UMN Extension Nutrient Management Podcast

University of Minnesota Nutrient Management Podcast Episode: “Soybean fertilizer management: IDC, sulfur, P and K soil tests, and more”
April 2024
Written transcripts are generated using a combination of speech recognition software and human transcribers, and may contain errors. Please check the corresponding audio before referencing content in print.

(Music)

Jack Wilcox:
Welcome back to University of Minnesota Extension's Nutrient Management podcast. I'm your host, Jack Wilcox, Communications Generalist here at U of M Extension. Today we're talking all about soybean nutrient management. We have three panelists here with us today. Can you each give us a quick introduction?

Dan Kaiser:
This is Daniel Kaiser. I'm a nutrient management specialist with the University of Minnesota. I'm located out of the St. Paul Campus.

Seth Naeve:
Seth Naeve. I'm soybean agronomist on St. Paul Campus.

Jeff Vetsch:
It's Jeff Vetsch. I'm a nutrient management researcher at the Southern Research and Outreach Center in Waseca.

Jack Wilcox:
Seth, let's start with you first. What should farmers who are growing soybeans this year be thinking about including, for example, IDC concerns from last year?

Seth Naeve:
I've had a number of calls over the winter and then as we approach spring about really concerns about IDC this year relative to some of the poor crop yields we had last year. And so this really comes around to this central question about residual nitrate. And so this is not my area of emphasis, but I think going back to George Ream years, we really determined that nitrate is a major player, residual nitrate is a major player in how soybeans respond to the environment and how much IDC that they seem to be sensitive to in the year.

Dan Kaiser:
I think the interesting thing here, Seth, will be how spotty some of these issues might be because that's one of the things that talking to a few growers over the winter, how much difference even within their own areas, within their own fields, how much difference in yield they had. And I know the one person talking to called both of us up, Seth, asking this very question about nitrate, wondering about it, and he's up around the... It's up in the with Southern Red River Valley, so that was kind of interesting talking to him and with his perspective on this.

But I know with IDC, a lot of issues last year and I know Jeff, I think south of you in some of those areas, maybe some increased incidents in some fields that farmers normally hadn't been seeing IDC in the past few years. So I think there's a lot of questions on that now, certainly I was down in Iowa at the end of last year talking at their ICM conference about IDC because north central Iowa, I know a lot of issues up there too. So there was a lot of interest in terms of what we can do and the main culprits for this. And I mean there's still some debate out there on this nitrate issue, but we know, at least from the data, I know Seth some of your work where you've applied nitrogen fertilizer, we know we can increase the incidence of severity.

So we know there is some tie-in, if you look at all the data now, there's always some argument, is it a chicken or the egg kind of thing? And the fact that the IDC is resulting in higher nitrate because the plants aren't effectively taking it up because they're poor. I know there's some arguments against that, but if you look at the data pretty clearly, if you apply it, it's going to be less.

So the question really this year is I think twofold. The one is how much residual nitrate do we have left? I think certainly where I'd be concerned in some of the field areas where you've had poor corn yield, there's probably likely going to be some substantial amount of nitrate. And I know the specific question then that we received was that positional availability, whether is it worse if it's in the top six inches? I mean if it's down and deeper in the profile, is it quite as bad? And that thing, I mean I really don't know in terms of the soybean plant, and that might be something, Seth, you could kind of address is just where you think some of that nitrate's being drawn out of because that's one of the things we've never really been able to do with IDC is come up with a set formula to predict severity.

It's one of those issues that it's multifaceted. It isn't necessarily one thing that impacts it, but we know where the general precursors and the risks are going to be. So we'll see what happens this year. I mean I would suspect, where we're going to see it again, those areas probably where the corn yields were the poorest and I would suspect that the nitrate's going to be a big issue because that's one of the things that we have seen at least from some of the soil testing labs is some reports of some high residual nitrates again this year.

Seth Naeve:
Thinking about eating this elephant one bite at a time here. So thinking about the difficulty in predicting IDC, I think part of the problem is, or part of my question around the challenges in predicting IDC with chemical tests is, okay, well if we can't predict it with any soil chemistry, there must be something that's moving around or something that we're not measuring.

