Published using Google Docs
Updated automatically every 5 minutes

University of Minnesota Nutrient Management Podcast Episode: “P and K guidelines”

September 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.


Paul McDivitt:         Welcome back to University of Minnesota extensions, Nutrient Management Podcast. I'm your host, Paul McDivitt, communications specialist here at U of M extension. In this episode, we're talking about phosphorus and potassium guidelines. We have two members of our nutrient management team and two out of state guests. Can you each give us a quick introduction?

Daniel Kaiser:         So this is Daniel Kaiser. I'm a nutrient management specialist with the University of Minnesota extension. I'm located out of the St. Paul campus. My area of specialization is in fertilizer guidelines, particularly corn, soybean and the majority of our agronomic crops across the state.

Jeff Vetch:         Hi, I'm Jeff Vetch. I'm a researcher for the Southern research and outreach center here in Waseca. My area of emphasis is actually nitrogen management, but I work considerably with Dan on long term P and K projects across the Southern part of the state.

Antonio Mallarino:         I am Antonio Mallarino. I am a soil fertility and nutrient management specialist at Iowa state.

Dorivar Ruiz Diaz:         I'm Dorivar Ruiz Diaz. So fertility specialist extension at Kansas State University, primarily work with corn, soybeans and obviously winter wheat also, which is a main crop for us here in Kansas.

Paul McDivitt:         Why do P and K guidelines differ from state to state?

Daniel Kaiser:         So that's a really good question, Paul. You look at a lot of our numbers. So we go back to the guidelines ourselves. If you look at the majority of the states around us, everything undergoes what we call correlation and calibration. So essentially the correlation step we're correlating crop response to a specific soil test method. That's one of the things that's important when you're looking at soil testing for both P and K, is that the numbers aren't universal across the different methods. So we have to go to the step of going through and doing that correlation step, then calibrating the soil test, essentially to make it useful for fertilizer applications or how much we should apply based on a given level. So when you look at that, a lot of work goes into that. And a lot of the differences across state really come to the philosophies of the researchers that are doing the work themselves.

        And if you look at that in the past, we have two main philosophies that are generally used for P and K. One's what we call the sufficiency approach, which essentially is only applying the amount of fertilizer that's needed to maximize economic yield, which tends to be less as we increase our soil test. So again, we generally with a sufficiency approach, we're counting for more of what the soil's supplying within a given year to try to minimize the amount of fertilizer we need. Now, one of the drawbacks that the approach is that we generally need more rigorous soil testing to make sure that we're getting into those areas where we're seeing drops, because we're more likely, since we're looking at not a removal rate to see some drops and soil test over time. The majority of the growers we see, particularly in Minnesota, you get to the Southern part of the state we'll practice something that we call a build and maintain.

        So essentially we're building to a certain soil test level, which is generally around a critical level, which the interesting thing, if you look across state lines is that we see a lot of agreement in what those critical levels are for given soil tests. So if you look at some of that underlying information, there, isn't a whole lot of difference between critical levels. Some of the probability of response data that we have for given soil test ranges that a lot of that underlying information is there. And generally what growers are going to do then with a build and maintain, they're going to just essentially apply a maintenance rate around a given soil test level. And I came out of Iowa. Antonio, you could answer that as much of your eyes, generally your optimum class. It's generally what I've always thought identifying as that's what you define as optimal for maintenance.

        The issue with the building maintain though is the fact that you get it to a certain point. If you're maintaining that you get to a situation where you are at a lower probability, that fertilizer is going to give you a yield response. So that's one of the things really about it, is if you look at it in discussions with some of my colleagues around, if you look at a lot of our numbers, the underlying numbers are the same, but it's just essentially that interpretation of the philosophy that's been ingrained.

        So in Minnesota with the sufficiency, that's more of a Western philosophy. So that's where some of our researchers came from at one point in time. So we see that where our recommendations are. I've been trying to more moderate towards looking at what we call hybrid approach, where we utilize both of them to try to get the best out of both of them with and try to help growers at least give them the information they need to make their own decisions. Because that's essentially what a lot of them are doing, they're working with their retailers and trying to make the best decision for them, what they can in their given circumstances.

