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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.
Hello and welcome back to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I am Jack Wilcox in Extension communications.
Jack Wilcox:Today, I'm here with Brad Carlson, Extension educator out of Mankato, and Jeff Vetsch, the lead researcher here at the Southern Research and Outreach Center in Waseca, Minnesota.
Jack Wilcox:Today, we're continuing our conversation on variable rate technology. Last time, we discussed sensors. Let's jump in with the PSNT or pre-sidedress nitrate test.
Brad Carlson:You know, the idea here is that you're going to be taking a soil test in season, so can be confused. We we call this PSNT, and sometimes it you know, farmers kinda get their their their brains get there's just too many acronyms, but we also say PPNT. PP is pre plant, and so the idea of pre plant is usually you're you're seeing how much residual is there, carryover through the winter from last fall, whether it be from mineralized sources or carryover from fertilizer or something from a manure credit or something of that sort. The PSNT, which is taken in season, usually somewhere around v two, four, six, something like that. Most of those situations, the way it's at least prescribed is you would split your nitrogen, you'd put maybe a half rate on, take your soil test, and then determine how much more you needed to supplement with.
Brad Carlson:And so, obviously, that would be a good way of being very prescriptive with nitrogen rates. It's an area that's been researched a lot. You know, doctor Mike Schmidt, who's currently our our associate dean for for agriculture and extension, did a lot of work in the nineties. And and I think some of that was done here, and Giles Randall helped with some of that stuff, and the whole nutrient management team at that time were were deeply involved in a lot of those activities. You know, and the comment from everybody I've talked to, and and down, is, you know, there's a feeling that there was something there, but there was just too much inconsistency in the data.
Brad Carlson:They couldn't correlate it and calibrate the test in order to make recommendations. We do know that Iowa State did make some come out with some recommendations in the nineties about that same time. Although the the publication that they put out, you know, it it it acknowledged the fact that this can be wildly inconsistent. Some of this stuff came back around in a major way back seven, eight years ago because there was a company marketing a piece of equipment intended to analyze soil samples on the spot. It was a portable unit.
Brad Carlson:I think the idea was you'd throw in your pickup truck, you could go out and take a soil sample yourself, bring it back, and you could actually make a nitrate measurement of the soil sample right there, get on the phone, and then dial up, call up the co op or whoever and and order a fertilizer application based on what you found. I know a farmer who has one of these, and we played around with that unit in on campus some. He lent it to us. We found that they're actually pretty accurate. The technology is sound on on those testing units.
Brad Carlson:I think there was some questions on the durability of it as far as if you really did just throw it in the back of the pickup truck, how much bouncing around could it really take before it started to have some problems that I couldn't comment on that. I don't know. That's just speculative looking at the thing that you may not want to be doing a lot of you know, you might only want it in your truck when you're using it and nothing nothing else. But, anyway, one of the hangups there's there's a number of hangups that we had with that. Okay.
Brad Carlson:One is they were recommending only taking a one foot soil sample. Now we recognize okay. First of all, because of the behavior of nitrate, it moves. It could be below one foot. Obviously, then if you only took a one foot sample, you might not be finding it.
Brad Carlson:Alright? But we also acknowledge the fact that who wants to go out and take two foot samples? Samples? You and I, we've done our share of not just two foot, but three foot samples with hand probes. It's not fun.
Brad Carlson:Nobody likes it. Okay? And so, you know, that that's a limitation as far as if you come out with a method and tell people, yeah, you gotta run around and take all these two foot soil samples. People don't like that. Now the other thing is is these things were designed to analyze the soil wet.
Brad Carlson:And meaning, you know, typically with a soil sample, you take them back, you put them in an oven, you dry them, and then you send them in for analysis, and that keeps what's in the sample stable. Wet analysis can and does work. However, if if we do it under laboratory situations, we also want to know what the moisture content is in the soil so that we can do some quality control on that and keep everything equal. These units were designed to just meter out a certain amount of extractant regardless of how wet the soil was. And so there was definitely the possibility that, for instance, the wetter the soil was, the more dilute your sample would be because it added extractant to the water that was already in the soil versus a drier sample.
