▶ Evaluating Nutrient Removal in Wisconsin Alfalfa Fields

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All right.

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Thank you very much, Melissa.

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Kevin, well done setting us up on the the

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alfalfa topic for today.

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Thanks everyone online for being here today.

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I am very excited to kind of introduce and and present and provide an overview

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on this this project that a number of people have been working on.

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So the title of the talk is actually the title of a, a,

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a research proposal that we submitted to the Dairy Innovation Hub last fall

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through their short term high impact grant program.

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Long story short, research team gets a year to go and, and,

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and do a thing in the field and, and come up with some pretty impactful

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results.

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And so we were lucky enough to be awarded with some, some funds to do this work.

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So really what we’re going to be focusing in on today is looking at alfalfa

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nutrient uptake and alfalfa nutrient removal rates.

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So how much nutrients is being removed per one ton of alfalfa dry matter?

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Also right off the top, like to thank Co-PIs Doctor Marta Kohmann

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and Luanna Queiroz for their support in this project.

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OK, let’s see here.

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Here we go.

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All right, so our game plan today, I’m gonna,

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I’m gonna spend a fair bit of time just kind of walking through the background of

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of where this project came from, what we’re doing, why we’re doing it,

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how we’re doing it.

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And then I’ll give you a quick sneak peek at some preliminary results.

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It is by no means going to be a thorough overview of all the information we’ve

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collected, but we only have 25 minutes to air today.

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So we’ll take what we can get and then I’ll leave you just kind of with what are

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with what are game plan is on the project moving forward.

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And so, so why, why do this alfalfa nutrient removal

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assessment project?

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Why, why are we doing that now?

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So rewind the clock back to last summer and last fall, a team of us here at UW,

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we’re working through updating the corn and soybean grain phosphorus and

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potassium soil test interpretation levels, P&K removal rates in those crops.

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So how much P or K per bushel of grain and then ultimately the fertilizer

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recommendation rates for those two crops.

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So we were working through that meeting with different stakeholders and partners

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and, and, and audiences such as those in the venue

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here today.

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And, and almost every time we gave the, the presentation where we, we,

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we updated these corn and soybean things related to P&K,

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it almost never failed.

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We would get a response such as cool, when are you looking at alfalfa almost

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like, you know, copy that.

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Great.

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That’s all fun and fine and dandy.

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Let’s talk about alfalfa.

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And sidebar, corn silage is another crop of interest

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by folks.

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So specifically when folks are asking us to, you know,

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consider looking at updating or at least evaluating some of these nutrient

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removals and soil test levels and things for, for alfalfa,

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really where where a lot of people were focusing was on potassium.

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A lot of sentiment from, from the last fall discussions and

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presentations as well as the previous eight years of,

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of my professional journey working at a soil testing lab in my previous life.

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A lot of folks that that I would talk to and work with,

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with their soil test results that are, that are trying to manage alfalfa fields

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are just struggling with potassium management.

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And specifically, you know, folks that were,

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that were trying to apply university recommended potash rates to either build

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or maintain soil test potassium and they were just struggling to do so.

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And so there, there were some questioning as to whether

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these removal rate assumptions that are built into the UW fertilizer guidelines

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are still accurate.

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They’re reflective of reality.

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So we’ll cover more of that.

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And so I guess the answer of when are you looking at alfalfa,

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I guess that answer is now.

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Again, hat tips, shout out and much appreciation to the

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Dairy Innovation Hub for their support.

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So we’re going to go through here what is being done, how it’s being done.

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And then also I really want to give a shout out to the who and where the work

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is being done.

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So to kind of start off early this growing season 2026 prior to alfalfa

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growth really ramping up for the year for first crop,

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we are our project collaborators, partners if you will,

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went out to the farm fields that were identified for the project and collected

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a zero to 6 inch soil fertility sample.

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We we were just trying to document current fertility status in these fields

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prior to rapid nutrient uptake by the alfalfa crop.

