Recommendations vary widely regarding how long you should wait to plant alfalfa after alfalfa. New data from the University of Missouri and Pioneer Hi-Bred International, Inc., now indicate that you should wait at least one year before seeding alfalfa into an old alfalfa field to reduce the impact of autotoxicity. This is the negative effect that well-established alfalfa plants have on the germination, vigor and emergence of new alfalfa seedlings.

Plant and soil bioassays show that this effect reduced germination of new plants, and stemmed from a slowing and killing of the primary root within the germinating seed when alfalfa was seeded before a year’s time elapsed. The surviving roots were smaller and more branched, which reduced the plant’s capacity to tolerate drought and made the plant less productive. In addition, the new findings show that alfalfa does not outgrow the initial effects of autotoxicity, which results in lower stand productivity over time.