And I just think that's why we talked a lot about water early on in IDC. We thought water was really a driver. I really wonder how much of that water is just moving dissolved solutes around and ions around in the soil, including nitrate and salts and where those are at in the soil and the concentration where they're at and where the soybean roots are at that time. I think if you put all those things together, if you understood all that stuff, you probably could know or predict or understand why we're seeing IDC in some areas and why we're not seeing it in other areas.

But this movement of solutes and ions with the water is really the complicated piece in this. And I think that's why I keep coming back to nitrate as a big driver here because it's something we don't measure very well and it's quite variable over years as well.

Jeff Vetsch:
Yeah. And I'd be willing to address a little bit about the residual soil nitrate. We've had nitrogen trials here in South Central and Southeast Minnesota, and obviously Southeast is in an area that's that big a concern for IODC, but I would say about three-fourths of my nitrogen trials had greater residual soil nitrate left in the profile after harvest than we've seen in previous years and seen in the last 10 to 15 years. So there's definitely that potential for greater residual soil nitrate. And where it was, generally in half of those sites, it was predominantly in the top one or two feet of soil.

And that, I think, gets a comment about the position on availability of some of the fertilizer that was applied last fall and that these fields that maybe only got half of the amount of normal growing season rainfall, that end never moved and then those plants later in the growing season, those corn plants were taking up their nitrogen and their nutrients at deeper depths and they removed all the nitrogen at the lower depths, but they left it in the soil surface because it just wasn't available to them because there was no water there. And I don't think we've had decent precip, now we're probably at four or five inches from the fall, but I don't think it's enough to move that nitrate very far. It was basically enough to replenish most of the soil profile. At least that's what our preliminary soil moisture data would suggest.

Seth Naeve:
We had a strange winter. So where did stuff move around in the soil? Where is it hanging out? I think you kind of alluded to this, Jeff, but if things were really dry and we had really dry soil profiles deep, that would indicate even if we had water moving down through the soil profile, we were probably not moving a lot of it out of the profile. We didn't have a lot of tile running. So, I assume that it means it's somewhere, even if it did leave the top six inches that it's somewhere around. Right?

Jeff Vetsch:
Yeah, I would agree with that, Seth. We do have a little bit of tile flow, but it has not been a tremendous amount and they've been flowing since that last week of March when we got about two and a half inches of rain and snow combined that period. And then we had another two-thirds of an inch twice since then. So I would agree, I think we've maybe moved it out of the top six inches or a foot, but we haven't moved it very far in the profile. We're just replenishing that profile's moisture deficit and we're not seeing a tremendous amount of tile flow that would suggest that it's moving out of the profile.

Seth Naeve:
The other side of this is that because we didn't have frozen soil, we didn't have a lot of water running off of the top until typically we get basically all the snow's running off the top until this time of year. And so I think we just had a very different kind of winter obviously. And I don't know that any of us know what it means, but we know it's going to mean something different than what we've seen in the past.

Dan Kaiser:
Well, and that's one of the things too, Seth, I mean it is really water I think is the main issue. And that's one of the things, I mean if you're sitting in say around Rochester and you've got high residual nitrates and you plant soybeans, I mean one thing that we know that soybeans will scavenge the nitrate out of the profile, so they're effectively utilized. I mean really the issue with, and the thing we can't measure is bicarbonate. Bicarbonate is really the main issue that results from iron chlorosis. So if you've got acidic soils or you've got well-drained soils, essentially that bicarbonate will decompose relatively quickly and it won't build and it won't stay in the profile and you won't have any issues with it. So we could be sitting with high nitrate and soybean and not have a problem in some of the fields. It's really the fields where you have high pH where it's just a culmination of issues.

The main being that you have to have enough moisture at a certain point in time where, especially I think you look at it on late May, early June where the soils are effectively saturated, the soils are cool and the plants are stressed, and then you tend to get IDC. So as I said, it's a culmination of issues. And if you've got where you were measuring residual nitrate and you don't have pHs above seven and a half, I wouldn't really be worried about it. I mean there's really not as much of an issue. The thing I'd be maybe more worried about is your potash levels, your potassium levels, because certainly there's been a couple years out of the last few where we've seen some problems with potash or we've seen some potassium, especially late season potassium deficiency in soybeans where the plants just tended to run out. So that's where the thing I'd be more concerned about on those ends than anything else.

