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In this episode of the Nutrient Management Podcast, we’re talking about soil test myths. First, why is it important to discuss these pervasive myths surrounding soil tests? Myth 1: the Mehlich-3 test is a better test for farmers to consider: Myth 2: I can predict my nitrogen requirement with the cation exchange capacity test. Myth 3: K base saturation is the better way to predict potassium. Myth 4: I need to run an analysis of all micronutrients.
Welcome to University of Minnesota Extension's Nutrient Management Podcast. Each month we bring you the latest research in nutrient management for crops and how you can incorporate the latest tips and best management practices to your farm.
University of Minnesota Nutrient Management Podcast Episode: Soil Test Myths
November 2022
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 Extension's Nutrient Management Podcast. I'm your host, Jack Wilcox, Communications Generalist here at U of M Extension. In this episode, we're talking about soil testing myths. We have three members of Extension's Nutrient Management Team 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 at the University of Minnesota, located at the St. Paul campus. One of my key areas of research is in soil testing, so this is an area that I've got a fair amount of experience with.
Carl Rosen:
Hi, I'm Carl Rosen, Soil Scientist at the University of Minnesota in the Department of Soil, Water and Climate, and my area of expertise is nutrient management, and I also have experience in soil testing.
Brad Carlson:
Brad Carlson, I'm an Extension educator in the University of Minnesota Extension, work out of our regional office in Mankato, statewide. A lot of focus on water quality issues, and so that's had me working on nitrogen a lot over the last several years.
Jack Wilcox:
Brad, can you give us some context to the soil testing discussion and why it's important that we talk about it?
Brad Carlson:
Jack, over the years throughout my career, it's been clear that there's a lot of farmers that consider soil science to be an intimidating or highly technical topic, and it can be, and I think we realize that for most farmers, there's so many things to keep track of these days as far as seed genetics and herbicide programs and so forth. And so frequently what ends up happening in the soil side is that's one area that a large percentage of farmers choose to just simply go external for their information because it seems easier to focus in other areas.
And so we hope the fact you're listening to us today that we're one of the sources that you go to for that information. We appreciate that, but there's obviously other places that are also providing information. And one of the things I've been concerned about over the years is the fact that some of this stuff, it's technical and occasionally I think it gets presented to farmers in an overly technical way to the point where it becomes confusing. And so I get concerned that it's being used to sell products or push information that's really not research based, and frequently can just end up costing farmers a lot of extra money in the long run.
Jack Wilcox:
Let's talk about myth number one: The Mehlich-3 test is a better test for farmers to consider.
Dan Kaiser:
Well, certainly that's one question I get from particularly a lot of state agencies because across the country, I think one thing a lot of our, particularly the NRCS would like to see as a singular soil test being used in all states across the country. And the Mehlich-3, if you look at it, you look at all the options we have, I mean Minnesota right now, we recommend either the Bray P1 or the Olson test as we have a significant amount of information really to back those up in terms of that they predict crop response. So the Mehlich-3, what it's meant really to do is to be a test that you could use across soils to particularly going from acidic to calcareous soils, and there's some advantages to that. The main issue though is we haven't been able to get it to work to all the soils in Minnesota.
So that's really the thing I stress to a lot of growers when we start talking about this is that we need to have backing research that shows that we can correlate the soil test to crop response so we can, if you are looking at a relative yield or deviation for maximum yield, that there's some relationship to it. So I think there's some utility there that where it could work. My main fear though is in particularly the western part of Minnesota, should we recommend this? So a lot of labs are going to go to it because it's a more high throughput test that we can't necessarily use it across all soils.
So then you're still looking at running two tests and in the end, I don't think it's really going to save us anything. And then the other thing with the Mehlich-3 is with any soil test, particularly with phosphorus, if you look at how the extraction is run, then how the analysis is done at the end point, is you can get different results. So you have to have that correlation data for if you change one little thing, it means you can use about any extraction solution you want to use. As long as you have the correlation data behind it, it's fine, but it's not going to give you the same number, so you can't use the same recommendations for the test. So that's really the main issue I have with it. And while it would be a good one in terms of cost for most labs, it's that prediction factor that really worries me the most.
