Fall soil sampling
Jack Wilcox:
Welcome back to the University of Minnesota Extension's Nutrient Management podcast. I'm your host, Jack Wilcox, communications generalist here at the U of M Extension. In this episode, we're talking all about fall soil sampling. We have four panelists here with us today. Can you each give us a quick introduction?
Dan Kaiser:
My name's Daniel Kaiser. I'm a Nutrient Management Specialist located out of the St. Paul Campus.
Brad Carlson:
Brad Carlson, I'm an extension educator located in the regional office in Mankato.
Lindsay Pease:
Hi, I'm Lindsey Pease. I am a Nutrient and Water Management Specialist at the Northwest Research and Outreach Center in Crookston.
Fabian Fernandez:
And I am Fabian Fernandez, also a Nutrient Management Specialist located in the St. Paul campus.
Jack Wilcox:
All right, let's jump right in. What do conditions look like around the state?
Lindsay Pease:
Well, the story is unfortunately a little similar than it's been the last couple of years for northwest Minnesota in that we have had a dry summer. This is probably the third one in a row, and we are still looking at dry conditions. As we're recording this, we have had a little bit of rain but not enough to make a big dent in all of the dry soils, especially if you are in one of the heavier clay areas of the valley. We're still looking at really pretty dry soils going into the winter.
Brad Carlson:
I would say in my area and across southern Minnesota, things are progressing really fast. The accumulation of heat units was such this year that we hit physiological maturity of the crop a lot quicker than normal. We started seeing corn coming out already about two weeks ago. Some of the larger farms with more acres to cover, maybe started pushing it a little bit as far as the moisture being high. Obviously, I don't think anybody went out before black layer, but things have switched to beans now, so soybean harvest well underway.
You do see a little bit of corn still coming out. One of my kids who's in school in southwestern Minnesota in the Marshall area was visiting this weekend, said that he thought maybe 25% of the crop was taken out in his area where he was at. And so, I think probably the main thing here is crops coming out a lot faster than it maybe normally does. We're going to have a whole lot more time this fall to be looking at doing field work and so forth.
I think really the key for most farmers with respect to this is not to get in a big rush because we don't have any reason to believe that freeze up or cool soil temperatures are going to come at any time other than when we normally expect them. We're just going to have a lot more time this fall to get stuff done in a timely fashion.
Dan Kaiser:
Yeah, that's one of the things. I've been around the southeast, the central part of Minnesota and stuff. I mean, dry I think is kind of the word, just looking at a lot of it. I mean, obviously we're looking at recording this around the 25th of September, so we're hitting some rain right now, but it's still going to take quite a bit of rain, I think, to start to alleviate some of the issues, particularly with some of the dry soils.
And I'll have some comments here and a little bit talking about that relative sampling because there's some things I think to think about moving forward. It was interesting to me, though, seeing the amount of corn going out. And just looking at some of our plots, particularly the ones that we had issues with drought, I mean, those, looking at the corn, one of our stations at Rosemount, I was looking at some stuff towards middle of third week of September, and just looking at some of the drier fields, the corn kind of looking like it's shut down.
I mean, amazingly enough, it doesn't look too bad in terms of yield. We'll kind of see when the combine goes through. But yeah, it's just looking at, especially going to the southeast, how dry it's been. It's been kind of that way this year. So, there will be a few things to think about, I think, moving forward, particularly when it comes to fall soil sampling that some people may want to consider.
Fabian Fernandez:
Yeah, and looking at a lot of the trials across the state, I would say that we are probably about two weeks ahead of the schedule than typical, and this is definitely a year where how soils have been managed in the past, it has kind of shown up. If you have done a good job with maintaining soils, tillage, those kinds of things, you definitely saw a difference because every drop of water was important for this crop this year, and areas where it's compacted or things like that where the soils has some issues, that's where the crop starts to fizzle out faster, fastest this year.
And same with soils that are kind of shallow or don't have a lot of capacity to store water. We didn't start the season for the most part with adequate amounts of water, not huge, not like the typical, but there was water there. And so, if you had soils with lower capacity to store water for whatever reason, for poor management or just the conditions of that soil, that's where you run out of water faster, and the crop started to fizzle out quicker this growing season.
