Variable rate zones: Field mapping, soil types, tools & more
Hello and welcome back to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I'm Jack Wilcox in communications with Extension.
Jack Wilcox:I'm here with Daniel Kaiser, Extension nutrient management specialist, and Brad Carlson, Extension educator.
Jack Wilcox:Today on the podcast, we'll talk about variable rate nitrogen. First, we're gonna cover some of the broader aspects of variable rate and then talk specifically about zones.
Jack Wilcox:Brad, what are some of the objectives overall of variable rate nitrogen?
Brad Carlson:Well Jack, we're gonna talk a little bit about what all these are and then kind of move into zones. There's a couple points though related to variable rate nitrogen I'd like to throw out first and that is if it's variable rate it's varying from what and that is what the flat rate application is and so one of the points that I like to make with this is that really the obviously the objective here is you're gonna make more money, right? And so in order to make more money there's really only two ways you're gonna do that you're gonna either increase the yield or you're going to decrease your inputs and save money on your inputs so that's really just the where it's at and so the thing about it is if the flat rate that you're varying from is already too high meaning you've already maximized yield, the only way you're gonna ever make money on this is to lower your rate of nitrogen and and those profits can be kind of small. I think really the key is to it's it's probably not so much a matter of that there's grossly underperforming places in the field where you're not getting your your maximum yield in more cases than not.
Brad Carlson:You're probably hitting the right amount of fertilizer in those spots anyway. And so what we really are talking about is an overall reduction in the total amount of nitrogen that we apply and then increasing it based on the specific parts of the field where it's necessary.
Daniel Kaiser:And it's one of the challenges that we deal with on the recommendation side is is trying to figure out you know, Brad mentioned varied from what? I mean, what is your starting rate? Because we know that nitrogen, from the standpoint of we'll just look at water quality that if we over apply, really, the only way we get that out of the system is there if there's something effectively to take it up. Otherwise, we have additional nitrate that's in the profile that is potentially there for loss. So that's one of the things I think as we talk a little bit further into this topic today is, you know, I think the really challenge is that starting point.
Daniel Kaiser:When we start talking about variable rate and trying to figure out kind of where do we go so we're not initially over applying, then what information do we use to vary the rate by? And that's kind of I think the bigger challenge for us on the research side is trying to come up with those things that growers should be utilizing to look at how they vary the rate because there's you know, I hear a lot of things out there what growers are using in terms of, making some of these these different rate decisions. And the problem is, you know, we talk a lot on Nitrogen Smart intro section, which is talking more about the fundamentals of nitrogen in the environment that it's pretty complex cycle. So the inputs output cycle becomes more really unpredictable, particularly if you're making your decision, say six months before that crop goes into the ground because a lot of these things are water driven and you really don't know what's going to happen at that, you know, when some of these decisions are being made. So I think so that's a challenge with variable rate nitrogen and why you don't see a firm recommendation from us here at the in the university is just there's still a lot of unknowns for this.
Daniel Kaiser:I mean, it's really what technology do you use to make these decisions is really what we're trying to work out at this point in time.
Brad Carlson:Right. And and so if I look at some of the the work that we've done in the past on variable rate nitrogen I think it's worthwhile looking at the non variable rate nitrogen work that we've done because if you do a nitrogen rate trial say you applied a 150 pounds of nitrogen and it was replicated four times you got four plots there's different yields for all four of those plots. Rarely are they all going to be the same you know and so there's variability right there just simply at the same nitrogen rate. Do that mean that needed different nitrogen rates? Well not necessarily it might have maximized the yield in that spot for that rate anyway and so that can be very difficult to try and figure that out.
Brad Carlson:So the other thing is try and get an idea what the confidence interval is if you're looking at research data and particularly so if you're starting to you know make some choices on what you're gonna use for variable rate you know and now you're looking at some data some research has been done looking at different rates and so forth. Try and figure out whether it is based on solid data or whether it in of itself had responses that were all over the board and whether you can actually be comfortable using it and I think is we got to be really careful because you know we've been all been, I shouldn't say part of but we've all been aware of private industry research that has cherry picked data that there's been you know we've seen trials that didn't look so good and you know, long behold, here's a magazine ad and the one that don't look so good doesn't get published. It's only the ones that look good. And so, you know, you as a producer or decision maker for what's going on in your field do need to look with a little skepticism at some of this research data.