Brad Carlson:
And I think historically we did a little bit of a disservice years ago by presenting results from these tests in pounds per acre. A lot of farmers then got the impression that's how much P I've got per acre, how much K I've got per acre, and therefore how much do I need, when in reality that's not what we're showing. I think way back at the very beginning of my career, almost 30 years ago, we changed those to just simply be reported in parts for a million. I think that's one of the big myths as a lot of farmers do think that that's what they're finding out when they do a soil test, but in reality it's just an index. It's how much of that nutrient was extracted in the laboratory, and there's lots of different methods that can be used for that extraction. Years and years ago, land grant institutions across the country ran basic research evaluating these methods and determined which method was best in each state, and there's a wide range of that across the US depending on the soil types and conditions.
And so based on that approved method, then from there research was conducted, establishing critical levels for soil test values as well as predicted crop response when you apply fertilizer. And so anytime you're using a non-standard soil test, you have to realize that there's not a backbone of information of research to stand on regarding what's going to happen if I use this number to base a fertility plan on. And so from that standpoint, again, we need to get across what you're getting back is not the pounds per acre. It's really an index of the extractable amount of that nutrient on that soil test report.
Carl Rosen:
And just to follow up on that, Brad, the Mehlich test is just one of many tests that can be used. It's what we call more or less a universal extraction. And the one advantage of that is that you can analyze all the essential nutrients at once, particularly phosphorus, potassium and some of the micronutrients. That's the one advantage of it. But you run into the same problems as Dan said with high calcareous soils. It will often fail on that similar to the Bray test. And so you're still going to end up in most cases, needing a separate analysis on those particular soils.
The other problem with the Mehlich is that and also as Dan mentioned, the way that it is actually analyzed will affect the result that you get, particularly for phosphorus. And so if you're using the Mehlich test in a soil testing laboratory, you're going to use a different analysis than you would in most cases for the Bray and the Olson. And so those numbers will need to be recalibrated if you use the Mehlich in that particular case. So it can be used, it's used a lot in the eastern part of the US now, it's becoming more popular. But again, you need to understand what the issues are if you choose to use that particular test.
Dan Kaiser:
And I wanted to follow up on one thing that Carl said. That's one of the issues that the Mehlich-3 can fall apart at times. And it's somewhat like the Bray. The Bray actually in high pH soils, particularly that have high carbonate, if you're above 5% calcium carbonate equivalency, a lot of times it'll neutralize the Bray. So what you'll end up with is almost a water extraction, which will hardly pull any phosphorus out of the soil in some of those. The Mehlich actually tends to go the other way in some of those soils. And I don't exactly know what's going on behind it, why it does it, but it actually will over extract. So you might actually end up with a situation where it tells you you have sufficient phosphorus in those areas and you may not. So it's mainly an issue with phosphorus. If you're dealing with potassium, the recommended procedures, the ammonium astate procedure we use here in Minnesota and in many other states, it'll give you the same numbers.
If you look at Southern Minnesota for phosphorus, if you use the colorimetric procedure, which is what we use for the Bray, I'm not going to get into the technical details of that other than that, if you look at it will extract about the same amount, maybe about a part per million higher or two. It's pretty similar. So if I'm dealing with a soil, say pH of seven or less, you probably could use, if it's the colorimetric, you could use it the same as what our current recommendations are. So given it's plus minus, maybe one or two PPM. The issue with a lot of labs, they run it what we call through an ICP, which analyzes everything all at once. And the issue when it does that is that it will read some of the organic phosphorus that's extracted. So what you'll tend to see in many cases with labs is you'll get about a 20% higher value than you would with the colorimetric.