Jeff Vetch:         When we think about phosphorus availability, some of the differences lie in the extracts that we use, when we get to the Western part of the corn belt, the Dakotas and Northwestern Minnesota, we have the Olson test, which fits better than the more universal malic three tests that you see in the Eastern corn belt. And that makes sense because it's, it works better on those soils, on those high pH soils. And when you think about, and actually sit down and look at the recommendations, as Dan said, there are a lot of similarities. And when you look at Minnesota, North Dakota and South Dakota, those P and K guidelines are very, very similar.

Daniel Kaiser:         And that's one of the things that I've looked at, and him and Antonio can address this a little bit more is we see more pressure, particularly from NRCS, with some of the universal extractions, like the maleic three coming in. And I think Antonio, you're probably the closest state to me that has recommendations for the maleic like three that is both ICP and color metric. And that's one of the challenges with that test is that, the test itself should extract the same amount, but how you read that test varies. So that's one of the things that when you're getting data back, you just have to be careful in terms of your interpretation because they're not always the same.

Antonio Mallarino:         Yes, precisely. Yeah. I have been working for years in this issue. And the main thing is that, it doesn't matter what soil test you use extract. If you use the traditional color metric determination of the extracted phosphorus, you get a number, but if you use the ICP to measure in the same extract, then you get a higher number because there are the polymetric method measures on the ortho phosphate, but the ICP also measures some other phosphorus form that are dissolved. So the only reason that, and this happened for soil extract, runoff extract, [inaudible] extract, everything for every test. The only reason that this Isn't allowed for the medic three, and that's how we have interpretation for both in Iowa, for the medic three quarter metric and the medic three ACP is that about 15 years ago, you see the ICP was a very expensive machine in the labs, but about 15, 18 years ago, it became cheaper.

        And many labs began abandoning the classic color metric determination for this ICP determination. But at the same time, because the medic three, supposedly is a universal test can be used for measure P, potassium and in some conditions, cations and even micronutrients, then labs began switching to it. And I believe now many labs in the region use actually the medic three. And this is another problem we have, that some labs use the medic three ACP, but express the results as a color metric. I know there are a couple of labs that use the medic three ACP, and they express the results as gray with some internal correlation with this. We have so many things confusing and so testing, but this is something that confuses things unnecessarily. So many labs don't even say in the reports, what method they're using. They may say Olsen, they may say maleic three, but they may not say, what is their use?

        This is something that we have been working on for many years with the NAPT and so forth, the proficient testing programs. So it is confused. But just in terms of the recommendations, I agree with what Dan said and Jeff too, most of our systems in the north central region are like a hybrid between the classic or strict sufficiency level and the build up and maintenance. There are some differences. For example, in Iowa, traditionally, we have decided that we will not use heal and removal for the low testing classes, you see. So our recommendations are to maximize yield. It doesn't matter the yield level. So that's not used for maintenance of what we call the optimum that we define as a range with a low probability of response, then recommend applying removal base. And these things are a bit different states. The main issue is that in spite of many of us being friends and we're together, I have been working 30 years here in Iowa, and we have not been able to come up with similar recommendations.

        For example, bordering solid series. The numbers are about the same. Now there are several reason for that. The philosophy of each of us has done said. Also that we are pushed by our stakeholders to have our data. So we need to have our data. We are in Iowa, we are not in Minnesota. So we want the recommendations for Iowa or for Minnesota. And it is difficult you see, it is difficult because Iowa relatively easy, we have about the same mixture of soils over the state. But for example, we go to Minnesota, it's huge. Southern Minnesota may be similar to Iowa, but Western Minnesota and central, Northern Minnesota is not.

        So then for some state is difficult to say, okay, let's get together. And let's have similar suggestion recommendations for neighboring soils. It's difficult. We are trying, there have been efforts, for example, in the tri-state area higher in Indiana, Michigan, they have some common things. And I believe that Minnesota, Sarasota and Aragota used to have what it was called, also some dry state staff. We have been started talking this summer, trying to see if we can come up to some at least uniform concepts. But as Dan said, overall, we are in general agreement. There are no major discrepancies between our recommendation.