Brad Carlson:And I think the other thing is is just because we're researching it, you know, we're kinda here to independently check things out. You know, you'll sometimes see in an advertisement, this has been university research. Yeah. So what? It doesn't mean that it was researched and found successful. Just because we're looking at it does not necessarily establish its legitimacy.
Daniel Kaiser:And, Brad, you know, brought up some points there that on the research side, we do take some flak because a lot of our work is done in a small plot setting. So we're dealing with situations where handled with nitrogen trials, like to be a minimum of 15 to 20 foot wide. So if you're dealing with 30 inches rows, it's six to eight rows by about, you know, 35 to 40. I mean, longer is better. Larger areas are better.
Daniel Kaiser:But we do know, I mean, as you're talking about variability that in a smaller area, if you get gaps in your stand or some other things that can occur that it can affect that, and that's why we you see some of that variability from from plot to plot because it isn't uncommon. We just, you know, talk about just our control yields, which are yields without nitrogen to see a fair amount of variation if we've got four or five, six replicates in a study in what those check yields are. Really, though, the thing is that we're focused on mostly with a lot of the ag research really is more of the response though, and it's not the absolute yield. And I think a lot of growers, you're looking at your bottom line, you're looking at your maximum yield produced, but from a nitrogen standpoint or from a nutrient standpoint, really my end, I'm more interested in what is that overall return per pound applied. So we don't really care quite as much, what that absolute number is, and we'll see that.
Daniel Kaiser:I mean, some growers I think would much prefer on farm research with with a larger combine, which we can even out. We don't have those issues with some of those gaps in stand. There's some though. I mean, you get a bad spot in the field and sometimes that has to be weeded out, but there's pros and cons of it. Know, normally what we see is if you compare the two is that that that return is about the same, but that maximum that's produced might be a little bit different.
Daniel Kaiser:And you know, some of that too, I'm always a little wary about, especially plot, or when you look at a plot combine versus actual production combine with yield monitors, calibration is a big issue. So there's some things there that need to be considered with that, and that's why we do a lot of things in a more controlled setting is because we can get things more compact, hopefully isolate more of that within field variability that we don't have I mean, you've got a 160 acre field out there, quarter section. I mean, you're not gonna get the same yield across that whole field, that there can be some variability induced with that. And it's just something to kind of consider with that in the ag research side is so there's pros and cons to everything.
Daniel Kaiser:And as as Brad was talking, what we call the confidence interval, which is essentially a measure of uncertainty is is really key when we look at a lot of these things.
Daniel Kaiser:And that's why on the nitrogen side with our current recommendations, we have that MRTN rate win or the maximum return to nitrogen rate window because that's, kind of in lieu of a confidence interval for our rates to kind of say that, you know, we're fairly confident that the optimal rate should be somewhere within that window.
Brad Carlson:You know, when scientific research happens in a laboratory, usually they like to be 95% plus stuff that's headed to consumers frequently has to be 99% because the company that's selling a product would be open to liability if the product didn't work. When you're dealing with biological systems you just can't do that. Mean so we would love 90% confidence intervals in reality 80% is quite good for ag research but what you got to remember that is if it's 80% you've got probably one out of five times you got a false positive it looks like it worked and didn't work. So you know, you do have to be kind of careful about that. You know, we'll see, you know, for instance, you know, kind of getting off the off the track here, but, you know, when we're looking at, like, some of our evaluation of biologicals, you know, and and you'll say, well, we had this one site where it really worked.
Brad Carlson:Well, did it really work? Was it if you had 90% confidence interval? One out of 10 sites will tell you give you a false positive. So you don't really you know, it can be really difficult to sort that out. And so from that standpoint, guess, you know, you do need to just continue to be kinda wary.
