Ag Geek Speak
GK Technology Inc Team Members, Jodi Boe and Sarah Lovas talk about precision agriculture, agriculture mapping, agronomy and drainage.
Ag Geek Speak
17. What's in a Soil Test? Getting the Answers with John Breker Pt. 1
Get the download on soil tests and what they actually mean in our latest episode of Ag Geek Speak featuring AGVISE Laboratories' John Breker. We dive into the world of soil testing methods, breaking down the pros and cons of phosphorus tests like Olsen and Bray, and the "new" Mehlich-3 method. Discover why Olsen is often preferred in the Great Plains and how the Mehlich-3 method, despite its promise as a universal extraction tool, might over-extract in calcareous soils. The discussion highlights the importance of selecting the right soil test for accurate nutrient analysis, a crucial step for any farmer or agronomist looking to optimize crop yields.
Managing soil pH and tackling nutrient deficiencies, especially iron deficiency chlorosis in soybeans, can be challenging. John provides an in-depth look at the role of calcium carbonate and the necessity of specific soil tests to combat IDC effectively. We also explore concepts like reserve acidity and cation exchange capacity, explaining how soil texture influences these factors and the difference between water pH and buffer pH. If you're keen on practical strategies for managing soil fertility and improving crop yields, this episode is a treasure trove of knowledge. Tune in and equip yourself with actionable insights from one of the field's leading experts!
And now it's time for Ag Geek Speak with GK Technologies, Sarah and Jodi friends and I can't wait to get in the fields again. No, I can't wait to get in the fields again. Welcome back to Ag Geek Speak. We are very excited for this new series of podcast episodes that we have going on. We have a very special guest here hailing from Northwood, North Dakota, and the great AGVISE Soil Analysis Laboratories up there, AGVISE Laboratories, John Breker. John Breker is a soil scientist with AGVISE Laboratories. We are very excited to have you today.
John Breker:Oh, thank you for having me. It's wonderful to be on.
Sarah:That's great. Well, let's just be real with everybody that's out there in the audience. John and Jodi and I we have known each other for many years. We are actually what I would call industry friends. Perhaps Right, yeah.
John Breker:We can use that word industry.
Sarah:Industry friends, soil friends, nerds, geeks, whatever Makes sense. So we know each other pretty well. But, John, why don't you go ahead and tell us a little bit about yourself and a little bit about your background? Where did you grow up and how did you get so interested in soil?
John Breker:Well, I grew up down in the humble hamlet of Rutland, north Dakota, down in the southeast corner of the state, outside of the Red River Valley into the Till Plain, so I had the pleasure of picking rocks as a youth. Anyway, I grew up on a mixed grain farm corn, wheat, soybeans. We also had hogs up until I was about middle school and then we got rid of those when the hog prices tanked. After that I went to NDSU. Originally I was going to study agricultural engineering because anyone who loves math and science is told you must become an engineer. I figured out within a week I did not want to be an engineer, I wanted to be more of a scientist. But I still have a strong affinity for the land, growing up on a farm, and eventually I found my way to soil science.
John Breker:I got my bachelor's at NDSU and I proceeded to get a master's at NDSU as well. I worked under Dr Dave Franzen and we recalibrated the potassium soil test for corn. So we did a lot of potassium field trials, looked at various soil test methods and in the end came out with a whole new set of guidelines that were largely structured on clay mineralogy. And following all of that work, many of the neighboring states and provinces have now looked at their potassium guidelines and it's kind of, I would say, fostered a little bit of a potassium renaissance, some new K research for the first time in 30, 40 years. Otherwise, the only person wandering around in the desert like Jeremiah was Antonio Mallorino in Iowa, so it's good to see many other people getting interested in potassium again.
John Breker:So, anyway, following that experience, I joined AGVISE Laboratories in 2017. And I've been here since. I'm working on our sales and technical support side, so answering customer questions, whether it be interpreting soil test results or figuring out nutrient management guidelines, et cetera, et cetera kind of take care of that customer facing side, and the great joy of that is I get to work with farmers, agronomists, crop consultants, precision mapping folks like yourself and university researchers, and so, anyway, it's been a fantastic career, even though I'm still pretty early into it. It's been a lot of fun.
