Soybean fertilizer management
University of Minnesota Nutrient Management Podcast Episode: “Soybean fertilizer management”
May 2023
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 the University of Minnesota Extensions Nutrient Management podcast. I'm your host, Jack Wilcox, communications generalist here at U of M Extension. In this episode, we're talking about soybean fertilizer management. We have four panelists here with us today. Can you each give us a quick introduction?
Fabian Fernandez:
Hi, I am Fabian Fernandez. I'm a nutrient management specialist located on the St. Paul campus.
Dan Kaiser:
This is Daniel Kaiser. I'm also a nutrient management specialist, also located on the St. Paul campus.
Seth Naeve:
And I'm Seth Naeve, soybean extension agronomist.
Jeff Vetsch:
Jeff Vetch, I'm a soil fertility researcher at the Southern Research and Outreach Center.
Jack Wilcox:
So there's more talk about farmers looking to foliar application of liquid fertilizer to soybean to increase yield. What research is out there on this practice?
Dan Kaiser:
So Jack, this is an interesting one because we take a lot of grief on this, particularly with a lot of our research we have. Because a lot of growers are pretty well, well, you see some that are really sold on these practices, particularly related to foliar application of nutrients in season because they're already going across the field. So it makes sense to just put a little bit of extra in the sprayer and put it on. But I've been involved with foliar application studies since I started my master's, that was back around 2001. We had, just for context, a few trials out there where we're looking at NPK blends and we really didn't see any consistent results. I mean, maybe in some sites that were low testing for phosphorus or potassium, maybe we saw a little bit with that. But if you look at it in compiling the data, and one of the interesting things, back around 2015, I started working with the North Central group where we put together a publication called Micronutrients for Soybean Production in the North Central Region. And there were kind of the similar questions around that time from just people in the area about compiling the data that we have on micronutrient application.
So a few things I just want to bring up from this. If you look at the data, so I'm just trying to pull this up. Of the number of field trials, I mean, they're looking at about a hundred field trials for boron, manganese and zinc where they had foliar applications and then around 60 for copper. Only one trial that was a manganese response trial, they saw a field location with a positive response. Now, one of the things here is some of these field trials may or may not have been targeted, the specific conditions, but there might be some benefit. But the issue is it's just not widespread. And if you look at the sales practices on a lot of these things, it isn't really targeted to specific conditions. So that's one of the things that makes this very difficult with looking at the data, that there one, isn't a lot of responsive data out there.
And then two, if you look at a lot of the sales tactics recently, it's been using the plant tissue analysis for making some of these determinations, which really looking at that data, it's kind of spotty at best too. So just historically, if you look at it, there just is no consistency of it. Although, I know there's growers out there that just swear by the foliar application. But one of the things that I really stress on that if you're going to do it, just make sure you have the appropriate checks in place. That's one of the things I see with a lot of these foliar applications, it isn't necessarily one nutrient that we're applying, it's more of a soup or combination of many. So it's just not a high probability. And kind of looking at, from my standpoint, if you've got growers that are soil testing, the best option really for them is to try to make some of the decisions up front with broadcast fertilizer applications because it's a whole lot cheaper per unit nutrient applied.
Seth Naeve:
Sorry, guys. Yeah, at the University of Minnesota, we've been collaborating with some other researchers on the agronomy side of this. So us agronomists do a lot of really applied work collectively as a group of agronomists across the States. And we kind of take a different tact on this and just look at products that are being sold to farmers and try to evaluate those broadly and see where they're working and where maybe they're not working. And maybe we'll help focus some of this attention for various products.
And so we recently published a paper, I think we had 46 site years of data across 16 states. We tested six products, pretty common national products, combination products on soybean. And we basically saw nothing. So really low response. Any of the minor responses were probably just by chance because we had a large number of locations. We fully expected that we'd see something somewhere. We had a couple locations that ended up testing low on P or K that showed a little bit of response. So as Dan mentioned, we can help make up for some problems after the fact, but as a prophylactic approach, as a yield enhancing application, is really what we were looking at in this particular study. We just found nothing there. So there was really disappointing results in terms of finding something that would help enhance yields in good high production soils.