So I mean it's one of those things that, again, it's I think something to watch out for. I just don't know the best way to assess where it's going to be, other than take, I mean just look at your residual nitrates, if they're relatively high, if you're taking a zero to six and a six to 24, if that zero to six is relatively high, I mean I didn't get the odds on or you're probably going to have a pretty good likelihood that you'll have IDCs, especially if you've got high pH. I mean if you don't, I wouldn't really worry about it.

Seth Naeve:
So I guess we're kind of coming around to this question about management and recommendations based on what we have. So, the way I am reading what you and Jeff, Dan, are saying is that we have a potential for having higher nitrate in the upper surface of the soil, upper six inches or so. We don't know what these actionable levels of nitrate are and they're specifically on IDC. So we can't say that there's some threshold, but we can say there's probably more in the top six inches where we're going to have those soybeans early in the year. And so I guess I would be willing to say that farmers that have had IDC issues in the past, and they had some corn acreage where they were well fertilized last year and their yields were substandard and they were lower than they expected, that they might be at somewhat higher risk of IDC in some areas than they had been in the past.

I'm trying to parse my words carefully here because I can't say that everybody's going to be at higher risk or anything like that, but I think farmers should think about their risk level. And I think that's the way farmers should be treating IDC is, what portions of their farms and how much of their farms are affected by IDC historically? And then what should they do with it? Obviously they need to choose better varieties if they think they're at higher risk. And then the questions are things like iron chelates and things like that. So if they have the ability to use an iron chelate in furrow, then if they feel that they are at higher risk this year than they have been in the past, it might be worth putting on spending some money on products like those because we know that iron chelates work when there is IDC. So, I guess I would be willing to put that out. Would you like to refute any of those comments, Dan? Or have other ideas or expand on those?

Dan Kaiser:
No, I think you're spot on. That's what I was actually going to bring up. I mean variety selection is your number one line of defense with IDC. I mean it isn't perfect, but it's still if all else fails, it's typically what you want to fall back to. And the other thing are these iron chelates, now one of the things that you do tend to see and some of these things are bad. Sometimes you get all these companies coming out of the woodwork with all these products in there.

I mean the thing you want to realize though with these chelates in IDC is that the ortho ortho EDDHA chelate is the one you really want to look out for. And there's several products out there, they differ in their quality with the EDDHA. They have higher or lower percentage of the ortho ortho. The more, the higher the percentage, the better it generally is because there's another isomer called ortho para that isn't as good. It's not going to give you as good a control. And that's a lot of the problems with other products like Iron HBE, is HBED I think is the other good one. There's another one, HEDDSA, or there's several others that aren't quite as good, but the two I'd be looking at are the ortho ortho EDDHA, something that's kind the active ingredient in soy green, Ferraline a lower concentration of ortho ortho EDDHA, but if you put enough on it'll do the trick. And then FeHBED is the other one.

Those are really the ones that are going to work the best and the rest of them just don't put a whole lot of stock in that, or our favorite biologicals, I just don't think you're going to do enough with any of those because it's a biological issue with soybean why it can't extract iron in the first place. So I don't know if you're really going to effectively be able to do anything with it.

So just be careful. If you haven't used these, just make sure that you know what you're using. You got any questions, then it's a good time to call one of us and just work through some of the stuff if we know about a specific product that you're wondering on. But I think those are the best options. I mean I don't know, you've looked at planting density too, Seth, and I just don't think that's probably consistent enough.

I mean we've also looked at cover or companion crops like oats, it can work, but just the consistency and the management involved, it's not something that you can just apply and forget, especially with the oats, you've got to have a higher level of management. These other things I think are a little bit easier to deal with.

Seth Naeve:
Yeah, the only thing I'd mention on populations is the farmers just should make sure they're not short of population. I think we want to make... I think our data basically says that we can increase yields, but only at about the same rate as we would with populations outside of a high pH or IDC area.

So, you're basically getting your money back for your seed, but there's not a big payback in it. But farmers definitely need to make sure that they're not short. If they're being really conservative, I know that there's questions about inputs this year and some people are pulling back and some farmers are probably considering reducing seeding rates. And so, I'd be more concerned on the short side than I would to get farmers to push their seeding rates higher.

Jeff Vetsch:
Dan, do we have any data following a rye cover crop for soybeans and the impact that might have on IDC? I mean we'd assume, if it was a good crop and it took up some, scavenged some nitrate, that it could benefit it?

