▶ Can Clover Cover Crops Provide Nitrogen Credits to Corn?

0:05
All right, thank you very much, Jerry.

0:06
Yes, well done on the weather report.

0:09
We’re we’re going to go ahead and do a hard gear shift here.

0:13
Like Jerry mentioned, we’re going to start zooming in talking about cover crops.

0:17
So whether we can believe it or not, it is early to mid-july already and that means that in the next four to six weeks we’ll have a fair bit of of small grain acres being harvested, processing crops being harvested.

0:33
And so kind of our first big kind of post harvest cover crop establishment window of the year.

0:39
And so we thought this would be a really good time to plug in a cover crop talk and specifically a Clover or maybe more broadly legume cover crop talk as summertime is a really good opportunity to get them established.

0:53
So as I titled the, the, the presentation today with a question, can Clover cover crops provide meaningful nitrogen credits to corn?

1:02
We’re going to spend some time on this path to, to an answer to that question.

1:08
And so to get started, we’ll, we’ll kind of just highlight overview what is a nitrogen credit?

1:13
How do we get one?

1:15
And really importantly, why do we care about this, this concept of nitrogen credits?

1:21
We’ll also kind of highlight specifically how cover crops tie into this nitrogen credit topic.

1:27
We, we typically don’t think of cover crops first when we think nitrogen credits, but we’ll, we’ll tie that in.

1:35
We will also look specifically at, at a project that wrapped up last fall.

1:41
And then we’ll highlight some other data in the state that can really give us some information on nitrogen credits from different legume cover crop species and what kind of put a bow on everything with some practical takeaways, both from the research we’ll talk about today as well as some other existing information available to you.

2:02
So a very basic definition of a nitrogen credit, it is the amount of nitrogen or N that is provided to the current cash crop by a previous organic nitrogen source.

2:15
All right.

2:16
And and so it wouldn’t be a good nitrogen talk without spending the next hour I think Jerry told me I have on the nitrogen cycle, just kidding.

2:26
We’re going to zoom in on some of the below ground aspects just for a few minutes of the nitrogen cycle when we’re thinking about nitrogen credits and what they are and how we get them.

2:37
So typically when we’re when we’re thinking about nitrogen credits where we’re really focused on generally manure.

2:45
So we’ve applied some manure.

2:47
How much nitrogen do we think we’ll get out of that manure application for my next crop?

2:53
We also think about this quite a bit in forage legume scenarios, such as alfalfa or a stand of Clover, something that’s been out there for 2-3 years, so on.

3:04
And so why, why legumes?

3:06
Why do we talk about N credits in the legume space, whether that’s forage stand or or cover crop stands?

3:14
So legumes do this really cool thing where they form symbiotic relationships with with soil rhizobia that’s fixed atmospheric nitrogen and then assimilate that nitrogen into the plant biomass.

3:28
And so then when that plant biomass is is is terminated via chemical termination, tillage incorporation, etcetera, that crop has a relatively low carbons and nitrogen ratio.

3:41
And, and So what that means is that as this, this underground nitrogen cycle starts to happen is our, our soil microbial communities start to break down that biomass, the, the nitrogen that’s in that biomass is readily available, generally speaking to the next crop.

4:00
It doesn’t get tied up in that, that breakdown process like it might if it, if those microbial communities are trying to break down something like oat straw or corn stover stuff with a lot more carbon relative to nitrogen.

4:14
And so again, we’re, we’re kind of zooming in on manure and legumes the, the, the big, the big problem right off the bat though, right, if we’re thinking about next year’s corn crop following these organic sources of nitrogen is that organic and is not, is not plant available.

4:29
So we need those microbial communities to break down these materials and convert that organic nitrogen into the plants available forms like ammonium and nitrate.

4:41
In addition to needing those microbial processes to occur underground, we also need them to occur kind of in a, in a timely matter, right.

4:51
So we we need that that biomass or that manure, whatever that organic source is to be decomposed and that nitrogen conversion process to be complete before say next year’s corn starts to take up nitrogen rapidly.

