UMN Extension Nutrient Management Podcast

Advancing Nitrogen Smart, from the University of Minnesota Nutrient Management Podcast:
“Ep 8 - Timing”

September 4, 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 Advancing Nitrogen Smart, a special podcast series that helps connect the science of nitrogen in the environment to practical, efficient nitrogen fertilizer management for Minnesota farmers. I'm Jack Wilcox and I'm a communications generalist here at University of Minnesota Extension.

As always here to explain the science of nitrogen's behavior in the environment we have Brad Carlson, Extension Educator, and Dan Kaiser Extension Nutrient Management Specialist.

Today we're going to talk about timing. Questions about timing are important, especially when we consider variable weather conditions.

Brad, what are some of your general thoughts about how being aware of timing can increase nitrogen fertilizer efficiency?

Brad Carlson:
Well, the really big question about timing for a lot of farmers is just simply do I do fall application? That's the thing that keeps coming back around. I think most people involved in agriculture of Minnesota are aware that we now have a prohibition or it's actually illegal to apply nitrogen in the fall in certain areas, primarily in the southeastern part of the state. But there's other places where there's coarse-sector soils where you can't do that, and that's because of the risk for nitrogen loss. And beyond that though, farmers who are not in those areas saying, "Well, if we really are that subject to losing nitrogen in the fall, what does that mean for me where I'm at? Should I even be doing it?" And that's a big question. One of the overarching topics we've talked about a lot with Nitrogen Smart, because we talk a lot about customizing your management based on the conditions, is that the loss of nitrogen in a lot of ways is tied to very specific environmental conditions that being too wet.

And so if those conditions don't exist that set yourself up for nitrogen loss for nitrate loss, well then it doesn't matter a lot how you manage it. And so over the last several years, it's been pretty dry and you could get away with almost anything because it's not been wet enough to lose nitrogen. And so you look at how wet it was during the 2024 growing season, a lot of those practices came back to haunt us. Some of the things that we don't really recommend, like fall urea and so forth. And so the assessment really needs to be for farmers is not so much in this particular case, is this something I can get away with this year?

Because if you look at last year, last fall, it was extremely dry In the fall of 2023, it was extremely dry and it seemed like, well, these are perfect conditions to just put on fall nitrogen because the risk of loss under these soil moisture conditions is very, very low. However, then it got extraordinarily wet in the spring of 2024 it actually turned into problem. So it's more of like, what are the odds? How often does this create a problem and therefore do you want to really bank on this being your standard management? If one out of five years, it falls on its face. So there's a lot of overarching questions, big picture, long-term questions that a lot of farmers need to ask themselves related to application timing.

Dan Kaiser:
And a lot of application timing really is looking at managing risk. And that's one of the things that I think if the option was there that we could apply all the nitrogen in the spring, I don't think there'd be any issues as long as it's out there. And that's one of the things when it comes to corn is when you start looking at timing, really the corn doesn't care when it's applied as long as the nitrogen's there when it needs it. And if you look at some of the more recent data, looking at some of our modern hybrids, just looking at how much nitrogen is taken up at certain growth stages when the crops up to about knee-high or around the V6 timeframe, only about 10% of total nitrogen is taken up at that point in time.

At V10, about 30% and VT about 70%. So if you look at that critical period really is that V10 to VT period in terms of availability, when looking at roughly 40% of the nitrogen's taken up. I mean certainly we know that there is some nitrogen taken up beyond the VT grow stage, but we get situations like 2024. We get a lot of questions from growers about later applications for rescue applications. One of the things you have to remember is that if you have issues with availability at some of those earlier growth stages, there could be some lost yield potential and that it's going to affect in terms of how much nitrogen would be applied, particularly for more of a rescue application.