Dan Kaiser:
No, and that's a good question, Jeff, and that's one of the things I've been wondering because we haven't looked at that full cover crop effect. I mean we've always looked at just a spring seeded oat, and if we get good growth out of that, we know it has an impact in terms of taking up nitrate. So, I mean it is conceivable that if you had a decent rye cover crop growing that, I mean you could have some benefit in terms of reducing IDC, but that's just something we don't know.

And the main thing on this, if you are doing something like that, I mean the thing that I've seen with soybean is soybean is awfully sensitive to letting that cover get too large. And especially with the oats, we don't recommend going anywhere beyond about 10 inches tall before you terminate because otherwise it tends to get a little bit too over... It tends to have more issues with taking up too much water and where we tend to see some yield reduction. So that's the only thing I said, when I talk about that, it's more management intensive. You just have to be out there and do things at a specific time if that's the issue and it could have some added benefits, but it'd be interesting to see, Jeff, I just don't know. But I would assume, just because what the oats do, that the rye potentially could do with a fall seeded rye.

Seth Naeve:
I think there's potential. I was just talking with a farmer that we're looking at cooperating on this for next year and getting some plots out. And I'll probably be working with Dan on that specific question and looking at it both from a nitrogen or nitrate uptake as well as this question about competition.

And unfortunately, I think from a practical standpoint in Minnesota, none of these things get much growth early in the season to take up much nitrate early. If you really want an early planted soybean, you're just not... Even with a really nice fall seeded, really good stand, high biomass fall rye, you're still not going to have a ton of it in the spring. So, I think we're just really limited on the uptake.

And so what it will end up coming down to, I'm sure, is this question about, what's the value of leaving that cover a few more days or a week longer relative to potential yield loss in your soybean. And that gets really dicey because I know you're going to take a yield hit every year on your soybean by delayed, and you're going to get some value in some years and some value in some other, and no value in other years for that IDC from that cover.

So I think it's a great, great, great question, and I want to do research on it, but I know it's just going to be a really naughty, kind of nasty thing to work on because it's going to vary a lot by year.

Jack Wilcox:
What does new research tell us about soybean and sulfur?

Dan Kaiser:
So, Jack, this is an interesting topic because I've gotten a lot of questions just because of Shaun Casteel's work out of Indiana, Shaun's out of Purdue, but a lot of interest in the topic because of what we've been seeing with corn research and sulfur. And I've been looking at sulfur and soybean, I think the first trials I had were back in 2008 and what I've seen early stages when we were doing a lot of work, we were seeing some direct benefit of sulfur applied to soybean, but these were mainly in fields that had been neglected with sulfur applications. And one thing that we've seen over time is that I think most of the growers in Minnesota, since they've been more cognizant of issues with sulfur as they've applied it, especially ahead of corn, they're usually applying some relatively high rates that it's getting, I think, less and less likely that soybeans are going to get any direct benefit to a direct application.

And I'm not going to discount Shaun's work. I mean it's interesting and I've seen some other work. I think he may have been involved with it, Jim Camberato, who's now retired, he was also at a Purdue where they were looking at carryover effects into the soybean from sulfur applied to the corn. He was showing some pictures last November at the North Central Extension Industry Soil Fertility Conference that were showing some definite differences in greenness in the strips where previously where sulfur had been applied. So we know that soybean, it needs sulfur, it's going to take it up. I think it's just been traditionally for us that being that soybean has been a later planted crop, that there's a greater likelihood that we'll be able to pick up enough sulfur through mineralization because they're just going to be planted at a point when the soils are going to be warming up more, that it's not as likely that needs it.

So, from my standpoint, what I've really been recommending to growers is not to be as concerned with it during the soybean year, but you'll focus on it in corn, maybe small grains, something that would precede those soybeans. You don't want to forget about it, but what I've seen with a lot of our applications is that, with the rates that most growers are applying, there's some carryover from one year to the next and the soybeans are directly picking that up. I've got two studies right now where we're looking at some placement in different source effects applied ahead of corn, and I'm not getting any direct yield benefit in the soybean side, but you can see it in terms of higher sulfur concentrations in the grain. So I know they're picking it up, I know they're picking it up where we've applied it.