But it will be kind of a mixed bag, I think, in terms of yields. I've seen some tremendous years of corn this year in some places, and in another, not too far from that one, there will be really low yield, way suboptimal. And so, it's kind of all over the place this year.
Brad Carlson:
Yeah, I've been talking to a few people, I haven't really heard any good yield updates, but some of the discussion I've had with some of my farmer friends were that some of the conditions were just right at just the right time as far as I'm hearing reports of there being 22 kernels around on the ear and so forth, but then it got dry at the wrong time, so we're hearing low test weights, and we're hearing kind of shallow fill on those kernels and tip dieback.
And I know we experienced a lot of the bean fields at the end of the year here, just never put pods on at the top because it just got way too dry right at the very end. And so, I think really the top end of the yields just didn't happen. And so, we were potentially going to see some really huge yields, and I don't think we're going to see that.
Dan Kaiser:
I'll kind of see what things look like too when we start getting yields back. We got hit with some hail and a few of the sites, so that'll be kind of the interesting thing to me to see what some of that looks like, particularly some of our field sites. We had field sites down by Rochester that really got hit pretty hard, just to see how that impacts, but I'll kind of echo those sentiments that Brad said.
At least some of the stuff I looked at, it didn't look too bad, but you can kind of tell the ears looked a little rubbery, and it seemed like the test weights are going to be a little bit lower. And that's kind of the thing about not having the moisture towards the end of the growing season. So, we'll see. I mean, I think we're better off probably than what we could have been had it been extremely, where we had gotten no rain, but there's going to be some areas that are worse than others, just when you start getting some of the yield back this fall.
Jack Wilcox:
Is there a best time to take soil samples in the fall?
Dan Kaiser:
Well, we see this a lot, particularly typically some of the, I know at least one of the soil testing labs, will put out an article usually about taking samples behind the combine, and I think certainly getting a sample is probably better than not getting a sample. If you're sampling for phosphorus and potassium, they're kind of two different animals when it comes to timing.
With phosphorus, generally the numbers will be consistent across the growing season. So, I mean, you can sample a fair amount earlier and not have any issues. And I think zinc, some of the other micros too, you're not going to see too much of an issue. With the potassium, we do know there is some effect that, just having actively growing crop out there, you can see some diurnal variation where the tests will go up and down, so the later you can wait, it's generally better.
However, fall, I don't know if you're going to see a whole lot of difference if you're talking about a month's time difference in the fall. So, I just try to plan where you can get the samples. I think that's going to be the main thing. And certainly if you can't get out this fall, I mean, there are some options, particularly if you've got a field going to beans, maybe about taking samples sometime around June if you don't want to get them taken in the spring. So, it's going to be kind of one of those things just to see what time is out there.
As Brad said, I mean, with the crop going out right now, I mean, there really shouldn't be any issues with being able to get some of the fall work done, but it'll also depend on what happens with the weather moving forward, where I think we got spoiled last year in the fact that I don't think my crew had a down day all fall because we could always go somewhere to get some work done, which I guess is kind of bad news for some of them because it means we can have a lot of work going on out there, but kind of good from a work standpoint in the fact that there really wasn't anything limiting us time-wise for being able to get some of the work done in the fall.
Brad Carlson:
When I look at some of the data, the averages that we put together or the numbers that we put together for the Advanced Nitrogen Smart session on adapting to climate, what we see is, at least at Waseca, is that the average date we get below 50 degrees soil temperature, so kind of the start of our nitrogen application season is October 18th. The average day that the soil freezes at Waseca is the 9th of December. That date has been marching later and later over the last 30 years. It used to be more like the 2nd or 3rd, 30 years ago.
But anyway, that kind of gives us an idea of what kind of window we're dealing with. As far as the amount of time we have this fall to do some things, I think really the key with a lot of this is from the soil sampling standpoint is if you're going to use the data then to do an application, how much time do you have to get that done?
So, obviously when we talk about the P and K part, that's kind of more reflective on trying to get this fall, the fall fertilizer application done if that's what you're up to. If you're talking nitrogen, I guess then it kind of depends on if you're sampling for nitrogen, but typically speaking, most parts of the state, we aren't really high on the fall nitrogen test, and so in a lot of cases we don't necessarily look at taking that test yet in the fall and then making a rate decision also in the fall. That would be kind of atypical.