Brad Carlson:Dan also was mentioning using full size combines and yield monitors. We do need to be a little bit careful you mentioned calibration that's important particularly a lot of farmers say well I just use this for advisory it's not really that important that it's that accurate and that's fine until you actually are using it to be accurate because we'll see the yields go up and down from the morning to the afternoon when the crop starts to dry out and so particular like with soybeans sometimes but but with corn that'll happen too, you'll see it change, they'll see the moisture percentage change in fields with a lot of terrain where the lower areas have stayed green and the hillsides that are a little more eroded are all dry. That will change what your actual yield is and so if you're doing for instance MRTN, mean that dries off of your yield and so that's gonna mess that up too. The other thing you gotta be careful about is remember that what is actually being measured in that combine is not the yield, it's actually the pressure of the grain striking a plate and that is calibrated to the yield.
Brad Carlson:And so the grain striking the plate that's giving you that measurement, that grain came from somewhere back there behind the combine when it was originally picked up. And so there are programs that will allow you to correct for that. In most cases farmers are not doing that because again it's not really deemed as necessary it's just another step and in some cases depending on the program you're using is difficult to do. But if you're evaluating some plots you set up you need to cut off that first fifty-sixty feet and the last fifty-sixty feet depending on the direction the combine was traveling. Also remember your nitrogen applicator in a lot of cases is not set up to the same width as your corn head.
Brad Carlson:So your planter in your corn head corresponds but the nitrogen applicator frequently does not especially if you're using urea and it's being sprint spread, you know, those some of those patterns, you know, can I mean, a lot of times the the coop can put on they can push a button and make it 50 feet, 60 feet, 70 feet, 80 feet, whatever you want it to be? So you also have to be careful with that individual combine pass at 12 rows you might have overlapped two different nitrogen treatments there. So as Dan said you wanna get down the middle of the treatment and so if you're doing your own evaluations out there you know be careful only to be looking at the strip that's running right through the heart of that treatment and not taking the full width of that because the edges might not be accurate.
Daniel Kaiser:So I mean really the question with a lot of this you know we kind of when we break this out when it comes to variable rate is really looking at how do we zone the fields. And I think that's, you know, one thing that Jack mentioned earlier. It's it's something we'll kinda talk about because, I mean, that's really key because really what you're trying to do if you look at, say, all of our sites in our NRA database we have essentially is you're trying to almost do the same thing that we do across fields within a field to try to make individual rate decisions based on what you know about that given area. And that's kind of the the challenge is, you know, for us even within the database we have across our our field sites, we can't necessarily come up with any sort of consistencies of why, you know, one site might deviate from the rest. And I have looked at this within fields.
Daniel Kaiser:I mean, this is something I've I've done. I've been working with Minnesota Department Ag for a number of years. We're doing our, their nutrient management initiative level two sites, which are, you know, farmer driven, where where we send them a map for application. They apply the fertilizer and come back in with the yield monitor. Then we assess the yield.
Daniel Kaiser:These are larger fields. Don't really though I have the ability in that type of situation though to really break those fields apart and that's kind of the challenge. I have done in the past with the small plot work where we've done 16 rep studies looking at a top slope to a toe slope area within fields to see if there's any variability. And one of the things that I've kind of found with that is, you know, it's amazing how much consistency there is in it, particularly in the end rate response that I mean, I'm you know, I was kind of wondering how much actual variability there is in the field, you know, some people listening might disagree saying, oh, there's all sorts of variability in in some of these fields with n rate response, but I just don't know. And that makes a lot of the stuff I've seen have been pretty consistent.
Daniel Kaiser:And even in situations where you had a lower yield potential, the response n was the same. So I got less yield, but if you look at the incremental increase per pound of n applied, it was about same. Right. With that. So it's it's it's not always a given with the variability and it kind of, you know, when you start looking at a lot of the research behind a lot of this variable rate where they've done large field studies with strip trials, you know, I kind of wonder if some of what we're seeing is an artifact of, you know, the size of the strips and where things are positioned in the field that that's one of the issues with statistics is sometimes, Brad was mentioning, we can kinda get feel fooled with the data.