So, as I said, I know it's there. Since we're not getting any direct yield benefit in these circumstances, I know it's probably not needed to maximize yield, so it's not a high priority on my end to look at, but it can have an impact. You see it affect cysteine methionine potentially, which are essential amino acids, maybe a little bit of an uptick in protein. It's not anything major, but there's some benefit there. But just in terms of marketable and direct yield, it's not a big worry unless it's a situation, you're going into a field that you don't know what's previously been applied. And if you've got lower organic matter, say 3% or less, then I might consider it just for an initial application if you're planting soybean that first year after taking over that field. So that'd be the only circumstance I think I'd be concerned about it.

The rest of the time, and I know, Seth, we've worked on this and we've been chasing this, looking at these high yield situations with sulfur timing, and we just haven't seen consistent results with sulfur fertilizer application. But yet, I haven't done a lot of testing in fields that are yielding 70, 80 bushel. So that's a thing. I mean I can't speak to with those higher yield conditions whether or not there might be something there, but looking at just I think the average field really the need, I think if you take care of it in front of the crops, you should be fine.

Seth Naeve:
Yeah. And I don't have any direct evidence either way on this, but I would say, just from a very high level philosophical position on this question about yield level and yield enhancement at the top is that I get really kind of tired of chasing this thing is that every product and every person that is claiming that they've got the secret sauce on this stuff is all talking about adding an extra five or 10 bushels on top of 80, 90, 100 bushel yields.

And when we do the work, we just don't see those things. We don't see interactions with yield, with inputs, our kitchen sink type work that we did. Every added input did not... Those things weren't more useful in high yield levels than low yield levels. And the thing, it really brings me back to this question about nitrogen is that there's still this wives tale out there that high yielding soybeans can't fix enough nitrogen, so you have to put some extra nitrogen on. And we've definitely found that that's not the case in the upper Midwest. I think in Kansas probably they can make this work for them, but we can't make it work for us here.

So I think a lot of folks rely on this idea that higher yields and if they really want those high yields, they're going to have to put a bunch of extra stuff on top. And in broad strokes, I just don't see those kinds of things. My guess is if they're getting those 80, 90 bushels in their soybeans, they're probably, they've built a system that also has plenty of sulfur availability for them to put on an extra five bushels if they weren't limited on something else.

Jeff Vetsch:
Dan, I would just add that one thing that, if there is a place where they might see it, it might be in no-till beans and probably an early season thing. And just like you said, kind of those low organic matter, those are eroded knolls, those would probably be the areas that would be most likely to respond to sulfur from a soybean standpoint.

But like you said, Dan, most of these growers are putting on 20 pounds or more of sulfur for corn. And if that's the case, there should be plenty of carryover for beans. But that's where I would be looking at it. And then I think the other thing to be thinking about is a lot of our sulfate sulfur sources contain nitrogen, and do we really want that on your beans? Because then you might make other issues or add to IDC or other challenges. So that's another thing to be thinking about if you're going to think about applying sulfur to soybeans.

Dan Kaiser:
Yeah. And the only thing that I have seen in addition to some yield effects, I mean consistently I see essentially, if you look at the beans, the beans get bigger, they get a bigger canopy, immune taller plants, and that isn't necessarily the best thing. I mean where I've had really good results with some of these, particularly these higher yield treatments, is really pushing the fertility ahead of the beans and the beans seem to do better on residual fertility than direct fertility because it doesn't seem to increase the biomass and you put the nutrients essentially where you want it, going toward seed production versus vegetative biomass.

And that's one of the things that I have some older data, but I mean it's pretty clear and I had some starter data where we looked at two by two applications of 10:30 furrow and ammonium thiosulfate, and it was about six inches taller beans down to the row where we had those treatments. And it didn't necessarily yield any better, particularly in fields that weren't sulfur deficient. It just wasn't any better for those larger beans. So it's one of the things with beans, I mean I don't know. I mean, Seth, maybe you could tell a little bit about that because just having shoulder-high beans isn't necessarily the best thing out there. I would generally assume just because of the diseases that are present, or can become the canopy with too much biomass out there.