Dan Kaiser:
And it's been one of the major questions that we've had too with a lot of these liquid fertilizer products is can they actually penetrate the leaf? I mean, you've got a wax layer on that leaf. You've got essentially when you start looking at most of these nutrients, they're salts, so they're going to be polar or charged. And if you know, kind of like dissolves like, you've got two things essentially that are opposite. So they aren't necessarily going to play very well to each other. So we know that in some circumstances like urea, if you've applied nitrogen fertilizer, that will readily penetrate through that wax layer, some chelates, certainly some of the iron chelates, looking for iron chlorosis, there can be some benefit there.
But for the most part, it's one of the things that when we started looking at some of the data that I did, that's back in my master's, is that kind of the general assumption that we had is that anything that we're seeing a benefit from was essentially washing off the leaf and going through the roots anyway. So that's kind of the struggle when I look at this. If it's doing that anyway, if again, you have any soil test, why wouldn't we want to make some of those decisions up front than trying to be reactive on some of what's going on? So that's the difficulty, is always that big question. Is it actually getting into the plant? And the other thing too with a lot of these micronutrients that you have to realize is that the majority of them are immobile in the plant. So even if they would get into the plant, then the question is do they translocate, which technically they shouldn't.
So essentially, if you do have a problem, to me, the problem's going to persist. And we see that with iron chlorosis most of the time with foliar applications. We need to make the application before the problem comes into play. And then we may need repeated applications because that iron may not be translocating within the plant. So to me, if I look at this, it just isn't the most efficient way to apply an annual cropping system. You can, I think, make the argument for some perennial crops or some high value crops, I think it's more common some of these foliar applications. But just for a lot of our annual cropping systems, it's just better off having it near the roots where the plant can feed off those nutrients versus trying to put it on then hope that it's going to get into the plant after a foliar application.
Seth Naeve:
Yeah, I guess to just tag on a little bit more on there, I think in thinking about farmer profitability and thinking about this from a farmer's standpoint, farmers in this economic environment that we're in with high rents and high crop values, farmers are pushing for high yields at an increased rate. We were always driven by yields, but right now, it's just accelerated that and pushed that even harder. And so this idea that there's a product that could help enhance these yields is really attractive to farmers. And I think that's really where farmers are going with this, is this idea that these are yield enhancers. This is going to get us an extra four bushels or two bushels or five bushels on top of what they're already getting. Maybe it's a little bit of frustration with some of their soybean yields in the past and thinking that maybe that there's some magic potion out there or even that they have some deficiency that they didn't know about. So there's a lot of psychological reasons, I think, that farmers are really attracted to these things. But from my standpoint, if they really need to spend the money, I think it would be prudent, wouldn't you think soil fertility guys, if they just spent it on fertilizer in the spring?
Dan Kaiser:
Yeah, I mean, that's kind of the thing I've really been stressing on that is just let's be proactive on what we do. And really with soybean, it's one of the things of soybean, they do just as well almost living off a residual fertilizer applications or applications made of the years ahead of the crop versus directly ahead of the crop. I mean, there's some obvious examples where this isn't the case. If you've got a high pH soil that's low in phosphorus, I mean, every year applications make sense in front of every crop because of some of the issues of how phosphorus reacts. But in most cases where I've seen some of my higher yields, it's where I've really pushed for high yields or really pushed my fertility program ahead of the corn.
And I think we'll talk about that here in a little bit here just with some of the other things that we've been doing. But it just seems like as long as you account for the bean crop in your fertility program at some point, it's generally OK. I mean, essentially, you don't need to be too aggressive in the soybean year. And we see that more and more, as Seth was saying, for growers trying to push for higher yields. It's trying to be more and more aggressive within the area. And certainly, I think there's some advantages in some cases, particularly with broadcast applications of P and K, but some of these foliars, it just gets kind of expensive. And you're not putting that much nutrient on. And that's the other thing. You look at what the plant's taking up, it's just little to nothing compared to some of what, particularly potassium, what that plant would take up based on what a lot of these liquid fertilizer sources contain.
Seth Naeve:
I think George Ream called these manure in a bottle, if I remember right.