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So this is kind of a baseline soil test then that the number 2 here.

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So just prior about three to five days prior to the farm taking first, second,

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third, fourth, in some cases 5th crop later on here as

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the as the fall comes in our, our partners,

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the project collaborators are going out to these farm fields and collecting

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alfalfa biomass samples at a 2 inch cutting height from a defined area.

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Some, some cases it’s three square foot, 3 1/2 square foot, 4 square feet.

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This kind of depends on the equipment that that the partner has.

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And so by collecting that fresh biomass in a defined area,

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we are able to determine fresh yield per acre, if you will.

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So after collecting those alfalfa biomass samples,

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they’re sent off to Dairyland Laboratories in this project’s case where

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we are getting that alfalfa tested for moisture content and total nutrient

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analysis.

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So phosphorus, potassium, calcium, magnesium and a couple other secondary

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and micronutrients.

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And so the number four, once we have now dry matter yield and

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nutrient concentration, we can determine total nutrient uptake by

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that alfalfa crop on a per acre basis.

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And then at least personally, most interestingly,

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we can look at alfalfa nutrient removal rates.

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So how much phosphorus per ton of dry matter was taken up or how much potash

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per ton of dry matter was taken up.

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And those are some of the pieces of information that we need to evaluate the

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current university fertilizer recommendations.

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OK.

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And then lastly #5 what we’ve been doing along the way is,

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is compiling all of this data from across the study.

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We’re, we’re trying to share things back with

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our project partners and host farms kind of on the fly.

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And we’re evaluating some of the data as we go.

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But the one thing, the one, you know, focus thing that we’re really trying to

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do throughout this project in, in this on farm research project is to

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have timely results sharing.

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And so we’ve got an effort where once all of the information comes back from the

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lab, say for first cutting, we compiled all of the first cutting

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alfalfa data, soil sample data and created a field

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summary report and that we would send back for a particular farm and field.

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And so that report we show the field average yield, nutrient concentrations,

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nutrient total uptake and then nutrient removal rates.

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And it would also show their field averages right next to the whole project,

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the study wide averages, if you will, just as a point of comparison to other

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alfalfa fields in, in the state.

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So just a, a quick snapshot of how we’re doing this

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data collection, this sample collection.

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So on the left, you’ve got that black, black square there that’s representing an

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alfalfa field.

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And then you you see 3 little green squares randomly placed throughout and

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those are identifying or representing those three random sampling points.

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So starting back at just prior to first crop being cut by the farm,

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the project partners’ boots on the ground help here went out and identified 3 sub

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sample locations and they either flagged them or GPS referenced them.

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And so every subsequent cut throughout the rest of the growing season,

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they would go back to those same 3 points and take that cutting sample.

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So we’re collecting biomass from approximately the same three parts of

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that field all season long.

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And then just to note on the soil sampling,

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the preseason or the early season soil and the postseason soil will be collected

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the same way where 4 cores are being collected around each of those 3 alfalfa

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sampling points.

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So 12 total cores being collected from across that field and those are being

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mixed and composited and sent off to the lab.

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So the objective by doing some replication and spreading things out a

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little bit is to capture some real world variability in yield and soil conditions

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and nutrient uptake and so on.

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This is my favorite slide in the entire presentation.

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This really does a nice job showing how collaborative this project has been.

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You know, I’ve been in the trenches behind the

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scenes on this project since day one, and it wasn’t until I really started kind

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of mapping this out and putting some numbers together for for you all today

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that I just really realized how many different people and farms are involved

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in this project.

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So the stars that are on this this map here, this Wisconsin counties map,

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what this is indicating is, is if a county has a star in it,

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that means there’s at least one field, alfalfa field being sampled as part of

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this project.

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I counted these yesterday, 10, 15.

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I there’s 21 counties being represented in this project,

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So very wide geographic coverage.

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All right.

