Nitrogen and sulfur: In-season application, nutrient interactions, precision tech & more
University of Minnesota Nutrient Management Podcast Episode: “Nitrogen and sulfur: In-season application, nutrient interactions, precision tech & more”
May 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.
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Jack Wilcox:
Welcome back to the University of Minnesota Extension's Nutrient Management Podcast. I'm your host, Jack Wilcox, and I'm a communications generalist here at U of M Extension. Today, we're talking about nitrogen and sulfur application. We have four 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 located on the University of Minnesota Saint Paul Campus.
Yuxin Miao:
This is Yuxin Miao, associate professor of precision agriculture and director of the Precision Agriculture Center on the Saint Paul Campus of University of Minnesota.
Jeff Coulter:
Hi, I'm Jeff Coulter. I'm an extension corn agronomist located on the Saint Paul Campus.
Fabian Fernandez:
And I am Fabian Fernandez, a nutrient management specialist focused on nitrogen management for corn cropping systems, and I am also located in the Saint Paul Campus of the University of Minnesota.
Jack Wilcox:
Yuxin and Jeff, I know you have some current nitrogen and sulfur research. Could you summarize those projects for us?
Yuxin Miao:
I have been working on nitrogen for a while, mainly focusing on on-farm nitrogen management, on-farm trials. So, I have been developing remote sensing-based, precision nitrogen management technology, and that has been evaluated using on-farm trials across Minnesota for the past three years. We have been expanding it to different situations like fields with irrigation and also fields with manure applications.
The results so far indicated the technology is very promising, and this year we are expanding to implementation mode. Some of the farmers are adopting this technology, and we are just trying to support them to use this technology on their farm.
Yes, this is the nitrogen one, and we are also doing on-farm sulfur trials, and so we have basically from zero to 40 pounds sulfur per acre, 10-pound interval, 10-pound per acre interval. The results has been very different in different fields, so different farms, and also change from year to year in one field on one farm. So, in 2022, it was very responsive to sulfur, but in 2023, it was not very responsive. We just found the year-to-year difference can be very significant. Yes, and this is the sulfur trials.
This year we are starting to ask to conduct nitrogen by sulfur interaction experiments. We have two fields. We have five nitrogen rates and three sulfur rates, and that's a big, on-farm trial. In addition to this, we are conducting a nitrogen by planting density on-farm trail. We have three planting densities, 30,000 seeds per acre and 34,000, 38,000, and with five nitrogen rates. Yeah, so these are for corn, and we are also doing nitrogen by irrigation interaction research for potato using small plot experiments.
Jeff Coulter:
With funding from the Minnesota Ag Fertilizer Research and Education Council, I've been doing trials in collaboration with Jeff Vetch of Waseca, Paulo Pagliari of Lamberton, and Dan Kaiser here on the Saint Paul Campus. We've been looking at basically split application of nitrogen, so applying some nitrogen at the V14 stage using the 360 Y-DROP system. Then we've also been looking at putting in an additional 10 pounds of sulfur per acre with that V14 nitrogen application to see the effect of that on corn yield, and then we've been comparing that for different hybrids and also planted at different planting rates. So, we're doing that on hybrids of around 100, 104, and 108 relative maturity. Each of those are planted at 34,000 and 38,000 seeds per acre in continuous corn, so trying to see where the split application of nitrogen with or without additional sulfur may provide a benefit to corn.
We've been doing that over the last two years, and we're starting our third year of research right now. Over the last two years, we have not found an advantage to split application of nitrogen at the V14 stage or to additional sulfur applied with that V14 nitrogen application.
Fabian Fernandez:
That's an interesting thing that you mentioning, Jeff, because there is a lot of advertisement out there about late applications of nitrogen or late applications of nutrients to the crop because when you look at when the crop is taking up nutrients, that's when it's happening. There is a lot of that happening at that point.