Jack Wilcox:
Phosphorus and potassium have been long suggested in some cases for soybean. What about other nutrients such as sulfur, nitrogen, etc.?
Fabian Fernandez:
Yeah, that's always a perennial question, I would say, in soil fertility for soybeans, when we talk about nitrogen especially. The question of how much nitrogen soybeans need and if we need to fertilize for them. And we know that soybeans, they produce their own nitrogen through nitrogen fixation, which is a great benefit for soybean, but they do also require quite a bit of nitrogen. And so the question is always, should we supplement some of their nitrogen needs with nitrogen fertilizers? And so over the years, there have been many studies looking at that. And I have done my fair share of those as well. And we have looked from many different angles and we just always come back to the same thing that others have shown before, that even if you get a response to nitrogen, it's pretty limited and it's definitely not financially viable. It's just too expensive for what you get.
We did a study a few years back where, well, we tried to target different things. One of them was the timing. Right? We know that nitrogen gets fixed by the rhizobium in the roots. And so the first question is, well, if we apply nitrogen, when do we do it so that it's most efficient? So we looked at that question applying early on in vegetative stages around the R1, when they start flowering and later, around R3, when the pods are developing, just to see if applying nitrogen early on makes the soybean plants lazy and they're not fixing nitrogen versus later. And we basically found in one year applying nitrogen reduce the yield, in one year it increased the yield and the third year, it did nothing. And that's pretty typical of what we see typically with nitrogen, is just that there is not a consistent response.
And the other interesting thing is that if you have a lot of residual nitrogen or you apply nitrogen early in the season, you can potentially reduce the amount of nitrogen fixed by the symbiotic relationship. That study basically showed that it really didn't make much of a difference. And so I think the best thing that we can do is let that biological process take place, fix as much nitrogen as the plant can use, and then allow the soil also through the process of mineralization to supply nitrogen. And then the plants are able to have all that they need. And then the other side of that or question that typically comes up with nitrogen and soybeans is high yielding soybeans. That's where you're really pushing the limits and that's where maybe applying nitrogen to help with protein production, things like that would be helpful.
And so again, we have looked at that question in high yielding soybean environments and applying a substantial amount of nitrogen. And again, we saw the same results that we saw with the other studies, where in some years you do get a small bump, two to three, maybe four bushels of yield difference with an application of nitrogen in very high yielding environments. But again, when you account for the cost of that additional nitrogen, you know that it just doesn't pay for itself. So my recommendation is don't apply nitrogen to soybeans, let them fix nitrogen and then allow the soil mineralization process to supply the rest.
The one situation where I have seen some potential benefit, and again it's not consistent, but where you may have more chance of seeing a response with nitrogen is where we have had no nitrogen apply to the previous corn crop and then we plant soybean with no nitrogen. And we do that for several years, where we are basically depleting on purpose, depleting the natural supply from the soil. That's where sometimes, and is again, not consistent, sometimes we see a benefit. But again, when we are talking of practical situations, no farmer is not going to apply zero nitrogen to their corn. So in essence, it's a moot point for commercial agriculture. We see this only in experiments where we are on purpose starving the system.
Dan Kaiser:
So it's one of the things too that I've looked at is with soybean, I think I mentioned this before, its vegetative biomass becomes kind of an issue with soybean out in fields. And that's one of the things I've seen with some of my higher fertility treatments. And certainly, we've seen this with manure. If you look at a lot of the data in manured fields, you tend to see soybeans, they get shoulder-high and you look at it in terms of, with soybean, to me, I want more pods, I want more beans. I don't necessarily want more leaves and more stems and all the other material out there. But I have seen it with sulfur.
In 2008 and 2009, when I started in Minnesota, we actually had some studies looking at two by two banded with the planter. It was the combinations of nitrogen, phosphorus and sulfur. It was like a 20-20-0-20 treatment. And a lot of the fields you could pick right down to the row. Where we had that treatment on there, the soybeans are about six inches taller. We had some instances too where you could see that they were turning at different rates. So the maturities were different. And of all the fields, when we come to sulfur, there was one that we had. And it was 2009, a field we had in by Theilman, which was in the southeastern part of the state, which had not had a lot of sulfur applied to any of the previous crops. We picked up a four to five bushel yield response to the beans. And I've tried to repeat that study over and over again, and the thing that we have more with more growers being more aggressive on sulfur in the corn years, there's just some sulfur that's carrying over from one year to the next that the soybean is feeding off.