5:08
But we also don’t want it to occur too early.

5:11
We don’t want that nitrogen to be sitting in the soil profile as nitrate too early relative to corn crop end demand because then we’re more susceptible for that that end that was made available to be lost via leaching or denitrification or immobilization and and other ways.

5:29
So really I just wanted to highlight what kind of needs to happen to these previous maneuvers or previous legumes to get that nitrogen available.

5:38
And so again, back to nitrogen credits here.

5:41
Why do we care so much?

5:43
All right.

5:43
And so the whole point of of talking about nitrogen credits is, is that we take the credit, we call it taking the nitrogen credit.

5:51
And so by by accounting for this credit, subtracting it off of our, our base fertilizer rates that we intend on applying it, it results in reduced end fertilizer application rates that we need to use fertilizer for, which is an economic benefit to us.

6:10
It taking these credits can improve fertilizer and use the efficiency of what we do apply and it ultimately reduces our negative impacts on water quality.

6:20
All right, So what’s kind of where the credits come from?

6:24
This is kind of why we care.

6:26
Now we’re, we’re going to zoom in and we’re going to spend a fair bit of time on this the rest of the day today, how we calculate these credits.

6:32
All right.

6:33
So this is likely familiar to to most folks, but we’re going to set the stage up with a, a classical end response figure here.

6:41
So on your horizontal axis, you’ll see nitrogen fertilizer application rate in pounds per acre.

6:48
In this example, we have nitrogen rate going from zero to 250 lbs per acre.

6:54
And then on the vertical axis, you have corn yield in bushels per acre.

6:58
And so we see corn yield increases as end rate increases up to a point corn yields flattens off.

7:04
OK.

7:05
So in this nitrogen credit discussion, we, we, we can use this yield response information to help us calculate the credit.

7:13
So again, in this example, you have two different colored lines.

7:17
The black line is representing corn yield response to nitrogen fertilizer rate when that corn did not follow a previous legume and the red is corn yield response to nitrogen fertilizer when corn did follow a previous legume.

7:34
OK.

7:35
And so you can see visually there’s something different about these two environments, these these two yield responses.

7:42
And so if we can apply some statistics and determine a few characteristics of each of these curves, that can help us calculate well what was the credit from the legume in this example.

7:54
And so the way that that we’re talking about nitrogen credits and how we’re calculating them, we’re using what’s called the difference method.

8:03
And as it’s the difference between what you’re thinking, it’s the difference in the economic optimum nitrogen rate for the EONR between the corns following no legume and the corns following the legume.

8:17
OK.

8:17
And that EONR is the rate where economic return to the applied fertilizer is maximized.

8:23
So here in in this concept EONRs where ROI from that nitrogen application was maximized.

8:31
All right.

8:31
So in this example, corn following no legume, the EONR was 150 lbs per acre.

8:38
Corn following the legume was 125 lbs per acre.

8:42
So using the difference method, our nitrogen credit is 25 lbs per acre.

8:48
And so zoom back out now we know how to define and calculate a credit.

8:54
How do we do this?

8:56
So what, how do we use this?

8:58
So again, I, I, I hinted at it before or earlier on this slide, but again, if in this environment, in this example, let’s say that our normal business as usual nitrogen application rate that we plan to apply is 150 lbs event per acre corn following in this case winter wheats a small grain.

9:20
If we have information be that through on farm research or through university guidelines or, or other experiences and we have an idea of what that credit might be, we should take that credit and subtract that credit off of that base rate.

9:35
So in this case, 150 was our base recommendation.

9:40
If we if we knew, if we had a good hunch that we were going to get 25 lbs and then we would have subtracted that from 1:50 and applied 125 lbs and to the field, right.

9:50
So taking the credit is a big deal.

9:55
So Speaking of some information that that is available to you currently in A2809, our state fertility guidelines, we have this table, it’s table 5.5, the kind of what we call the new A2809 version online.