Brad Carlson:The the individual I borrowed this the unit from that we kinda played around with, I asked him or or kinda mentioned it to him in conversation, and his response to me was, oh, well, I dry all my samples. First of all, I don't take the thing around to the field. I collect my samples. I take them back to the shop, and then I dry them before I analyze them. Well, you know, that was a good use of that machine.
Brad Carlson:I don't think this didn't really ever take off. And and but but there are definitely some of the fertilizer dealers who have wanted to offer this as a service. And so, you know, we engaged in a research project a number of years ago, kind of a follow-up again related to the some of the research that Mike had done, you know, twenty years earlier. And so maybe you wanna explain a little bit of what we did.
Jeff Vetsch:Yeah. So, you know, the idea was just what you said, Brad. We're gonna put some men out there, and I think we had three treatments. We had a fixed rate treatment where we put on the MRTN or the university, a a near university rate, and it was just blanket, preplant incorporated. That's the way it was.
Jeff Vetsch:Then we had a treatment where we were gonna plan a side dress, where we put on a reduced rate. I think it was about two thirds of the total, and then we we planned a side dress at v five, v six with the other third. And then the third treatment was this what we called variable treatment, where we were gonna put on that same or similar reduced rate, and then take the samples, and we'd sampled it two different times. I think we started sampling around v two, and then we would sample again. Often, it was about ten days to two weeks later between v four, v five, and tried to get them done before v six, because we know that once we get to v six and later, the plants go to this rapid uptake phase, and the amount of nitrogen that's in the top foot can de deplete very rapidly.
Jeff Vetsch:And several people and Fabian has done a lot of this work in his research and shows that that this happens. So the window of opportunity to do this is, you know, in that, like you said, v two to v six probably. So then once we had those samples, I think we took them on about a it was a 200 foot grid or a 100 foot? I think it was about a 200 foot grid. And we looked we we sent half of them moist to this lab where they were gonna measure them with this instrument that you mentioned.
Jeff Vetsch:The other half, we dried them and sent them to a conventional commercial lab that would run them after, you know, the traditional analysis. We also, as you said, we measured to two feet because the earlier work that was done in Minnesota by Mike Schmidt and others back in the nineties, primarily or late eighties, showed that the reason why we didn't adopt the PSNT in Minnesota back in that period was that the one foot test alone did not always provide enough information. Sometimes it took two feet, but yet people were not really nobody wanted to do two feet, especially that time of the year because if the soils are moist and these clay soils or glacial till soils, just sampling is so difficult. Even getting good samples is difficult.
Brad Carlson:And getting out of the tube is if the when there's clay, you get it in the tube, then they expand in the tube, and you can't even get it out sometimes.
Jeff Vetsch:So, yeah, the one foot sample is much easier to do. But we did it we did go to two feet in this study because we wanted to look at that second foot to see if it was valuable. But the long and the short of it is is that, you know, we got some really good data. The first year, a couple of our sites were extraordinarily wet, and we found very little nitrate after these, you know, reduced applications. And it was kind of a moment that, yeah, these fields need more n, but how much more n do they need?
Jeff Vetsch:And that was the challenge, is trying to and I think even Iowa State recognizes this, that the the calibration of these data is the challenge, and that's the tough part.
Brad Carlson:Well, in that that particular that year in in 2014 where we lost so much nitrogen, you know, in essence, we just mentioned this with the whole sensor issue was using it for variable rate or using it for rescue. In essence, we were using it for a rescue treatment at that point, which was really not the objective we set out to do with the project. You know? And so from that standpoint, it, we definitely well, because we lost so much nitrogen because of the weather conditions, I think that site we had down by Blooming Prairie was saturated for almost two weeks. And we know that, you know, the just kind of the standard data is if the soil temperature is about 80 degrees, which it will be in June, and it's saturated for for ten days plus, you can lose about half your nitrogen.
Brad Carlson:And we were saturated longer than that, and the and our samples proved that.
Jeff Vetsch:Yeah. And and, you know, our soil sample you're right. Our soil samples proved it. Our yields were poor, But that year was kind of a no brainer that that site was gonna need supplemental land. So the question then is, can the soil samples tell you how much?
Jeff Vetsch:And they really weren't great at that. They were real the concentrations were really low, so it suggested that, yes, we need more. But again, then you get back to this return on investment. How much more before you need to cut your losses?