And I've done a fair number of sulfur studies with soybean in the last five, 10 years. And the only studies that I've seen where we've seen a response at Staples we had an irrigated sand, if you looked at the irrigation water, no sulfur in it, they're pulling out of a surface pond that didn't have a high sulfur concentration. We saw response at that location. And then at any other locations, at best, it's about a bushel per acre. And my best results have always come from when I look at applying near the upper end of the recommended range for corn, it just seems to carry over the soybean the previous year. So that's one of the things.
I haven't looked at nitrogen as much, but the sulfur side of it, we see more growers interested in it because of what they're seeing with corn that the rates they're putting on corn, in most cases, if you look at, we've done carryover studies, it is carrying over to the soybean crop. I've seen it, I mean, I've seen instances where I've seen a five bushel yield response where it applied ahead of corn, where it carried over and the beans still picked up some of what was left from that previous year. But it seems to, again, be situations where we're more limited in terms of sulfur supply. So that's really the thing with sulfur, it just isn't a given across the state that you're going to see. And I would focus on crops that are going to be more responsive because it seems to be more beneficial for those crops and the soybean can, with how it's rooted, seem to take up some of what's left.
Fabian Fernandez:
Dan, you reminded me of something when you were mentioning sulfur and coming kind of back to nitrogen. The carryover nitrogen, we've looked at the question too, well, if you're applying excess nitrogen to corn or you had a poor year in corn, then they carryover nitrogen, does that make a difference? And we have seen no benefit on that either. And then in terms of vegetative growth, that's also an important thing to keep in mind, especially coming out of the last few years where we had droughty conditions. I've seen, actually, the problem of reduction in yield when you have too much vegetative growth because the plants are basically using up water faster and quicker, and so they run out of water earlier in the season. And I have seen that also with corn. I mean, we are talking about soybeans too, but I've seen it in corn too. Where in the last few years if you had too much nitrogen, too much vegetative growth early on, those plants ended up running out of water earlier and you actually reduce the yield. So instead of getting kind of a plateau, typically that we see with corn, we ended up having kind of more of a quadratic response where the yield starts to taper off at the higher end rates.
Jeff Vetsch:
Dan, I would add that I think growers here say, "Well, there's enough carryover from sulfur for applied to corn that we don't need to apply sulfur to soybean," but that doesn't mean that the rate of sulfur for corn has to be increased to get that carryover either. I think the standard practice that I see or hear about is a hundred pounds of AMS. And that's more than enough for corn and more than enough carryover. And I think in many times, that's more than we need in many of these fields and it could be reduced significantly.
Dan Kaiser:
Yeah, Jeff. And I mean, looking at the data we've got, the studies that I was quoting where we were looking at, these are six-year trials where we had corn soybean rotations. So we're applying 25 pounds of sulfur. So roughly, that hundred pounds that you're talking about ahead of the corn crop. And we didn't see as much the first year, but years two and three is when, or the first soybean crop, so it'd been year two, then years four and six is where we picked up some pretty sizable yield increases where we had sulfur applied ahead of the corn. And I agree with you. I think if I'm in southeastern Minnesota or I'm on a situation where I'm in a more eroded area, like a three percent organic matter or less, 20 to 25 pounds of sulfur ahead of the corn should be enough to carry it through.
And I think kind of where you're at, Jeff, at Waseca on those heavier, those high organic matter soils, you probably could look at about half that, maybe 15 pounds and still see some carryover. Because we know that a lot of those soils only require about, corn, about five to 10 pounds on an annual basis. So it's amazing the sulfur doesn't take a lot and still the soil is supplying substantial amount. It's just the problem is we've got a little bit of a window there where the soil can't supply it all, where we tend to have our problems with it.
