Sulfur management: In-season, source, carryover, soybean & more
Welcome back to University of Minnesota Extension's Nutrient Management Podcast. I'm Jack Wilcox in communications here with Extension.
Jack Wilcox:This month's episode is all about sulfur. We have four panelists here with us today. Can you each please introduce yourselves?
Jeff Coulter:Jeff Coulter, Extension corn agronomist.
Jeff Vetsch:Jeff Vetsch, researcher at the Southern Research and Outreach Center.
Seth Naeve:Seth Naeve, Extension soybean agronomist.
Daniel Kaiser:Daniel Kaiser, Extension soil fertility specialist located out of the Saint Paul campus.
Jack Wilcox:Dan, let's start with you. There are some guidelines to fertilizer inputs that are gonna be updated. Are there any looming changes that are gonna be made to the sulfur guidelines specifically?
Daniel Kaiser:Well, Jack, I've been thinking about this a little bit because we made changes. It's about when I started here. It's when I updated the fertilizer guidelines. We put sulfur recommendations in for some of the crops in our non irrigated sandy soils, and that'd been a big change. And, I thought I was done with a lot of the research, and then I got kinda roped into doing some stuff.
Daniel Kaiser:It was probably an eight well, eight, ten years ago. I'm starting, looking at some sulfur sources, and I think that's the main thing, that there may be some updates here. You know, if we do make just some tweaks, and it would just be talking a little bit about availability and what we know right now about some of the the various sources that are out there because I think that's one of the things that many producers don't always think about. I mean, you just go to the retailer. You say, I want, you know, 20 pounds of sulfur.
Daniel Kaiser:You don't really realize what exactly they're applying, and that can be of some issue, mainly if they're using products like Tiger 90, and that's been the, you know, the biggest push I've had the last, you know, ten years is looking at some of our elemental sulfur products that are out there. I mean, I think Tiger 90 is pretty common, but, you know, you got products like Micro Essentials, the SC or s 10, that has some elemental. It's it's a fifty fifty ammonium sulfate AMS mix. And then, there's some of the nutrient outlets I know are are carrying some of their MST mixes, which is a finely ground, elemental sulfur. So the question on a lot of what I've been looking at is whether or not we get any oxidation of that sulfur.
Daniel Kaiser:And, you know, the key of it, we it's sulfur is not mineralized. It's oxidized. And that's a process. I mean, it's it's similar, but it that it's impacted by microorganisms, but it's it's a little different in terms of what organisms can oxidize, and it's also a slower process. So that's been kind of the the question I've had because, you know, we we consider when you apply salt, any fertilizer that you put it in the soil and it dissolves and all the nutrients will go into solution.
Daniel Kaiser:That's not the case with sulfur. Sulfur doesn't do that. So you have to treat it differently in incorporation, that's been the big thing I've seen, particularly with, products like Tiger 90 in high clay soils. Incorporation's a big problem, and it takes a long time for it to become available because, you essentially get it where the material won't, it it doesn't dissolve and it won't disperse. So it just is a big clump of sulfur there that if you kinda know, if any of you lime, you know that, you know, the finer the material, the quicker the reaction.
Daniel Kaiser:Same thing with with elemental sulfur. So I think that'll be the main thing. We were looking at rates, and I know there's a lot of consultants out there really pushing higher and higher rates. I mean, I'll I'll have some comments about that, I think, a little bit later, but, you know, I just looking at the numbers and, you know, you know, a few on here have had some research. I mean, we don't need as much as we think we need, but, I mean, you know, obviously, I think it's more consistent we see across the rotations that there's there's probably more consistent need for sulfur.
Daniel Kaiser:So, you know, again, I think that'll be the main thing is is just talking more about sources to be more clear in in terms of when these things are becoming available.