Brad Carlson:Well, exactly. If you already applied a full rate and all your samples say put on another full rate, I mean, you've just doubled your fertilizer cost, your nitrogen cost for that, and did did that make sense?
Jeff Vetsch:Correct. But then the the the smart thing was is that we started with just one site in that study the first year, and then we went to the second and third year, and we had a better feeling, I think, and understanding of what we needed to do. And we also learned a valuable lesson that the moist samples had to be refrigerated or frozen rapidly because sitting around in a bag moist when the temperature outside is in the seventies and eighties is not conducive to maintaining the quality of the sample, and I think the people at the lab learned that too.
Brad Carlson:Well, I and and I've I've used that in my teaching throughout, you know, the time since then is the nitrogen cycle is real. It will happen in the field. It will happen if you have a soil sample in a Ziploc bag. It it does you you will get denitrification when there's no oxygen.
Jeff Vetsch:So, yeah, as we moved into the second year of the study and further, I thought we had some really good sites. And a couple of them showed an advantage to the variable application, but at the same time, was it just an advantage to the variable rate treatment often got more nitrogen? More total N was applied, and in a couple of these sites, that resulted in greater yield.
Brad Carlson:And particularly, Jeff, you guys can have kind of a long track record. One of the sites was always here at the research station. You guys tend to find need for more nitrogen here than almost anywhere else in the region, and it is probably just simply related to your cell types and your drainage and, you know, and and maybe a little bit of past management because there's been a research plots and somewhere. But regardless, there's a long track record of needing needing higher rates of nitrogen here than elsewhere. So it really didn't come as a surprise that we found that out at Waseca.
Jeff Vetsch:Correct. A couple of the interesting sites were the ones in Rice County where we had what I would consider not very, very different soils for that region, but different soils for this kind of transition between the Southeast Minnesota and the glacial till soils. And those sites actually, I thought, were the most interesting, because we would get pretty wide ranging differences in nitrate concentrations just over a period of you know, most of these fields, we these strip trials were about a thousand feet in length or 800 feet. Typically, the length of the field was a 40 or an 80, depending upon the size of the field. And we might go from fourteen, twelve, fourteen, fifteen par per million nitrate in some of these strip to as high as 25 or 30 in that same strip, and these were treated the same, and all we were doing was going across the landscape.
Jeff Vetsch:So this was kind of an eye opening moment too. Is this are these differences real? Yes. I mean, the data showed what they were, but at the same time, are we can we manage this at that scale? And is that scale gonna be consistent?
Jeff Vetsch:And then the other factor, which just gets back to the economics of it, is how what type of scale are we gonna have to actually sample these fields?
Brad Carlson:Right.
Jeff Vetsch:And is that practical? We're not gonna be able to take three or four samples for every ten, fifteen acre or do zone management because the differences within that zone might be way larger than what we're getting.
Brad Carlson:I mean, it's the whole issue of, like, when you grid sample for p and k, how big do you make the grid? I mean, you know, I know guys who do their own sampling that do, like, half acre grid. I mean, that's like a crazy number samples, but they do it themselves, and they're, like, really into it. That's what they like. You know?
Brad Carlson:But from a commercial standpoint, you know, we're up to, like, two and a half acres from a lot of, you know, what we do we think is kind of if you're paying to have it done.
Jeff Vetsch:Yeah. And I think that's that's the point. So I think that the theory behind this was that, you know, we could do it on a zone management system, and maybe a field has three, or maybe it has four zones, and we'd only end up needing maybe six or eight samples. But our data showed that the variability across these strips was pretty significant, and that wasn't gonna cut it. So if you're gonna go down now to a 200 foot grid, and take these samples just a a week or so before you have to make this decision, all of a sudden, this is a lot of work.
Jeff Vetsch:It's extraordinarily time consuming. You gotta turn this analysis around quick and make a prescription map, and maybe this isn't gonna be as applicable and doable as we thought it was. Right.
Brad Carlson:And and I the the the site I found very fascinating was our site down in Clarks Grove down towards the Iowa border. That turned out to be an unbelievably consistent site. We've done a number of research projects down there, and we were coming up with least significant difference of, like, two bushels an acre. I'm not sure I want if something's only two bushels apart and the statistics say there's a difference, I don't know that I wanna hang my hat on that. I mean, that's that's getting to be really splitting some pretty fine hairs there.