Really, when it comes to in-season applications, the question really is can you get back into the field and when? So that's one of the things when it comes to rescue applications, if you understand the amount of nitrogen that's taken up at points in time, really then it factors in a lot on what you really should be doing in terms of whether it's worth applying more at nitrogen or not, and will the crop recover. So that's been one of the, I know the key questions we've had a lot in 2024 has been really looking at whether or not it's worth going back in there and actually making some applications. But I mean really the main thing though is to really just understand that we want maximum availability. When you start seeing that crop going through the rapid growth stage, particularly after V6 is really where we want maximum availability of nitrogen.

Brad Carlson:
Dan, part of what plays a role in some of this, and we continue to hear this, well, we just can't get it all done in the springtime. And we remind people, well, in southeastern Minnesota, they get all their nitrogen applied in the spring and they've been doing that now for a very long time. We recognize that certainly there's parts of the state that there's not been the tradition of having to do it all. And so maybe to some extent the labor pool at the dealer and the equipment availability isn't quite ideal and they want to do some fall stuff.

But from a practical standpoint, I guess we've seen plenty of cases where putting it all on in the spring is feasible, I guess pending what your field conditions are like and so forth. And particularly a lot of farmers who are getting themselves in a position now to do their own application, really that's an ideal situation. There's been some long-term research that's been done at the Research and outreach center in Waseca on the drainage plots that's looked at timing, and that's one of the earlier things that Giles Randall looked at there. And one of the things that we've seen consistently is that spring applied nitrogen out yields fall applied nitrogen. And what's really fascinating about it, because these plots are tied into the drainage tile and we collect water samples and analyze them for nitrates, is we don't see a big difference in nitrate concentration in the water between the spring and the fall applied.

However, we see a yield difference. And that brings about this big question where you've got over, for instance, this four-year study that happened from 2000 to 2003 where you've got this 14 bushel an acre average yield difference between spring versus fall at the same nitrogen rate. And so we're pretty sure because of the heavy soils that we've got down there, we're getting denitrification loss. And I know there's a lot of farmers in southern Minnesota who will say, "I realize that there's this issue with nitrogen loss for fall application because of how heavy our soils are. They stay saturated in the spring and if I applied it in the fall, I'm going to lose a percentage."

Dan Kaiser:
And that's one of the things, I mean, there's some areas that we do recommend inhibitors. I mean inhibitors aren't bulletproof when we start talking about timing, where they'll actually make it so we can get particularly fall to behave a lot like spring application. And that was one piece out of that timing inhibitor work that Giles Randall did is, I mean they did have 120 pounds of add in the fall with a nitrification inhibitor versus the same in the spring. And as Brad said, a 14 bushel per acre yield difference, but no difference in terms of the amount nitrate loss. So we focus a lot on loss when it comes to nitrate loss. And denitrification is a big issue in some of these soils. And one of the interesting things, I think out of some of that data out of Waseca is, you'll see where they've looked at some different studies, long-term trials, that there are times if you look at the numbers fall versus spring, where the averages might not that much different, but if you look at the actual years where there was a big difference, they were relatively large.

So let's, one of the things that when you look at data, it's just realize that should all know there's conditions out there that are going to be more favorable for loss. So then it starts going back to this timing issue is the question, if I am applying it in the fall, do I put it all in the fall? I mean, do I put it all in the fall and maybe or put a portion onto the fall to mitigate some of that risk and then come back in the spring when I know where conditions are early in the growing season for potential for loss? And I mean, one of the big things about we start talking about corn production is we're making a lot of decisions really before we know what the environmental conditions are. And that's a lot of risk involved with that. So it's a challenge, but there's certainly things I think growers need to think about moving forward.

Brad Carlson:
Well, I think one of the other issues related to fall application, Dan, we were talking a little bit before we started recording, is this whole issue of just applying more nitrogen in the fall rate wise than in the spring, just simply acknowledging that you're going to lose some of it and you really need to be thinking big picture from an industry standpoint if that's really a good practice anymore. I think a lot of guys have justified that from a cost standpoint, like, "Well, I can get my application cost per acre is a lot lower in the fall than in the spring, and so I can actually just use that extra money and buy a little extra nitrogen.