Seth Naeve:I've got a question about this availability, I think, that that always interests me, especially with soybean development. This year is an interesting year in that we have got corn and soybean crops that are really putting root that really did a good job putting root down, and they really look really good and uniform and even in fields because they I assume because we've got we've got roots exploring the rhizosphere kinda broadly, and they're able to to find nutrients that they need. So Dan mentioned this availability question about there's a there's a question about the physical availability. There's a question about, you know, the the chemical availability of the form, but there's also timing and, you know, the spatial availability within the soil profile. So I don't know if if those if this is the time to chat a little bit about that, if it interacts with tillage, it interacts with water movement, interacts with soils.
Seth Naeve:All those things can have an effect. Do you think that that's part of our conundrum with with sulfur that we've got these other availability questions that that interact with all the things that you discussed earlier, Dan?
Daniel Kaiser:Well, know it's interesting, Seth. I mean, recently, I was kind of in a meeting with Larry Chahasek from North Dakota State University, and he he's done some work on sulfur before. And in one of his comments was, you know, just how complicated sulfur chemistry is in the soil. And that's one of the things that I don't think we fully understand what happens. I mean, I we have an idea.
Daniel Kaiser:I mean, I have an idea what happens essentially when I apply sulfur, but we'd have no idea what happens with the forms of sulfur over time. That's been one of the things. I mean, Seth, you brought up some some things, you know, with soil conditions that I've seen. I mean, we'll have springs that we have a lot of striping, you know, and and, it's a problem, and they said there's some things I think we don't know that what's what's going on in those soils that might be impacting availability. Because I you know, commonly, I see that with corn where, you know, whether it's a growth issue where it's it's growing too fast and it can't take up enough and it'll stripe early on, or there just isn't enough available.
Daniel Kaiser:But as we start mineralizing, you know, soils get warm around, you know, v five, v six, then we can kinda catch up and things start to green up. So it's complex. That's kinda the issue that I just I don't know in terms of what, I mean, we could probably there's probably a lot of fields that are getting sulfur that don't need it, but how do you pick that? I mean, the main thing that I've I've really kind of been looking at is just trying to at least keep the the rates that are being applied more on a reasonable level. Because it's one of the, I think, the big misnomers that people have on sulfur since sulfate is an anion.
Daniel Kaiser:It's a negative charge that it leaches, and it yes. It does. But the rate of leaching isn't as quick as, say, nitrate. You know, in terms of loss potential, you know, we get years that, you know, we get a lot of rainfall where I've taken two foot soil tests, and I may not see the sulfate in the top foot, but it might be in the one to two foot range. And I've seen that, especially with soybean, in in looking at carryover studies where it's still picking it up.
Daniel Kaiser:So, you know, we know there is some movement. It's it's it's dynamic, and it's it's a little more complicated. And, you know, whether I'd be recommending, you know, most people apply it, If you're putting on, say, five, ten pounds annually, I mean, I think you can make the argument for that across many fields. But there's obviously obviously gonna be some fields that it just doesn't need it. Just, you know, consequently, I've got another, field site with alfalfa this year, you know, 2025 at Rosemont, and it's another area that's very sulfur deficient.
Daniel Kaiser:I can see down to the line where we've applied it, and it's it's just amazing what it can do when it is actually deficient, the the kind of yield responses we can see.
Jack Wilcox:Jeff Coulter, what is current research telling us about managing sulfur in Minnesota crops?
Jeff Coulter:Well, I've had a couple trials that I've been doing in collaboration with Jeff Vetch, Dan Kaiser, and Paulo Pagliari. One of them was funded by the Minnesota Ag Fertilizer and Research and Education Council. And what we were looking at in that study, was basically nitrogen and sulfur management in continuous corn. So we had trials at Lamberton and at Waseca over the last three growing seasons, And the organic matter in those trials was, between 3.8% and 5.7%. So they were pretty highly productive soils.
Jeff Coulter:And we looked we had plots that had no sulfur. We had some plots that had preplanned sulfur at a rate of 25 pounds of sulfur per acre in continuous corn. And then we also had some plots that had 25 pounds of sulfur per acre preplanned plus an additional 10 pounds of sulfur per acre included with a side dress application applied at the v 14 stage with a wide drop system. And what we found was in about one third of the cases, we had a yield response to sulfur fertilizer, and that yield response was typically in the eight to 10 bushel per acre range. Some interesting things that we saw was that in some years, in in some locations, we found that, there is pretty significant sulfur deficiency symptoms showing up by about the v five stage.