10:12
It’s table 9.5, I believe from the 2012 version of A2809.

10:18
But this table, this is about nitrogen credits from green manures and and so you’ll see you’ve got different legume crops.

10:25
You have alfalfa in there, red Clover, sweet Clover, Crimson and vetch.

10:31
The The idea here is that these legumes were planted the season before corn and then terminated and incorporated before corn was planted.

10:40
And so current guidelines based on research suggest that if these legumes had less than 6 inches of growth at the time of termination or incorporation, you would take a 40 lb credit.

10:54
If you had more than 6 inches of growth, you’ll see a range.

10:57
And, and those the numbers in that range are higher than that 40 LB base credit, generally speaking.

11:03
And, and so there, there’s some other new ones that, that you can certainly read about in A2809 on which end of the range to use.

11:09
But there’s 1 Clover missing from this table that we’ve, we’ve been working on in the background over the past few years.

11:17
And, and that’s where we’re going to segue to now.

11:20
OK.

11:20
So again, we’ve we’ve talked about what a credit is, where it comes from, how to calculate it, some existing information.

11:27
We’re going to add some new information that’s available to you all.

11:31
So Berseem Clover this, this is the the unveiling year of some Berseem Clover work that’s been going on typically doing this nice using credit work in the cover crop world.

11:44
We’re targeting field with a small grain crop, the head of corn.

11:48
So, oh, it’s winter wheat, rye for grain processing crops you could throw in here.

11:53
Really what we’re after is that earlier cover crop planting window.

11:57
So we can get these clovers pounded in the ground as early as possible so we can put on a good biomass.

12:04
All right.

12:04
So, you know, we’re not going to spend a ton of time on, you know, all of the goals of all different cover crops.

12:10
But when we think about these legume cover crops, some of the the goals that we’re that we’re after in using them late summer through late fall ground cover living roots.

12:22
So we’re getting some of those soil health and soil conservation benefits throughout the fall.

12:27
A lot of them will winterkill, some of them may overwinter.

12:31
Generally we’re looking at fall soil health benefits.

12:34
But really one of the primary goals is what you’ll hear called growing our own nitrogen, right?

12:39
We’re after these nitrogen credits.

12:41
So it’s all about pumping biomass before that winterkill and dormancy.

12:45
So going into this Berseem Clover research that that we’re going to step into here in just a minute, 2 primary questions that that we set off the answer #1 how much nitrogen can Berseem Clover provide to corn?

13:00
And #2 does Berseem Clover cover crops affect corn yield for the better or for the worse?

13:07
OK, so let’s go ahead and dive in here.

13:11
So this this is some work that was done in northeastern Wisconsin.

13:15
Hat tip right off the bat to Kevin Jarek and Scott Reuss.

13:19
They are our local regional crops and soils educators up in this region.

13:25
They sought the farmers and the crop consultants that were curious and asking similar questions.

13:31
They did most the field work, data collection, so on and so forth.

13:34
So a huge thank you to them.

13:35
Shout out to Dan Marzu for extra field help in the field.

13:39
And then thank you, Dr. Matt Ruark for helping support this, this project with some funding and a harvest group.

13:47
Obviously huge shout out to our host farms for letting us bother you for a year and a half.

13:52
So what do we do here so that the timeline of a, of a project like this?

13:56
We, we’re starting off in this case, August, about August 15th through September 5th, just depending on the farm.

14:03
Again, there’s five farms represented here is when we established the cover crop.

14:08
So in each field we had strips of receding Clover and then we managed and maintained strips of just winter wheat stubble and winter wheat regrowth.

14:18
So you have strips of both.

14:21
Fast forward to November of 2024.

14:24
Right before that killing frost is about a week before the gun beer season.

14:28
Scott and Kevin went out and collected the above ground receding Clover cover crop biomass samples so we can understand how much biomass that we get out there.

14:38
Fast forward to spring 2025, all the bursting Clover winter killed generally have a mat of dead bursting Clover on the ground.