Seth Naeve:
Well, I'm now at the age I can say that this is a problem that I would like to solve, but it'll probably be after I retire, is this question about vegetative versus reproductive development in soybean. And I actually think that this is the holy grail. We've been chasing a lot of things around in soybeans and a lot of farmers are really frustrated with our yield advancements and what we've done with technology. But if there's one thing that I wish that we could do with technology and soybean is better predict what the perfect canopy size would be relative to what we need to put in for seed growth.

And Dan hit on this question, and the way I talk about it with farmers is I tell them they all have had tomatoes in their garden that they get these giant tomatoes out there and then they have six small little tomatoes at the end of the year and then they've got one row over, they've got some little puny thing and it's just full of tomatoes at the end. And that latter one just put all of its energy into growing the tomatoes. And the first one put all its energy into growing vegetative biomass.

Part of that's nitrogen driven in our gardens and part of that's the same way in these fields that we push them a little bit with fertility and they end up ripping through too much water. I think that's the big canopy problem that you might see in your situation, Dan, is that too big a canopy can hurt us if we don't have the right conditions at the end. If we have perfect conditions late in the season, a big canopy is probably okay for us, but we need to have good water all the way through August and early September to support that final growth.

But I do totally agree, I think, ideally, that creating a bigger canopy should be the right way to go if that soybean could then finish it off, but sometimes the soybean puts too much energy into vegetative growth and there's just not enough left for the seed.

Jack Wilcox:
Jeff, are there other nutrients or practices that you do or don't suggest for soybean based on current research?

Jeff Vetsch:
Well, I have completed this study looking at ban versus broadcast, and it was kind of a sidebar to look at what the effects of banning and broadcasting P&K fertilizers for corn were on soybeans. And the general, to make a long story short, is there just was not much effect and it's kind of what we expected. And as Dan mentioned earlier, I totally agree, you can manage P&K fertility for beans in your corn in a corn bean rotation and it works just fine and it has for decades.

The only other thing that I would add is that soybeans, I see more and more farmers putting crop removal on their corn and beans and building soil test phosphorus really very high, often much higher than is necessary for corn and soybeans probably need even lower or can get by with even lower soil test phosphorus. They definitely do not need very high soil test P. Medium to high is more than enough.

But from a potassium standpoint, as Dan mentioned, we have seen the last couple of years with some drier conditions where we've seen some potassium deficiency mid-season, mid to late season. So managing that potassium at 150 part per million or greater on medium and fine textured soils is probably where you need to be to minimize that potential in these drier years.

And the other thing is that in some of these years, or recent years, we've seen some soil test K that's a little bit lower and it gets affected by moisture, soil moisture when you sample. So if you get all of a sudden it dropped 20, 30 per million from where you're at, you can't be alarmed but that's just kind of sometimes the way the variability is in that soil test from year to year.

Dan Kaiser:
And this is an interesting question because I get this question a lot in terms of P&K fertility because there's some out there that I think are just perfectly fine with applying a head of corn and really relying on the fact that the soybeans are going to be able to live off the residual effects of P&K. As long as you account for soybean, I don't think there's really much of an issue. The only case I would say that would be a consideration I would make in terms of a direct application would be with phosphorus, particularly if you have soil pHs say above seven and a half, your carbonate content, your calcium carbonate equivalency is 3% or higher, situations where the Olsen test is better than the Bray in terms of assessing availability, then I would maybe consider a every year application on the phosphorus side.

On the potassium side, it's been a little hit or miss. Now I've had some circumstances where a split application every year has made some sense, but you're talking some pretty isolated circumstances and I'm not sure why in this particular case, I think it was one site out of many that I've had that actually had a response why it was that way. But overall, I mean we know that generally if you look at timing, I mean soybean is less taller and, as Jeff said, maybe not needing as high of soil fertility, particularly a phosphorus. And I know that's one of the criticisms for some of you that might be listening closer in southern Minnesota. If you look at Iowa's recommendation where they're a bit more liberal on their fertilizer applications for phosphorus, that wondering what's the deal here? And I can't explain it, but if we look at our data, I mean medium class, we don't see that strong of a yield response where in Iowa they would suggest essentially fertilizing up into the high class, would be our high class with the Bray and the Olsen.

So I mean I can't argue that there might be some circumstances out there the farther south you go, but if you look far and away across the state, we just don't see as strong a response. I mean the main place I would look at though is the high pH situations. If you have issues with phosphorus tie up, then every year application makes some sense.