And then I think the other thing is of course to be cognizant of is the manure application window, which I think a lot of folks are... Typically, what we see is as soon as the crop gets out, people want to get started on that. Just realize that when the soils are still warm, and there's a lot of time, really puts those nutrients at risk.
And so, again, the topic du jour here is soil sampling, not necessarily our fall fertilizer outlook, but I think it is worth at least keeping that in the back of your mind, that if you're thinking you need to rush out there because you also are going to get going right away on those fertilizer applications, like I already said, remember there's a lot of time left.
Fabian Fernandez:
Yeah, I just kind of want to second what just Brad mentioned, because it is the typical thing where we have an early fall, to be out of the field with the harvest, and kind of do the schedule like you normally would, where in a typical year you'll harvest, and then you will start soil sampling pretty quick after that.
This year, as Brad said, there will be plenty of time. And the other thing, too, is that the soils have been so dry that even if we start getting more rain, it will take quite a while before the soils get to a point where it will be difficult to do field work, so don't get too antsy if you start to see some rain. It's actually a good thing that we will get some rain. Hopefully we'll get more to improve water in the soil, but also in terms of soil sampling, especially when we are talking about nitrogen sampling that is deeper, you'll have an easier time getting that probe into the ground.
The other thing with nitrogen, too, is that we've had two, three years of fairly dry conditions. And so, there could be potentially quite a bit of nitrogen in the soil. And what we see typically is after the crop goes to physiological maturity, there is no more nitrogen uptake. So, nitrogen values start to go up too, so if you want to get a good idea of how much nitrogen you have in the field, that's also important to wait, so that process of mineralization has time to occur, and so you have a better estimate of how much nitrogen you have in the soil ahead of a fall application if that's what you're planning to do.
But like Brad mentioned, normally we don't really encourage people to do too much with nitrogen in the fall, just simply because the big elephant in the room is spring conditions when it comes to nitrogen management. We could measure nitrogen now in the fall, but that doesn't necessarily tell us anything about nitrogen availability for the next crop, because nitrogen loss tends to happen mostly in the spring once the soils are defrosted, and we start getting some rain and water flowing through the soil.
So, don't get too excited about definitely nitrogen sampling, and like Dan said, for the other nutrients, for P and K. Just also wait because, as he said, in my previous life when I was working more on P and K, I remember looking at the question, and potassium is definitely one, where if you want to look at the values and have any relationship to previous years, you definitely need to wait until you have about the same conditions as in previous years so that those numbers are representative of what you saw in previous seasons.
Brad Carlson:
Yeah. I just want to echo what Fabian said and maybe build on it a little more, a conversation that I had with a farmer that I know a couple of weeks ago. We were talking about the potential for carryover nitrogen, and his first comment to me was, "Well, then I need to be thinking about doing more corn on corn so I can use that nitrogen next year."
Well, I don't know if that's necessarily the case, although this particular individual did have a long manure history on a lot of his fields, and so I suggested that because we've had several dry years in a row, and a lot of those fields have historically had manure on them, that coming out of soybeans this year is one of the scenarios where we do need to think about sampling for soil nitrate.
And then the point that Fabian made that a lot of our accumulation of that nitrate is driven by the mineralization that happens late in the year because the crop reached maturity early. It's still very warm. We're going to continue to see that mineralization, especially now that we've started to get some water. It's going to help the microbial activity move along. It's obviously not real wet, but a lot of the state's got at least an inch or two of rain now over the last week or so, and so we're getting a little more moisture at the top.
So, if what you're looking at is trying to capture that and measure that, you need to wait for it to actually happen before you're going to find it. The thing that you need to remember about the soil test for nitrate is it is for nitrate. It's not testing all sources of nitrogen. And so, if that nitrogen's there but it's in an organic form, in the case of places where we have a manure history, you're not finding that. And so, you're not able to really adequately credit that. And so, yeah, it's worth thinking about. Those are the fields where you want a sample for residual nitrate. It's also worth thinking about that maybe that needs to just wait until spring to happen.