So that's just one of the things that I kind of stress to growers is you look at it with sulfur as corn and alfalfa are the two main ones if you look at the majority of central to southern Minnesota that I would focus on. The rest of the crops, it just doesn't seem like there's any consistency in our data. I think a lot of it has to deal with how we're going onto these fields where growers have previously applied sulfur, that the concentrations are elevated, that these other crops they don't need a lot and they're just being able to pick up and scavenge what they need in the soil from what was previously applied.
Seth Naeve:
And just to restate what you've said earlier, Dan, is that soybean is really, really efficient at utilizing these mineralized nutrients. And in fact, in many cases, it doesn't seem to take up as well in season or preseason than previous. So some of this may be even related to this factor too. And Jeff, before our talk here reminded me that I was part of another study where we did an N&S study with the same group of folks and we found very similar response to what Fabian and Dan have talked about with nitrogen and sulfur in soybean, is that very rarely did we see anything. And I've been working on nitrogen forever. And I've had a real interest in increasing the quality of soybeans, increasing protein level. And even nitrogen does a poor job of doing that. Sometimes we can get a yield bump, sometimes we can get protein. Both rarely and never do we see both coincidentally. So there's definitely some trade-offs here.
And then one thing I did did want to jump back on, another thing is this whole question about canopy development is really, really interesting to me. And it's honestly, as a soybean agronomist and physiologist, I think our biggest, the holy grail in soybean is really trying to figure out the right canopy for the right year. And if you could design the growth of your individual soybean for the weather you're going to have that year, that's the way we get our yields. Dan's absolutely right. Sometimes we get too big a canopy. The soybean puts way too much effort, too much energy into building that big canopy and then it isn't able to fill the pods. It doesn't set as many pods. I mean, every farmer gives examples of these two feet tall soybeans that they harvested that were 50 or 60 bushels or six feet tall soybeans that yielded 20.
So this is a huge problem in soybean. We get too big a canopy, we rip through too much water, like Fabian said, or we get lodging and white mold and other problems that ding us. On the other hand, we do have to have a good canopy to absorb light and store resources to mobilize the seed at the end of the year. And so if we knew exactly what kind of weather we would have, I think we could do a little bit better job. But sometimes the soybean is doing some funny things out there where it just doesn't, it's getting tricked into either thinking it's got too long a season and it needs to grow another couple nodes or it feels like things are really tough and it just needs to hang out and put on pods now at this kind of 10 nodes. And so I think there's an opportunity to learn here and move forward both from a breeding and genetics side and from a management side to figure out how to build the right canopy for the right year.
Fabian Fernandez:
And I don't know much of about physiology, Seth, but one of the issues too, I think, is that when you have too many leaves, you end up with a whole bunch of leaves underneath the canopy. They just sit there, use resources and do nothing for the plant or for producing the seed. Correct?
Seth Naeve:
That is correct. But there is some really good research that looks at the energetics of that and they've basically determined that the soybean pretty efficiently reabsorbs the nutrients from those lower leaves. And even though they come at some cost, even though they're shaded for a lot of the year, the soybean actually is able to basically kind of like a senescence type process where it pulls those back. And the findings indicate that that probably isn't as big of a deal probably as height, height costs money or costs resources of course. But I think also this water thing that you mentioned is really important.
Jack Wilcox:
Are there any nutrients or any other practices that you would not suggest for soybean?
Dan Kaiser:
It's an interesting question because I sometimes think it's a lot easier for me to kill the soybean plant than is for me to increase yield with a lot of my studies. So one of the things we kind of look at with it is you look at things like boron. I've had some pretty good success about inducing boron toxicity, and that's one of the things that you hear a lot of people talk about. Because a lot of times you start seeing dry weather conditions, you pull a tissue analysis and just low boron concentration and dry weather tend to go together. So then foliar applications are applying some other treatment. If you overdo it, that tends to be kind of a real knife's edge when it comes to toxicity. So that's one of the things that does tend to come up.
I am looking right now at potash chloride. Roughly 50% of the material is chloride. If you're buying potash fertilizer, it's slightly less but it's pretty close. And soybean, our northern varieties are not tolerant to chloride applications. So we're seeing this. If you look at Morris, some Crookston, Lamberton, Western Minnesota, seeing issues with chloride being carried over from one year to the next from high applications. And it was around 2014, it tipped me off, I was at Morris looking at some of my long-term plots and it was just a stair step where I thought it was actually a rate increase, but it was actually the opposite. As he went to lower rates, the beans were taller. And as he went to higher rates, the beans were shorter. And it showed up in yield. And it's not something you're going to see always.