But I think what you're describing matches pretty closely with some of the work that I've been doing, not so much with sulfur, but more related to nitrogen, where if you apply nitrogen in early side rates around V6, V8, the chance of nitrogen loss at that point is pretty low. So, whatever nitrogen you apply there will be there for the crop, and later applications will not necessarily make a difference.
In fact, sometimes if you delay the application, you can run into issues where if it gets dry, the application may not actually get into the root zone. So, you could actually create more harm than benefit by delaying those applications. That has been my experience.
Dan Kaiser:
It's one of the interesting things that I've seen too ... and Jeff, I don't know if you can comment on this stuff phenotypically ... is we do see differences in some of the hybrids and how they tend to yellow at certain times. I know I've noticed, long noticed actually since we started sulfur research, some of the DeKalb hybrids we had, we tend to see a little bit of striping on the leaves early on. I don't know if that's necessarily the fact that these hybrids are more responsive to sulfur. It just seems like the way they might be growing might be how they're translocating some of these nutrients. One of the things in one of my current trials, there was some questions from a consultant who was looking at some of the Pioneer versus the DeKalb and just how they tend to yellow, some of them more than others, near the top of the canopy late in the growing season.
I think it goes into a lot of what you're doing, Jeff. It's those questions of whether or not these late applications might be needed just because of what's happening within these plants. I haven't been able to clearly identify anything. Jeff, it doesn't sound like you've been either to do that, but it's interesting because it just seems like these plants might be starving themselves at certain points. But I just haven't been able to figure out a set combination to try to get it where it seems like it really matters in the end.
It's one of the things early on, I was just looking at some of the data I had just with greenness at V10. We got a DeKalb and a Pioneer where the DeKalb was greener early on, but then it was, or no. Actually, it was the other way. The Pioneer was greener early on, but then it was yellow near the upper canopy later on, and in the end, really, there were some yield differences, but it wasn't anything where it was consistent across all my location that one was better than the other.
So, while we see these consistent greening or yellowing in some of these plants, I don't know if it really matters anyway, and it's probably something I guess we don't really understand right now in terms of how these companies are breeding these, whether or not there's any differences. It's one of the reasons I just haven't really decided to change our recommendations and make any changes based on what hybrid's being grown in a field.
Jeff Coulter:
Yeah, to follow up on that, I think it was two years ago at Waseca when we were doing this trial, and in the plot where we didn't have sulfur, there was definite sulfur deficiency symptoms visible on the plants, but by the end of the year, there was no difference in yield between the sulfur fertilized and the non-sulfur fertilized plots. So, I think early deficiency of sulfur, those symptoms don't necessarily mean that it's going to be a yield penalty, but I think the later those symptoms are visible on the plants, the more likely it is that it's going to be translated into a yield difference.
Last year at Lamberton, I think, we had some visible sulfur deficiency at the V14 stage, and that did translate into some yield differences between the plots that received sulfur pre-plant versus those that did not. One of the premises for my study, why we were looking at putting on sulfur at the V14 stage, was because corn takes up sulfur a little bit later than it takes up nitrogen. By the V14 stage, which is about 11 days before tasseling, corn has taken up almost 60% of the total amount of nitrogen that it will take up.
In comparison, at that same stage, corn has only taken up 25% of the total amount of sulfur that it will take up. So, that was why I thought that putting on some sulfur late in the vegetative stages might be advantageous just to help make sure that that plant doesn't run out of sulfur by the end of the year and to help to maximize grain filling. So far, over two years in two locations, we haven't seen an advantage to that.
We had two years of drought. We had one or two site years of drought, one site year of very high yields, and then one site year with moderate yields, so we're repeating this study again this year at two locations, and we hope to be able to get a little better handle on this.
Fabian Fernandez:
I think, Jeff, what you said about those sites with early deficiency symptoms not really making any difference in the yield later, but do see in differences in yield when you have issues later in the season is actually something pretty telling about how the sulfur cycle works and how the plants need sulfur. Early in the season, as you said, there is not a lot of sulfur needs for the crop and the soils may be a little low just because the mineralization process really hasn't started yet, and so that would not really translate into any long-term issue.