Daniel Kaiser:Just, you know, even if we have things laid out right, that there can be some issues, especially the larger we go with a lot of these studies.
Brad Carlson:The concept of making zones in the field is one of the oldest ones relative to variable rate of any fertilizer product. Guess I go back to when I started in graduate school in the early 1990s, 1992 when I started in graduate school, they were talking about farming by soil type. And of course that's getting back to, you know, there definitely are factors related to soil type that are important, there's water holding capacity as a percent of organic matter, there's you know maybe like in Southeast Minnesota there's depth of bedrock, there certainly are factors there. However, we also discovered that that didn't work because in a lot of cases management trumped the soil type. And so what's happened management wise over the last fifty years, seventy years, hundred years has really kind of thrown that out the window and so we don't necessarily see response following soil type lines.
Brad Carlson:However, it's kind of a combination of the two because if you change major soil types say, you know my area where I live in that's the transition zone between where there was hardwood forest in the prairie there's alphasols and there's mollisols and they can be in the same field and you're going to see some differences and I don't like my own property in LeSour County the eastern side of that are mollisols and the western side of it are alphasols and the percent organic matter drops by one to one and a half percent when you change those cell types and so there's just a lot of factors. If you look on the overall picture of variable rate nitrogen there's there's many different technologies and we are gonna simply talk about zones today, but I guess it's worth mentioning that, you know, that there's sensing technologies and there's there's crop models and and there's been a few other things that have been proposed. In a lot of cases, those technologies are looking at applying a base rate of nitrogen and then coming back in season to make an adjustment after you've gathered more information. In a lot of cases, zone management, there's probably nothing that's going to change in season.
Brad Carlson:So you probably have a better opportunity of variable rating the nitrogen right from the get go if that's what your decision is versus some of those other technologies.
Daniel Kaiser:I think it's one of the challenge, I mean, especially when you start talking about soil types and the boundaries. If you look at a go pull a map up, just look at it, you'll find all these clear distinct boundaries drawn on these fields where one soil type changes to the other. But, you know, I think we all know that that's a little bit more fluid when it comes to the field setting and that are the things a little bit more I mean, those maps live in kind of a black and white world and things are a bit more gray.
Brad Carlson:If you actually, Dan, if you read the definition, a lot of times it'll say, with this soil type inclusions, meaning there's little spots of something here and there all over the place.
Daniel Kaiser:So the big thing is, I mean, look at your fields and, I mean, I think some growers zoning have used organic matter, which I think might work. Although, just coming up with a simple equation on organic matter, looking at high organic matter versus low and looking at the ability to supply nitrogen. Well, general, the more o m you have, I mean, the more the higher the mineralization rate should be in some of those areas. You get into situations in Minnesota like out in Renville County where you got those potholes, and those areas are high in organic matter, but they're they're so wet and saturated that it's likely the opposite in those cases. The reason why they're high is because essentially, they don't lose the organic matter because it doesn't mineralize because of lack of oxygen.
Daniel Kaiser:So it isn't a perfect scenario, though I'm kind of around Brad, your area in that transition zones a lot of those Lester's. Mean, eroded hilltops, I mean, probably gonna need, I would say, slightly more in than some of the lower areas of the field where you might have some flexibility. The I mean, the issue is we've never really been able to come up, think, with a simple equation for some growers. I think some growers have kind of developed some things on their own in terms of that. I mean, I know with sugar beet production at one point in time, they were zoning fields based on organic matter.
Daniel Kaiser:I don't know how much that is anymore, but there's certainly some things you can do. And, you know, that's you know, looking at the information that you have, that's probably the best that we have if we're trying to make a decision up front. And I think that's what's really key with a lot of this is, you know, again, you can't go back in and take the nitrogen out that you've applied. It doesn't bank, so you have to essentially not over apply where the crop is it's in excess of what that crop needs. So that's kind of the issue.