It's all the same." But that research at Waseca where they did in this case, they were looking at the time, a recommended rate of 120 pounds of nitrogen following soybeans, and they increased that rate to 160 pounds. So an extra 40 pounds fall applied. For one thing that still didn't out yield the spring application of 120 pounds. Then in addition to that, it greatly increased the amount of nitrate running through the tile line. And so that really is a case where these soils are just simply telling us a fall is not a good time to be applying nitrogen under these circumstances. And so I think everybody knows we wrestle with these issues of nitrates in water, we're going to have to start looking at some of this stuff and making some difficult decisions that are going to improve water quality.

Dan Kaiser:
And one of the big things too we're seeing now, I think that's more problematic, is a shift away from anhydrous. And that's one of the things that we know with timing, that there's a pretty strong interaction with source, how the nitrogen converts from one form to the other. There's certain sources that aren't as I would say, stable, but that they take a shorter period of time to convert and urea is one of those that we can't substitute urea with anhydrous. There's nothing we can put on it to make it act like anhydrous. So that's one of the bigger problems especially if we're going to get into more of a urea based system, which in Minnesota urea sales or outnumber anhydrous sales right now, I mean we've seen a big shift in the last 15 years where anhydrous now is number two and urea is number one for nitrogen. So that's one of the things to think about when it comes to timing is that there certainly are some aspects you need to think about just based on what source you have available to you.

Brad Carlson:
And so then the other part of timing that we've maybe talked a lot more about the last couple of years is split application because that became very popular over the last five or six years. In a large part because of the ability to do it. Historically, we didn't have a lot of infrastructure to be going into the standing crop and applying. But if you look at the data on that, and particularly if we look at those same drainage plots we just referenced at Waseca where they did a study looking at either applying a full rate preplant or then just split applying the same rate, now they really didn't see a really big yield advantage as far as that's concerned.

And they saw maybe a slight reduction in nitrate loss, but overall there wasn't a whole lot of differences. And so that again gets back to one of the points we've been hammering with Nitrogen Smart is there's no such thing as fresh nitrogen. The spoon-feeding it's just not a thing. I mean, this nitrogen is just nitrogen. It's either there or it's not there. It doesn't really matter if it was applied yesterday or last fall. If it's there, the crop will take it up and if it's not there, it can't. So again, some of these soils that are not real prone to leach and lose nitrogen that way aren't going to see on most years a big benefit for split applications either. And so if you're worried about, "Well, it's really expensive to apply it in the spring versus the fall." Well then don't compound that by split applying it if it's not really necessary.

Dan Kaiser:
I mean, really split application is more of a risk mitigation tool. It's really what it is. I mean, honestly, the thing about a lot of growers, I think a lot of their concerns are really if they could recoup the cost of that additional application with the split. Now we would like to see more consistently that if we split that we could apply less nitrogen. It isn't always, as Brad said, the case that we can apply less. I mean, the nice thing though about the split is the ability to make some adjustments because once the nitrogen is out there, we can't take it back. The other thing with loss is loss is always a percentage of the total. It isn't that you're just going to lose five pounds no matter what it is.

It's a percentage of the total you apply. So the less you apply, the less you're risking to lose. We'd like to see a better advantage. I mean certainly irrigated sands, you're going to see a much lower rate required for a split application, but for most of medium to fine textured soils, we see that. I mean, I've had several studies that it's taken the same amount of nitrogen whether I applied it all pre-plant versus a split application. So that really just tells me that when it comes to timing, really probably the bigger benefit we've seen in the state is a switch from fall to spring and from spring to split. It's a little hit or miss. We'd like to see probably more spring application. I think that would put some things at less risk, but certainly we know there's some issues out there and getting all the nitrogen on, I know that's a big concern for a lot of the co-ops and the growers that are out there.

