it can be interseeded with forage grasses or clover to help extend stand life 1-2 years.

Spring Alfalfa Seeding
When preparing for spring seeding of alfalfa there are several factors that should be considered so that you reach production goals over the life of the stand. Mistakes made prior to and during seeding can reduce alfalfa quality, yield and stand persistence throughout the life of the stand. A few key management practices to consider before seeding:

  • Field Selection
    • žSelect well-drained fields with good fertility.
    • žAvoid seeding into a field that’s previous crop was alfalfa due to autotoxicity.
  • Prepare a firm seed bed while planting ½” – ¼” in heavier soils and ½” – 1” on sandy soil.
    • žSeeding rate around 15-20 lbs/acre.
    • žNo need to adjust seeding rates higher for coated seed.
  • Maintain adequate soil pH and fertility.
    • žKeep pH 6.5-7.0 for optimal yield potential.
    • žApply phosphorus, potassium, sulfur and boron to soil test and yield potential.
  • Control weeds to avoid competition and improve forage quality.
    • žConsider Roundup Ready alfalfa for broad spectrum weed control and excellent crop safety.
    • žIf establishing an alfalfa stand with a companion crop, timely harvest before it lodges or competes excessively for light or moisture is critical.
  • Variety selection can make a difference.
    • žPlant a variety with proven high yield and forage quality.
    • žSelect a variety adapted to your region with appropriate winter hardiness, fall dormancy, persistence and resistance to key diseases.
    • žLG Seeds offers a strong lineup of conventional and Roundup Ready varieties.

Following stand establishment; other important management practices include minimizing traffic during harvest activities. Avoid heavy traffic on wet soils that can lead to compaction.  To further minimize traffic damage to growing plants it is suggested that you complete driving over the field as soon as possible after cutting so you don’t break growing shoots. Research has shown 6% less yield for every day after cutting the field is driven over. 

It’s also recommended to allow plants to store root carbohydrates and proteins for winter survival by properly scheduling harvest around the first killing frost date. Alfalfa must be cut early enough in the fall to regrow and replenish root carbohydrates and proteins, or late enough so the plant does not regrow using stored carbohydrates, to assure maximum winter survival and spring green up.

Product Selection
LG Seeds offers a strong alfalfa lineup for a variety of uses and needs. Below is a brief overview on our current lineup so that you can make the best decision for your goals.

HG4001 - NEW variety for spring 2017 that offers Hi-Gestâ Low Lignin Technology. This product reduces whole plant lignin, improving fiber digestibility & forage quality. It also offers high yield potential along with a strong disease package including Race 2 aphanomyces resistance.
9200RR - The Genuity® Roundup Ready® Alfalfa allows flexible weed management early in establishment and higher first season yields. Best suited for growers looking for optimum weed management and premium quality from weed free alfalfa. This variety has strong winter hardiness and agronomics.
eXterra - Our newest conventional variety that has been in strong demand in the field. Latest generation of Standfast alfalfa screened for high yield potential, superb winter hardiness and forage quality. Ideally suited for producers looking to maximize total forage yield under intensive cutting schedules.
eXalt - Popular variety that has been a key product for several years. Best positioned where high forage digestibility is a top priority while having high tonnage capability.
PRO - Dependable variety that performs well across various alfalfa cropping systems.

If you have any questions, please contact your District Sales Manager or Sales Agronomist. Have a safe spring.

Sources and additional information:

Undersander, D. Effect of Wheel Traffic on Alfalfa Yield. University of Wisconsin Extension.
Undersander, D. and Cosgrove, D. Seeding Alfalfa Fields Back Into Alfalfa. University of Wisconsin Extension.
Undersander, D. et al. 2009. Alfalfa Management Guide.

Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
Weather Trends 360® is a trademark of Weather Trends International, Inc. Hi-Gest® is a trademark of Dow Chemical Company. Genuity® and Roundup Ready® are trademarks of Monsanto Technology LLC.
LG Seeds and design are trademarks of SCA Limagrain.

Download a copy of this technical bulletin: Tech_327 - Spring Alfalfa Stand Assessment