But if you do see those deficiencies developing later in the season, that's probably telling you that the soil is not mineralizing. It has not really a capacity to mineralize a lot of sulfur because at that point in the season, it's warm, there is moisture. So, if there is sulfur to be mineralized, it should already be mineralized. If you're seeing deficiencies at that point, that's probably telling you that that soil will be, or those situations will be places where you would want to make sure that you supply some additional sulfur so that you don't run into that deficiency.
Dan Kaiser:
Yeah, I think looking at some of the stuff, Yuxin, you've been seeing out west on some of those soils, I'm wondering too how much reduction of sulfate we get annually. I think it's cyclical in our soils where the sulfate will reduce to less available forms as we get towards the end of the season, then be in that same position early in the season. Where the farther west you go, especially in these high pH soils, there's something doing with that too. That might be why ...It's my interest in why you're seeing some things that I'm not seeing in terms of the rates with that. It's one of the things that I've been wondering. It's a complicated cycle. It's more complicated, I think, than we think it is with that. It's interesting. You can get a lot of pretty big yield to response with a small rate of sulfur, but there's some questions, I think, that are still left to be addressed just based on what I've been seeing.
Yuxin Miao:
Yes, on-farm situation's quite complicated. We have been using organic matter as an indicator, but I see in some fields organic matter is very high but still quite responsive to sulfur. But some fields, the organic matter is low, but it may not be responding to sulfur as we expected. It seems in addition to organic matter, some other variables are also quite important. One is water. One is in a very dry year, and the yield is very low. It's not very responsive to sulfur. Also, landscape conditions can also influence the response to sulfur and texture, so texture. Just quite complicated in on-farm conditions.
Jack Wilcox:
We talked about this a little bit, Jeff, but what do we know about the relationship between nitrogen and sulfur in crops?
Jeff Coulter:
I think the big thing is that the uptake of nitrogen occurs earlier than the uptake of sulfur. Just thinking about we want to try to time the nutrient applications to match the time of uptake. But in the case of later sulfur applications to match that later uptake of sulfur by the crop, it just hasn't really been panning out per se.
But I think there's more research that we can do. What I've been doing in my trials has been looking at putting on a pre-plant rate but then applying extra sulfur at the V14 stage. An alternative approach may be to look at instead of applying the sulfur pre-plant, applying it in season, say with an early side-dress or split application of it. But the issue is we really don't need that much sulfur, so it gets hard to justify split applications and stuff like that.
Dan Kaiser:
This is one of the questions I've gotten. I think that the thought is that if you apply sulfur that you need more nitrogen, and it's really, I think, the other way around. If you have what I've seen with a lot of my studies ... and, Yuxin, it will be interesting to see what you get from some of your on-farm trials ... but it just seems like with low N, you just don't get a very good utilization of S. That's what I've seen in a number of my small plot trials where we actually looked at that N by S interaction with that.
I think Fabian hit the nail on the head here with what I think's happening in a lot of these fields is looking at Minnesota, I think we're more of an issue being short of sulfur early on. So, May is really a critical time period, and I've seen this in several of my sites that as long as we can start mineralizing sulfur by about V5, we tend to not see as much of a benefit.
I've seen it. I've got a field study at Rosemont, and it's interesting. Yuxin, this would be one that I think we should be looking at aerial imaging because you'll see a lot of sulfur deficiency early on, say through about V10, but then it starts to go away. If you would image that field, there's some spots that would still throw some deficiencies by R1 to R2, so by about silking, but a lot of it tends to go away. Then you contrast that with Waseca where it's just yellow the whole season, and then we get into that interaction because what I tend to see in a lot of times is I tend to see some of my low sulfur plots run out of N a lot quicker. Whether that's just the roots not developing very well and exploiting the soil, there's a number of things that could be occurring in that.
It's one of those things I don't think that if you apply high sulfur you need more nitrogen. I think the interaction is more since we need more nitrogen, it's more the other way around that you just get very low utilization of sulfur if you have low N. So, it's one of the things to see with some of this, and it's one of the things it's talked about a lot is that interaction and whether there's an optimal ratio of N to S.