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So the kind of the breakdown here, we have soil and alfalfa samples being

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collected from 53 unique fields on 40 individual farms by 17 different people

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from 7 different organizations.

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OK.

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So there’s, there’s again a lot of moving parts and a

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lot of people involved in this effort.

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Of the 40 individual farms, 38 are real working farm,

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two are just pretend agricultural research stations that the university

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manages.

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I’m just kidding.

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So Ashley Blackburn and Mike Bertram, if you’re watching, I’m just joking,

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2 university farms also participating in this effort as well.

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So again, a a good variety of management, soils, environments,

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so on and so forth being represented.

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Of course, we’ve got university extension staff

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involved.

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This is our boots on the ground people.

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So extension staff, county land and water departments have

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folks out there and a couple independent consultants from the state as well.

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We have a formal partnership with the Wisconsin Alfalfa Yield and Persistence

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program that Mike Bertram facilitates.

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I think they’re in their 20th year if I’m not mistaken.

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They’re sampling alfalfa on a much larger scale where you know, say pick,

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pick an alfalfa field, every wagon or every chopper box,

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what have you comes off that field is getting weighed.

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They’re taking a grab sample from those, from those wagons and sending that to the

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lab for forage quality.

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In this WAYP program this year, we’ve asked, hey,

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can we provide funding to have you add the, the nutrient analysis that,

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that we need to determine total nutrient uptake and all those things.

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So we’ve been able to, to partner with, with that program and we’re very thankful

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for that opportunity as well.

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And the last partnership I want to highlight, so Drs. Marta Kohamann,

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Brian Luck, Francisco Arriaga and probably a couple

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others that I ought to know off the top of my head.

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I’ve been working for several years doing a lot of research in the effect of

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machinery traffic, i.e. compaction on alfalfa production.

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Again, the, these funds from Dairy Innovation Hub and

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this project are able to then support those efforts to get a nutrients analysis

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tested from those research plots.

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And so they’ll be able to look at the effect of machinery traffic and soil

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compaction on alfalfa and nutrient uptake.

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And I think that’ll be a really powerful add for for them and for for this project

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as well.

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So again, just thank you right up front here to all

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the different people and farms, host farms that are involved in this

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project.

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So, all right, so that’s kind of the the quick elevator

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over elevator pitch overview of the project.

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I’m just going to show a little bit some of the preliminary results.

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My disclaimer here because the project is only part way through,

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everything here is subject to change, whether it’s a number,

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an approach that we’re taking to analyze the data, so on and so forth.

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This is very preliminary and it’s certainly not going to be a comprehensive

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overview of all the data today.

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We’re just going to zoom in on potassium.

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So just step back a minute and think about how does this project tie into

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potassium management in alfalfa in general?

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So if we ask the question, what goes into an alfalfa hay fertilizer

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recommendation today in Wisconsin, kind of a three-part equation.

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So the first step is having a soil test and we interpret that soil test and we’re

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going to be looking at something very low through excessively high.

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All right.

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And depending on where that that soil test K level is at,

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our approach to fertilization changes.

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And so in Wisconsin, we use a philosophy that has three

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different components.

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1 is a, a, a build where we’re trying to build soil

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test levels from something that is low or very low up into that optimum range.

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We have a maintain approach.

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So if we’re testing in that optimum range, our objective is to stay in that optimum

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range.

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And so we’re going to fertilize really just that expected crop removal of

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potassium.

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And the, the, the assumption there is that if we just

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apply what the crop is going to use, our soil test level shouldn’t change much.

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We should stay in that optimum range.

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And then if we’re testing high or very high,

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we we have a drawdown approach where we’re still going to apply a little bit

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of potash or potassium, whatever your source is,

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but to a lesser extent than full crop removal with the objective of slowly

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drawing that soil test level down into that optimum range.

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OK, so soil test starts us off.

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Then the second piece is we want to have some realistic yield goal assumption

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being made.