Now that's one of the things now, if you switch labs, say you had a Bray run and you're now switching to a Mehlich-3, and you all of a sudden get higher values, it's probably because of how they're analyzing it at the end. So that's one of the things that you get concerned there. That's one of my main points before is that you need a different correlation for it. So the numbers aren't going to be the same, more often than not. So it's mainly an issue with phosphorus. Again, potassium is the same and then micronutrients are a mess. The zinc levels kind of correlate with one another. The Mehlich-3 tends to give higher levels than the DTPA procedure that we recommend. But if you look at a lot of the data, I was on a regional project with several states in the north central region, and there's almost no correlation between the copper, manganese and a few of the other tests that are commonly with the DTPA and the Mehlich-3.
So fortunately, we generally don't recommend using any of that because we don't have a documented need for many of those other micros. But if you're running them, realize the fact that you just cannot use the same set of guidelines across tests. So you've got to look for them specifically. The other thing too is if you're getting a Mehlich-3, make sure it's a Mehlich-3. I had a grower a couple years ago and sent some samples out on the cheap, he wanted to get a good deal, so he sent them out the state and they sent him back a Mehlich one, which is a completely different test from the Mehlich-3. It's like the Bray P1 that we recommend and the Bray P2.
They extract different amounts and he wanted me to help him come up with some interpretations. And based on the data I've seen, there's absolutely no relationship between the Mehlich one and some of our other tests. So that's the issue with, its better off trying to get something or if you're analyzing soil do it or within the region you're in. So hopefully then you can make it a lot easier to get yourself some recommendations in the end.
Carl Rosen:
Yeah, I think the bottom line is that you need to know what the test is that you're running and you have to be sure that you know there's good correlation with what those numbers actually mean.
Dan Kaiser:
And in some labs will actually, I've heard of it that they'll run a Mehlich-3 ICP and they'll re report the data based on some in-house correlations as a Bray or an Olson, which there's some danger there with that because you're getting a lot of assumptions with some of that. So I'm not outing any specific labs with that, but that's why I always say it's really good to have if you're running samples, at least to do it regionally or try to stay within the region you're in because the labs are generally going to run. The recommended tests for that are more applicable for the soils you have.
Jack Wilcox:
Myth number two: I can predict my nitrogen requirement with the cation exchange capacity test.
Brad Carlson:
Well, the cation exchange number is a part of the soil test report. Farmers have long seen that number and thought, well, what do I do with that? Really it's an index that correlates very strongly to the amount of clay in your soil. So clay particles are negatively charged and therefore the more clay there is, the more ability there is to hold cations. In the southern United States, this is a big deal because when clay particles weather, they lose those exchange sites. So if you get, for instance, down in Mississippi or Arkansas, you can actually have a lot of clay in the soil and not have the ability to hold cation or have a lot of soil fertility because of the nature of the clay and the soil. In Minnesota, this isn't a thing. We actually have separate nitrogen recommendations just simply based on soil texture.
And this is a case where I think things are really being overthought as far as this research or I keep having people throw this out. Oh, the cation exchange capacity tells us how much nitrogen the soil can hold. Well, tell me what that means because, so you apply anhydrous ammonia and it turns into the ammonium form, that's a cation. So if it doesn't hold it, what are you saying? That there's cation leaching? It's an ion, it's not going off into the atmosphere. And not only that, but the nitrogen cycle is a real thing. The ammonium turns itself into nitrate, and that's nitrates not a cation. And it makes no difference what the cation exchange capacity is once the nitrogen's in the ion form when it's nitrate. So just really isn't a factor as far as how we manage nitrogen. You really need to concentrate on the four R's in terms of what's most appropriate for application timing to prevent loss.
And so particularly on these sandier soils, we look at splitting the application and using multiple splits. From that standpoint if you have soils that are prone to saturation or a lot of water movement through them, you're better off moving the application closer to the time of planting or the time of nitrogen use by the plant. But realistically, the cation exchange capacity of the soil has no bearing on either how much nitrogen you can apply in the soil or potentially what the crop needs. That's completely independent. It's just again, I think it's an area where some people have just decided to get real technical and I think it's just being done to confuse farmers in a lot of cases.
