Don’t follow alfalfa with alfalfa
Alfalfa plants don’t play nice with each other. That’s why we don’t follow alfalfa with alfalfa.
A mature alfalfa plants excretes a chemical that inhibits the germination and growth of a newly-seeded alfalfa, says University of Minnesota Extension agronomist M. Samantha Wells. That’s called alfalfa autotoxicity.
“The production of compounds by one plant species that are toxic to another is known as allelopathy. The production of chemical compounds by a plant that are toxic to members of the same species is known as autotoxicity. Plants produce these compounds to help “carve out” a space for themselves and reduce competition from other plants for water, nutrients and light. ”
The toxin impedes the seedling root system by inhibiting the root from elongating. Fewer seedlings grow, and those that do are often stunted from their inability to take up enough phosphorus, water, and nutrients. Plants affected by alfalfa autotoxicity do not recover.
To avoid alfalfa autotoxicity, Wells recommends these management practices:
Allow at least one year after terminating an alfalfa stand before planting a new stand.
Don’t plant alfalfa in thinning stands of existing alfalfa fields. New seedlings planted within 8 to 16 inches of an old alfalfa plant will experience yield reductions from toxicity and competition, per the University of Missouri.
Capitalize on residual alfalfa nitrogen by planting a grass crop after alfalfa.
“Plants that are healthy in fall and then winterkill will not release the toxins from the roots until they thaw,” according to a University of Wisconsin report. “Even if thawing takes place during a winter warm up, little leaching or microbial degradation of these compounds will take place until spring.
“This means that the autotoxic effect of a winterkilled stand would be similar to that of a stand killed in early spring. There will be significant yield reductions if these stands are spring seeded back to alfalfa unless they are less than two years old.
“These stands should be rotated out of alfalfa, or late summer seeded following oats or some other annual crop.”
Source: Dennis Cosgrove and DAn Undersander, University of Wisconsin - Madison
Source: M. Samantha Wells, University of Minnesota Extension Agronomist
Editor: Judy Bingman, Grazing and Forage Hub Coordinator
Reference: Reducing autotoxicity in alfalfa, University of Minnesota Extension
Reference: Seeding Alfalfa Fields Back Into Alfalfa, University of Wisconsin Extension