• Plant nutrition
  • Apr 17, 2020

Safeguard Your Alfalfa Stands This Spring

Alfalfa Field

Weather patterns in Central and Northern Wisconsin were especially challenging to alfalfa stands during the winter and spring of 2018–2019. Several winter rain events on already-saturated soils, lack of snow cover during the coldest part of winter and ice conditions in much of the Upper Midwest produced difficult conditions for alfalfa survival. Extended icing is a double negative because it allows soil heat to escape into the atmosphere and can reduce crown respiration. Even minimal snow cover can be important to alfalfa winter survival during the coldest weather conditions.         

You can’t predict or control the weather. But there are steps that you as an alfalfa grower can take to better manage your crop.

1. Cut alfalfa less frequently.

The less often alfalfa plants are defoliated, the greater the chances the plant will be stronger and have more energy to live through the winter and green-up in spring. Alfalfa crowns and crown buds are living organisms and, like any perennial plant, they need to consume stored energy to stay alive all winter long. Like you would fill up your gas tank before embarking on a long drive across the desert, you should fill the “gas tank” in your alfalfa plants before winter. If you cut too frequently or too late in the season, you’re hindering the plant’s ability to turn sunlight energy into sugars and carbohydrates to fill its gas tank prior to the winter so it can survive.  

Management tip: If you’re cutting alfalfa after October 15, do not cut stems down to the soil surface. Leaving a minimum of 3 to 4 inches of stubble protruding in icy conditions allows for the exchange of oxygen and carbon dioxide, and minimizes the risk of crown suffocation. Also, although leaving the September 1 to October 15 growth seems like an expensive decision, this growth will improve the chance of snow retention and provide stored energy for faster spring growth. Data has indicated that leaving late fall growth increases first cutting yield by about equal tonnage (Walgenbach, USDA, 2000).                          

Recommendations for alfalfa cutting schedules have changed over time. Historically, alfalfa in the Upper Midwest used to be harvested three times a year. To improve forage quality, nutritionists and agronomists started to recommend cutting alfalfa more frequently to achieve higher forage quality. In short, the trend over the last 25 years has been to simply cut alfalfa earlier in the spring and more frequently between cuttings. Although this practice increases forage quality, it reduces yield, increases weed pressure and potentially reduces stand persistence.          

Studies support the benefits of less frequent cuttings. Dr. Dan Undersander at the University of Wisconsin has performed research testing a three-cut versus a four-cut alfalfa system and the effect on yield. In trials performed in Arlington, Wisconsin, a four-cut system yielded nearly 16% less than a three-cut system did in year two (a season total of 6.53 tons per acre for the four-cut and 7.55 tons per acre for the three-cut). In year three, those numbers were 4.07 tons per acre for four cuts and 5.09 tons per acre for three cuts, a 25% yield advantage for the three-cut system.1 This implies that with higher yield in year three, stands have higher persistence and better health due to less harvest stress. The additive effect of cutting alfalfa too frequently means slower plant recovery following harvest, decreased stand persistence and reduced yield. In other words, cut more and get less.

2. Rank your fields. Read your stands. Count your stems.

In a typical rotation scenario (not like with last year’s winter damage), rotate alfalfa stands out of production based on their root scores and stem counts. As alfalfa plants age, root health and stand density decline. Roots are rated from a zero, which indicates a healthy root, to a 5, which indicates a nearly dead root. You want to achieve a root score of 3 or better. Your agronomist can work with you to rank your fields and assess the health of your stands by digging roots, analyzing them and rating them according to root scores and stand density. The goal is to rotate about one-third of your alfalfa stands out of production and replace those with one-third new stands. Nitrogen credit from alfalfa is an important benefit to the following corn crop.             

Also, talk with your trusted agronomist about stem counts. You should have about 55 alfalfa stems per square foot. Once that number starts to dip below 55, you’re losing yield potential. To reach this density, generally five to seven plants per square foot in mature stands are needed.

Management tip: Remember that alfalfa must not be planted back on alfalfa ground for at least two years. Rotate those fields to another crop to create “fresh ground,” meaning a field that has not been in alfalfa for two years and has no herbicide carryover risk.

Don’t underestimate the contribution that new seedings can add to your alfalfa supply. Controlling weeds using glyphosate-resistant alfalfa will add both more yield and more quality.            

3. Add advanced alfalfa technology to your portfolio.

New alfalfa technologies allow you to cut less frequently and still retain yield without sacrificing forage quality. For example, the HarvXtra® Alfalfa trait maximizes quality by reducing the amount of lignin in the plant compared to conventional alfalfa at the same stage of maturity. This trait enables growers to lengthen times between cuttings, increase yield, place less stress on plants and potentially lower harvest costs.

Newer alfalfa genetics offer even greater disease resistance than older varieties. One of the benefits of exceptional disease resistance is that it allows alfalfa plants to survive in conditions that are less than ideal and then quickly recover after periods of extended wet soil stress. Minimizing “root nibbling” by diseases improves uptake of water and nutrients, and improves nitrogen production from the rhizobium bacteria. Healthy roots, even in wet soils, mean faster establishment and higher yield.

Management tip: Disease resistance paired with Roundup Ready® weed control and the capability for a wider cutting window is a powerful combination to achieve alfalfa production success.

4. Consider the risks of herbicide carryover before seeding alfalfa.

Work with your agronomist to select a weed-control plan for your corn, soybeans or wheat that won’t be detrimental to your newly seeded alfalfa. Herbicides applied to control weeds in corn, soybeans and wheat may contain a residual effect. New chemistry used to control difficult weeds like waterhemp can increase carryover risk to seedling alfalfa. In many cases, residual chemistry is being confused with seedling diseases that can also hinder alfalfa establishment.     

Management tip: Be sure to review herbicide labels carefully to ensure that seeding alfalfa falls within the guidelines of the manufacturer of the chemistry. Keep in mind, new chemistry residuals may not be affected by simply reducing rates or assuming that high rainfall conditions have diluted residual effects. Follow label guidelines before seeding alfalfa.    

Work with your agronomist and your applicator to keep accurate records, including the rates at which specific herbicides were applied and where they were applied. Careful recordkeeping and tank cleanout will save you money and stress in the long run. Pairing this with less frequent cutting and careful in-field scouting, and adding newer alfalfa technologies to your crop mix will help you diversify your portfolio and make your alfalfa crop more manageable.

 

1 University of Wisconsin Extension, Dr. Dan Undersander, 2009. Testing performed in Arlington, Wisconsin.




Plant nutrition

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