Daniel Kaiser:And with zoning, you know, I get questions a lot in terms of what's my minimum zone size. I mean, a lot of growers have used two and a half acre grids. I mean, with nitrogen, maybe you could go with a little bit larger, maybe zoning by soil type. I think landscape position is probably a better option in some of these cases to look at that, but there isn't really a right or wrong answer. It's all on a field by field basis, and, you know, Brad mentioned this before, his his previous management is a key.
Daniel Kaiser:I mean, the the thing a big thing, if you're going into fields, if there were any old feedlots or anything in some of these areas that may have been plowed up, it's amazing that how long that those can show up, put a small grain out there because, you over apply there and the and it goes flat, and you can kind of tell that it's still supplying some nitrogen. It's not necessarily that way from corn, but that's what we're dealing with is, you know, there's there's man made variability and natural variability and those two interact a lot. So it becomes a little bit more of a gray area than how how to effectively break up your fields into zones given you know some of these interactions and what can be occurring out there.
Brad Carlson:One of the main messages we try to get across with Nitrogen Smart in our education in this area is one size doesn't necessarily fit all however our recommendations are intended to address most of the situations. The thing about it is where there is variability a lot of the time and most of the time those factors are knowable. So it has to do with whether the area is prone to saturate and hold water, has to do with just overall rainfall, it has to do with organic matter, soil type, soil texture, you know it has to do with what hybrids you're planting and what all you put on for your fertilizer package. There's a lot of things and so from that standpoint you can use those factors to base your decision making on with the zones, you know, where you have changes in those things where you say, this area is usually wet it's gonna lose nitrogen to denitrification and needs a higher rate. Well, also if that area is that wet it also may be a place where you choose to put less on early and come back and put it on a side dress time because you've avoided the wettest time of the year when you might have lost that nitrogen, you know, and so forth.
Brad Carlson:But but you can use those factors in in a lot of cases your own personal experience will tell you where a lot of that stuff is where where, you know, one year you applied hog manure, but you ran out halfway across the field. Where was that? Do you see some differences on one side or the other? You know, all that kind of stuff will go into this.
Daniel Kaiser:And that's one of the things I think now with more growers having yield monitors. I think that's one of the advantages with the yield monitor. You've got the data to look at the fields and look at your overall productivity and look at those areas that might be consistently high yielding or consistently low yielding or maybe some that are consistently variable for using that information to zone and and try to see, okay, what's going on? Can we make some decisions? I think with AI, there might be some some ways to kinda maybe eventually growers to do a little bit more mining into that because, you know, I know a lot of you out there, if you are farming, you got a lot to do.
Daniel Kaiser:So it isn't necessarily probably first in your mind to sit down with all your yield maps and really crank into that data to, put the time in really to try to figure out things, just look at better managing the fields. But, but that I think that's one of the things that with yield maps, I think there is some some things that could be done. It just a lot of the programs are pretty simplistic in terms of just getting you that pretty picture and really not mining much into the data to see what's actually telling us.
Brad Carlson:Well, and the other thing with yield maps, Dan, is there's been a lot of abuse of those. There's been a lot of folks have have flipped those things around and and used them as more or less crop removal and therefore variable rated the nitrogen just simply based on yield. As you mentioned before, Dan, you've done studies that showed that the response to nitrogen was identical in various parts of the field. However, the yield was different based on the parts of the field. So in those cases, the lower yielding spots needed just as much nitrogen as the higher yielding spots the higher yielding spots didn't respond to more nitrogen they didn't need more supplied in a lot of cases it's the better soils that are building the better yields not the input and so if you're using those yield maps by just simply saying, well, we had 280 bushel corn out here, so we're gonna apply 220 bushels or 220 pounds of nitrogen on that spot because that's what it needed.
Brad Carlson:Well, that didn't isn't necessarily what it needed. I mean, we've had I've had enough experience with with variable rate technology to show that the in a lot of cases, it was our best yielding spots that actually needed the lowest amounts of nitrogen. So I I know we were just talking this morning, Jeff Vetch was telling us that that they had a a research site this year in Southeast Minnesota that had a manure history on and they had 240 bushel corn with zero nitrogen applied. So that obviously, you didn't need to go out there and flip your yield map and say, oh, well, we needed to apply 200 pounds of nitrogen to get that. Well, you didn't.