Brad Carlson:So, you know, from that standpoint, you know, the the other issue, Jeff, and you've already mentioned this, is that that the nitrogen rates in this study probably were too high. And so, you know, from a research standpoint, and and I know frequently a lot of our researchers, depending on the type of what they what it is exactly they're looking at, you'll oftentimes want to short the crop a little bit because then you're gonna get some differentiation with your treatments. If you put on too much nitrogen, it all washes out, and then you never know, you know, whether your treatment actually did something or not. And and this was kind of the case on this study. I mean, the the the fields were corn following soybeans, well, these were these were corn on corn, I guess.
Brad Carlson:I forgot about that. But but, you know, we we actually had, you know, what we considered our recommended rate of a 165 at that time. I think it's worth noting that our recommended rates now are actually closer to 200. You know? And so but but the problem was we were actually comparing a flat rate preplan of $1.65 to a total side dress package at 200, and now all of a sudden, you couldn't really pick apart.
Brad Carlson:Did I have a side dress effect? Did I have a variable rate effect, or was it a nitrogen effect? You know? And and that kinda gets into kind of our world of when you do research, you need to make sure you've designed this project to make sure you can answer your question, and this one maybe didn't quite it kinda fell short on some of those.
Jeff Vetsch:Yeah. We were we were clearly comparing a a systems approach and not necessarily a true research approach, and that was partly because we were collaborating with a local retailer on this project. And the good thing is we had a combination of corn after soybean sites and corn after corn sites, and as you mentioned, typically what the treatments were is our fixed MRTN rate was was our very close to our current recommendation at that time. And then the the other two treatments resulted in a preplant application that was just a little bit less than that, and then followed by a side dress application that was planned that was gonna be either varied or at a fixed rate, but it always, almost always turned out to be more total n than what our our our U of M application rate was. So, yeah, it was definitely confounded by that factor.
Jeff Vetsch:But at the same time, it did give us some interesting information because there was about a third or more of the sites that did not respond to the extra N that was applied in the in the split application treatment that was just guaranteed to be, you know, one fifty start and then another 50, and that's that's what we were gonna do. The variable rate treatment, though, at times, found areas of the field that didn't need more, but it also found areas of the field that did need more.
Brad Carlson:And when we averaged out the strip of the variable rate, it often was pretty similar to the total rate that we applied in the fixed split application, but it was almost always more than what we applied in the MRTN. You know, I think another aspect of this is and and spoiler alert, we're gonna get to the fact that we now actually have a University of Minnesota recommendation, not based on this project, but on another project that Fabian worked on. Our recommendations, and this applies to the PPNT also, are based on that soil analysis in parts per million. And so, it's important to recognize that, first of all, we consider there to be a background level of nitrate in the soil. And so if you're at, like, six parts per million, we don't usually credit that at all because we figure that's what's always there, okay? Then when you start going up from there, you know, we also have to figure the thing we've always tried to discern was what's the critical value where when you get to this number, it's enough, and we don't have to put any more nitrogen on. So Iowa State's critical value is 25 parts per million. And so, you know, those are numbers that I think farmers should familiarize themselves with. Occasionally, when you send these samples off to a laboratory, you'll get back results in pounds per acre of nitrogen.
Brad Carlson:That that is a little bit of a relic of the fact that that is how we do our recommendations in sugar beets. And so a lot of these labs are getting soil nitrate samples from sugar beet producers, and then that's how they're reporting the results. The corn tests don't use that. And so we do need to caution that if you're gonna use this PSNT and the results come back in pounds per acre, realize, like, for instance, if we disregard six parts per million below, when you convert that to pounds per acre, there's a number there. Right?
Brad Carlson:And so you have to subtract that off. And so I know John Lamb, retired cell scientist with us, did a lot of the work with the sugar beet test, and I discussed this with him about, you know, the fact that we were looking at some of these numbers, for instance, coming from other laboratories in out west, and they were coming back in pounds per acre. And I asked him, what do you do with the numbers if they're in pounds per acre? He said use 60%. And so that was kind of the recommendation with that.
Brad Carlson:But preferably, you know, if you're gonna do this, we do want these in in in parts per million. And so really kind of the key with all of this then is, you know, that's kind of your range. You're running from six to 25. How do you interpret that in the middle as far as how much nitrogen you apply? Yeah.