Now with potash, it's one of the things growers will look at the removal and how much the soybean grain is removing and see that it's removing more, if you look at a two-year rotation versus what the corn is in that rotation, I mean I still don't see where it seems to make any difference to apply it directly ahead of the soybeans. In fact, with soybean not liking particularly high levels of chloride applied directly ahead of it, I've got a lot of data on that right now, it makes more sense to apply it ahead of the corn. And what I'm really looking at for potash fall application is better than spring if you want to limit chloride uptake, because I've got some data on that right now, but it's what I'm looking at with one of my AFREC studies is a comparison of fall versus spring with some different levels of potassium chloride application because that's where we get the bulk of the chloride.

So it's something to be concerned about. But if I'm looking at just yield benefits, I mean it's phosphorus. I mean phosphorus is number one and if you've got soils that are low, then high pH soils, then I would consider applying ahead of soybean. But in most other cases, I think you can save yourself the application charge and just take care of it ahead of the corn because corn's going to be by far and away more responsive to both P and K. I mean you're going to get probably a greater return or potential return than you would with soybean. And then just don't forget about it. And that's kind of the main thing.

So the things I'd look at, some growers have looked at starter and I absolutely would not be doing a liquid and furrow application of starter. I do have some data on that. We had a study funded by the Minnesota Soybean Research and Promotion Council. I started that last year. I'll continue it this year, looking at 10:30 furrow versus a low salt, we were using 24:6 or 3:18:18, one of those two. And it doesn't seem to matter. Liquid starter on the seed is a very bad idea for soybean. I've been looking at the precision planning system where you can place a dual-band beside the seed onto the side of the seed, that seems to get away from some of the issues with emergence.

But I know talking to them, I know they have concerns about plugging on some of that equipment because those are some pretty small orifices they use for fertilizer injection. But these high clay soils, it isn't really the best option. So, I would just broadcast is really your best option and just make that decision based on pH and it's mainly based on phosphorus and the rest of these nutrients, I think the soybean should be a pretty good scavenger and you shouldn't have to worry about it moving forward.

Jack Wilcox:
What tips do you have for Minnesota soybean growers looking to increase yield? I know we talked about this just a little bit right now.

Seth Naeve:
This is another unpopular opinion among farmers and crop consultants, but the reality with soybean is that farmers just need to set their crop up for success and then let it go. The idea here is that we're really waiting for August, September conditions, and so we need a really healthy, good, vigorous crop at that time, and then let mother nature really take care of things.

There's very little that we can do to add yield onto a soybean crop. I think I would put soil fertility into this category of yield maintenance or maintaining yield potential. We're setting the crop up for success. And then there's a few things that farmers need to do with weed control and other pest control to make sure they don't have any problems in there, but otherwise they really have to step back from it. And farmers really want to buy some product that's going to buy them an extra two or three or five bushels, but those things just don't really exist. I think we have to go back to that old agronomy wisdom that says, the greatest yield potential is the day they plant that seed and everything is just walking back that potential from there. And so really set that crop up and let her go and protect the yield as we go through the season.

Dan Kaiser:
And that's where it concerns me a little bit too on prioritizing some of these smaller inputs that might give you these one or two bushel because I mean I agree with you, Seth, I don't really think they're out there and if they are out there, I mean is it some other issue that was neglected early on? Because to me, fertility wise, I'd rather set myself up initially, try to be proactive in the situation than trying to react to the season. And that's one of the things I think a lot of growers do. They rely on things like tissue testing to tell them if they're short. And I think all that tissue testing does is it's a read on essentially the nutrient uptake and availability as moderated by the environmental conditions that that plant is growing in. I mean I think it's nothing more than that, because we see that with many nutrients that it gets dry and they just tend to go low and you get rainfall and then they tend to go higher.

So, it's one of the things that I just would set yourself up, if you can, I mean as best as possible. And then you're just kind of reliant on the weather because we always go back to Liebig's Law of the Minimum, which is focused a lot on plant nutrients in terms of the fact that the yield is directly proportional to the nutrient in most limited quantity. And I think you can expand that out. And with beans, it's probably environmental or weather. You talked, Seth, it's what conditions are in August that are probably the most yield-limiting factor? And anything else, essentially you're just setting yourself up to get to that point.