Jeff Coulter:So that's pretty early on, but yet that did not always correspond to a yield reduction. And this would these were in the plots that did not receive preplanned sulfur. So it appears that in some cases, that corn can grow out of that sulfur deficiency. And as those roots develop and as the mineralization occurs, the roots can access some of that sulfur and kinda grow out of it and not experience any yield reduction compared to the plots that did have sulfur applied. Another thing that we looked at was whether an extra 10 pounds of sulfur per acre applied as the side dress would be an advantage on top of the 25 pounds of preplanned sulfur, and in no case did we find that to improve yield.
Jeff Coulter:Another thing that we noticed is that at the v 14 stage, when we were applying our sidedress applications, and if we looked in the plots that did not have preplanned sulfur applied, in some cases, we could see the sulfur deficiency at that v 14 stage. And when we could see that deficiency at the v 14 stage, that quite commonly corresponded to a yield loss compared to the plots that did receive sulfur. So it appears that, you know, sulfur deficiency at v five, the corn can sometimes grow out of it. But at the v 14 stage, if no more sulfur is applied and we're seeing those sulfur deficiency symptoms, it seems like it's more likely for a yield reduction to occur. In addition, we've had another trial that we've been doing that last year was the first year where we had real data from it.
Jeff Coulter:And in that study, we were looking at applying sulfur preplant versus as a starter application in corn following corn and in continuous corn. And this is at Waseca, Minnesota, fairly high organic matter at that site. And last year, we did find a yield response to the sulfur fertilizer, but we did not find any difference in yield between pre plant versus a starter application that was applied two inches from the row on the soil surface.
Jack Wilcox:Was it surprising that the crop could grow out of the sulfur deficiency?
Jeff Coulter:I was shocked, actually. When we saw the symptoms at b five, oftentimes, they were quite strong and very prevalent. You know? It's great to take a picture of them because it was amazing. But, you know, I was just shocked that in about half of the cases, it would grow out of it.
Jeff Coulter:So it appears that you know? But I shouldn't be that surprised by it because when we look at the nutrient uptake curves that have been generated by other researchers, basically, they show that corn doesn't really take up much sulfur until about the v nine stage. And at v nine, it only takes up about it's only taken up about 15% of the total sulfur. By v 14, which is about ten days before tasseling, it's only taken about 45% of the total amount of sulfur. So corn takes up sulfur, but it it takes it up a little later in the season than it does nitrogen.
Jeff Coulter:So I think that may be in part why oftentimes those early sulfur deficiency symptoms don't always translate to a yield reduction.
Jeff Vetsch:Something that Dan touched on, we'd talk about current research versus some of our older research in sulfur fertilization. Well, our older work, we found some really large yield responses, and I think that was in some of these situations where these fields had not seen sulfur fertilization in a long time. Once we started applying and farmers were applying sulfur regularly, now I think some of the responses, as Jeff mentioned, are maybe a little bit smaller and maybe a little more inconsistent, especially on our higher organic matter soils. And when we look at these higher organic matter soils, we have to remember that most of the yield response, especially in something like corn, is gonna come from a relatively small amount of sulfur fertilizer, maybe five or 10 pounds. However, I've also seen years when either it was really dry in the spring or really wet in the spring like last year, where those conditions and whether it's the chemistry, Dan, or something else, it seems like it reduces the sulfur availability to corn.
Jeff Vetsch:So if farmers or retailers are applying 20 pounds of sulfur for corn after beans as a broadcast or 25 pounds for corn after corn or corn after small grains, I really don't have a problem with that. They probably don't need that much. But I do agree with Dan and Jeff. If you're doing that, putting on 20 or 25 pounds, you don't need to go out there and wide drop some more. I think that at that point, there should be plenty there.
Jeff Vetsch:And as Dan said, it may not be all in the top foot, but it doesn't mean that the plant's not gonna get to it later.