Jodi:You mentioned before, as you're talking about your master's research, that you helped to recalibrate the potassium guidelines for North Dakota. What does that mean when you talk about guidelines and calibration, and what do farmers see at the end of that process?
John Breker:Yeah, so when any new soil test method is introduced, there's a couple of steps that are required before you can get to that final usable number, because at the end of the day the farmer has to take a number out to the field that is that fertilizer rate that's being spread on the field. But there's a few steps along that process. When you begin with just a simple soil test method so let's just look at the olsen phosphorus method, for example um or any test like a soil test is designed to mimic some aspect of plant availability and it extracts a number. You might get a number that is like six part per million. It could be 45 part per million, but that number itself doesn't inform anything about what fertilizer rate should be spread on that field. So we go through the process called soil test correlation. That's step one and then calibration being step two, to eventually get you to that fertilizer rate. So the first step, correlation, is relating that soil test method, that extracted value. So you know you get a range of numbers that might go from zero part per million up to 20 or 25. Or for something like potassium it could be 400 part per million. So there's big ranges in these numbers depending on what nutrient and method we're looking at. Then you relate that to fertilizer response data. So you get a crop response when you put on fertilizer At least that's our hope, right why we're putting on fertilizer so you get some kind of yield increase and if you have a lower soil test level you're going to get a bigger yield response than you would if you had a high soil test level. But so far we don't really even know what defines a high soil test level. So when you put out these fertilizer response trials you end up building what we call a response curve and at some point that curve will start to plateau out and that is where we draw a line and call that the critical level or the sufficiency level At what point you no longer expect to see a crop response to fertilizer. If you get above that and that's where we call it a high soil test level and there's nothing intuitive about that and actually putting out fertilizer response trials over multiple years on multiple soils at various soil test levels to actually build a good scatter diagram that you can actually build that curve through.
John Breker:The next step, the calibration step, is actually figuring out how much fertilizer is needed at those particular soil test levels to actually maximize your crop yield response at the end of the day. And so that's where, when you start with any soil test method, you have to do the field work. Don't assume the field work has been done. You've got to actually go through the real process of doing field trials and eventually then you will get to the point where you can actually calculate what is the required amount of fertilizer to maximize that crop response at that given soil test level. So you can have a very high soil test level and you would see, yep, doesn't take a lot of fertilizer to actually maximize that yield response. Or you could be have, you know, very low soil test level and be like, yep, it actually requires a lot of fertilizer. So that is the steps and really kind of the statistics behind what goes into starting with a soil test method and finally having a usable result that the farmer can take to the field.
Jodi:So I think what I hear you're saying is that Sarah and I couldn't just start a ag geek speak phosphorus test using like Diet Coke as an extractant and then use those numbers even though we might get results of like 0 to 25 ppm of phosphorus from that that result because we don't have any field work that relates to crop response. We couldn't just say that 0 is low and 25 is high. We would actually need to have some field work behind that and like yield collection to give meaning to those numbers.
John Breker:Yeah, that is absolutely correct and I mean you very well could create the Diet Coke phosphorus extraction method. But you just have to go and do the field work to develop those interpretation curves to make it a meaningful soil test. But that extractant might or might not be better than existing methods. So, like up in our region, here there's principally two methods that are used, Olsen and Bray.
Sarah:But depending on your Phosphorus test. Right Olsen and Bray for phosphorus.
John Breker:Correct. Yeah, we're still on phosphorus. We always talk about phosphorus. We should talk about different nutrients someday. But here you have an example of two methods. But they're suitable for different types of soils and certain ones have stronger correlations with the data than others. And certain ones have stronger correlations with the data than others. So that's why people use different methods in different parts of the country is because there's just not one universal test that extracts all nutrients in all soils. There's little nuances to to those nutrients and crop responses and that's why every given state has different soil tests. Well, not only different methods. There is some universality, I mean, between different methods, like throughout this north central region of the US and into the Canadian prairies. We use the same methods. But that's different than folks in the southeast. They use different methods because their soils are a little bit different. But every region has that local calibration data set so they can actually make meaningful recommendations out of that soil test data.