Daniel Kaiser:And I think that's the big thing I think that's probably somewhat hard for some people to understand is when it comes down to the maximum yield produced, there's really no relationship. And I've seen the same thing. We had a we had some soils down at the Rosemont station and Loess soils similar to the Karst area, Southeast Minnesota. And one thing about those soils, when you have moisture, they tend to be pretty well drained and you get a lot of mineralization. So what you tend to see essentially for setting up high yield potential is you see kind of high yield potential and high mineralization rates kind of go hand in hand with each other because what's good for the plants also good for the microbes actually in the soil.
Daniel Kaiser:So, I mean, in those cases, I think I mean, I could make the argument that those are the likely soils that are gonna need less versus maybe you got an eroded area that field, you know, area that doesn't have a lot of organic matter, the subsoil is exposed. It's an area you're probably gonna need more with that. And that's one of the things that, you know, I'd really like to get set up at some point is just to, you know, pay growers to put to small areas of the field with no nitrogen down, no additional end down and just see what yield they're producing compared to where they have adequate end just to see that difference because really that difference, what we call the delta yield or the difference in yield from the minimum to the max, really relates very well to the optimal nitrogen rate. You know, it should make sense to people if the more you can produce without, you should need less overall with it. So there's some really some things to kind of look at with that that we could consider and you know, it's it's a total of an acre area and you know, a 160 acre field that you have no nitrogen that you're getting you're having some reduction on, yeah, you'd be losing a little bit in those areas.
Daniel Kaiser:But I think the knowledge you're going to be gaining is much more at that point in time, and potentially looking at how to manage some of these areas because looking at it, if I look at our database, it's really about the only thing that I can really relate back to the optimal nitrate within a given field. It's not maximum yield produced. It's it's really that that delta or that difference in yield between the zero and the the fully fertilized, really relates pretty well to where we have a higher percentage of the yield produced by the controller or fields that have had lower than what the MRTN predicts in terms of the optimal nitrogen rate within with across all these fields.
Brad Carlson:And Dan if you look at various nitrogen rate response trials and you calculate what the maximum return to nitrogen is in any given field and what the yield was so how much nitrogen there was in that field that was necessary and then what the yield was at that spot and you plot them on a chart you end up getting this total shotgun pattern there's just no relationship if you could actually say we need X pounds of nitrogen for this many bushels of corn that would be a straight line and they just flat out are a shotgun blast pattern. And so if you're trying to make a variable rate recommendation based on the yield map, you're assuming it's a straight line and there is absolutely no data to support that that's the way it works. Just simply has to do with factors on that actual site where that specific rate is going on are trumping that what that total yield is on that site and so you know we just can't stress that enough that that's just not a valid method for variable rate nitrogen.
Daniel Kaiser:If you look at corn too, it's interesting I mean like any other plant that, you know, generally, even in years where your yield is maybe limited by something else like drought, I mean, if there's nitrogen there, the plant's gonna be taking it up. So it's typically when we start talking about things like nitrogen use efficiency, which essentially, generally, what we do is a differentiation between the total taken up at optimal yield versus zero yield. Take that difference, and then we, you know, divide the amount of N applied. That gives us kind of our what we deem as our nitrogen use efficiency. That really where I get really efficient use of nitrogen is situations where I get high yield potential.
Daniel Kaiser:So nothing else really is limited in that circumstance. So that's, you know, kind of the trick here and you'll see people look at that pounds of n per bushel, and, you know, where have we seen where those numbers have been high, Brad? I mean, it's been 93.
Brad Carlson:It's been wet years.
Daniel Kaiser:It's been wet years or years where we've been our yield's been limited by something else that it gets relatively high. So I mean it's really when it comes to nitrogen use efficiency, the best thing we can do is try to maximize yield potential as much as possible, but you know, then again try not to over apply in which is that that just that to push and pull is is really difficult.