Lindsay Pease:
Yeah, and just to add on, I always like to remind people that the temperature of your refrigerator is 40 degrees to keep microbial activity slow, and similar things happen with soil. That's why we talk about waiting until the soils are at 50 degrees to put on nitrogen. It's because that's when the microbes start to slow down. So, yeah, we are getting a little water. That can increase their activity. The temperatures are still warm, so there's still a lot of activity happening out in the soils.
The other kind of argument for waiting is definitely big, because as we've mentioned before, the soils are dry this year. And there's definitely a Goldilocks principle for soil conditions. If anybody's ever done hand sampling, you know exactly what I mean. So, you want those soils to be at the right moisture to come out nicely, out of a hand probe, because if it's too dry or too wet, it's really, really difficult.
Dan Kaiser:
And I'm kind curious, I mean in terms of the number of people that are using or taking the samples that are actually using some of this soil nitrate data, because in the end, taking the test and not using it or not following through with it, I think there's some issues there, particularly with the amount of work that is involved in taking the test.
But as Fabian said, we know that it's likely that we'll see some change in the amount of nitrate in the soil over time. We always do. Now, the question is with this dry weather, does that slow some of the microbial activity? It might. However, I've kind of been thinking a little bit more about this fall sampling issue, and at least from a screening standpoint, I think there might still be some potential value in looking for some of these fields that may be carrying more than what we normally consider to be kind of an average amount of soil nitrate nitrogen.
And I'm kind of looking at just some of the data that I've collected in the last few years, just the number of sites where I think it would help me at least if I had the data in the fall, possibly to look at some of the things in the spring. I mean, the issue that we're having anymore, though, is when the decisions are being made in terms of what to apply. I mean, a lot of that generally goes, comes in place before some of this stuff actually, these samples get pulled.
So, I mean, I think there's some room. And that's the thing, kind of just looking at some of the data that Agvise sent, they had some early samples. I think this was sent to me around... Let's look here. Around the end of September, that they're talking roughly 15 to 30% of their soil samples have almost twice of what they're normally carrying at nitrate nitrogen on an annual basis.
So, I think it's something to think about. I mean, there are definitely going to be some circumstances out there, I think, where the rate can be cut. It's just essentially how much you want to believe taking a sample in the fall, how accurate that's going to be in the spring. And the data that I have shows that we're no more likely to be higher or lower or the same in the amount of residual nitrate.
So, it's a toss up. It's just a question of how much difference we're going to see from fall to spring. And if you're dealing with a situation where we're getting into soil nitrate levels that we can almost get into a full credit of nitrogen, I don't think you're really going to see that big of a difference where that's all going to disappear. So, I think that's kind of a good thought for maybe some future research is just looking at the consistency of this stuff over time, and then just trying to look at some of these fields because I think it's a good way to maybe look at areas or fields that you might have a higher residual nitrate level.
And I think one of those would be manure history fields are likely those that you're likely going to probably see some carryover. So, I guess some things to think about with it in terms of timing, why we'd like to delay. I think, though, getting that data is probably the best thing you can do, at least. At least to have some information to make a decision off of.
Brad Carlson:
Well, and I think another point on that, Dan, you raise an interesting point as far as just seeing what it is in the fall. Remember that our recommendations to credit soil nitrate are for a two-foot test, typically done zero to one and one to two feet, and obviously P and K samples are usually only to six inches. And I know there's been individuals in the past that have thought, "Well, let me just, let's test the nitrate too and see what it is." Those numbers are not correlated to overall credit or to any kind of a recommendation.
However, it may give you a heads-up, if you get a high number there, go back and take the zero to two, particularly if we're talking about maybe doing it in the spring. So, I wouldn't say that a number that is completely unusable. However, it's not probably adequate for making a final rate decision.
Jack Wilcox:
What should you watch out for when sampling dry fields?
Dan Kaiser:
Well, I think Lindsay hit it earlier is just sampling depth is a thing I would kind of watch out for. It means you've got hydraulics or something where you can get a consistent depth. I think you'll have some advantage this fall. I mean, just trying to take samples in mid-September. We're down by Rochester, and usually it's like sampling through butter down there. It's nice. It's the best sampling we usually have, but this year I could barely get the probe in the ground.