Brad Carlson:
I think back to 2024 with some of the nitrogen deficiency, we saw the need to come back and rescue, and there's a lot of things that could be debriefed about that situation. How often does that happen? It maybe does happen once every 10 years, or at least as wet as it's been, it's shaking out that way. But the other thing you have to realize is getting wet in June does put you at extreme risk for loss of nitrogen. It's very difficult to manage your way out of that. But in addition to that, we had in 2024, so much of that crop then just simply got flooded and killed, it didn't really matter one way or another. Yhat's a hard thing to make management decisions based on.

Dan Kaiser:
I mean, if you look at a normal year just looking at tile line loss is that we know that if you look at the water budget overall, that if we have an actively growing crop, like I said, an actively growing crop out there, we know that we can significantly reduce the amount of potential for nitrate loss. Because in Minnesota, typically when we look at tile drainage, we have the greatest amount of drainage in April, May, and June. So that's where really our risk for losses are greater because we've got a small crop with a low demand at that point in time that isn't taking up water or taking up some of the nitrates.

Certainly 2024, I think Waseca was the outlier with the amount of rain they got in May and June. I know Jeff Fetch looked at some of the numbers from the tile drainage plots, a lot of nitrate there just because it's just way too much of the crop can take up. So we know there's going to be some years out there that there can be issues. But looking at it in terms of loss potential, it's really what we're trying to mitigate is not have a minimum amount of nitrate in the soil profile at the start of the growing season just because we know that that's where we're going to have the greatest risk for loss.

Brad Carlson:
I think one of the other aspects we have to also keep in mind is that corn on corn is going to behave differently than corn following soybeans. It's not so much a matter of that crop needs more nitrogen. It's that we have the decomposition of last year's residue going on in the soil that will actually rob nitrogen out of the soil. It's not gone forever, but it's gone at the point when the crop needs it. And so that's one of the reasons why you do need to have a little bit higher rate up front with corn on corn, A lot of cases, corn on soybeans, particularly if it's not been excessively wet, you can get away with putting no nitrogen on until you got a crop out of the ground.

Dan Kaiser:
So one thing that came up in 2024, which was interesting, is I was getting a few calls questioning the amount of nitrate we should have in the soil at certain points in time. We do have what we call the Pre-Side dress Nitrate Test, which we have some guidance on that. If you have above, I believe it's 25, 26 part per million in the top foot. This is at late May to early June up to the crop. When it's up to about a foot tall, that that should be sufficient to carry you through. But if you look at, as things go along, if you look at our optimal nitrogen rates, we know that as we get to those peak demand or past the peak demand, there ain't a whole lot left in the soil at that point in time of nitrate. I mean, you're going to find pretty much on your background levels at that point in time where the crop is drawn off as much as it can.

And that's a good thing. We don't necessarily want high, especially we get beyond VT or RR1, we don't want excessive or high nitrate levels at that point in time because the demand has peaked and we get a lot of mineralization at that point, which likely can meet the demand and things start to slow down. So with many of our soils, if you look at V4 or V8 around V12, we see essentially around our optimal levels where things have really started to draw down or we're near background levels of nitrate. So it speaks to a lot the ability for that corn crop to scavenge it, and that reduces the risk substantially for losses at that point in time. So it's one of the things, again, reiterate that is 10% by V6, by VT, around 70% is taken up.

So you look at, again, peak demand between those two, and that's really where we want to try to maximize availability. Our sandy soils are a little bit different. We know that they're going to run out a little bit quicker. So if you want to talk about split applications, there's a reason we recommend that because the leaching potential and the ability to hold nutrients is a lot lower. And we see things start to, especially with a single application, run out a lot sooner, which makes sense. I mean, everybody’s going to understand that you're going to run out sooner in a sandy soil versus a medium or fine textured soil, but the principles are somewhat the same, although split application is need to maintain more availability over time in those sandy sites.