14:49
Corn was planted across the entire field.

14:51
So again corn was planted in the no cover crop strips and in the bursting Clover cover crop strips.

14:59
Fast forward about another month, we get to June and we that implemented our nitrogen rate study over the top of those cover crop treatments.

15:08
And so we ended up pardon me, we ended up applying 6 different rates of N 0 to 250 lbs of nitrogen.

15:16
And and so now what we set up is the ability to have corn grain yield response to nitrogen fertilizer when corn followed goes the bursin Clover and no cover crops.

15:27
So you have that comparison to determine the credit.

15:31
And then of course, we hurry up and wait patiently or or maybe not till fall to harvest the grain.

15:37
So here’s just an example of what one of these fields looks like, kind of the the study design.

15:44
Those green strips are your perceive Clover.

15:47
There’s four of them typically on most of the farms.

15:51
And then that yellow, brown, orange color, whatever that is to you.

15:55
That’s your no cover crop strip.

15:56
So just an example of what this looks like out in the field.

16:00
OK.

16:01
So what did we find with Berseem biomass, Berseem Clover biomass?

16:06
So again, we planted these mid August to early September, harvested and then subsequently winter killed mid November.

16:16
We had a wide range in biomass across the five farms.

16:20
We have one location on the left.

16:22
It’s hard to see, but there’s a deer hoof in the picture.

16:26
We, we had very little biomass accumulation at this site at the time of sampling.

16:31
Turns out deer love Clover.

16:33
So if you’re a food plot enthusiast, by all means, bracine is for you.

16:37
But then we had two locations here, what we called moderate biomass, so about 1000 lbs ± 100 lbs.

16:46
And then we had two sites that had tons of Berseem Clover biomass.

16:51
So the one on the left just shy of two ton, the one on the right, just over 2 ton of dry matter out there.

16:58
So wide range in observation, some takeaways from, you know, we, we tried to look at, you know, OK, it’s only 5 farms, it’s only one year.

17:08
We had some other information at our fingertips, some soil test information trying to look at was there any trends that help explain why, you know, one location had almost none and two locations had a lot.

17:21
What was pretty, pretty evident in this small observational data set here is that soil test potassium and soil pH we’re highly correlated to perceiving Clover biomass.

17:32
So generally speaking, when soil test K was over 120 part per million, so kind of right in that optimum range or higher.

17:40
And when soil pH was managed above 6 three, we saw the higher biomass production.

17:48
So kind of makes sense.

17:50
We know that when we’re growing alfalfa or forage, you know, forage Clover stands, We know that potassium and pH are both important.

17:58
Interesting to see that translate into this cover crop setting where we’re just going for a couple months of growth.

18:03
So site selection matters, planting date also matters.

18:07
This was kind of just zooming out from this study in and of itself.

18:12
We just generally speaking, I think we get a little bit lots of days of cold when we talk about cover crop establishment after small grains because, you know, it’s like, hey, we got all fall in front of us to get these cover crops out there.

18:24
No hurry whatsoever.

18:26
And in reality, if we’re using these clovers, these legume species, they take some time to get out of the ground and get going.

18:33
So we should be chasing that combine or that harvest crew out of the field with the drill.

18:38
So, so planting day certainly matters in spoiler alert, more biomass means more higher nitrogen credits.

18:44
All right, so we’ll, we’ll get there in just a second.

18:48
Big picture again, looking across all 5 farms in this study, bursin Clover cover crops did not affect the corn grain yield.

18:57
So you’ll see the Gray bar is the average corn grain yield where we had no previous cover crop, and the red is the average yield across the all 5 farms following bursin Clover cover crops.

19:10
2 bushel difference.

19:11
They’re, they’re essentially the same number at the individual farm level, again across all nitrogen rates, just with and without covered crop.

19:21
Is the only comparison happening here?

19:24
No, No differences in corn yield at all.

19:27
A couple numerical differences, but nothing popping out as being practically different.

