Reducing autotoxicity in alfalfa

What you need to know

  • Allow at least one year between terminating an old alfalfa stand and re-seeding alfalfa.

  • Don’t delay spring reseeding. This can result in significant yield losses during the reseeding year.

  • Don’t thicken thinning stands of alfalfa with alfalfa. Use red clover or terminate the stand and seed something else.

Autotoxicity is when a plant chemically inhibits the growth or germination of another plant of the same species.

Although several factors influence autotoxicity -- such as soil texture, rainfall and termination timing -- research indicates the need for a break in the production and/or crop rotation to avoid potential stand establishment problems.

Typically, autotoxicity in alfalfa isn’t an issue, given the rotational schemes (e.g., corn following alfalfa). However, there are growers that wish to renovate their current alfalfa fields, and commonly ask about the impacts of doing so.

Research: Alfalfa autotoxicity

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alfalfa test plot with almost no new regrowth, mostly bare ground
Figure 1: Full plant incorporation of alfalfa (i.e., roots and shoots) and subsequent impacts on re-seeded alfalfa establishment.
alfalfa test plot with a little new regrowth, mostly bare ground
Figure 2: Incorporated alfalfa roots and subsequent alfalfa autotoxicity on re-seeded alfalfa establishment.
alfalfa test plot with full regrowth
Figure 3: Non-autotoxicity alfalfa check plots. Alfalfa seeded following fall fallow.

Recommendations

We recommend the following management guidelines for reducing alfalfa autotoxicity.

  1. Allow at least one year between terminating an old alfalfa stand and reseeding alfalfa, when possible. Though we were able to effectively establish alfalfa within a shorter window, evidence of auto-conditioning suggests a longer rotation interval may be better. Seed fall-, winter- or spring-killed alfalfa stands to something else in spring, and safely reseed to alfalfa possibly in late summer but, preferably, the following spring.

  2. Remember that delaying spring seeding won't help. Delaying spring reseeding two to four weeks after tillage of a killed stand is not an effective strategy to alleviate autotoxicity. Delayed seeding can still result in significant yield losses during the reseeding year.

  3. Don’t thicken alfalfa with alfalfa. When considering overall risk associated with alfalfa autotoxicity, it’s less risky to not attempt to thicken thinning stands of alfalfa with alfalfa, if possible. Use red clover or terminate the stand and seed something else. However, depending on soil type, alfalfa stand age, precipitation and termination timing, there are opportunities. This is especially true if you’re reseeding during the seeding year. Alfalfa autotoxicity risk calculator.

M. Scott Wells, Extension agronomist; David Nicolai, Extension educator and Roger Becker, Extension weed scientist

Reviewed in 2018

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