Daniel Kaiser:It's it's more of a question of availability, of some of that stuff. And and looking at it, I mean, you know, the the plant's gonna only take up probably about 20 to 25 pounds anyway total. You look at kind of it's about half in the grain, half in the stover, so that's about all it really needs. So in effect, when you look at some people talking about thirty, forty, you know, 50 pounds of sulfur, I mean, I don't necessarily under understand it unless the soil is converting the sulfur to less available forms. And, Jeff, one of the comments you made on wet soils, I think that does happen, particularly around where you're at, Waseca, you know, Central Minnesota, Western Minnesota, those prairie pothole regions, that we do tend to get some sulfate reduction.
Daniel Kaiser:And that's kind of the same process by which we lose nitrate denitrification. When bacteria when the soil goes anaerobic or it doesn't have oxygen, it'll look for another oxygen source where it first goes to nitrate, then technically, next, it goes to sulfate, but it you know, a lot of people think that the nitrate has to be depleted first, and I don't think that's case. So I think that's kinda what happens. We we get some of these years, it's wet cold, and we get a little bit more reduction where the soils need to be a little bit better aerated to see some of that that sulfur go come back to the available forms? That's why we get into some of those situations where, Jeff Coulter was talking about where you get those nice deficiencies early on, and they tend to go away.
Daniel Kaiser:And, you know, Jeff Coulter, I kinda wonder, you know, maybe if there was a response there, but it was just so small in terms of the number of bushels that when we talk about, you know, the variability you have in the field, if you've got a large field trial, you just can't detect it. And that could be part of it that there's something there. It's just, know, maybe it's one, two bushels, and it's really hard to to detect that in some of our our yield differences. But, you know, one of the things I am seeing, and I finally have the data, you know, we had a a study with AFRIC where we did for four years. We, continuous corn.
Daniel Kaiser:We applied it was, three rates of sulfur with, three different products applied to the same plots yearly. What I did in year five then is cut off half of the we used half the plot. We cut off applications so you can start to look at drawdown. And it's interesting looking at this because I'm from these 20 pound rates, I'm still, you know, I'm three years in, right now. I bet we'll still see where there's some carried over sulfur from, you know, those those first four years of application, and it takes a while to bleed it out.
Daniel Kaiser:I mean, if you're going into a field, you know, I agree with Jeff, with many growers now applying it, it's not a given that we're gonna see a response within many of these fields because we've we've gone from maybe needing, you know, initially 10 to 20 pounds of sulfur down to maybe five to 10 just because we're getting a little bit carried over. And I think that's the main thing with sulfur that, you know, we talked about acid rain and the and the reduction in of some of that, you know, the the sulfate deposition. There's a cumulative effect to that that kind of occurs. And as you, you know, cut that off, I think it's cumulatively decreased where we start to see those responses show up more.
Jack Wilcox:Dan, remind us what you mean about the acid rain issue, and how did that pertain to Minnesota farmers?
Daniel Kaiser:So acid rain, we know that, you know, when they when they had reductions in we we talked about, like, diesel fuel and, you know, some of the the industrial reductions in sulfate being released to the atmosphere that we had a lot of sulfur being, deposited on a per acre basis through rainfall, initially. It was more concentrated around industrial centers, obviously. I mean, Minnesota, we've seen it drop maybe, I think, four to five pounds on average, and that doesn't have a cumulative effect over years. I mean, I think that it's part of the reason why we've probably seen responses increase more. I think the, decrease in animal agricultural has some of it too.
Daniel Kaiser:There's just less manure going on. So we had more sulfur being applied historically, through other sources that wasn't being accounted for. We still see a little bit you've got a couple percent in your map and dApp that's being applied annually that you might be applying, you know, two, three, four pounds of sulfur with whatever you're applying for phosphate. And, you know, all that adds up. Those are these little incidental applications where it reduces the sulfur requirement.
