How to control Birds foot trefoil

Question: Birds foot trefoil is invading my savannah restoration project.
This article implies that birds foot trefoil can be "controlled" by  "controlling nitrogen levels in the soil."
https://extension.umn.edu/weeds/birdsfoot-trefoil?fbclid=IwZXh0bgNhZW0CMTAAAR2G_1uP2omsTfJytrMltiRS99lpW2ZTvVptqVHzlyjtL6fi5VPuVt-uTmg_aem_E55q2G5zu-NAwG-limrYpw
Could you, please, point me to the research showing what "level" of nitrogen they mean?  what type of nitrogen was used?  Frequency, etc?
The study was probably done on turf, but I'd like to try it on my 4 acre native area 
I see no other choice.

responder: MaryKay, Master Gardener, Tree Care Advisor Replied July 05, 2024, 9:10 AM EDT
response: The article you referenced is saying that keeping nitrogen soil levels high is a preventive measure not a treatment.  It’s meant to prevent further spread and support natives. Low nitrogen levels do not support natives and encourage trefoil to spread among the natives.  It is not a treatment to eradicate birds foot trefoil.  Treatments are described in detail at the first website below.  You may also want to do a soil test.  1. https://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/birdsfoottrefoil.html 2.  https://soiltest.cfans.umn.edu/

responder: The Question Asker Replied July 05, 2024, 9:36 AM EDT
response: Thank you.What is the "high" nitrogen level that is needed for prevention?  For sure, I want to keep it from spreading. Is there anyway you could share the link of the study that was done, with the scientific detail? Thank you.   On Fri, Jul 5, 2024 at 8:10 AM Ask Extension <<personal data hidden>> wrote:

responder: MaryKay, Master Gardener, Tree Care Advisor Replied July 05, 2024, 12:24 PM EDT
response: The above website is not a study/research report.  It is an article for publication.  Scientific studies are mostly related to growing birds foot trefoil as a foraging crop. In this capacity as a legume it improves soil by adding nitrogen.   You can google using “birds foot trefoil prairie eradication research site:.edu”.  Mostly you will get foraging studies. Here is an example of what you will get that is not a foraging study:https://accs.uaa.alaska.edu/wp-content/uploads/Lotus_corniculatus_BIO_LOCO6.pdf  The means for control from the scientific literature are:  1. Mowing it low to prevent seed development, usually recommended at 2-3”  This will not work in your prairie because it will also prevent the desirable plants from developing. It does work for lawns.  2. Digging it out.  This is the preferred way in the study stated above. It might take a few years but it overcomes the problem with mowing because it removes the undesirable plant and gives you the opportunity to fill the space either through natural spread or seeding with desirable plants.  3. Use of chemicals.  This will be difficult to do without destroying the other desirable prairie plants.  Early in the season you may be able to isolate the birds foot trefoil enough with bottomless a coffee can or other devise to use a chemical effectively.  The danger is that it may kill some of the desirable plants.  4. Fertilizing the prairie to increase the nitrogen without removing the birds foot tree foil will not work because it will also boost the birds foot trefoil growth.  On the other hand nitrogen fertilizing a lawn will increase the turf capacity to crowd out the birds foot trefoil.  But it will not eliminate birds foot trefoil, just give it less space to invade and  make it easier to use other control methods.  This is what I hear you suggesting—I want to see the research that says increasing the nitrogen will help me manage the prairie.  You can’t take a recommendation for turf and apply it to a prairie for all the above reasons.  The statements in the article you reference are for lawns not prairies. A turf with soil that is high in nitrogen—think well fertilized grass with added nitrogen-will promote thick grass to crowd out birds foot trefoil.  When farmers grow birds foot trefoil for forage they are adding nitrogen because legumes, such birds foot trefoil, fix nitrogen in the soil.  They are promoting birds foot trefoil not eradicating it.  Don’t be confused by this research.  However it does inform those scientists who are working on eradication. I hope this I helpful. Some people are misinformed when they think establishing a prairie is a simple project. It takes work.  My 10 acre 25+ year old restored prairie is less work now. But it took a few years to get it established. Best wishes for a successful endeavor.

responder: The Question Asker Replied July 07, 2024, 8:17 AM EDT
response: Thank you for this thorough explanation.Patsy   On Fri, Jul 5, 2024 at 11:24 AM Ask Extension <<personal data hidden>> wrote:

responder: MaryKay, Master Gardener, Tree Care Advisor Replied July 07, 2024, 8:29 AM EDT
response: You are welcome.