Brad Carlson:
Well, one of the other things that happened in 2024 is and Dan, you and I both had this happen with farmers contacting us with soil test numbers for in-season soil nitrate tests. The numbers were very low. In some cases the numbers were low and the crop didn't look real bad. And so what we also have to realize is the limitations of that test. And one being that it could be that some of that nitrogen is deeper in the profile and deeper than you soil sample for, but also that we know that our soils have the ability to supply a lot of nitrogen through mineralization. The crop itself is probably scavenging that as fast as it's become available. If the demand goes beyond the ability of the soil to supply it, then of course you're going to see deficiency. But it's also one of the reasons why we don't see a lot of response when we put on late applied nitrogen because at that point we are supplying a fairly decent amount of nitrogen out of just simply mineralized sources in our high organic matter soils.

Dan Kaiser:
And the thing to remember is that a lot of key metrics when it comes to some of our yield metrics are set early in the growing season. So for starving the plant at certain points in time, we're likely going to be setting it back so the yield potential is going to be a lot less. So that's one of the things to just watch out for. We know we might be able to catch a little bit of a boost late season for some nitrogen say for rescue treatment in grain if we look at the seed mass. But overall, if you look at the number of kernels on the year, a lot of that's going to be set earlier in the growing season. So that's always the question when it comes to how much do I apply? And one of the things I will stress is that if you're using something like that Pre-Side dress Nitrate Test, the value is really up through about a foot tall or up to about V6.

Beyond that, looking at the data, we know that the soil starts to draw down and that we don't have an accurate calibration for the number that would be sufficient at other growth stages. Brad you mentioned too, if you look at, as I said, if we have up to 70% of our end taken up by the VT growth stage, we only have 30% for that later. If you're going in with a late application as a rescue treatment it doesn't make any sense what 80% of your total in you'd need at that point in time as the plant can't take it up physically. So you need to understand essentially what you can do. And in many cases, we look at a lot of our recommendations in 2024 with some of these fields that had some excessively wet conditions was about 30 to 40 pounds an additional, it wasn't that full rate of nitrogen in some of those because it's just looking at the overall benefit, it's really hard to see the benefit.

I mean, there's certain circumstances if you can get in early enough, maybe a higher rate would be effective, but you need to have time for that nitrogen to get to the roots to become plant available. And that's really I think the key and Brad, I think where you're talking about the spoon-feeding, I think where you struggle on that is just if you're too close to the time where that crop needs, it takes some time to get into the plant and you could actually be starving it. Irrigation, fertigation, different story. I mean, if you've got that in your portfolio with the water there, you can get it into the plant. But that's really the key thing is, is it going to be in time for that plant to effectively use it or am I going to be starving it where I've already lost yield? So that's the decision that needs to be made when it comes to a lot of these timing decisions.

Brad Carlson:
We're getting close to wrapping this up, and a lot of farmers say, "Well, what do you think the ideal management is?" Very particularly farmers need to assess their soils, their fields that are at high risk to loss and just simply not fall apply in those areas. If you've got coarse-structure soils, of course, and in a lot of cases those you're not even allowed to fall apply there, but also places that are excessively wet that are poorly drained are also at a high risk. Just simply don't apply fall nitrogen in those spots' because you're at the high risk of losing that. I think that's really probably the key for any of this. And after that, it's more of a matter. We've talked about a lot as far as knowing what the options are that you have available for application and working with those.

Dan Kaiser:
Well, I think that is the key. I think logistics do factor into a lot of this, but you look at situations like you were talking about Brad, fields with high levels of denitrification. I mean, those are ones, if I was fall applying, I mean I would maybe have the tendency to go with a lower rate, put only a partial amount of the nitrogen and then come back in the spring because then you can make a decision. That was one, I think the tough choice in 2024 for growers was, do I pull the plug on this or not? Do I just leave it alone or do I come back in and I put additional nitrogen on? And it isn't an easy decision, particularly if you have lower commodity prices and if you've got still what I would say pretty strong to high nitrogen or fertilizer prices, is am I going to get enough to pay for that additional management?