I'm not necessarily sure there is an optimal ratio. Maybe if you look at the plant, there is something in there, but the thing is for us supplying it that a lot of that can be achieved through mineralization. That's what we see in a lot of our soils with these high organic matter contents.
Yuxin Miao:
Yes, North Dakota State conducted a sulfur by nitrogen interaction study for corn, and it seems they found low nitrogen like zero nitrogen and high nitrogen, 240-pound per acre nitrogen, the yield increased with sulfur rate from zero to 10-pound per acre to 20-pound per acre. But at 60 to 80 pound per acre nitrogen rates, it seems just 10-pound per acre sulfur had highest yield. So, it seems the sulfur and nitrogen interaction is not very significant. That's what they found. But it would be interesting to see what I can guide from the on-farm trials, yeah.
Jack Wilcox:
Dan, what if any considerations should farmers make when applying S? Do N application rates need to be changed?
Dan Kaiser:
Looking at the N application, I don't think I'd be changing much based on that. I think the main consideration that growers need to be making is knowing what source they're applying because we talk about sulfur here amongst the whole group and the plant's taking up it as sulfate. So, looking at our fertilizer forms, we generally have two forms. We have sulfate forms, so you've got gypsum, ammonium sulfate most common, some potassium sulfate in the market, or you've got elemental sulfur forms, so something like Tiger-90, which is sulfur plus bentonite or MST, which is another elemental sulfur form, or something like MicroEssentials, which is AMS and elemental combination.
The main thing with that, the consideration is really how the sulfur is getting to that available form because the elemental forms take a longer period of time. That's one of the things that I'm looking at with a lot of my current research is comparing those just to see how quickly we get elemental sulfur. I'm seeing, especially with these finely ground forms like are in that MST product that I've been using, that we can get some available sulfur within the year that the crop's being grown. But if I look at Tiger-90 where I incorporated immediately, which isn't the best thing to do with it, that a lot of the responses they seem to be getting are the previous sulfur applications that were done the previous years.
So, if you're looking at immediate need means something like a sulfate form or even Jeff's been, I think, looking at ammonium thio in a lot of his work with the side-dress applications, those are probably the better two options. That's one of the considerations that you need to make as a grower is when do I need it. If I'm going into a new field that I haven't farmed before, really looking at something more in the sulfate form is what I would recommend.
Then if you're looking at some of these elemental forms, they are a longer- term type approach, and I'm looking at that right now, how long they can last in the soil. Sulfate doesn't leach like nitrate, so we don't see it leaving the profile as quickly. I do know even with sulfate, I get multi-year benefits. So, it's one of the things.
I think the starting point that I talk with a lot of growers really is what form you're applying and knowing what form you're applying because you need to have a good handle on that to know what you're trying to get and just make sure that, particularly if you're in elemental form, that if you are in a situation where you might be highly responsive that you might want something else down initially. That's where I think that split system like Jeff's talking about would give you some flexibility, particularly with ammonium thio, but at least to get something early on.
What we've seen ... and this is something, Jeff, I will be interested in looking at again ... is looking at some of these applications around V5 or so, V4 because I had a study in the past where we looked at planting or post-planting application, and I was still able to get maximum yield potential with a V5 application of ammonium sulfate over the soil surface in season. So, I know that as long as it's applied at that point, typically I shouldn't have a yield reduction. You don't need to get all of it on, but it's just a question then is it any better to have maybe a split application? I've not been one that's really been a proponent of that, but if you're already going back through with, say, UAN, it may not be the worst thing in the world to slip a few gallons of ammonium thio in.
It's one of the things with sulfur is that there's a lot of flexibility in what you can do as long as you understand the availability issues with the forms you're applying.