Dorivar Ruiz Diaz:         Well, I think this is a great question. Why recommendations change in different states? And I completely agree with Dan a part of philosophy in the case of Kansas, we do have a clearly hybrid system, really a sufficiency option. And we also offer a build and maintain option for producers. And there are many reasons for that. Obviously the data and the research other colleagues mentioned already is very similar. However, we do have some things that are different for different regions. For example, in our case, for example, we do have quite a bit of winter wheat in the rotation, which is a group that has a different response typically. And so the cropping system play a role there. So that's one factor. For example, Jeff mentioned already situations of IPH, which is very common for us in Kansas as well. If we do have a grading of pH from acidic soils in the east to a very high pH in the west.

        And again, that also creates a challenge in terms of Westworld methods we use and what works better for us compared to other states. And so those are key things that happens. One thing also, and this goes to the philosophy. For us, something that is a challenge is that especially central and Western Kansas, we do have drought. And so this is oftentimes the most limiting factor for many producers. So oftentimes, and again, this goes really more on the philosophy. Many producers say, okay, I'd rather have everything that I can control at the optimum of our above optimum, obviously, including fertility, then be ready when we have the moisture to maximize gels. And so again, these are some things that are very unique to different regions and maybe goes beyond what we have in terms of data, which again, could be very similar across different states.

Antonio Mallarino:        This are a great point that Dorivar just made because I have almost an extension program in south America. And I grew up and worked there. This issue of the concept of maintenance, if you go to some countries or the world, and you suggest that they may say, who is this guy might be coming from Pluto. This is ridiculous because what happened is that in the north central region, the great plains, most of our soils have not much what we call fixation.

        So the issue build up, draw down, maintain, makes sense. But you go to some extremely calcareous soils, maybe not even the ones we have in Iowa, Minnesota, but you go to the mountain states that you may have 40, 50, 60%, and you go to some volcanic soils, basaltic soils or some soils in the Southeast where we have exchangeable aluminum that you talk about this concept of maintenance, it doesn't make sense.

        So in our cases, we can do that. Especially for farmers that have safe land tenure, at least 2, 3, 4, 5 years ahead, applying a bit too much, say one year or two, it is not a big deal. That phosphorus or potassium will be, there will be available in the future so we can count on that. And it's like a bank. Now it's a kind of bank that charges the farmer interest as I say, because you have runoff, for example, you have losses. There may be in some situation, little bit of retention. We are lucky in the north central region that we can have this concept that provide flexibility for the farmer. So depending on the philosophy of the farmer or the consultant, then you can go one way or another. This is to me, one other issue, of course we could talk hours.

        Is that really, we need to be careful because we can recommend, we can suggest, but there is not one best solution for fertility things. There are many, you see, I remember when the IP and I started for our concept, let's say there is no four hours. There are a million for us. So especially in our region and for PK management, what is our suggestions assume? Because many things that we recommend, we are assuming what the stakeholder has in his mind, and we cannot go too far with that. So that's why I think we need to provide data information, explain what are our assumptions when we make the recommendations, but then let people decide and then consider land tenure, consider their attitude towards risk. For example, some farmers, they prefer to apply a little bit less so they are sure that they have a high return to the investment on those pounds of fertilizer that they apply and maybe, okay. And they don't care too much about getting maximum yield.

        But most farmers says, they tell me, Antonio you'll pay the bills. So then some others say, no, I prefer to have a little bit more, I'm okay. I'm not going to go broke. So I prefer to be a bit high. So then all the other things that we have to spend on, very expensive, high risk land and combines pick up tracks, all that stuff, then they produce. So it's really important that when we talk and we all have been trying to do it for many years, is to explain our philosophies and explain to consultant farmers that there has to be a good discussion, especially between consultants and crops. Every business and the farmers in terms of what is the farmer philosophy about input management. This is something that is complicated. And that's why I believe that flexibility in the suggestion of recommendations is important.