Brad Carlson:And Iowa State does have a a calibration curve or calibration equation that they use to determine how much you need to apply, and and you can reference that.
Jeff Vetsch:I won't go into it, but and and I think we've used theirs on as an example many times. I I will say if you if you look at for the PSNT test in Iowa, you're not gonna find it because they call it the LSNT, which, again, it's Us Us scientists in our acronyms, so we gotta have something unique in each state sometimes. Yeah. Late season Late season end test, but it's the same thing. And again, it it's crucial.
Jeff Vetsch:Let's take it to one foot. Most of the states agree that that is the proper sampling depth. People like to say, well, I'm gonna just do my six inch samples in June, and I'm gonna use those for p and k and all my other micronutrients and stuff. And then at the same time, I'm gonna send them to the lab and get an get a p p p PSNT sample out of it. I wouldn't recommend that because it's not the same sampling depth and your the numbers do not
Brad Carlson:It's gonna be higher.
Jeff Vetsch:You're gonna probably have higher values. So Yeah.
Brad Carlson:And I think the other aspect that we also have to realize with the with sampling for nitrogen is how you applied your nitrogen is is a factor. So if you broadcast urea in the spring, it's probably fine, you know, no matter what you do UAN or anything else. But if you knifed in anhydrous, now you got a problem because we are you are definitely gonna find a higher nitrogen concentration where that knife went through versus in between. And so if if that was the application method, you have to be very careful about how you take that soil sample to make sure that you're you're not you didn't hit hot spots or you didn't conversely just completely miss where the nitrogen was.
Jeff Vetsch:Yeah. And we tripped that into play when we did our studies back, you know, where we were studying this. We always if we had anhydrous ammonia, especially if it was spring applied, we had a grid pattern that we followed exclusively to make sure that we were sampling at recommended distances to ensure that we would get near the band at least one out of four cores or one out of three cores, and that that hopefully would integrate in if we mix that sample well, and we grind it well, and and we should still get a fairly accurate number. But definitely, that is a factor. And I would say that that is a huge factor when you have fairly dry spring conditions, because that nitrogen isn't gonna move very far.
Jeff Vetsch:It's gonna be very focused in that concentrated area. And in general, I would not recommend this practice. If you've put fertilizer down in the spring, whether it was broadcast or whatever, and it's been a relatively dry year, the data that I've collected, forty some site years in Southeast Minnesota, shows that you almost always are going to get a a greater value than you should get if it's been quite dry. The nitrogen's going to be primarily in that top foot. It's going to be concentrated in that sample in early June when you're taking it, and you're probably gonna get a value that's higher than it should be.
Jeff Vetsch:Now, if you've had normal rainfall, or maybe it's been wet, if you can get good samples, this is a tool that you can use to help identify whether that crop needs more. And like Brad said, you can use the 25 part per million critical value that Iowa has. If you actually, if you read their publication, they put that up and down a little bit. It then goes up or down by a couple part per million based on some economic considerations, whether the crop looks good, whether the the cost of nitrogen versus the crop, and things like that. It's very much like our our MRTN approach.
Jeff Vetsch:The U of M recent publication actually, I think, came up with a critical value that's a little bit lower. 20.
Brad Carlson:And I think, yeah, I think it's worth noting. And so I I we were kinda laughing all winter because I was doing presentations on this. I've been asked to do some presentations on it. Fabian has been away, and he's been in Argentina this winter. And and the critical value they came up with was 20.
Brad Carlson:However, Dan says, I don't like that. That's too low. That's dangerous if you're if you get 20 and then you don't put something on, I'm just not convinced. So Dan's been Dan instructed me, and he's been telling everybody else, still use that Iowa State number of 25. You know?
Brad Carlson:I think Fabian's back. I think we're gonna lock them in a room and have them decide what it's gonna be. But but, regardless, that's kinda where we're at, and the the the research showed that they get about a 12 nitrogen credit for every part per million. And so if you take I guess, depends on where you wanna be. If you wanna take 20 or you wanna take 25, take what you actually got, subtract it, multiply times 12.
Brad Carlson:That's how much supplemental nitrogen they were recommending based on their research.