So, it's going to be one of those things that you have to remember that are soil tests our based on a set depth. I mean, you can be plus or minus maybe a little bit on them, but if normally you set a six-inch depth, and maybe you can only get the probe in the ground four inches, I mean, what's likely going to happen is we're generally going to see some stratification of the nutrients near the soil surface where you'll likely skew things high.
So, it's one of those things I guess I'd watch out for is just make sure your probes are in good shape, if you're hand probing this fall. If you've got hydraulics, you definitely have an advantage, but just keep an eye on the depth of your sampling because you could have some issues if we don't get enough rainfall to get it to a point at which the soils can sample easily.
So, that's kind of the main thing I'd be afraid of on that is just to kind of watch the depth, just to make sure you're getting the depth you need for the nutrients you're trying to analyze for.
Fabian Fernandez:
Yeah, that's the main point is this, so sampling depth for P and K. From the nitrogen side, we alluded a little bit to these, but with the dry conditions is the fact that mineralization of nitrogen starts, I mean, it happens through the whole growing season. That's what actually allows plants to have all the nitrogen that they need. They depend heavily on that mineralization part.
But once the plants get to physiological maturity, that's where we start to see the buildup because basically there is nothing to take that up, but it does take time. And as Brad alluded, the first thing that happens in that process of mineralization is for nitrogen to go into the ammonium form, and then it takes a little bit longer to go into nitrate. And so, if the soils are dry, what we've seen in drier conditions is that typically ammonium tends to build up, and it takes longer to be converted to nitrate.
So, if you go out and soil sample, chances are that you might not pick up as much nitrogen as you have in there simply because it's sitting there in the ammonium form, which is not what you're testing for. There are tests that you can use to look at that. And in research we do. And so, that's why I know that some years we have actually more ammonium than we have nitrate in the fall, in the first part of the season especially, or the first part of the fall. And that's exacerbated if it's in drier conditions. So, that's another reason to wait longer into the fall if you're going to take samples for nitrogen.
Dan Kaiser:
And Fabian mentioned potassium earlier, and that's one of the things that we know that potassium does get recycled out of the crop residue. So, I think one thing to think about, so if you're sampling ahead of a soybean crop, if it's coming out of corn, it might be better just to not sample this fall, and wait or start switching some of your sampling to the spring or to June if you can at all do that.
I mean, we know that you can still get to the field when the soybeans are small, so it's not a bad time to consider sampling. The thing if you do that, though, you have to realize if you're trying to assess your overall fertility program over time, that a fall versus a spring sample, given all things, best case scenario, that you're likely going to see differences when it comes to potassium.
So, that's one of the main things. I'll get some questions here and there, some numbers coming back screwy in dry years. I mean, I attribute a fair amount of that to the residue recycling, although if you're following corn, we're not really getting a whole lot of that recycled. I think some of the data I've seen, we at best get about 50% of whatever's taken up out of that residue by about May timeframe.
So, it's just the size, and the ability of that residue to break down is slow. So, the recovery is slow. The soybean, your sampling following soybean, I mean, that's less of an issue just because if you go out to a field, and you see that the leaves kind of tend to disappear pretty quickly in the fall that we have less of an issue. So, I mean, that could be something you could see with potassium. That's where I've kind of stressed a little bit to people taking samples maybe to switch timing if they can do it.
I mean, the issue is if you're going to be putting fertilizer down in the fall, you do not want to be sampling after the fertilizer application. So, that's one of the things. Again, getting the numbers better, but you've got to get it at a point at which you have it before the fertilizer goes on. So, it's just kind of one of the things to think about.
But there is some flexibility, if you're just taking zero to six-inch samples to potentially look at changing the timing, particularly airing more towards spring. And I think for potassium, it might give you a little bit better results long term. But again, looking at the data, just make sure you know that those numbers may not always be comparable.
Fabian Fernandez:
You're comment, Dan, took me back about a decade back when I was doing a lot of P and K work in Illinois, and just like you said, I saw that for phosphorus it's not a problem, but for potassium, man, the variability in the fall because of all of these things that you mentioned, the soil, the conditions in the soil, how much potassium has leached out of the crop, all of these variables make it complicated to know how much potassium you have on a consistent basis.