Dan Kaiser:
Well, and that's one of the things too, if you look at a lot of the early information regarding this. I mean the majority of it or all of it actually was geared towards anhydrous. So if you're looking at any of your other nitrogen sources, I don't think there's a whole lot of bearing there. Urea is completely different. You apply urea, its neutral molecule, it isn't held on your soil and it won't be potentially held until it converts to ammonium. And at that point, if things are going well, it's going to essentially convert over to nitrate relatively quickly. So you got to consider that these things were developed at one point in time or somebody developed them. This is one that we've had some regional discussions on it, we have not been able to figure out where exactly that information came from. Where is CEC times 10?
Where did that come from, because we cannot find any literature that has those values in it. I think a lot of it... Maybe where it came from is a anhydrous study where they were looking at it essentially the increase in the amount of ammonium in the soil based on after application, and then somebody just assumed that that's what it can hold. So what it does do a good job telling you though is areas where you need to split or potentially your timing. So we know our lower CEC soils, we want to avoid applications far ahead of when the crop's going to need it. But in terms of telling you how much to apply, I mean Carl can speak to this. The low CEC soils on some of these sands that we deal with, that the rates you can apply are much higher than I think what they say CEC times 10 in a single application. But you just need to make that application at a point in time when that crop is actively growing, taking up nitrogen.
Carl Rosen:
Yeah, that's right, Dan. Yes, sandy soils have low CECs. We do not recommend large amounts of nitrogen on there. So that does play into the cation exchange relationship, but it really does not tell you how much to apply at any one time. We more or less go with the type of crop. And again, if you're on that low CEC soil to apply it during the time of active growth and that's when it should be. And so also to reiterate what Brad said, if you have a high cation exchange soil, that usually means you have more clay, it's going to be more prone to saturation as well. So you might be losing nitrogen in other ways, not just by legion. You can lose it by de-nitrification. And so just because you have a high CEC and you apply this nitrogen doesn't mean it's not subject to loss. It can be lost.
Dan Kaiser:
And I think if you look at the calculations too, the soil will hold more nitrogen. It would technically hold more than what you're applying on or reasonable application anyway. It means that in terms of this rule of thumb, we don't know where it came from. And the interesting one to me, Brad and I were at a meeting I think last year, and there was a grower that was growing some corn on sands and they were actually making their nitrogen recommended, their rates based on CEC and that's one that I don't know where exactly that one came from as well. So normally what the myth is is that you can, through the holding capacity and not exactly the rate that can be predicted, but just one of the things that I really wouldn't be making adjustments based on that. The thing I guess to think about is it's a good proxy for soil texture. And soil texture generally dictates particularly timing when we start talking about the four R's and somewhat rate. But timing is the big one in terms of what the consideration needs to be in terms of a nitrogen application.
Brad Carlson:
And I think the last point is with anhydrous ammonia, because of the anhydrous nature, what it's looking for is water. It's not worrying about what your soil is. When it gets let go under the soil surface, it's immediately looking for water. And so you're more likely, if you're worried about that coming up through the air or coming back out, you're worried about being too dry or potentially with the slots not closing behind the anhydrous knife. Neither of those factors have anything to do with the CEC of the soil.
Jack Wilcox:
Myth three: K base saturation is the better way to predict potassium.
Carl Rosen:
Normally we base our potassium recommendations on the amount that's extracted. The amount that's extracted is expressed as parts per million. This can be converted to an equivalent or milli equivalents per hundred grams, which is what the saturation is based on. And the cation exchange capacity is what we call the total amount of cations in that soil that the soil can hold onto. The K base saturation is what percentage of that cation exchange capacity is occupied by potassium. So there are recommendations that have been made on that. It usually is hard to adjust your base saturation to any large degree. It also comes into the myth about having an ideal cation saturation ratio between potassium, calcium and magnesium and trying to adjust those gets very difficult. And usually it's not related to yield in most cases.
