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Thumb of Michigan | Well, it depends on soil type, moisture, time & weather conditions.
See the worksheet that Dan Undersander and others put together out a couple of years ago on auto toxicity.
Here's what I do planting alfalfa on alfalfa.
My CEC numbers are around 5-7 (higher numbers take more time). I cut and take the crop by the 1st of June, spray RU around or shortly after the 15th. Spray RU again around the 10th of August, plant 12-15th of August. All no-till, shoot for 16-18# of actual seed per acre. Have been doing this for years (20+). With a fall kill, I would re-plant HERE. I've experiment enough with MY fields to be comfortable doing this. YMMV.
Presently my oldest alfalfa field was planted in 2010, still has 50% alfalfa (OG is the major grass). This field is producing my highest dollar hay (selling last year's 3rd cutting for $12 a bale at local feed store). A mixed hay sells better most year around here, straight alfalfa is sometimes tough to sell.
The worksheet told me that I could plant as early as 2 weeks after killing IF I got a decent amount of moisture (to flush auto toxicity down/out of the soil). Now, if I tilled the ground, that would change the flushing structure (IMHO, MSU disagrees with me). Re-mixing the auto toxicity back to the top of the soil plus horizontally. My understanding is auto toxicity is greatest within 8 inches of old plant.
If the following links to the spreadsheet doesn't work, e-mail is in my profile; I'll send the Excel risk spreadsheet if desired.
https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Ffyi....
https://fyi.extension.wisc.edu › forage › files › 2014 › 01 › autotoxicity_worksheet-2.xls | |
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Reseeding hay into old hay field