Dorivar Ruiz Diaz:         I think that's a great point Antonio, talk about dollars and cash flow and all of that. And obviously with the fertilizer prices we have today, this has been a big issue. One situation we saw a lot in Kansas this past year is that those producers who were maintaining salt tests at optimum level, they were able to cut back on rates without analyzing yields so much. Obviously that's a challenge in a sufficiency system where you essentially still have to apply for [inaudible 00:17:41] otherwise, we are losing money. And so that's exactly an excellent point. I think we have to keep in mind that the producer also have different philosophy based on what worked for them, land tenure, cash flow and so on. And I think we really saw that issue with the high fertilizer prices.

Antonio Mallarino:         The problem, what it is that all of us need to deal with our EPAs or department of natural resources and our state NRCS. And of course the technic personnel of those agencies, they want to do a good job. And many of them adopt our suggestion or recommendations. Of course they include some of them in regulations. And this is something that complicates our lives too, because when we provide all this flexibility, which I believe we should, they may not be able to. So then if we are too flexible in our suggestion recommendation, they come to us and say, come on. Essentially what you're saying is the farmer can do whatever they want. Well, so this is something that also, we need to do a great job with our partners, state and federal agencies. So they understand that we are here to make suggestions, to provide guidance.

        It's not the role of land grant universities to establish regulations or recommendations. So when they adapt or require from us information, they need to understand, and farmers needs to understand too, that often what those agencies say may not be exactly what we are saying out there, but that's understandable. So this is another thing why sometimes we focus in our state borders for our research because of the demands, not just the farmers, but also the state agencies in terms of where we have.

        Now, you guys have mentioned wheat, of course, there's no wheat in Iowa. It's a wheat and essentially corn, soybean and apart from pasture. So we do have some recommendations, suggestion for B and K for wheat and some flour, things like that. So we cannot possibly do the research to support those suggestions. So what we do, we actually check with our neighbors and we do a mix of recommendations from Missouri, from Nebraska, from Minnesota, Wisconsin. So we provide that, but we don't have the research to support those. And that's something that maybe some of your states do the same thing because not everybody has the funding to really work in every single field of state and every single crop. So this is where the interstate discussions and collaborations like the one we are doing today is very, very important and useful.

Paul McDivitt:         In your opinion, what is the best way to collect soil samples? Are there benefits from grid sampling?

Daniel Kaiser:         I got this question a lot and I think, I remember Antonio, you saying something about, essentially when you start looking at inner grid, the variation within fields is about as much variation as you can get within a grid. So I think some of the things that you're saying before, looking at the, not of the four Rs and saying that there's many four Rs, is that there's not a one best strategy across all sites. It's really on a site by site basis. And that's what I tell to a lot of our growers. And I don't know, just Iowa, just generally hear the opinions and stuff for what you generally down there, what you generally tell your growers. So it's what I'm interested in hearing too, is some of that around the regions, if it matches with some of the stuff we've been seeing a lot of our growers here in Minnesota.

Antonio Mallarino:         Well, you guys know that I've done lots of work on [inaudible 00:21:34] and grid sampling. I think that since I started work in Iowa, 30 years ago, the overall ground level in the state went down a couple of inches with all the samples that we have taken here. But it is exactly what Dan said. I am known for being particularly pushing for a well done grid sampling, not just taking four course around the four Wheeler, well done grid within enough course, and use of whatever rate. Because I see in Iowa, what Dan said, that in many fields, the variability within those, so map units or yield map units is as high as the variation or the fields. And I think this will become even worse in the future because things are getting larger.

        I remember 30 years ago, there were a few 160 acres fields in Iowa. Now there are many out there fences are going out. So I believe that these tools are very useful. The other issue is that when we do this management zone sampling, we look at all the layers that may tell us where either the nutrient levels or the efficiency of fertilizer may be different. We may end up with as many samples, composite samples or zones that if we do grid sample. And of course for many farmers and dealer and consultants, it's much cheaper to send a guy with a four wheeler to get samples than many people. Tell me, Antonio, in order to do a good management zone, I need to have PhD in my office. And so that takes money too. Now what I tell them, by doing a manage zone sampling and getting all these layers of information, you are learning more about the fields.