So our recommendations are primarily based on the amount there in the soil in parts per million as opposed to milli equivalents per hundred grams or the amount that's occupied relative to the total amount of potassium in the soil. So it's not a very good predictor in most cases. And if you start trying to adjust these ratios, it can be very expensive. And so we don't use it in our recommendations. There are some labs that report it, but they'll also report parts per million. And in most cases, the recommendation is based on parts per million potassium, not on the base saturation of potassium.
Dan Kaiser:
So this is one of the things that bothers me particularly, and I think as Brad's saying, some of that complicated nature that people view soil science to be is when the lab, you get these standard packages where they'll run everything in the kitchen sink with it. And a lot of times if you run CEC, they're going to also give you a base saturation value on your report. And a lot of growers, I get this with our soil testing lab report too, there's extra information on there that you just do not need to be looking at. And it's amazing to me this K base saturation, how much legs it tends to have and how it tends to come and go. It's been hanging around here for probably the last, I would say, 10 years I hear it off and on. And it's one of the things that, as Carl said, there just really isn't a good way to push the needle.
I think the myth here is that you need, on some of our high clay soils, a 2% K base saturation, you just really hard to get that to move with the amount of other nutrients that are in the soil. You've got to put a lot of potassium on, more than what it's going to be economically feasible or where it's going to be economically justifiable for the crop. And I've been starting to look at some of my data where we can get some CEC values to look at the base saturation just to see where it is. And if you look at the majority of the data, I've got a lot of nonresponsive sites that are anywhere from one to a 2% K base saturation. And that's what a lot of people see. If you look at a lot of the research around that, there just is no relationship to it.
And if you really dig into this one, I know Carl might be able to back me up, but I only think there's a couple papers, maybe two out there that really talk about this. One is out of Missouri, there was some work done that's probably been 50 years ago or more. And then something out of New Jersey. And a lot of times you look at this data, it was on sandier soils where it's a lot easier to adjust some of these values. And what they were reporting essentially is what their optimal yield was and then what these ratios were, which really isn't a prediction of anything when you come down to it. It's just more of a saying that this is what it was when we had high yield, but it doesn't necessarily say that that's what you need for high yield.
Carl Rosen:
Yeah, that's right Dan. A lot of this is based on research that was originally developed, as Dan said in Missouri and New Jersey. And this is back in the forties, that's how old this is. And it continues to be used. But again, you need this calibration and correlation. There really isn't any evidence to show that it's going to work. And our methods of using experimental field results and correlating that with our soil test and calibrating it with our soil test is the way to go. And we just don't see that using potassium based saturation for potassium recommendations.
Jack Wilcox:
Myth four: I need to run an analysis of all micronutrients.
Dan Kaiser:
So this goes back to a point I just made is looking at these standard packages, many of these labs have, they're running the Mehlich-3. A lot of times that you'll be running all these micros. And I think that's one of the arguments for running the Mehlich-3, if you're going to do it, you might as well get all this data to look at it. The problem with all that data is not all of it really has any meaningful value to it. And that's one of the issues. If we don't have a good correlation or any good response trials for micronutrients, getting a value back really is pointless because a lot of times you'll get a number back. Maybe a lab will report it as low, which I don't exactly know where they get their information from. The saying that it's low really doesn't mean anything.
And micronutrients really are the tricky ones because we know that zinc, particularly in corn and dry beans across the state, there is a need. We know that. And so if you're looking at one to get, I would always recommend maybe getting zinc and looking at it. Most of the time if you're above a half part per million with the DTPA, you're generally not going to see a response to it. But it is the one to look at. But iron in our soils, I mean our soils have plenty of iron, that number really doesn't matter. Manganese and copper, that can matter, specifically copper. But a lot of times we see copper recommendations made on organic soils and not on mineral soils.
And you can't take the same set of recommendations or the same set of values where you'd recommend applications across the two of them. You look at it in terms of it, there's just two different animals with it. So it's one of the things, do you need it? Yeah, it's interesting getting some of that data, but you've got to really look at what makes the more sense in terms of the crop you're growing, what information you need and not get any more than that because it just really causes too much confusion for most growers. And that's when I start getting questions on what they need to do because of the results they've gotten back.