Daniel Kaiser:I've got some data now that clearly demonstrates that and, know, how it does carry over. And, you know, some of these studies we have, that's why I try to keep them in place for years, is it may take a couple years, you know, if we're going into a field that's had some even low rates of sulfur applied to get to a point where we get responses. And that's, you know, been the challenge. I think that's why I kinda gave up, in the mid twenty tens around 2015 on doing sulfur research because we're going to farmer fields and not seeing responses anymore, and it was situations where the growers were applying it. I think there's just enough carrying over that we're seeing some benefits.
Daniel Kaiser:So that's kind of the the the big thing.
Jack Wilcox:So we've been batting this question, or this topic around a little bit. Should you just always include sulfur in crops, or is there not the need to do that? Jeff Vetsch?
Jeff Vetsch:Yeah. You know, I think when you're looking at corn and soybean or corn and alfalfa, I would say in most fields, yes, you probably still need an application. But as Dan just said, some of these fields are not gonna respond. The ones that I have seen that that typically don't respond as much anymore as they used to are the high soil organic matter fields that are silt loam soils in Southeast Minnesota, and also, just as Dan mentioned, these fields that have had a history of really high broadcast rates for the last maybe ten or fifteen years where they're putting on 25 pounds or more, there's some years where those fields just don't respond either because there's there's just that residual of that legacy sulfur that's out there. The other kind of caveat to that is other crops.
Jeff Vetsch:So and I don't know, Dan, you can address the small grains. I I don't think we've had the consistency of response with small grains, but there is some issues or concern or questions about sulfur. With soybeans, if you're broadcasting 20 or 25 pounds in a corn bean rotation, I doubt you're gonna see a response the next year in soybeans to making an additional application, and I think Seth might have some data that supports that. The only exception is possibly no till beans or if they're planted following a cereal rye cover crop, and, you know, our colleagues at Purdue have shown that, but it it, you know, it may just be one or two fields or one or two geographies or certain soil types. Whether that's the case across all of Minnesota, we don't have the data to really address that, but it is something to pay attention to.
Jack Wilcox:Are there any last words or final takeaways that you would like farmers and agronomists to know about regarding sulfur?
Daniel Kaiser:So I think those comments that Jeff had, I mean, in terms of, you know, Sean Casteel's work, I mean, it's it's you look at that data, and I don't know, Seth. I mean, you talked to a lot of soybean growers. I mean, there's get it gets a lot of interest in that with the the yield increase they've had with that. But, you know, from what I've seen, we'll look at just a corn soybean rotation, and I've been that's so that's been my focus. I've got two studies right now.
Daniel Kaiser:One's funded by AFREC, one's funded by Minnesota Soybean Research and Promotion Council, where I'm applying, you know, fairly high rates ahead of corn, and then looking at the follow-up soybean year, we'll see this year. I'm interested in what happens as we had some yield responses in corn. This is the the second corn crop or the third year of the study. Last year in 2024, I'm I'm interested in all these sites if they respond in 2025. Because, you know, every field that I've done with soybeans where I've applied ahead of the corn, if I get, you know, at least ten, twenty pounds, if you go the next year, even if I don't get a yield response in the soybean, I can pick up increased tissue concentrations.
Daniel Kaiser:We also look at amino acids. I mean, cysteine, methionine, our two sulfur containing amino acids. A lot of times, we'll see, you know, maybe a little bit more shift towards some of those aminos. That the plant's actually taking it up. It's there.
Daniel Kaiser:So it just doesn't need it. And that's kind of the the thing with this every year application that it concerns me somewhat from acidification aspect because it's one of the things that you have to watch out for. Ammonium sulfate and elemental sulfur are acidifying. So that if you are in a situation where you need limestone, you might come to situations where that might just worsen that need. But it it's just not a given, and the big thing with any of this research is you have to focus on the fact that, you know, a lot of times, you'll you'll get one of these studies that you get these big responses, and it might be really specific to that particular location where you can't translate it out to anywhere else.
Daniel Kaiser:And that was one of the things that's came up recently. Somebody asked that particular question about some of, the Indiana work here on some of our soils, and, I mean, I don't know much about that site. I don't know. You might know more, Seth, but it looks like it's kind of a sandier site, and it might have a more propensity to respond to sulfur. But the big thing, it's it's not a magic.
