When a producer plants an alfalfa field, there is an expectation that the field will remain productive for several years. Alfalfa is a perennial crop but there is a limit to its longevity, since all alfalfa fields naturally thin over time. As fields get older, eventually the loss of plants goes below the minimum threshold for stand density to a level where the resulting yield reduction makes it uneconomical to keep in production.

Miller don
Donald Miller
Technical Forage Adviser / Mountain View Seeds / Nampa, Idaho
Miller was formerly the director of product development for Alforex Seeds.

In simple terms, the stand longevity and ultimately the profitability of an alfalfa field is dependent on maintaining a stand density above the minimum economic threshold of six plants per square foot. Multiple factors can influence the rate of stand decline, and some fields may reach the minimum threshold in two to three years while others may take five to eight years. The rate of stand decline can vary from field to field but is influenced by three main factors: genetics of the alfalfa variety, stand density at establishment and implementation of crop management techniques that minimize plant stress.

The following is a list of factors for each of the three categories that can aid in maintaining stand densities and/or extend the life of an alfalfa stand to meet a producer's forage production goals.

Genetics of the alfalfa variety

Probably the most important thing that influences alfalfa stand life is the variety choice. Producers should avoid the temptation of buying alfalfa seed based solely on price. Often those varieties are short-lived since they lack one or more of the basic genetic traits needed to minimize stand thinning over time. The following is a list of variety attributes that should be considered when selecting an alfalfa variety.

  1. Fall dormancy and winter survival rating (WSR): Select a variety adapted to your location and that has a fall dormancy and winter survival rating recommended for your growing region. If winterkill is a concern, select a variety with a WSR of 2.2 or greater.
  2. Disease, insect and nematode resistance: Select a variety with a Resistance (R) or High Resistance (HR) level of genetic resistance to the major pests known to be a problem in your area.
  3. Abiotic tolerance (Drought, soil salinity and extreme weather): “Climate-ready forage varieties” are now available with traits that help combat the negative effects of climate change.
  4. Variety yield performance over multiple years: Producers that want alfalfa stands to last longer than three years should pick varieties whose yield data shows better-than-average performance in the third and fourth year. This is a good indicator of stand persistence.
  5. Traffic tolerance: Varieties with deeper-set crowns (sunken crown) are more tolerant of wheel traffic damage.
  6. Specialty traits for specific uses:
    1. Grazing tolerance: If an alfalfa field is going to be grazed, an alfalfa variety selected for grazing tolerance will persist longer than a non-grazing variety.
    2. High water table and/or hard pan: Branched-rooted varieties tend to persist better than tap-rooted varieties under these conditions.
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Dense initial stands reduce weeds and aid in maintaining plant numbers above the minimum stand density threshold of six plants per square foot. Courtesy photo.

Stand density at establishment

It is critical to start out with a thick dense stand. As a field ages, an initial stand density (in the first year) of 25 to 35 plants per square foot will aid in maintaining the stand density above the minimum threshold of six plants per square foot.

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Stand establishment guidelines

    1. Seed treatment: Use a fungicide treatment to increase seedling survival.
    2. Fertility and weed control: Test for both macro- and micronutrients and fertilize as needed. Use a preplant herbicide to aid in stand establishment.
    3. Seedbed preparation: The seedbed should be firm. Before planting, walk across the seedbed. The sole of your shoe should be visible.
    4. Seeding rate: For irrigated acres, use 15 pounds to 20 pounds per acre. For dryland acres, use 8 pounds to 12 pounds per acre.
    5. Nurse crops: If a nurse crop is needed for stand establishment, use a light planting rate (i.e., oats or barley at 10 pounds to 25 pounds per acre) and harvest at or before the boot stage.
    6. Seed depth (1/4- to 1/2-inch): This is especially important! Most alfalfa stand failures are due to planting the seed too deep.
    7. Fall planting dates: To ensure winter survival of a new fall-planted alfalfa, plant six weeks to eight weeks before the historic killing frost.

Implementing crop management techniques that minimize plant stress

After genetics, crop management is the next most important factor that can influence how long an alfalfa field can remain productive. Poor management practices can contribute to premature stand thinning which ultimately result in shorter-than-desired stand life. The following are some best management practices that promote plant health and minimize plant stresses to help maintain stand densities:

  1. First cut after planting: Allow the alfalfa stand's first growth to reach full maturity before cutting. This allows the plants time to develop a strong root system needed for proper stand establishment.
  2. Cutting intervals: If a frequent harvest strategy is used early in the season to produce dairy-quality hay, it is especially important to extend the cutting interval of a later cut to adequately recharge the root reserves.
  3. Timing of last cut in fall: The last cut must be made to ensure the plants have optimal root reserves going into the winter. We want the field to either be cut early enough in the fall to regrow and replenish root reserves, or late enough so it does not regrow and waste its root reserves on short growth that doesn’t replenish the root reserves.
  4. Wheel traffic timing: Wheel traffic in the field can cause physical damage to the alfalfa crown and may allow entry of disease. Wheel traffic five days after cutting causes significantly more stand damage than wheel traffic at two days.

Summary

The desired longevity of an alfalfa field may vary depending on each producer’s rotation plan and/or forage needs. In most cases, the desired stand life can be achieved by utilizing improved genetics and crop management techniques that aid in maintaining the stand density.

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Ideal initial stand density is 25 to 35 plants per square foot. Courtesy photo.