        But now on the other hand, I really believe that farmers have for a long time underestimated the values of testing and overestimated the cost. If you look at the cost of soil sampling and testing, now it's about half what it used to be 30 years ago. Farmers very willingly spend money and new hybrids and new pickup tracks and new combines and some things that most likely are snake oil out there. But when you tell them, Hey, do a better soil sampling, do a grid sampling and sample every two years, not every 40 years. And see, come on, we are in the 21st century. We cannot keep managing fields for the abitors. It doesn't make sense. Oh no, I cannot afford it. See, I think that this has to change. It's not that I trust too much or this sometimes I'm very well aware of the pitfalls that we may discuss that in some other session, but we need to get soil samples, we need to do soil samples more often, we need to use these precision technologies.

        But of course, if a farmer has an field that has been working on it for 50 years and it's flat a table and then maybe it's not worth it. If the farmers are maintaining a high level, when they should not, half of the farmers in the north central region are applying maintenance to high levels that if they could stop applying for ly for 10, 15 years before there is a likely response there. So why in the world they're going to spend in some expensive soil, sampling test. On the other day, we go to Southern Iowa or maybe some part of Missouri where all this fields for a farmer are extremely low, whether they're going to spend money and then something, when they should do just put fertilizer down, that's the main thing.

        So depending on the situation, then I think that one thing is better. But I believe that we need to start be with management zones based with re-sampling. We need to recognize the internal variability that in fields and farmers should start. Every farmer should have a yield monitor by now. Most crop offer the price to just uniform rate with a floater on whatever rate is about the same. So I believe that we should included farmers to use these technologies.

Daniel Kaiser:        One of the major mistakes, I think a lot of growers are making right now too, is you see, and this came up at our meeting with our fertilizer research and education, our effort council, is the number that are just strictly going with removal, not even testing any of their fields. And the thing is with, as Dorivar said, with the prices they're at, they've got a definite advantage if they want to cut back on costs at some point. If you know where you're at, particularly if you high already, you've banked some phosphorus for a few years there where you could cut back and not worry about it. The problem is, I think there's just this general fear. What I get with some growers that when we call this mass balance, that inputs in outputs out that these things balance out the way that if you don't apply one year, that your soil test is going to crash. And it just doesn't work that way.

        Just when you look at the phosphorus there, there's a lot of total phosphorus there. And you look at it, there's an available pool. You look at then some moderately available pool and some less available pools that, I'd like to throw fixation out there, Antonio, I know that's your favorite word, but we know that these pools that they're dynamic and things shift back and forth. So it isn't exactly that I put so many pounds in that I can actually essentially see that those pounds coming out based on the soil test. So I think the thing is just, at least having something is a good start to know where you're at. Obviously, if your soil tests are in that 50 part per million range, it's less across the field. It's less important that you do grid sampling across that field, but you might get to a point at which you hit a low spot, but I think that if you look at mistakes right now, it's just not knowing it's the big thing.

        And just going in blindly, putting in what you took off the field, because we started looking at removal rates. It's one of the things that you need to get a news release out at some point, just showing the reality of removal rates, that it isn't one number that crop is removing. It's a range in numbers and being precise down to the pound really as it needed when it comes to phosphorus and likely potassium. Potassium is whole different animal just with how the soil test changes over time. But yeah, knowledge is power in these cases. And if you've got high prices, phosphorus is probably the easiest one to cut, just because our information is so much better when it comes to the probability or response. Potassium is a mess, but phosphorus is one of the easiest ones that we can get a better assessment on what that availability is going to be within a given year.

Dorivar Ruiz Diaz:         Completely agree. I think the key here is that we have to have the right information to make decisions. And one thing that I often encourage farmers, especially those who are starting to farm new ground, I think they have to do grid sample to really know what's there. Oftentimes it's possible that they may not have to do grid sampling again in the future, if they feel is uniform, and now they have a history of management. But without knowing is very challenging. So that's one key point. Another aspect, another thing that Dan also mentioned in terms of the removal and we seeing these very often here, is that some farmers rely a lot on removal values, but we have to recognize these are average numbers and there's really a range. And so it's not uncommon to see our prices after a few years when farmers are managing things that way.

        The other key point I wanted to mention also, and goes back to the economics is that we are talking about P and K from early, but in some cases for us, for example, we need to apply line. And that's a very expensive input and we really need to apply it in the right place. We also have the risk of over-applying. And so to me, there's no question. It has to be a great example. It has to be variable rate for very expensive inputs, like lime. And phosphorus, to be honest with the prices today, it's also the same situation.