Carl Rosen:
And for some micronutrients, just the simple pH measurement might tell you more about potential availability than the actual number that you get with a micronutrient extraction, for example iron. If you're in highly alkaline and calcareous soils, that's all you really need to know that you're probably going to run into some iron issues, particularly if you're growing soybeans. The other micronutrients, manganese and copper, again, mostly are important on organic soils, high organic matter soils, that might be a place where you would want a test there. And high pH will also indicate potential manganese problems as well. So those are things that we look at in the test. And getting an actual number may or may not mean anything for some of these tests. And pH may actually be more important.
Brad Carlson:
Dan, you've done a ton of work with sulfur. I know when we started, you were starting to roll out a lot of our sulfur recommendations, which changed or was a departure from what had happened through really, I guess throughout most of our cropping history through the late nineties, you found that the sulfur test was just really not a good predictor of whether we needed sulfur, that it was tended to be a lot more situation specific and soil specific than the soil test. Have we had any improvement on that sulfur test since then? Is it even worth doing? Or farmers just need to still look at the situations where we need sulfur and go with that and not worry about the soil test?
Dan Kaiser:
Well, and that's one of the things too, I was actually, Brad, you caught me. I was just going to mention this too, that sulfur isn't a micro, so it's one of the first things on, if you look at sulfur, calcium, magnesium, they're what we call secondary macronutrients. So they're generally nutrients that are in the soil, enough quantity where we don't need to apply them sulfur. It's a little iffy because there's some soils we know that there's a need for it. But the thing about sulfur is there is a standard test that we recommend. It's generally recommended for the north central region. If I look at the three labs here in Minnesota, I look at NVTL in New Willmar, or I look at AgVice up in Benson versus our soil testing lab, all three run three different soil sulfur tests. So when you get a number back, that's one that, it's interesting. If I get a really high number back, a lot of times it kind of points me to a situation where we probably have free gypsum in the profile.
But normally if I look at a lot of my sites where we have responses or non responses, you see three, four, five, maybe six part per million. You see that range and it really doesn't relate back at all to where that responses occur. Initially the sulfur soil test of recommendations were based on sandy soils, which it may work better there because if you've got low organic matter, really your pool of sulfur is a lot lower. And what I recommend mostly to growers is to look at it's more situational. I think we can predict just based on tillage and also on organic matter where we're going to see a sulfur response. So if you're going to get something, the organic matter is something you can get. Although I don't think you really need to do organic matter all that often because you get a number back and a number really shouldn't change all that much with it.
But it's one of the things that I don't really recommend using any of that information because we just have not found a good correlation between the sulfur soil test. I've run all three, I've compared all three on that AgVice NVTL and our lab are using, and none of them are really any better at predicting responses than the others. So it's interesting, I had a site that was back around 2010 that we had a really strong sulfur response. This was out in Renville County, and I looked at the test out of our lab. And the difference between the responsive and the nonresponsive area is about one part per million and all the labs will report data out to the nearest one part per million. So if you look at just an overall error there, there just isn't enough fine of a scale there to be able to test where you will and won't see a difference.
So again, it's one of those things I put as interesting, but not necessarily as effective. I'd recommend most growers, bare minimum, you get a phosphorus test, you get a potassium test, you want a pH, maybe a zinc, those are probably the big four that you need. If you're going into a field for the first time, maybe you want an organic matter map just to see what those changes are. But the rest of it, we really don't have anything built into our recommendation to use. So you can run all the micros and it's what the myth here was, but it's just going to cause more confusion and probably more sales or things that somebody's going to want to come and sell you based on your tests that are likely not going to be needed because there's really no documented evidence it is.