19:33
What I’ll mention is that at the 0 nitrogen rates, I don’t have the figure for this, but at the 0 nitrogen rates at three of the five locations we saw corn yield being statistically higher following bursting Clover than than the no cover crop.

19:49
The idea there is that in those low nitrogen supply environments though the nitrogen coming out of that perceived Clover is turning into yield and but not at, not at every farm, just that three of the five farms if we see that OK.

20:06
So what was the nitrogen credit?

20:08
So looking at this figure, it’s very, it’s set up very similar to the example I showed a few minutes back.

20:14
Berseem Clover did affect corn yield response and and we did see an average credit.

20:21
We saw a credit across all 5 sites averaged together here.

20:24
So Gray is the average corn yield response following no cover.

20:28
Red is that following Berseem And now to get into what the credit was, we’re going to pick apart these these curves a little bit.

20:37
Just interestingly, if we look at the what we call the AONR or the agronomic optimum nitrogen rate, this is the rate that maximizes corn yield.

20:47
Following no cover crop, we needed about 233 units of N Following Berseem, we only needed 179.

20:55
That’s usually if my mass is right, a 54 LB difference and, and, and we got the same yield.

21:00
All right.

21:01
So that’s interesting.

21:02
If we were shooting for Max yield, I’m really more interested in maximizing ROI.

21:07
So looking at E1R, you can see that we had an average 32 LB nitrogen credit when corn followed Berseem Clover.

21:18
OK.

21:18
So on the average 32 lbs.

21:22
However, I did mention that biomass matters.

21:24
So really quickly at that low biomass site where we had 160 lbs of dry matter, we did not see a nitrogen credit.

21:33
OK.

21:34
Those optimum nitrogen rates between the cover crop treatments are right on top of each other.

21:39
So no credit there.

21:42
At this moderate biomass site, about just shy of 0.5 ton, we see a 46 LB nitrogen credit show up there.

21:51
I’ll note that at the other moderate biomass site where we had a exactly 0.5 a ton, the N credit was 51 lbs per acre.

21:58
So pretty, pretty consistent observation there.

22:02
And then when we get to these really high biomass stands, right?

22:05
So this is the example of the 1.8-ton-per-acre we see something interesting.

22:12
So again looking at corns following noburseem that Gray line we needed 90 lbs of N to to maximize ROI that that 90 LB EO and are there that red line is flat.

22:24
So that that means that corn yield was not responsive to nitrogen fertilizer when it when the corns followed per seam Clover.

22:32
OK.

22:33
So all of the N that that corn needed was supplied by the breakdown of that per seam Clover biomass and other other soil supplied nitrogen.

22:43
OK.

22:43
So and then the other other high biomass that we had, it looked very similar.

22:50
The credit was 100 lbs.

22:52
So the corn following no cover was 100.

22:55
Corn following that 2.1-ton stand was 0.

22:59
So 100 LB credit from there.

23:01
So key takeaways here, bursting Clover doesn’t appear to be affecting grain yield up in the Northeast.

23:08
You have a stand, but it’s less than 0.5 ton.

23:10
Generally, we’re seeing 20 to 50 LB end credits.

23:13
When you have huge stands, credits are much higher.

23:16
So everything, it’s all about biomass.

23:19
OK, so that’s kind of the overview of this Northeastern study that we just wrapped up really quickly.

23:26
Matt Ruark and others about 10 years ago worked up a very similar study looking at N credits from Berseem clover cover crops down in Sheboygan County.

23:37
They found that that that any credit was typically between 15 and 40 lbs per acre.

23:43
So kind of right in with with what we observed.

23:45
The big difference down there is they, they saw a pretty consistent 13 to 15 bushel increase when corn followed the bursin cover crop compared to no cover crop just the week, the winter week as the previous crops down in the southwest part of the state.

24:02
This this little bit older information that Matt Ruark and Gym Studio summarized they they found average N credits to be about 20 lbs per acre with a menial yield increase as well.

24:16
All right.