So, that's the thing. I mean even with beans, if you look at the yield, I mean it doesn't take a whole lot of bushels to pay $4 or $5 per acre input cost, but if you go with the logic of everybody that's out there trying to sell you something, you should be growing 200 bushel beans by adding all these little one or two or three bushels over time, you should be able to greatly increase your yield and it really doesn't come down to that.

So the main thing on the fertility side, I mean just set things up as best as you can, but I wouldn't go too crazy and overspend on fertility if you're neglecting some other things, especially weed control. I mean that's the one that worries me the most, you look at grower that would prioritize some of these little inputs when you neglect a pre-emerge and then you end up with a field full of waterhemp, giant ragweed stuff that's really hard to control for a post application.

So, looking at that, I think you're looking at prioritizing money where it makes most sense first. Then if you've got a little extra spending money and you want to try some of these little inputs to see, I mean do it on a test basis and just see if they do anything. But I do get a lot of flack about that because a lot of growers do these foliar applications.

They feel they're getting a good benefit to them, but we just don't see the benefit. And that's the thing. I mean I have the research in front of me that I see what I've done and if I don't see a direct benefit, I can't tell you that this is something that you should be doing. And so I just kind of focus on the basics with a lot of this because to me, I mean growing a crop, it should be relatively simple. You just set yourself up and you get yourself protected well enough where your crop shouldn't be overly limited and then it's kind of up to mother nature in terms of what you get at the end of the season.

Seth Naeve:
Yeah. And just to back up Dan's comments, I work with a lot of agronomists nationwide and we dabble in a lot of things and we are not trying to be specialists in all these areas, but we're trying to test things as farmers see them. And so, one of the things that we tested a few years ago was these foliar products, nutrient products, because farmers had questions about which ones work and where they work and things like that.

And we basically put these things out all over the US, and I don't remember, like 60 sites or something like that. And we only had a handful of responses and those all traced back to sites that we could identify some deficit in soil nutrition on those that we ended up kind of correcting or helping to correct a problem in the soil.

So, I keep coming back to this idea that these products are sold to farmers to add bushels on to an existing yield, but I just don't see any of the plant physiology that really says that any of these things, whether it's a biological seed treatment or a foliar application of various kinds of products, antioxidants or nutrient type products, none of them are really acting to add any additional yield on top of what that plant had the potential to do. So, I look very skeptically at a lot of these products and I think farmers should be really considering those as well, especially in years when the economics are pretty tight.

Jeff Vetsch:
Yeah. The only thing I would add would be I think soybeans compared to corn, and this is partly true for corn too, is just getting the right variety and the best disease-resistant packages that you need on those fields. Especially pay attention to SCN, make sure you've got an effective SCN resistance package for your field. And then as everyone has said that all these other products, you really have to think about this year and next year's economics. The prices for these commodities is not where it has been the last several years. So that's going to have to be considered when you start purchasing some of these other products to add on when it's probably less than likely that they're going to produce a lot of bushels and maybe even pay for themselves.

Dan Kaiser:
And the other thing we never talked about was lime, and I could probably wait for another time to talk about that. I mean we could probably talk for a whole podcast about that, but we are looking at that now. I mean for the most part, if you're in the mid-up or fives to lower sixes, you're probably fine in terms of pH with soybean. But it's one thing we're looking at right now because there's always that question on economics, particularly in areas if you don't have a good source of lime available to you where it can be kind of expensive to truck in. So we're looking at that now. I'll save that for a later date though, because that's one of the things that we're trying to get a better handle on is the economics long-term in corn-soybean rotations of limestone application.

Jack Wilcox:
Are there any last words from the group today?

Seth Naeve:
I just hope that we have a good spring and farmers have a successful planting season here coming up and I hope that they can get in between the rain showers, get that crop off and growing and we get a good recharge on our soil profile and everybody has a safe spring going forward. I think that's really all that we can really hope for.

Jack Wilcox:
Before we go, if you have a question or comment for our panel or a topic you'd like discussed in a future episode, please email us at nutmgmt@umn.edu. Thanks and we look forward to hearing from you.

And that about does it for this episode of the Nutrient Management Podcast. We'd like to thank the Agricultural Fertilizer Research and Education Council, or AFREC, for supporting the podcast. Thanks for listening.

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