Brad Carlson:
You, earlier in my career, we were involved with, and I know Dan, you spoke a couple times, I can't remember Carl if we ever had you, but we had an organic crop stay. I think it's still going on in Oton in Minnesota for organic producers. And one of the nutrients that they just love is calcium, but we just can't see a response. It's almost always based on testimonial and their experience and so forth. And there's really nothing about an organic production system that should be any different for crop response than a conventional production system. And it gets back to where I started this and that is that if we don't have soil tests that are correlated to some critical value in crop response, they're just a number and they don't really mean anything. And so that's where we're at with a lot of that stuff. And I've heard this couched as soil test, what do I really need? And then they come back and tell you, you need everything but the kitchen sink. That's just a waste of money.
Dan Kaiser:
So it's one of the things that we have too, with having a smartphone or computer, it's really easy to find information on the internet. And I think the adage is that they don't put anything that's not true on the internet. It's just one of those things that it's really easy to find, particularly if you're looking for something, find somebody that's got a similar opinion to you or back up whatever thought you have in terms of what you've been hearing out there. And it's one of those things, if I look at it, we can really make this nutrient management thing overcomplicated with all the information you can have out here when it's generally simple. You just have to make sure there's enough available nutrients out there.
Most of the time, NPK or our big ones, maybe sulfur. And then beyond that, I mean the rest of it, if you're really looking at, you're just really grasping at some very small yield increases that you're trying to pull out of it other than maybe some isolated areas. So I always say that I really try to be the one to screw up so farmers don't have to look at this because you can really get pretty quick into getting increasing your costs just based on some of the information is out there when back to the basics approach is really a good thing due to particularly when fertilizer prices are high.
Carl Rosen:
And if you look at the name micro, it just means that it's needed in very small quantities. So in terms of an acre basis, you're only taking up maybe ounces per acre as opposed to something like your macronutrients where you're looking at multiple pounds, tens to hundreds of pounds per acre depending on the macronutrients. So micronutrients are needed in very small quantities. Most of our soils have sufficient amounts to support crop growth. But as Dan said, there are isolated cases where those micronutrients may be needed and a lot of times the soil might have sufficient amounts. It's just not available because of what I mentioned previously, the pH. So those are things that you need to consider.
Dan Kaiser:
So there are a couple things here. I'll just back this up with what Carl said, like zinc for corn. I mean, corn crop's probably going to remove somewhere between a quarter and a half pound per acre. Half is generally in the grain, half is in the stover. So there's half of that that's going to go back into the system. So you're not going to see, I should say not removed, but take up a quarter two half. The other thing too is with tissue analysis, a lot of times this is in a tissue analysis talk, but a grower will get back these low micronutrients.
And I think a lot of times it's a macronutrients issue because what we see essentially is uptake of one nutrient isn't necessarily alone, doesn't happen in a vacuum. You see it affect the uptake of others. So if you impact growth, you may impact the uptake of plant's growth, the uptake of other micros. So the big thing is just make sure you're correcting the right thing on that. And don't get too crazy because particularly with the micronutrient packages, they get pretty expensive and we see a pretty poor return.
Jack Wilcox:
Any last words from the group?
Dan Kaiser:
Well, I just want to reiterate, when you're getting a report back, just don't get too much. I said it's really, I think, the easiest way to do it is to simplify things down and get really only what you need because it can be really confusing if you get too much on a soil test report. So that's one of the things. And you've got other people saying that, well, you need to do X, Y, and Z, or you need to run this particular test because of said reason, you really want to make sure that what you're running, and I said this also before, is that you can actually get some recommendations for it. And that's the thing I struggle with is when I get a call from a grower that had a test run that wasn't a standard test, now they're trying to interpret it as it becomes fairly difficult to do that with some of our recommendations. So it just always good just to know what you're running and just make sure that it's applicable for the region that you're trying to grow a crop in.
Carl Rosen:
And the last thing I'd like to say is that the best recommendations are going to come from research that's conducted locally or regionally. And that's where you should be getting your information from.
Brad Carlson:
And I'll just wrap with, don't over complicate this. It's just simply not that difficult for the vast majority of farmers.
Jack Wilcox:
All right. That about does it for this episode of the Nutrient Management Podcast. We'd like to thank the Agricultural Fertilizer Research and Education Council, AFREC for supporting the podcast. Thanks for listening.
(Music)