Fabian Fernandez:
Dan, you mentioned they need to make sure that you apply sulfur sources that are available when the crop needs it. Of course, for a pre-plant or a side-dress application, you definitely would want something with sulfate form. But if you're using elemental sulfur, what would you say is the best timing to do that? Is it the fall, or is it even the year before, the spring of the year before you want that to be available? What have you seen in terms of that elemental becoming available for the crop? How long does it take?
Dan Kaiser:
Fabian, it really depends on what form you're applying. If I'm applying something like a Tiger-90, what the company recommends essentially is surface application and letting it sit for about two weeks and getting rained on a few times to disperse it. That's one of the things that I'm seeing, and it's one of the things that I know what's happening, why I'm struggling to see a real positive benefit to Tiger-90 with immediate incorporation is that our soils are just too tight.
One thing about elemental sulfur is it's not water-soluble. Like other fertilizers which tend to dissolve and can move after they dissolve, elemental sulfur will not do that. It's just going to sit there, and if you've got it buried in a soil with a very tight clays, essentially it's going to pack that elemental sulfur together. When you talk about elemental sulfur, it's just like limestone in the fact that the smaller the particle size, the quicker the reaction.
When you're looking at that material, what I'd look at if I was applying something like Tiger-90, if you could slip it in with your fall application, I think it's a good option to do. But you can't immediately incorporate it because if you immediately incorporate it, that's really where the issue is.
That's one of the things that, Yuxin, with some of your variable rate work, it's one of the things that I start questioning is because we start looking at what all we can variable rate. So, if you've got two bins on an applicator, it's how much a grower is willing to look at doing that with sulfur if they can only variable rate so much. I think while I agree there's probably a need to variable rate in some of these fields, it's just a question of whether or not that's effective, especially if you're going to be putting it in with P and K. Would they be able to effectively do it on some of these landscapes? Because I think it is a better option, particularly with elemental to do that.
With elemental, looking at it, it's a cheaper option, but a lot of times, I'm seeing where if the availability is only a quarter to a half of what I get with sulfate. If you've got to apply double, is it really going to matter economically in the end with that, where you could be looking at some other source? It's said it's a tough decision with that on that. It's what works best in terms of when you can apply it, but then what source you have available for you and then what rate.
Really, we know that a low rate can go a long ways, but we get differences with products and availability, then you may have to make some adjustments, and just it's a complicated issue. It's a lot. It depends, Fabian, but one of the things with a lot of these sources if you're dealing with something like MicroEssentials or this MST product, I think you can immediately incorporate it, but if I was looking at elemental like Tiger-90, I'd try to leave it on the surface for a little while to see if you can get the material to disperse a little bit better.
Jack Wilcox:
Fabian, with an early planting window this year, will there be any issues related to nitrogen and sulfur that growers should be concerned about?
Fabian Fernandez:
Earlier this year in February during the nitrogen conference, I talked a little bit about back to basics and talked about nutrient availability. I think that's really relevant to this topic. I think we are having an early spring to a certain degree. Weather-wise, it's been warmer. This whole winter has been warmer than normal, and so we had some degree of mineralization happening for both nitrogen and sulfur in the soil. So, that availability of both sulfur and nitrogen will definitely help the crop get going this year.
In terms of planting, I thought that we were going to be really early planted this year, but here we are the first week of May, and I still have quite a bit of corn to get planted. I have some that was planted, but not all of it. So, the big question, I think, becomes what is going to happen the rest of this spring. If the conditions continue to be the way that they are where we are having a good amount of moisture and the temperatures are warming up, I think we'll be in pretty good shape. I don't think that it will be a lot of concern for either nitrogen or sulfur being available again because we are mineralizing. Then if we don't have excessive rain, there will be very little potential for whatever is mineralized or we apply through fertilizers that will be subject to loss. So, in that regard, I think we'll be in pretty good shape.
One thing, though, that I've been a little worried about and wondering what it will look like this year is mostly related to nitrogen. Both April and so far May has been really windy. I've seen a lot of strong winds, and because of the early conditions where we could be out in the field, I suspect that there has been a lot of urea broadcast in the fields. With the strong winds, I am a little concerned about the distribution of that urea.