Jeff Vetch:         One thing I'd like to add to what Antonio mentioned, and it also aligns with what Dorivar just talked about is, one of the mistakes that I think people do or too many farmers do is, and maybe this is related to who they hire to do. Their soil testing is they send the samples to the lab and they test for way too many things, especially with grid sampling. That might be fine first time you create a field, but you don't need to test for CEC and organic matter and all these micronutrients every time. And that's adds dramatically to the cost. If it's a field that you just acquired and you might only have it on a short term rental, just get PHP and K and probably be confident with that. And hopefully it's going to cost a lot less. And I think that's a big mistake that people make, is they test for the whole suite of everything. It costs 40 $50 per sample, and it's just not necessary.

Antonio Mallarino:         That's a great point, Jeff. Organic matter, for example, why in the world are going to be testing organic matter more frequently than say every four, sic years. This CC, that could be important for some things, but not much for fertility management, especially for P and K, we know that. So labs has all these packages, but I believe there should be more information. And then farmers, of course, I believe, I don't know who of you mentioned that. They don't have to do the same thing every time, they can do a very dense grid sampling well done once, and then they can use that as another layer for the future to use it as for management zone, something like that. But of course, what happens is that, at least in Iowa, much of the sampling is done by consultants or companies, you know that this is not the farmer.

        And that's another thing that I believe is important for something that we should emphasize. Even when farmers want to do soil testing, they don't pay much attention to the sample collection. They don't understand that there is all these variabilities, all these issues, the sampling death, especially with [inaudible 00:32:06] and no-till we have this certification. So the people that take the samples most likely are not the same ones from year to year. So everybody has its bias. When they take those samples and get those results, they build a castle with a recommendation based on that, but they don't pay much attention how the sample is collected and what that means. So the person that take this for samples is not the one that make the decision, is not the one that has to pay the bills. So we need to talk more to the samplers, especially the professional samplers.

        They need to pay attention to that. Everybody's in a hurry. Everybody wants to finish something before night or before snow, but need to do the pay attention to that sample, need to spend the time needed, need to take the samples of course. If not, then you can analyze, grab it in your backyard and it's the same thing. So we need to pay much more attention to that. The cost of the analysis could be reduced if they do, for example, pH BK, for example, frequently. And then some of the other things over alert time, great points.

Paul McDivitt:         Are there any new technologies out there that may replace soil testing in the future?

Daniel Kaiser:         This is always the interesting thing when you start looking at it because there's always new technologies coming out and will they replace it? I don't know. These scanners and everything else that can do things on the go, are they any better? Recently we were working with the soil optics. I had one of their demo units out. And I don't actually have the data back now just to look at comparison. I was using it in some of my current studies where we have multiple rates. And when I start talking about technology, I think there's still some core principles we need to follow when it goes back to that correlation calibration step, just to make sure we have some certainty that these things are relating to something that we can effectively control and actually make some difference in the end for the grower for making them at least some profits.

        So they know it's the main thing with it. You see these things come and go, but tried and true. When you look at soil testing. I look at my numbers said, I talked about this before with phosphorus, you look at the numbers for probability of response. You look at what we're at now versus what we were maybe 20 years ago, the stuff is consistent. If I've got something that's consistently, that helps me at least forward predict, which a lot of times we can with at least phosphorus. I'm not going to get into too much with potassium, we know there's issues with that. And we know that Antonio is working on that moist test, we know there's some benefits to some of that. Although that's not really new technology, that's been around and it was just forgotten about for a while. There's some other options out there, but it's really hard to beat, just that tried and true, taking a sample from a field, sending it to the lab and getting that data back just because the predictability of it, particularly with phosphorus, I've got a lot of confidence in that data.

        That tells us if we're going to get a given yield response within a given soil test from a field. So looking at it, there might be some things to help growers in terms of the mapping side. I think that's where the soil optics is because still that has to be calibrated based on soil tests, that there might be some things there to look at catching some that variability within fields. But I don't know if we're ever necessarily going to be ever manage all that variability. So one of those things that time will tell, if we don't have that Starship enterprise sensor that tells us what we need for given acre, precisely without actually having to go out there and do the work. We still have to do the work to get the samples.