24:17
So when we take the Northeast study that we went in depth on the the work Matt, Matt Ruark did 10 years ago and that that other Jim Stute and Matt Ruark effort, we put all those on, on the one slide here.

24:31
So there’s nine different observations that we have in total with Persine Clover cover crops.

24:37
The average is 42 pounds per acre.

24:39
OK.

24:41
Obviously, again, biomass growth matters.

24:44
So to kind of put a bow on on this here today, key takeaways for your planning over the next four to six weeks.

24:51
If you’re looking to to pound a legume cover or a Clover cover crop in the ground here, they can provide meaningful nitrogen credits.

24:59
It’s all about that biomass and this, this comment here incorporation not required.

25:05
I’ll, I’ll say that maybe the assumption with those green manure credits that we looked at before is that that those previous clovers or vetch were plowed under a head of the corn planting in our northeastern Wisconsin study, four of the five farms actually no tilled corn right into that dead Berseem biomass and we still saw those credits.

25:30
And so there’s also some some work that’s been done with alfalfa corn, first year corn following alfalfa tillage may or may not affect the amount of nitrogen you actually get from that previous alfalfa stand.

25:46
A spoiler alert or a teaser, stay tuned.

25:49
Over the next few years, Dr. Natasha Rayne and others will be doing some exploration here in Wisconsin on that specific topic.

25:58
So take the credits.

25:59
That’s the whole point here.

26:01
These cover crops can give you substantial amounts of nitrogen.

26:05
So take that base MRTN nitrogen recommendation and then subtract off those these Legum green manure credits.

26:13
OK, Biggest thing too is just set yourself up for for success.

26:18
So early establishment or get these small grain or processing crop rotations.

26:24
You know, there may be some inter or over seeding opportunities to get these these clovers established in in, you know, non small grain crops.

26:33
Of course, frost seeding red Clover into wheat works really well.

26:37
So really just be be pushing the envelope to get seed in the ground as early as you can, because it’s all about biomass.

26:44
Pick species and varieties that that are tried and true in your region.

26:49
Make sure your drill is calibrated and that it’s working.

26:52
It’s putting the seed where you want it.

26:53
You know how much seed you want going out there.

26:56
Do all the right things to set yourself up.

26:58
And again, site selection appears to be important.

27:02
So let’s not spend money on on more expensive, you know, Clover covered crops like you can cover crops and put them in in soil types and soil conditions that may or may not be conducive to prolific biomass production.

27:17
All right, I’ll just give a quick shameless plug for on farm research there.

27:23
There’s a lot of folks at at UW Extension that that would love to help you think of a study like the ones that we’ve talked about today.

27:31
If you’re curious and you want to explore what these credits are on your ground, lots of folks would be willing to help you think through that.

27:39
And that leads me to just bring up through the NOPP program that DATCP facilitates in conjunction with UW, there are 10 farms across the state of Wisconsin currently doing large plot studies, corn following different legume cover crop mixes, looking to document ice using credits across the state.

28:00
So a really cool project with lots of folks involved in that.

28:04
So again, just to, to screen grab if you, if you want these in your back pocket here, we’re adding bursting Clover to our, to our guidelines moving forward that less than 6 inch of growth will it’ll also be 40 lbs.

28:20
So they’re kind of all right in that, that same 40 LB range with a 40 to 60 LB range.

28:25
If you get a, a better stand, obviously, if you just get a, a knockout stand, a ton of biomass out there, it is potentially even even higher than that 60 lbs.

28:35
So with that, I’ll just, I’ll kind of just stop here and and let our wranglers get get the rest of these resources posted in the chat.

28:44
We’ve got cover crops one O 1.

28:46
That’s just a great resource that has lots of different cover crop species, planting based seeding rates after different major economic crops.

28:56
It’s just a great starting resource for folks that are interested.

29:00
Just all, all sorts of other general resources here that’ll be in the chat for you to, to go back and, and dive more into this information.

29:08
So with that, thank you for your time.

29:11
And if there’s any questions, I’m happy to take them.