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So is this a, a two or three ton system for the year?

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Is it a 5 or 6 ton across all the cuttings for the year?

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What do we think we’re going to realistically get?

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And then what’s really relevant for today is,

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is what I’m calling this K2O removal assumption.

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So again, how many pounds of of potassium are we

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removing per one ton of dry matter yield produced?

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And so currently in our university guidelines,

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we have an assumption of 60 lbs of K2O being removed per one ton of alfalfy dry

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matter.

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Doctor Marta Kohmann, Co-PI on the project,

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has some some other data from the state unpublished preliminary kind of

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observational from the Prairie du Sac and Arlington areas.

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If I’m recalling correctly, where they they saw these removal

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coefficients or removal rates ranging from 74 to 81,

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so a little bit higher than what’s currently in the university guidelines.

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And so, so in for, you know, this is specifically what we’re really

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trying to address on the potassium end of things in this study is,

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is that assumption of 60 lbs of K2O per acre still reflective of reality on

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working alfalfa farms across the state because and,

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and we’ll come back to it later, this crop removal piece.

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So the yield times, the amount of K removed per unit of yield,

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that’s the single biggest chunk, if you will,

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of the total application rate recommendation.

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If we’re trying to build soil test levels up,

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it’s the crop removal piece plus maybe 30 to 45 lbs or 45 to 60 lbs extra.

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But that crop removal piece is a really big deal.

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It’s a huge component.

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So it’s in our best interest to kind of have a good understanding of what reality

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is.

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And so diving into some of the some of the relevant info to to address that

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today, just give you an idea of the the yield

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that we’re seeing in the project.

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So from the first crop we had 35 fields were sampled that we’re including in

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today’s data set, 114 total samples being represented here.

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The average yield, dry matter yield was about two ton per

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acre.

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And I have this thing called the typical range that’s this is the middle 50% of

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the data.

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So across all 114 samples, the middle 50% yield range from 1.66 to 2.

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36. 18:23 -> 18:26
    And, and so you can, you can see the range we have some lower

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yielding environments, some higher yielding environments.

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And I should also note that none of these are first year or seeding year alfalfa

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stands.

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These, these are all at least in their first

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full production year or older.

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I’ll throw that out there as well.

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2nd crop.

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As expected, we see the the average dry matter yield a

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little bit lower than first crop down to about a ton and a half of dry matter with

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a range of 1.1 to 1.7.

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You’ll notice that the number of fields and the number of samples included here

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are lower than from first crop.

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One of the realities with on farm research is that you can make a plan and

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you think you’re going to get out there and get your sampling done or your

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treatments applied or whatever the thing is.

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And then life happens.

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Reality on the farm happens, schedules get busy,

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communication breaks down.

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We’re not going to cry over spilled milk.

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This stuff happens in on farm research.

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So we just we missed a few a few sampling windows before,

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before the field had to get knocked down and and hay had to get made.

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So that’s why those numbers are a little bit different.

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OK, so diving into the the this K2O removal

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coefficient or these removal rates again A28O9 currently has an assumption of 60

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lbs. per ton.

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Looking at first crop, we see the average across all fields and

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samples.

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The average was 73 lbs per ton and that typical range again that middle 50% was

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63 to 82 OK for second crop.

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The average was 80 lbs per ton with a range of about 70 to 90.

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And so and then the average across both both 1st and 2nd crop was 75 ± 10.

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OK.

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So one other interesting thing that I’ll note here.

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We’re talking averages and these typical ranges and all that.

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One of the things that’s commonly done certainly in the corn and soybean world

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when we’re talking about these removal rates,

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but I think it’s also happened in in this alfalfa space as well,

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is that researchers doing this kind of work will, will,

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will use the what we call the 75th percentile of,

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of observed values when they publish or or put a number into their recommendation

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system.

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So what that means, go ahead, Melissa, 5 minute warning for you.

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Copy that.

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Thank you.