Sarah:So let's back up here for one second. You were talking about how the Bray phosphorus test and the Olson phosphorus test have different correlation data and that they're appropriate for different soil situations. Let's call it soil, soil situations, let's call it. When we're talking about different correlation data, what you mean is that the stronger the correlation, the greater that that soil test will be able to predict what the level is for the phosphorus in the soil under those circumstances, or can you explain that? What does a good correlation look like and what does that mean?
John Breker:can you explain that? What does a good correlation look like and what does that mean? Yeah, so if you have a strong correlation, you know when people look at like R-squareds of the correlation, you want to make sure that that test method you're using has a high correlation with that crop response. So when a new test comes out you want to make sure that that data is tight and actually predicts. I mean, because at the end of the day these are predictive relationships. You know if you have a low soil test, we're predicting a high probability of a strong crop response.
John Breker:So we'll just kind of, I guess, dig into Olson and Bray and kind of how those two methods got around, because up in our northern plains region we always talk about Olson. You get down into kind of the Corn Belt proper Iowa, illinois, you know they're always talking about Bray. Well, the reason why they use Bray versus us up here using Olson is partly historical. Us up here using Olson is partly historical. The Bray method is the older of the two methods. It was developed back in 1934, and it's a strong acid and it does a great job of extracting phosphorus in those soils and they have decades of crop response data using that Bray method, so it works very well in their soils.
John Breker:When they tried to implement Bray farther west into the Great Plains, we have high pH soils that have carbonates at the surface and the carbonates calcium carbonate the same thing as free lime actually neutralizes that strong acid extraction. And Dr Olson at the University of Nebraska-Lincoln in 1954 developed you guessed it the Olson method and that was designed to work on high pH soils, but it also works on low pH soils too. That's kind of one of the, I guess, nuances that I always like to tease out. People think that Olson is only suitable on high pH soils. Bray is only suitable on low pH soils. Well, it's true that Bray is only suitable on low pH soils, but Olsen actually has a lot more pH range. I mean it can operate in both low and high pH soils.
Sarah:Yeah, it's easier to run an Olsen on a soil with a lower pH than it is to run a Bray on a higher, on a greater soil pH.
John Breker:Yeah, because on the high pHs Bray you'll end up getting these failed results. So because of that, when you get into the Great Plains, our local calibration data is all done with Olson, because if you were to use the bray test it would have very poor correlations with predicting crop response. So what that means is that all of our local correlation data is built with Olson and is going to have a tighter relationship with our local crop responses than Bray would. Even if we had a low pH soil and we wanted to go with Bray and when I say we, I'm like talking those of us up in North Dakota I would still go with Olson on an acidic soil because all of our local calibration data was developed with Olsen, not Bray, like the nearest Bray data that actually has field response. It would be like somewhere in southern Minnesota, a little different type of cropping system, different type of soils than what we have up here. So that's why always stay with your kind of more localized data.
Sarah:Well, to this point, but maybe off the topic just a little bit. Since we're talking about phosphorus testing, talk to me about the Malik-3 and where that fits in to soil analysis and maybe even some of the other extractants that you can do with the Malik.
Jodi:And can we back up for a second to like, when we're talking about bray failing on these soils that have high pHs. What does that mean and what does that usually look like? What kind of results are we getting and why are they? Or like, how do they show up on the test? And then we'll move on to Malik.
John Breker:Yeah. So when you see like a failed bray, you'll often see those soil test results come back as like a two or three but it's like equivalent value in the Olson method. Like, say, you had a high Olson value at, say, 15 and that Bray high value should correlate somewhere around 20. But when you see those results coming back at two to three part per million, that's a clear indication that that Bray method is failing and that would be because of the high pHs and the carbonates that are neutralizing that acid.