Antonio Mallarino:         Yeah. I agree with Dan. And it's nice that you mentioned the enterprise because I am a tricky and I tell the guys, we can send a sensor to Mars or to Pluto or whatever, and point to a rock and know exactly the total elemental composition, but trying to figure out with a sensor, what is available in the soil, that's a very complex and up today, it's not possible. So some of those things are sensing on the goal. Things like that are useful mainly in my view to use as other layers for the zoning of the field. But you need to go there and using just soil testing and analysis to see really how it does. And sometimes they correlate well, but it is like a correlation of a correlation because in some field it may work. Now, if you correlate that with the soil test, then we may get a nice factor, but you go to a field 10 miles away and doesn't work like that.

        So this is very attractive, but we are not there. We cannot have a sensing of what portion of the phosphorus in the organic matter, in the place, in the solution, in the carbon, its how much of that is really available. For now, this is not possible. So in my view, yes, welcome the new technologies, but don't trust correlations too much because they will not apply for different regions or different fields. And I have experience with that with the victory of connectivity, for example, and potassium and even organic matter. So you go to some states that you can use sensing for organic matter, for example is pretty good. You come to Iowa, actually we work with a company here in Iowa and Iowa doesn't work because the color where you are sensing, it's organic matter, but it's also manganate, it's all things that give color.

        So you may have a variability of two to 8% organic matter in Iowa and the sensing roughly tells you, this is low, this is high. But it's not even close to be precise. So I think that we need to be careful. Also this is another issue that some people are looking at using sensing infrared and all things in the lab. Where you get the soil analysis, the soil sample, you grind it and then you measure with some sensors, and it's the same thing. It does work for some things for others fall apart when you have different soil types with constructing different properties. So when you want to use those things that are cheaper so you could do many more analysis, or in the field you could have many more points, but then you need to have correlations with the real thing.

        And then you have a correlation of a correlation, I'm not sure how that applies to different soils, different fields. So it is not simple. So I am an old geezer, but I work with some new technologies, but I think that this will need more time in order to really be able to pinpoint. We cannot even define by conventional analysis where the fossil is coming from, different forms. We cannot do that. So then why would the sensor magically tell us about that? So we need to be very careful.

Dorivar Ruiz Diaz:         I'm always excited to see new things that we are trying. And I think that's always potential there. Hopefully we'll get there, but I completely agree with Dan and Antonio. Some of these, especially on the sensor side, I think still need work because ultimately like Antonio said, this needs to be related to deal response. And I think that's what that's maybe the missing part in many cases. Then when it comes to new technology, something that I just want to touch a little bit, seems like we often also talk about new soil test methods and we're saying, are these new methods, better soil test and that's all welcome. But again, at the end of the day, is this new method related to your response, is a correlated calibrated for the region. And I think that's often we're also missing.

        I think oftentimes, we tend to go immediately to commercial applications without doing the research and without being able to provide recommendations. I see this all the time, go talk to farmers, come up with a report of some type of sensor or a new salt test and ask me for recommendations. And the reality is that we have no idea because we haven't done any of that yet. Again, we always have to go back to the field and again goes back to the initial discussion today, like Dan mentioned, we have to rely on that field correlation calibration for any of these new technology.

Daniel Kaiser:         Well, I think one of the key things there is that yield response, isn't the absolute yield in your field. And that's one of the things that I think some people think you can just take a yield map and relate it back to the soil test, get an idea. But you got to remember that there's a lot of things that impact yield, soil tests are one of them, moisture is another one. So it's a chicken or the egg type thing. When you start looking at that, there is something driving, what's driving what there. So I think that's key to what you said, I think is looking at that. It's why we still spend a lot of time doing correlation, calibration work, even though I think a lot of people think it's not exciting, it's just needed. We need that data that says that this is the expected yield response based on some certain factor, whether it's a sensor value or where it's a soil test value. That's really the important key to get a lot of these things to work.

Paul McDivitt:         All right. Well 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.