source: Farm and Food Report
Producers concerned with old alfalfa stands dying out after several years of production should avoid reseeding directly back to alfalfa. Mature alfalfa plants produce toxins that result in a form of autoxicity in the soil, which prevents the establishment of new seedlings.
Trevor Lennox is a Forage Industry Development Specialist with SAFRR. "The specific toxin produced is called medicarpin. It is present mostly in the leaves and stems, rather than in the root system itself. The toxin leaches into the ground surrounding old alfalfa plants up to a radius of 16 inches."
Lennox points out that this autoxicity will affect seed germination and decrease plant density over time. "As forage resource-people, we are often asked if reseeding directly into an old alfalfa stand is an option. It is not a recommended practice."
According to Trevor Lennox, "the most effective way to deal with autotoxicity is to rotate to another crop for a year or two. It is recommended that producers seed an annual cereal crop for a minimum of 1 year to give the soil a chance to cleanse itself and to take advantage of the nitrogen-rich soil nutrients the broad-leafed legume has synthesized over the years."
While there is no real consensus on how long it takes for the toxicity to disappear, there are variables that can affect the return of conditions more conducive to seedling vigour.
"The toxin is water soluble, which means that heavier soils with reduced drainage ability will exhibit the problem longer than lighter soils which are more permeable. Tillage can help reduce the autoxicity effect. In fact, producers are advised to remove top growth before tillage to help reduce leaching risks," says Lennox.
Producers should also be aware that higher temperatures are known to break down the toxic compound more rapidly and that heavier rains can move them away from the root zone faster.
An important point to note is that toxins are not produced in the first year of new seedlings. Therefore, seeding failures or new seedlings that were winterkilled can be reseeded without any autotoxicity affect.
Producers concerned with old alfalfa stands dying out after several years of production should avoid reseeding directly back to alfalfa. Mature alfalfa plants produce toxins that result in a form of autoxicity in the soil, which prevents the establishment of new seedlings.
Trevor Lennox is a Forage Industry Development Specialist with SAFRR. "The specific toxin produced is called medicarpin. It is present mostly in the leaves and stems, rather than in the root system itself. The toxin leaches into the ground surrounding old alfalfa plants up to a radius of 16 inches."
Lennox points out that this autoxicity will affect seed germination and decrease plant density over time. "As forage resource-people, we are often asked if reseeding directly into an old alfalfa stand is an option. It is not a recommended practice."
According to Trevor Lennox, "the most effective way to deal with autotoxicity is to rotate to another crop for a year or two. It is recommended that producers seed an annual cereal crop for a minimum of 1 year to give the soil a chance to cleanse itself and to take advantage of the nitrogen-rich soil nutrients the broad-leafed legume has synthesized over the years."
While there is no real consensus on how long it takes for the toxicity to disappear, there are variables that can affect the return of conditions more conducive to seedling vigour.
"The toxin is water soluble, which means that heavier soils with reduced drainage ability will exhibit the problem longer than lighter soils which are more permeable. Tillage can help reduce the autoxicity effect. In fact, producers are advised to remove top growth before tillage to help reduce leaching risks," says Lennox.
Producers should also be aware that higher temperatures are known to break down the toxic compound more rapidly and that heavier rains can move them away from the root zone faster.
An important point to note is that toxins are not produced in the first year of new seedlings. Therefore, seeding failures or new seedlings that were winterkilled can be reseeded without any autotoxicity affect.
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