Daniel Kaiser:It seems like it sometimes. It might be sort of magic nutrient that can increase yields. Amazing what the low rate of sulfur can do. It seems like sometimes nitrogen response levels with that, but, you know, it's it's really specific crops. Small grains, Jeff, you you mentioned that.
Daniel Kaiser:I do have recommendations for that, but very eroded, low organic matter soils. Edible bean is one of the things I've got some studies out now. Last year, we had some red kidney beans. A field we just top dressed some gypsum, over by Glencoe, and the growers claim they could see, you know, some greening effect, but that greening effect, as as Jeff Coulter said, isn't always carry into yields. So, you know, one of the things with it, it it can look like it's doing something, but that's why we take things out to yield and and try to see whether or not it does anything at the end because there may not be anything there.
Daniel Kaiser:So, you know, I would just really recommend right now that the two crops that I have a lot of data on, well, we don't do much work with canola, but, obviously, that's one that's it's really sulfur sensitive, but corn and alfalfa are kinda my two targets. Growers, put a little extra on in the corn year, get about 20 pounds on. I don't really worry too much about soybean the next year. I mean, unless, you know, Jeff brought up a few situations where I might have some concerns.
Jeff Vetsch:The only thing I would add is, you know, these manured fields are still kind of a question. You know? Typically, I think most of these manure applications have enough sulfur in them for that corn crop. Whether that manure or the sulfur in that manure is in the sulfate form or if it's organic or elemental, we don't really know. The tests don't really tell us that.
Jeff Vetsch:And I've seen cornfields that look sulfur deficient after receiving liquid swine manure, so if they didn't get another sulfur source of application. So that's something to still kinda pay attention to and to be cognizant of. Whether a little bit with the planter is all that's needed there is probably maybe that's the best solution. I don't think you have to go out and broadcast another 20 pounds if you're already putting on 10 or 15 with your manure source, but there's that's kind of one of the question marks that that we still don't have all the answers for too.
Seth Naeve:You know, from a nonfertility person, I just wanna remind people that there's a lot of limiting factors out there for yields in our crops, and sometimes adding something that gives us a little bit benefit early on may not translate to yield simply because we've got other things in that field that are holding down yields. Now I think farmers get around this question by saying, well, I'm hopeful that I'm gonna have 300 bushel corn crop this year. And so, you know, they're they're they're looking for that. They're optimistic for that, and they wanna they wanna have a program that would support that even if it doesn't necessarily isn't in the bank. The other side of this, I think, that's that's interesting on the on the sulfur side, though, is that you might have symptoms early on, but, you know, as long as that crop can can pick it up later elsewhere in the profile or in another form, that that looks like that's probably an opportunity for it.
Seth Naeve:That means that that early stage of that crop probably wasn't super essential that it had a 100% productivity during that one week period at, you know, v six or whatever that you see a little bit of this this symptomology gets a little bit yellow, maybe that particular time wasn't the yield limiting portion of the of the year, which is almost is very, very likely considering we really need to have our productivity in both corn and soybean. We need to optimize things very late in the season. So, really, we're building this crop for that tasseling period in corn, and then we're building the soybean crop for that efficiency of of, you know, optimization of of performance for soybean crop, clear out the r five and a half or something like that late in the season. So so we're just we're just trying to build this plant so that we have the right machinery to to put in that yield very late in the season. And some of this stuff that happens very early in the season doesn't end up turning into yield limiting factors, I guess, is is all I'd like to say again from a a nonfertility type person.
Jack Wilcox:That was Jeff Coulter, Jeff Vetsch, Seth Naeve, who you just heard, and Daniel Kaiser. Guys, thank you very much.
Jeff Vetsch:Thank you.
Seth Naeve:Thank you.
Jack Wilcox:Do you have a question about something on your farm? Just send us an email here at nutmgmt@umn.edu. Thanks a lot for listening, and we look forward to seeing you next time.
Jack Wilcox:We'd like to thank the Agricultural Fertilizer Research and Education Council, or AFREC, for supporting the podcast.