Jodi:And then you'd get a guideline that would probably tell you to apply a lot more phosphorus in what you need for the situation.
John Breker:You bet Okay, malik, that was a method introduced by Adolph Malik, who was a professor at North Carolina State University back in the 80s. So as soil testing developed, you have all these different methods that are being introduced to get at different aspects of nutrient availability. And, doc Malek, he wanted to come up with a universal multi-nutrient extraction so you could have one chemical extractant and extract all of these nutrients and run them on one instrument and run it on an ICP in order to get all of this. So it would really reduce time and cost for any soil testing lab.
Jodi:And let's take a second. What is an ICP measure and why is it different from like? Why is it so efficient to use that machine versus other machines in a soil testing lab?
John Breker:Yes, we have many different types of instruments for determining nutrients. Some of these are what we call colorimetric methods, where, say, you have a nitrate ion that you've extracted, you react that using the cadmium reduction method and there we're actually measuring the intensity of that color that results from that colorimetric reaction and that's related back to the concentration in your standard sets For phosphorus. For measuring, like orthophosphate, inorganic phosphate, we use the molybdate blue method, so a different version of that. There are different analytical equipment called AAs or atomic absorption spectrometers, and those you can measure like one particular element at a time. So you could just measure a potassium ion or you could measure a zinc ion at that time.
John Breker:An ICP that can. Actually it's like having multiple AAs, so that ICP stands for inductively coupled plasma and there it can look at many different elements all at the same time. In fact, hospitals use ICPs all the time for like doing blood work. If you had blood drawn and they wanted to measure your potassium, sodium, calcium levels in your blood, they'd run it through an ICP, and so they're very efficient units but, depending on what we're trying to accomplish, not always the best tool right. It's just like a toolbox. You know, not every problem is solved with a hammer. But the beauty of an ICP and the malic extraction is that you would be able to extract all of these elements and determine them all at the same time.
John Breker:But there's a catch, and that first catch is you got to make sure that you have the field calibration data to use those numbers. And one of the things that Malik was designed to do is work both on acid soils and high pH soils and, to his credit, it actually correlates very well with Bray. On acidic soils it correlates very well with potassium extractions. But when you start getting into the high pH soils, particularly the very calcareous soils, the Malik method actually over extracts phosphorus in some cases, and so there's been work to try to calibrate it in Minnesota. So there you have a good state where the southern half of the state has acidic soils, the northern half a lot more calcareous soils, and it would be advantageous to have the malic extraction to have one set of guidelines for the entire state of Minnesota. But when they start getting into these calcareous soils up north, they would get these high flyers every now and then. That would not correlate back to what an Olson value should be. So that is a major issue for calibration.
John Breker:The other thing is the way that the malic extraction works. It has some fluoride in it, so the fluoride can also bind up with calcium and magnesium, so it can actually under extract calcium in our calcareous soils. So and you're trying to use the calcium values off the malic or any of the subsequent cation calculations, base saturation calculations. Those are a little bit screwy, I think that's the technical term. And the other thing is the micronutrients. It doesn't matter where you are in the US, there's actually no correlation data with the micronutrients. So, like the traditional method for the north central region would for all the goals of that malic extraction, it has not done a very good job of replacing all the different soil test methods that we use already. But if it did work we would use it all the time because it would be far simpler and far cheaper. But unfortunately it just has not performed very well in our northern region.
Sarah:And just to back up for a second, the DTPA test that you were talking about. That is kind of the standard test in this neck of the woods or prairie for extracting micronutrients, correct? Yep, and you're comparing that to the Malik 3 extraction? I didn't realize that the micronutrients on the Malik were that uncorrelated. That's interesting.
Jodi:I think this is a really good time to point out anybody using a soil test any place, whatever laboratory. It's really important that you at least have some place on the test or know exactly what methods are being used. And just know that, like with the Malik right, you're using one extraction for multiple nutrients, so it most likely will be cheaper than doing like an Olson. So just think about, even though you might be getting a cheaper phosphorus soil test results and maybe some other nutrients too, it's important to think about. Okay, I did get a cheaper test, which is awesome, but is it actually getting the information that's going to help me maximize crop yield that following year?