Jeff Vetsch:Yeah. And I I also know I've seen the paper, and I contributed data to that paper, and I and I agree with them that there's probably situations where 20 is the number. But it I also agree with Dan. It seems a little lower than what we've seen at our neighboring states and in other publications. So, yeah, there's reason to debate it, and we're not gonna do that here, but there's certainly reason to do that.
Jeff Vetsch:But at the same time, like I said, where I see this working well is if you suspect you have carryover n from the previous year, and you've also put on some n, if you put on a full rate, and you've seen a lot of weather that would suggest you may have lost some, you could go out there and take some samples and say, okay. I'm less than 20 or I'm less than 25. I did lose some. Is it justified to make a supplemental and application, and when am I gonna do that? I don't have a lot of time to make that decision.
Jeff Vetsch:So the weather that happens after that is probably the most critical.
Brad Carlson:Right? Now, Jeff, it's important to remember that, you know, in the scenario you're laying out, we're still talking PSNT, pre side dress. We're talking about doing it in June because, again, we're measuring nitrate. We're not measuring ammonium. And so if you applied anhydrous in the fall, don't run out there in the April and take a nitrate test because you're not gonna catch it all.
Brad Carlson:It's some of that's not gonna be in the nitrate form. However, by the time we get to June, PSNT time, it should all be whatever's there should be nitrate, and then you should pick be able to pick it up in the test.
Jeff Vetsch:Yeah. I would totally agree. And then the other challenge then is how do you interpret manure? And, generally, the the thought process is is is twofold. One is gets back to this is all the N in the nitrate form or some of it in the ammonium form?
Jeff Vetsch:So if you put on a manure source that doesn't have a tremendous amount of inorganic N and a lot of the N is in the organic form, this PSNT may not be a good good decision because there might be n there that it's just not gonna measure. And it wouldn't have measured if you mow measured ammonia, neither.
Brad Carlson:And not to mention, I've had people say, well, Ken, well, let's just measure organic n. Well, how are gonna start picking up the organic matter in the soil, and you probably got 4,000 pounds of nitrogen tied up in organic matter? That that's gonna the manure application is gonna be lost in that fraction, so you won't know by measuring that.
Jeff Vetsch:Now if you put on a fall, you know, liquid swine finishing manure application, and maybe you put it on a little early because your barn was full, and you put it out there when the soil temps are really warm, and you wanna go measure nitrate in June the next year to see how much is still around in that top foot, I don't have a problem with that.
Brad Carlson:However, it's also worth noting though, Jeff, if you did that and then planted a cover crop and that grew, now some of that nitrogen might be tied up in that cover crop residue, and you're also not gonna find it in the silt.
Jeff Vetsch:Yeah. But my my guess is if you were in a corn bean rotation, you may well, yeah. You may have planted a cover crop, but if you did, it probably didn't probably didn't create a ton of biomass. But it also depends upon, obviously, when you terminated it. So, yeah, there's a lot of a lot of factors that go into place.
Jeff Vetsch:And clearly, the cover crop thing is becoming more and more popular and is a is a kind of a it really throws a cog into It's dipper. Dipper samples. Yeah. Any of this spring soil sampling if you had a cover if you had a cereal rye or a grass cover crop out there.
Brad Carlson:So there's one more aspect I wanna talk about related to this that I think is a very important point, and and I don't think we're getting a little long here. But when we were doing these sampling dates and we were doing them doing it twice, which is not what a producer would do. You wouldn't go and do it twice. We were doing it twice cause we were trying to get enough data to try and calibrate the test and see how well it was working. We were finding we were georeferencing where we were taking the samples with handheld units, so you knew you were at the same spot.
Brad Carlson:We were getting some wild inconsistencies on that same site, and then I know there's one graphic I've been using for several years now of one single site, one year, and the sampling dates were only eight days apart. And we were seeing some of those samples had doubled in eight days, and some of them had lost 80% of their nitrogen. And so, you know, of course, one of the questions is, well, was the test accurate? Well, it might have been. It probably was.
Brad Carlson:We think it was, but we really think was happening, though, was that there was nitrogen immobilized by the decomposition of residue and soil organic matter on that site. That the nitrogen, if it if the number got low, it wasn't necessarily gone, but it wasn't nitrate. It was being tied up in this microbial process and in some organic form. The point on that is well, a couple things. One is that there is definitely some sensitivity to that making the number accurate, but the other thing is it indicates that it's possible to get a false negative on this, that it's low, but it's actually not low.