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So what that means if you look at that middle 50% number,

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that typical range of say 85 here in the middle, that is the 75th percentile,

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meaning 75% of observations have a removal rate below that and 25% of

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observations in this project have a value higher than that.

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And and a lot of times the justification for using that number rather than the

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average or some other lower number is to really avoid under fertilizing these

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valuable crops.

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So just wanted to kind of drop that out there.

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But nonetheless, it’s looking like reality is a little

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higher than what’s currently on the books.

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This will maybe not be a surprise to some folks.

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It turns out that soil test potassium is driving a lot of the variation that we

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see in these removal coefficients across the farms in this study.

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So what I’ve done here, you have soil test potassium on the

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horizontal axis and that potassium removal coefficient on the vertical axis.

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That dashed horizontal line, that Gray horizontal line at 60 again is

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the university assumption of of 60 lbs per ton.

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You’ll notice there’s a lot of observations above that 60 lb per ton

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line.

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And and as soil test levels increase, that removal rate generally increases as

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well.

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So interesting trend that I thought I’d point out.

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And, and if we simplify that a little bit, if we take those soil test potassium

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numbers and put them into kind of grouped interpretation classes.

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So I put the very low and the low testing fields in one,

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one bucket here on the left.

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The optimum and high are all grouped together in the middle and then the very

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high and excessively high on the right.

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And you can see that those average removal coefficients are in fact

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different between those soil test interpretation classes.

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And so I think there’s a couple of things that we need to be considering whether

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that’s us as researchers, y’all as farmers or consultants,

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advisors to the farm.

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You know the question that I’m asking and that we’ll ask here internally as we as

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we continue going down this, this path is should we be using different

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removal rate assumptions depending on the field, soil test, potassium level and,

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and to kind of maybe a get at why we might do that is just a really quick

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walkthrough example.

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So what we’re going to do in this little exercise,

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we have a 5 ton yield level and we have 4 different removal rates,

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potassium removal rates along the top ranging from 60,

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our current assumption up to 90, this number 300, 350, 400 450,

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that would be the estimated total amount of K2O removed per acre at those

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different removal rates.

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And then below that is for loamy and sandy soils,

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the expected change in soil test potassium given that five ton yield and

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those different removal coefficients that total K2O uptake.

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And so the point that I’m trying to make here,

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accurate assumptions of K removal in our fertilizer fertility programs is

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extremely important for managing K inputs.

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You can see that we could be seeing a either a 46 or almost a 70 part per

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million reduction in soil test K in one season, depending on which number,

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what removal rate assumption we make.

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All right.

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And again, this this crop removal is the biggest

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single chunk of a fertilizer recommendation.

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And so it’s in our interest to at least be less wrong if we can be.

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So just wanted to kind of show you some of that as as we kick this project off.

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So next steps, keep keep collecting data and compiling

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everything.

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We’ll get postseason soil sample to look at how soil tests responded to that crop

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being produced and any inputs that happen throughout the course of the growing

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season.

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Of course, we’ll look at all of the other nutrients,

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not just potassium.

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We also are going to be asking the the farms to fill out field and management

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survey surveys so we can have all those other little Nuggets of information that

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could potentially help explain what we see.

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And, and so like I said, this project will formally wrap up into

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the calendar year and then there’ll be a lot of outreach and conversations

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happening beyond there.

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So I just want to again, thank the Dairy Innovation Hub for their

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support of this work.

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Doctor Marta Coleman and Luanna again for their support behind the scenes.

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A huge thank you to all of the host farms that are allowing this work to happen.

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And then I wanted to leave on screen by name,

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all of the people that are the actual boots on the ground,

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pulling these samples, maintaining those relationships with our

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host farms, making sure information is getting back

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to them or from them back to us behind the scenes.

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And so huge shout out to all of you.

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None of this would happen without you.

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So with that, thank you so much for your time.

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And I’m also happy to take any questions if we have any.