John Breker:Yeah, that's where it all comes back to soil test interpretation backed by correlation and calibration, you might get very fun data, but you got to make sure you can use it. This is where I want to start my bumper sticker business. I got all sorts of things. One of the bumper stickers I want to create says data without a decision is just trivia, so if you can't use that data, it's really hard to justify. I'm always about generating useful data that people can actually implement. Same with you folks. I mean making maps that people can use.
Sarah:I think that's actually a really important thing, a really important point to bring up, because I always talk about how, when you've got a map, that's only so good as it actually making agronomic sense and being relevant agronomically to the field and it's only as good as actually being able to get it into the controller and make it work. And you can't do either one of those things if you don't have actionable data that actually makes sense. So that is a really important point.
Jodi:And it doesn't have to be complicated either. Right, like the way they were talking about this it might sound, it sounds like there's a lot of details involved, but what's important is that if you have an agronomist that you work with or a soil testing laboratory wherever a trusted advisor they should know these details and should be able to give you trustworthy zone maps that you can soil sample off of in the first place or maybe they're soil sampling off of and when you call your expert at the laboratory or call to talk about the soil test results with your agronomist, they should know and understand these things so that you can then take that data, you can trust it and then you can use it on your farm to go ahead and get your best yields next year.
Sarah:There really is a lot that goes into soil analysis methods and how they actually get used to developing those fertilizer recommendations. And to Joda's point, yeah, we got to make sure that you're working with people that know what they're doing. We were talking about a whole bunch of soil tests that are actually on the soil test report. I'd like to bring up a question about the calcium carbonate equivalency test. When we're trying to manage iron chlorosis, it seems to be a pretty good indicator of calcium carbonate, Kind of what. How does that test work? Where do you recommend that people are using that? What are some of the most important reasons for running a calcium carbonate test?
John Breker:Yeah, so kind of a big theme of our northern Great Plains region is we have fairly young glaciated soils and there is a lot of naturally occurring calcium carbonate or free lime still present at the surface. For people that live farther to the south or farther to the east, carbonates are just a fond geologic memory, but for those of us up here they are still present. And for certain nutrient deficiencies like you brought up, iron deficiency, chlorosis, major problem in soybeans. Like you brought up, iron deficiency, chlorosis major problem in soybeans, also flax, but soybeans is kind of the big driver. It is one of the primary risk factors.
John Breker:And calcium carbonate first. What it does is it buffers high soil pH, kind of keeps them up around that seven, eight to eight two pH range give or take. You know a 10th here or there range give or take, you know a 10th year there. And that naturally occurring carbonate buffers our high pHs and makes them very difficult to change. You know folks in parts of the US or parts of the world that have acidic soils. They add calcium carbonate to increase that soil pH so they don't have issues with like aluminum toxicity or other things. That's there'll be a different discussion for later. Let's not wander down the acid soil route just yet.
John Breker:But anyway, for our soybeans the calcium carbonate test is one of those principal risk factors because it really inhibits with the soybean plant's ability to actually take up iron because one of its first steps in iron uptake for well, there's two different types of iron uptake that plants have, but for the soybean case it tries to acidify that root zone to start with.
John Breker:That is step one and if you have a bunch of calcium carbonate there, that carbonate neutralizes that acidity and it can't really accomplish step one before it can move on to step two to actually bring that iron into the plant. So if you have soils that have three, four, five percent calcium carbonate at the surface, that is a lot for that soybean plant to contend with, and we have soils that have 10 or 15% calcium carbonate at the surface. So that is a test that we include with any of our soybean soil test options as well as any of our complete soil test options. So particularly for soybean growers, I would make sure you get those fields tested for carbonates. If you know you have acidic soils, well then you know you don't have carbonate at the surface. But for anybody with pHs that are 7.5 or higher. I would make sure those soil tests have carbonate in it.