And at that time when I was doing that work, I really was encouraging farmers to, if they could do it, of course it doesn't work very well if you're in a rented situation where you're renting the land and things like that. But if you could, to start moving your program towards a spring sampling rather than doing fall sampling for P and K, and then use that information for the following crop, because the values for potassium are a lot more reliable and more consistent with a spring sampling because you allow for all of those things... Potassium coming out of the residue and all the chemistry that happens in the soil with potassium getting fixed and released, and all of these things to take place so that when you actually take a soil sample, it's reliable and more consistent.
Brad Carlson:
On the other point there, and actually I've been hit with this question in the past, Dan mentioned about not taking a soil test after fertilizer has been applied, with the prevalence of split application and nitrogen, and a lot of folks are, for instance, applying half their nitrogen in the fall and then applying the rest at a side-dress time. We've had people say, "Oh, well, it's good to know that there might be a big nitrogen credit. I only put half of mine on in the fall. Now can I go take a soil test and find out how much more I need?" Well, no, we do not have, the test is not correlated or calibrated for that application, particularly if you've already applied some nitrogen. There's just no good way of knowing whether you actually picked that up in your sampling or not to be able to then use that number for a credit. So, while you certainly can do a soil test prior to a fertilizer application, know your residual nitrate, and use that in your overall nitrogen budget. That certainly can affect how much you side-dress or even reducing the amount that you side-dress. We're not able to go in and take that test after you've done an application, particularly like a fall anhydrous application. It's just depending on what the weather's like between the time the application happened and when you take that test, it's almost impossible to interpret the results. So, don't be thinking that's a thing to do.
Fabian Fernandez:
Yeah, that's a really good point, Brad. And something you mentioned also reminded me of the fact that with the split applications, and again, fall sampling for nitrogen is debatable because of how useful it is, just because can we really predict how much of that will be available for the next crop?
But that aside, the other thing that is interesting that I've seen pretty consistent in my research is that when you do a split application, you tend to have more residual nitrogen than you would when you apply all of your nitrogen before planting. And so, that's another thing that you can keep in mind. If you have that split application, chances are that your result test values for nitrogen will be slightly higher.
Jack Wilcox:
Any new thoughts on grid versus zone sampling?
Fabian Fernandez:
Well, that's a question that always comes up, and my standard answer for that, it depends. It depends on what your objectives are. The zone sampling works very well where you know that you have differences, substantial differences in your field, whether it's topographic or past management or things like that, where that may be a better approach to identify what you have for that specific situation. The grid sampling is the other approach, of course, where you just take samples at equal distances throughout the field that you're interested in, and look at those values.
And so, it really kind of depends on your situation and your objectives. Both of them are useful tools, but it kind of depends on those conditions. So, that's what I would say. I haven't seen any recent research that has come up with something different, and that's what I always talk to farmers about.
Brad Carlson:
The tendency is to want to zone it, and I don't disagree with that, because it saves time and money if you're using, ending up with taking less samples than just simply going on a grid basis. Unfortunately, though, if you look at grid sample numbers, and then you lay them over where you think you might've done a zone frequently, they don't really match up well. And our data indicates that your fertilizer application rate should be based on soil test value.
And so, I think zoning is a good practice and a fine practice provided you've got it worked out as far as what those zones are and what you can get away with as far as reducing the total number of samples. But on the other side, we also have to be cognizant with a grid sample. If you have a dividing line between some major topography or soil types running diagonally through a grid, did that grid represent one side or the other? Or maybe neither because you averaged them out. So, those are also some things to think about.
There's one other thing I guess I'd like to mention while I'm thinking about it when it comes down to this, and that is I've heard advertisements on the radio recently of some computer programs which are taking your yield maps and turning them into fertility plans, and that does not involve soil sampling at all. And so, a reminder that crop removal has not been shown to be really a great strategy.
And so, I guess I'd just be careful about that. It seems quick and easy, but frankly, if it really was that quick and easy, we'd have been doing that decades ago already. And so, maybe do some investigation or buyer beware as far as using that from a technology standpoint.