Brad Carlson:It's not very likely it's gonna be a false positive. It's not very likely it's gonna give you a high number that's inaccurate. And so from that standpoint, I don't think it poses a great risk for anybody using it because, I mean, maybe environmental risk that if you found the you know, if you found a low number, but actually you had more out there, now you put on too much nitrogen, it could be lost in the environment. From a crop productivity and economic standpoint, though, you're probably not gonna lose any yield. I mean, you if you apply more nitrogen, then that's not gonna cost you any yield.
Brad Carlson:It's gonna cost you the value of the fertilizer if you didn't need it. But you know? And so so I guess what I'm saying is I don't think that there's a big risk for using this technology in terms of hurting yourself on a from a yield standpoint.
Jeff Vetsch:I think that's a pretty good common sense approach, and and I think going back to that study, yeah, we we looked at two different sampling times because we know that in general, every cornfield in in Southern Minnesota is at v four plus or minus within a few days often. So your window of opportunity to do this is is pretty small. So we wanted to see, can we stretch that window by sampling earlier? And and possibly what we experienced at a couple of these sites where we did that is that some of that fertilizer N maybe was not all nitrified in some of these situations at that earlier applicator earlier sampling time, and that may have influenced our results. But you're right.
Jeff Vetsch:The immobilization factor, the weather in between.
Brad Carlson:Well, where it was high, and then it went down. Yeah. You know? Right. When it was low and went high, it might not have been mineralized, but where it was high and it went down Nitrified.
Brad Carlson:Right. We thought it was immobilized.
Jeff Vetsch:Yeah. So if yeah. If it was high and went down, it, you know, did we have weather that would have denitrified that much in that short time? Probably not. So, yeah, did it immobilize?
Jeff Vetsch:All I can say is what I've seen in in some of these other studies where they take these fields and they sample weekly or biweekly all year long. And once you get to that point where that crop starts rapidly taking up n, all bets are off because the the concentration in the surface foot's gonna go down really fast, and it's not gonna rebound unless you make another n application. And that's really clear in all these studies. So that's the key thing to think of. Don't think that you can go out there in fact, in 2024, I had a farmer, and he's a local guy, and most of the people in this area would know him, but I'm not gonna mention his name.
Jeff Vetsch:But he talked to me about some sites that he had, some fields, and they were really concerned about end loss, and how much more they should side dress, because they had planned on doing supplemental land on most of their fields, and they were it was justified. That was a really wet year. And he said they had some fields that they sampled a little earlier, and they had some fields that they sampled a little later, and they found the exact same thing. Some of the fields went up, some of them went down to nothing. And he was kind of like scratching his head.
Jeff Vetsch:It's like, how can you explain this? And we we had the basically the same conversation. And and I the the gist of it was, it's like, yeah, you know, what point in time that you take these measurements, you're making a lot of decisions based on that point in time. And is is that consistent over over time and and how impactful that could be in your prediction? And that is a factor.
Brad Carlson:I remember that year because I remember I had a big garage sale over the July 4, and I actually had neighbors were walking in coming they weren't coming to the garage sale. They were walking in with cell tests because they knew I was gonna be there. They're like, can you explain this to me? He's like, well, it's the July 4. Not really. You know? So anyway, well, I think I think we've we've we've pretty well hit this topic pretty good, Jeff. I thank you. Normally, it's me and Dan. I appreciate you being here to to cover this stuff, some things that definitely you're you're quite an expert on. So thank thanks for joining us this morning.
Jeff Vetsch:These types of analysis and and research has been a significant part of my career for many years.
Jack Wilcox:Thanks, Brad Carlson, Extension Educator, and Jeff Vetsch, Lead Researcher at the Southern Research and Outreach Center here in Waseca, Minnesota. We appreciate all the information.
Jeff Vetsch:Thanks.
Jack Wilcox:Do you have a question about something on your farm? Just send us an email here at nutmgmt@umn.edu. Thanks a lot for listening and we look forward to seeing you next time.
Jack Wilcox:Advancing Nitrogen Smart is proud to be supported by the farm families of Minnesota and their corn checkoff investment through Minnesota Corn.