Jodi:Is there anything unique about the way that AgBi's tests for calcium carbonate equivalency versus other labs?
John Breker:I think we're probably one of the only labs that routinely delivers back a quantified carbonate value. So when you determine carbonate, it's actually a very simple test. You start off with hydrochloric acid and the hydrochloric acid reacts with the carbonates and it produces carbon dioxide and it produces that gas. The routine field method, like if I was a soil mapper, is you just kind of classify that effervescence that results as like low, medium or high. Well, when we're trying to manage for IDC low, medium, high doesn't get us very far. Trying to manage for IDC low, medium, high doesn't get us very far. So instead we actually quantify that calcium carbonate and deliver back a percent value like 3% carbonate, 5% carbonate, and then that can give you a much stronger tool, especially when you're trying to build, like a variable rate map for an iron fertilizer application.
Sarah:Absolutely Selfishly. Iron chlorosis is one of my favorite nutrient deficiencies. Everybody has one of those, right, everybody's got to have one of those, but that's my favorite one, and so I really appreciate that conversation on calcium carbonate equivalency. But since we're talking about all of these soil analysis methods and largely we just got done talking about calcium carbonate equivalencies and you know the idea of that being in high pH and John even led us to that conversation about low pH let's talk about some of the acid soils and some of the things we deal with in that realm of everything.
Sarah:And one of the questions that I have is about buffer pH tests thing, and one of the questions that I have is about buffer pH tests. What is a buffer pH test? How do we use it? And maybe we should calcium carbonate, its other name, lime how do we figure out how much lime to apply in certain scenarios? And our audience is all over the United States. But one of the things that we've really noticed in North Dakota is some issues with low soil pHs out in Western North Dakota, which is kind of a new concept for us yet, and so I'm just going to lob that all up and and pitch the ball. And and John Jodi. What do you guys think?
Jodi:If you want to start just talking about pH versus buffer pH and why, why you want to do both if we're suspecting there's an acid and soil someplace out there?
John Breker:Yeah, so the I think I'll start with thinking about what is active acidity versus reserve acidity. So active acidity is what the water pH test measures. This would be your routine, regular soil pH that you find on any soil test and this measures the acidity which would be hydrogen ions dissolved in the soil solution and this is what the plant root actually experiences and what is really driving any of the reactions or toxicities that that plant root sees. Then there's reserve acidity and this would be acids like hydrogen or aluminum that are hanging out on cation exchange sites and this varies based on soil texture and your cation exchange capacity. If you have a sandy soil, you're going to have a lower reserve acidity because you have a lower cation exchange capacity. If you have like a clay, loam or clay, you're going to have a much larger potential reserve acidity and that's the acidity that can come into the soil solution and will more or less buffer and maintain that that soil pH.
John Breker:So when we lime, like if you were to just lime and neutralize the active acidity in the soil solution, it wouldn't take very much, but you got to account for all that reserve acidity on there as well. So the water pH test tells you if you have to lime. The buffer pH test encompasses that reserve acidity, that's hanging out on the cation exchange sites and accounts for all of that, and that is what you would actually use to figure out how much lime to add on any given field. So this is where, just to break it down in simple terms, water pH tells me if I need to apply lime. The buffer pH tells me how much lime to apply because it accounts for the acidity and the cation exchange capacity.
Jodi:This is a fantastic place to stop the first part of this conversation. It's really great to cover concepts again, thinking about you know, what does a pH mean versus a buffer pH mean? They're very similar words but they do mean different things and it's important when we're managing these acid soils to know both of those to get us in the right direction for how to manage that and speaking of. We're going to end here this week, but when we pick up with John again in our next episode, we're going to start by talking about how we actually go ahead and manage these soils when they are low in pH or if they're acidic. So thank you very much, John. We really appreciated you spending time with us today, with me and Sarah, and explaining all these concepts when it comes to soil testing and with that, thank you so much for joining us. And remember, with GK Technology, we have a map and an app for that.