Fabian Fernandez:
Yeah, I was just thinking exactly the same, Brad, that I've seen that quite a bit with people that take soil samples, and then they try to use that information and mash it together with yield removal and things like that to manage their P and K. And it's really a bad idea. The analogy that I use for that, and having looked at data like that, is when you do that is try to drive by looking at the front wheel of your tractor and make a straight line. You cannot do that. It's going to be a disaster. It just doesn't work out. We've tried it. We've looked at it. I'm sure Dan can talk more about this, but it is a problem.
And the other thing that I would mention with whatever you use, grid or zone sampling, you are taking samples, and typically you're analyzing them for P and K. Do look at those values and see what you need. Because in my experience, again, going back to when I was doing more work on phosphorus and potassium, is that in general, people tend to apply more phosphorus than what they need. I mean, they have the soil test information, K is deficient, phosphorus is sufficient, and they go in and apply what they normally have done for years.
And I think there is a huge opportunity there to save on costs, and maybe shifting some of those dollars from the nutrient that you don't need to apply as much or any to the one that you need more. So, do pay attention to those values, and use them to your advantage.
Dan Kaiser:
Yeah, and I think if you look at profitability, I mean, I think Fabian hit the nail on the head. If you look at growers that have just been doing crop removal year after year after year, I think they're grossly over applying phosphorus. I think you'd probably find them of vast majority of them the phosphorus is well above the critical level and point at which you're going to see any possible return from them.
And it seems like we've been so ingrained, particularly since a lot of these soils were low in phosphorus, that they just need it. It almost becomes an addiction to apply it. So, I think just looking at what worries me right now is the fact that we're overestimating the value of phosphorus in many of these soils that are likely able to carry the crop, and they're underestimating potassium. I mean, it seems like essentially phosphorus, potassium, now maybe sulfur ahead of potassium, that I've been seeing some issues with potassium soil test drops.
So, it's one of the things I just watch with that. And if you're zoning, the grid versus zone, I mean, there is a difference too in the quality of how people are gridding. If you're just taking a single point from the center of that grid, expect a lot of variability from that.
I mean, you really still need to do a decent job of getting a good representative area within those grids if you are sampling. Otherwise, we know there can be some significant error involved in plus or minus what that actual soil test is, what the actual value is out there.
So, just be careful with that. The two-and-a-half figure grid, there's nothing wrong with it. I think there's nothing wrong with zones in some fields, but there's really, I think, not a best system overall. It's just whatever fits the particular field.
Lindsay Pease:
Yeah, and I think if you're interested in trying a zone sampling, one of the tools that we use as researchers all the time is obviously the Web Soil Survey, which is free. You can look up your field online. So, that's a tool to use. It is kind of worth that caveat of, it may not be exactly right because they didn't necessarily take those samples from your field. So, if you are using Web Soil Survey, just make sure you're also kind of overlaying your knowledge, your personal knowledge of the fields too, because sometimes you'll notice things about those fields that don't quite line up with maybe the borders that the Web Soil Survey says.
So, your instincts could very well be correct that there might be, you want to factor that into your zones. So, those are just some kind of things that I've noticed from looking at Web Soil Survey over the years versus where we have had at the Research and Outreach Center a very detailed soil survey that does differ in some places. So, those are just some things to keep in mind.
Jack Wilcox:
Are there any last words from the group?
Brad Carlson:
Well, I guess one thing I'd like to point out, and it a little bit builds on what Dan just said. One of the analyses I've been doing for the last several years is to look at the MNSCU Adult Farm Management Program record summaries that are available to anybody on the FINBIN website. You can actually break down the most profitable farms versus the least profitable farms and look at their crop budgets. And what we've discovered now for the last seven or eight years is that the least profitable farms overspend on fertilizer by 20% to 30% compared to the most profitable farms. We don't know specifically what practices those people are engaging in, but this has been consistent year in and year out. We are not seeing over-expense on other crop inputs the way we see over-expense on fertilizer. So, just kind of be cognizant of that.
Fabian Fernandez:
The other thing that I would just say, a reminder not related to the topic, but fall is a busy time in the farm. Be cautious, get good rest if you can, but be safe above all because I know that people put really long days, and just take care of yourself too.
Jack Wilcox:
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.