If I look at Waseca or I look at southeastern Minnesota, I look at my data and I might be catching maybe a bushel lower yield with some of these higher application rates. If growers got 70, 75 bushels, if they had 69 or 74 bushels, would they even notice that? I mean, that's kind of one of the things. That one's a hidden one and it can be really severe if you put on high rates like I like to do, is I kind of like to salt the earth when it comes to some of the rates we're applying with chloride just to induce the problem. And you can see some pretty substantial yield reductions. But in most cases, growers, if they are seeing it, it's probably so little that they would never really notice it. Yet you're spending money on fertilizer that's actually seeing a cut in yield doesn't make a whole lot of sense to me. So it's one of the things that I'm kind of wrapping that up now. We'll probably look at some more data with that.
I've got some information in the soybean fertilizer in Bolton, talking a little bit about just trying to limit rates. If you're putting any potash ahead of soybeans, particularly in the western part of the state, I just try to stick to about a hundred pounds or less and just be more aggressive in years where you have corn, wheat, some crops that tend to handle it better. And I do have data now looking at fall versus spring application. A lot of the studies that we were looking at were a fall applied potash and we're still seeing the issue, but it does tend to reduce significantly the amount of chloride in the plant with a fall application. But I don't think it necessarily eliminates the problem. So those are kind of a couple good examples.
The other one is starter. A lot of growers have starter on the planter. You have the units, you want to look at boosting yield, increasing early growth. You see the same effects, these effects in corn ans why not soybean? And one of the things that you have to realize is that soybean is pretty sensitive, the seed to salt, pneumonia, anything near in the seed furl. So seedling damage becomes kind of a problem with that. And phosphorus is kind of the main one we see growers is trying to supplement phosphorus on high pH soils. And no, there's no phosphorus product out there that doesn't contain nitrogen. So that's kind of my general concern with that. And we are starting some work this year. I do have a set of furrow jets that I'm putting on. So I'm going to kind of play around looking at low salt fertilizer sources compared to, I'll probably use 7-21-7 instead of 10-34-0 for the higher salt mix.
But just seeing what these dual side bands and kind of what I'm expecting to see is pretty similar results to on-seed placement. So there's a few things out there I'd avoid. I think those are some couple good examples. I mean, really it's one of those things that you think about soybean being something that you can just fertilize and kind of forget in some of the crops, but you do have to have some thought, I think, into it because there are some things that can go backwards on you. So that's one of the things that just more fertilizers are necessarily better, particularly fresh soybean crop.
Jeff Vetsch:
Yeah, Dan, I've seen that, to what you mentioned earlier, that kind of tailing off of the yield response to potash on occasion in soybean fields as well. And two or three different studies. And often it's not significantly different. But you just notice a bushel or two, maybe three bushels less as you get to those really high rates of K put on in front of soybeans, either in the fall or in the spring. And then I think back to some of the studies we did in the nineties when I first came here. John Schmidt, a grad student of Mike Schmidtz, we did a study looking at variety differences in soybeans with and without different rates of manure. And there was always a couple varieties that did poorly with higher rates of manure. And whether that was a chloride effect, whether it was just too much biomass growth, as you mentioned, Seth, and then you get white mold. I know we had white mold in some of those because we'd squirt it for white mold. We had lodging issues and stuff like that. But there's other factors. And I think if there's something that you don't want to do for soybeans from a fertility standpoint is it put a high rate of manure on right in front of them.
Jack Wilcox:
Are there any last words from the group?
Dan Kaiser:
Well, as I said kind of previously, I don't want to have this emphasis that what I'm saying here is that we should just forget about soybean. I think they need to be planned or part of the plan when you come with your overall fertility program. But I think with direct application of fertilizer, I mean, we talked a lot about potash. It's what I see more growers interested in because soybean removes more potassium per unit bushel basis than corn. So you can actually see the pounds per acre. If you look at a two-year rotation, probably about two thirds of what's removed in that rotation comes from the soybean year versus phosphorus, it's the opposite where the corn removes more. So there's a greater emphasis that we need to be applying potassium directly ahead of the soybean. But it isn't as simple as that.