So, I am predicting that we may see some kind of weird patterns happening this spring in the fields where urea might not be spread uniformly. You may see areas where have the streaks of lighter color corn in some areas. Then the other part too is for those that did not incorporate urea, the conditions this spring because of the wind have been kind of ideal for volatilization loss. The soils have adequate moisture right now, and when you have a moist soil that dissolves urea quickly and then you have drying conditions because of the wind, that creates ideal conditions for volatilization loss, so there could be some potential for nitrogen loss that way through volatilization.
Again, just something that I've been wondering about because of the windy conditions we've seen this year, a lot windier than I think I have ever seen in Minnesota in the 10-plus years I've been here.
Jack Wilcox:
Are there any last words from the group?
Dan Kaiser:
Well, on the sulfur side, I'm going to have a few, hopefully a couple news releases coming out here at some point here. We just finished the alfalfa trial that I had going on that was three to four years at two locations. What I'm finding with sulfur is the site at Morris more of a breakeven but was still a positive benefit for sulfur application out there. The one at Rosemont where we had lower organic matter is where we tended to see a bigger response.
One of the things though with sulfur, and it's one of the reasons I don't recommend really high rates for most growers, is you have to remember that there is still some incidental application of sulfur being applied on some of your fields, particularly the MAP and DAP you apply still has a small percentage of it that's not accounted for in the fertilizer analysis, so it's one of the things I've been doing with many of my studies now is I've been eliminating that as much as possible to try to sort out differences among sources or treatments. Because in many cases, five to 10 pounds is adequate to essentially get us going, and what Jeff was talking about is then we see a lot more of the uptake occurring later in the season that we don't need a whole lot at least to start things off.
Looking at that from the standpoint of rates, a lot of growers will talk about maybe upping the rate with sulfur application. I think certainly some of the sources you might need to do that, but typically, I think corn ... Jeff, you could correct me, but it should be somewhere between 20 to 30 pounds total sulfur taken up. Around 25, I think, was average, and about half of that's in the grain, half of that's in the stock. Looking at most of our soils can supply probably at least two-thirds to three-quarters of that.
If even in a deficient state that you look at what we actually need, 10 to 20 pounds is typically enough. So, I will get some information more about that though because again, a few things have finished up. There's a few things I'm looking at now on that with Sourcewise. I wanted to update, but it's just a little bit too much to talk about today.
Fabian Fernandez:
Dan, just a quick thing, you did mention alfalfa, but I've been thinking the whole discussion here has been on corn. Do we need to think differently or anything specific for other crops like soybean or even potatoes or other crops that we have not really talked about?
Dan Kaiser:
Well, I think potato, it's more critical. We did have a podcast a couple months ago on soybeans, so if anybody wants to hear a bit more about that, just you can go back and read that. We talked more about sulfur at that point.
Yuxin Miao:
Yeah, for potato, we are testing a new variety. This variety is very efficient in utilizing nitrogen, so we can reduce nitrogen by about 50% compared with the commonly planted Russell Burbank variety. We can still achieve similar or even higher yield, so this is very interesting. Now, we are trying to see how this new variety will respond to different irrigation, so that's why we are conducting the nitrogen by irrigation by variety trial right now with potato.
For new research this year, we are also testing a biostimulant under on-farm conditions. That's called ReGen. That is a biostimulant that can facilitate the decomposition of crop residues. We have a normal nitrogen rate without the ReGen, and also we have normal nitrogen rate with ReGen, and also 90% of the normal rate of nitrogen and with the ReGen, and also 80% of normal nitrogen rate with ReGen. So, we want to see whether we can reduce nitrogen rate and still achieve similar or even higher yield with this new product.
This is the first time for us to do this under on-farm conditions. We have several fields with this, so I will be happy to share the results at the end of the year.
Jack Wilcox:
Before we go, if you have a question or comment for one of our guests or a topic that you'd like to see discussed in a future episode, please email us at nutmgmt@umn.edu. Thanks, and we look forward to hearing from you.
All right, 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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