I don't envy a lot of growers on that because when you look at, I know what you've got at stake out there with the crop you have out there, I mean it can be a big difference in terms of that. But we know that especially the later applications that most often, if you're looking at really late season post-tasseling applications, a lot of those rescue treatments, and we've only seen very limited number of years where those have actually effectively worked. I mean, this might be one if we've got some moisture later on that can get the nitrogen down. But looking at it, if you're making that, I would really making that decision to apply late, I really wouldn't be putting on more than maybe about 30 pounds if not less, because the crop's not going to use it. That's one of the biggest challenges.

Brad Carlson:
So I guess to wrap things up, as we struggle with the issue of needing to reduce the amount of nitrogen loss into our surface water by 45%, that's the goal That was set by the Nutrient Reduction Strategy. That's a nationwide goal for the Mississippi River. The question becomes how much of that can be done with nitrogen management and how much needs other sources? And I think really the key to all this is let's not make it worse before we go anywhere else.

And one of the issues, and we've spent the podcast this time talking about timing, but when we talk about nitrogen rate, one of the issues we talk about with nitrogen rate is don't use rate to compensate for making less than desirable decisions in other aspects. And particularly that other aspect is timing. And so when we talk about timing, choose the ideal timing for your site and then select the appropriate rate, don't just choose the timing that you would like in a lot of cases being fall and then just jacking your nitrogen rate up because you're going to lose a bunch of it. That's just simply not a sustainable practice for us as an industry.

Dan Kaiser:
And one parting comment for me too, it's really the source thing I think is a big issue, and that's one of the things that sources do matter. When it comes to timing, particularly urea. We've really been pushing, or we've been providing a lot of information that we've had showing that fall urea, we generally, if not always take a yield hit on it. If you look at comparing it with anhydrous ammonia, you're going to at least 75% of the time out-yield fall urea with fall anhydrous. It just isn't a very good practice. And that's one of the things that I guess concerns me with some shifts in just ammonia versus urea being sold across the state is there's no way right now to safen that urea to make it where it will behave like anhydrous. So that's one of the things that there is a, if you look at it, there's a big source by timing interaction that does come into play that looking at it, you need to weigh your options.

And we know that especially in-season application, that there are a lot of things you can do with urea in-season where if you have the time to get it on after planting, you wouldn't really need to worry about a fall application. Strip-till something where urea is banded, I think might be a slightly different story. But for broadcast applications, there's just really no way to safen it. So if I could leave somebody with that out of this discussion is to know that these sources aren't all the same, and don't let anybody tell you that they are, that they can essentially take one product and make it behave like another, because the transformation pathways are always completely different, particularly with a lot of these sources. So just be cautious of that because really it's not worth having to go back and replace half the fertilizer in the spring or as a side dress when you put it on in the fall where you thought you had enough.

There's too much risk there, especially these sources like urea for loss, where you're likely going to be more often than not coming back in and reapplying at some point with an additional application. It just isn't really a good practice to consider. It's one of the things we'll see probably going away in many parts of the state is that acceptable practice of fall urea in the western part of the state. It just isn't as much anymore with that. So that's the main thing I think to look at is that, is just watch your sources and make sure you know what you're applying and that you're getting the most availability You can.

Jack Wilcox:
Dan Kaiser, Extension Nutrient Manager and Specialist and Brad Carlson Extension Educator. Thank you both for all of this helpful information.

Dan Kaiser:
Thanks.

Brad Carlson:
Thank you.

Jack Wilcox:
Have a question about something you see on your farm? Send an email to Brad Carlson or Dan Kaiser at nutmgmt@umn.edu. Thank you for listening, and we look forward to seeing you next time.

Advancing Nitrogen Smart is proud to be supported by the Farm Families of Minnesota and their corn checkoff investment through Minnesota Corn.

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