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Alfalfa Toxicity Affects Seedling Emergence and Growth

05 June 2013
Alberta Agriculture, Food and Rural Development

CANADA - Alfalfa toxicity is a problem that can affect both seedling emergence and growth. Studies have shown yield reductions when alfalfa has been seeded after alfalfa, with no break in between.

These yield reductions can be anywhere from 8 to 52 per cent and persist for years. Stands affected by autotoxicity are also slower to regrow after harvest.

“Both seedling emergence and growth are reduced by alfalfa autotoxicity,” says Stephanie Kosinski, forage specialist, Alberta Ag-Info Centre.

“Plants that do emerge are often stunted and may show purpling, indicating a lack of nutrients. Root growth is most severely affected. Roots are swollen, discoloured, curled and lack root hairs. They end up branching more than normal and tend to be shallower. This negatively impacts the longevity of the stand, as it reduces the plants’ abilities to take up water and nutrients.”

“When it comes reseeding a field to alfalfa, if your alfalfa field is more than two years old, you should seed an alternate crop for at least one year after taking it out,” says Kosinski. “This will give time for the autotoxic chemicals the old alfalfa stand released into the soil to dissipate.

“If you have a seeding failure in the year of establishment or winterkill right after establishment, you can successfully reseed that field the same summer or the spring following. The toxins are not present in the first year in new seedlings, meaning you don’t have to worry about autotoxicity until the stand is two years old.”

It is not recommended to try to thicken an old stand of alfalfa with alfalfa, says Kosinski. “While you might get germination and seedling growth at the start, those plants will likely die out over the summer. This is because the size of the autotoxic zone around established alfalfa plants does not leave much space in a field where new seedlings could survive.”

Studies have shown that the autotoxic zone is a 16 inch radius from an established alfalfa plant. New seedlings within 8 inches of established alfalfa plants often die, while those 8 to 16 inches away survive, but have stunted shoot growth and poor root development.

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