Alfalfa is a rather wonderful plant. If it were a person, I'd want to interview it for a few hours. What makes you happy? Who are your friends? What makes you not want to keep growing in the same place for too long? Is this a clue to your purpose? Are you a pioneer? Is your
job to team up with other plants we haven't considered?
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I'm guessing that for such a significant, conventional crop, there are too many stakeholders concerned with the effects autotoxicity for it to be a mere misdiagnosis of a soil imbalance? "The internet" tells me the actual compounds causing autotoxicity are not fully understood (though they have suspects).
I noticed at minute 2:30 of Neil Kinsey's Hands On Soil Agronomy
video, he mentions an alfalfa field that lost productivity. He goes on to say that on a simple soil test, the pH can look great-- but in a more detailed analyses, the pH could look great and there still be an excess or lack of key pH-influencing minerals. But surely major stakeholders including researchers like Purdue University ("U" being a silly abbreviation for University) wouldn't overlook this... would they?
I really wish Mr. Kinsey had come back to that particular alfalfa case! Can a detailed soil test and adjustments solve the problem?
This possibly dated article from Purdue.
https://www.extension.purdue.edu/extmedia/AY/AY-324-W.pdf shows that seedlings within 15" of the established plant are most effected.
The wild alfalfa thriving in the badlands-- is it growing densely, or is it scattered among things like wild sages and grasses?
Could Alfalfa and
Dandelions be friends? Both are edible. Both have
roots that dig deep for nutrients. Our neighbors have an alfalfa patch that just won't die. A couple times a year, they bring in a pair of young bulls to graze it short in the period of 2 or 3 weeks (and thus fertilize it, too). The effect is noticeable, but what I notice is the increasing density of dandelions.
I have 5-7 years to wait before I can experienced with a thinning alfalfa cover of my own. I look forward to leaving a small section of that indefinitely and seeing what nature does with it.