And that's one of the things I said. Soybean frustrates me from a research standpoint because some things that I think that should be simple, that we should see, that it tends to be more complicated just because of how it impacts their growth. So it isn't as simple. Corn, a lot of times, we just put it on and if it doesn't utilize it, it doesn't necessarily negatively impact it and it would be available for the next crop. Where soybean, it can be the opposite. And I'm just trying to balance some of these growth issues. I mean, I've seen some of the things that Seth was talking about in some of my sulfur trials, looking at just seed size coming through the combine. As I'm sitting in there taking samples with the sulfur plots, the plants are about the same height out there, but you see bigger seed coming through.
So it's amazing to me in how the plant itself adjusts to some of this stuff and kind of how it reacts to it. But then yet again, more is not better when applying to it. So it's a balance and it's, to me, more of a integrating system than corn is even in terms of trying to maintain some of these higher yields. And it's more of a challenge to me on the research side trying because more growers want to know what that secret is, and I just don't have a good answer to it just because it's, again, a lot easier for me to see some of these negative effects sometimes than it is these positive effects from some of what should be beneficial applications of nutrients for that given crop within a given year.
Jeff Vetsch:
Dan, I would also emphasize that if a grower picks up a rented piece of ground and he runs some soil tests and comes back and his potash is low or medium, I mean, I wouldn't be scared to put potash on soybeans in front of them. I mean, the critical values that I've seen, Dan, you can interject too as well, here in the glacial till soils in Waseca, around 150 part per million is kind of the critical value, maybe a little bit less than that in southeast Minnesota on the loess soils and probably in that 90 to a hundred part per million at Becker on the irrigated sands. If you're below that, putting some out there and like you said, Dan, maybe a hundred pounds of potash or 60 pounds of K2O, we've seen some good yield responses in soybeans to potash.
Dan Kaiser:
Yeah, and I guess I don't want to make it seem like I'm saying not to apply it because you're exactly right, Jeff. If it's low, your soil test is low, apply it. The issue really boils down for anybody doing maintenance rates on something that might be towards that high testing range or just wants to put removal based applications, is that some of those applications looking at it and you see they might be giving you a little bit of a ding, something you're not necessarily measuring. It just might be better off if putting on ahead of a different crop. So if it's low, apply it. If it's not, I think then there's kind of where that thought has to come into play is that it's not necessarily beneficial year after year for removal based application to put it ahead of the soybean crop.
Seth Naeve:
As a token true agronomy guy here, I'm going to throw this out, is that just to remember with soybean, is that as we all know, yield is made at the very end of the year, in kind of that late August, early September timeframe, and that's when the yields occur. And that's make it or break at time. So we got to get the crop to that point. And so do the best we can. We talked a little bit earlier about trying to get soybeans off to a good start. I think that's a very good idea. It just isn't as critical as what we end up with the end of the year, but we don't have control over that. So I keep coming back to what do we really have control over? And honestly, as much as I hate to say it, it's variety selection. Farmers have to continue to do the best job of variety selection. That's how you're going to get the yields.
And it just amazes me that farmers are willing to add a bunch of products and secret sauce on things, but then they're going to buy some cheap seed from their neighbor. And that's not always the case, so that's maybe a little bit of a narrow stereotype, but I think it does happen occasionally. And we just have to remember that the yield driver is really the variety out there. And there isn't as much we can control with soybean as corn. And so keeping it simple is still a good idea. Doing a good job of just managing that soybean crop at the very least is really what farmers need to do. And I think some of the things that Dan has talked about is tweaking this around the edges is very, very important. But just soybean 101, get them, plant them in a decent soil and get them going as early as we can and then just take care of them for the rest of the year.
Jack Wilcox:
Alright, that about does it for this episode of the Nutrient Management Podcast. We’d like to thank the Agricultural Fertilizer Research and Education Council – AFREC – for supporting the podcast. Thanks for listening.
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