Brad Carlson:Well, and and so I am coming back to something that I mentioned at the start of the podcast, which is, you know, what are you varying your rate from? And so if we look at our nitrogen rate calculator and what it's telling you to do under most circumstances in you know, for corn on corn or corn falling beans, whatever that rate is at whatever price ratio you wanna use, then the question becomes how often does it need more than that? How often does it need less than that? And I think it's important to realize that the model that fits that recommendation is a quadratic plateau and it encompasses most of the years. There are circumstances, sites in years that need higher amounts of nitrogen but most of them are going to fall underneath that plateau and so if you're trying to get the exact right nitrogen rate it's more likely, way more likely to need less nitrogen than the flat rate than more.
Brad Carlson:And so as we've said throughout this with the zone situation is the cases where you need higher rates of nitrogen usually those circumstances are knowable And so you should be able to pick those out in the field to make those. And and so in a lot of cases, you know, my my research that I've worked with over the the last decade on variable rate nitrogen, honest to God, almost, you know, I would say 90% of the time, the products that we've shown to actually work were telling us to apply less than the recommended rate of nitrogen. And so you were savings a few pounds of applied nitrogen and getting the same yield. You weren't increasing the yield because you found some spot that that needed more nitrogen than you were putting on. And so it's just really important to stress that that's really kind of the the hard cold facts of what's going on out there.
Daniel Kaiser:I like the data you have. I think it was Rice or Steel County you did a number of years ago where you're looking at testing or comparing some of those models and those, think, what, two seventy, two eighty Two eighty. Two eighty. Bushel corn and a 150 pounds and corn following corn?
Brad Carlson:Correct. And that was that that field was was a half a mile long. It was it was a half section.
Daniel Kaiser:So, I mean, I think a lot of people out there, growers out there say you're crazy. I mean, because a lot of them probably you're looking at two eighty. They'd be, you know, probably over 200 pounds of N at least thinking that they would need to apply that amount. But I mean, there are there are good soils out there and, you know, looking at especially with manure histories and, you know, even even if manure hasn't been applied the last ten, twenty years, I mean, you still might be picking up some of that effect over time if it was long term ahead of that. So, I mean, that's so that's a challenge with any fields.
Daniel Kaiser:And, you know, if we just go and look at just the the soil survey data, it doesn't tell us the history of what's going on there. And I think that history is almost as important or more important than the soil types that are out there just in terms of what could be supplying nitrogen.
Brad Carlson:Well, think about the amount of erosion you use you know, everybody that studied agriculture, you know, has heard about all the terrible erosion back in the 1920s and thirties because of the way we farmed. That's a 100 years ago. No nobody really knows anymore. You've got a field that you're farming what that looked like a 100 years ago. It could be the same soil type as one across the road was managed completely different.
Brad Carlson:And so you got the same soil type and they're just gonna behave completely differently. So I guess, you know, let's just kind of wrap this thing up. As far as if you're looking at making some management zones are going to use them for nitrogen. Soil characteristics are where you start it has merit but then the next thing is how do you adjust And that's gonna be based on other things such as management, some of what your yield maps tell you. You can use relative yield.
Brad Carlson:The yield's gonna vary from one year to the next. If you take your maximum yield, of course, you gotta clean the data. You're always gonna have some points that tell you you had 650 bushels or something. Take those out. That that was an error in the combine.
Brad Carlson:But if you've got clean data, you can you can you can make maps based on a 100% and then how it varies from that. And then you can start comparing, you know five years and and there's computer programs that will correlate those and show you where your yield is consistent and where your yield is varying you know and so forth and and so from there you can start finding those places where it's varying and then start thinking about where the factors are that are making it vary. You know? Is it is it the low areas? Is it the hillsides?
Brad Carlson:Is it, you know, because it's close to the woods and every year it gets dry, you don't get yield too close to the woods, we can't you can't fertilize out of that, you know, and so forth. So so you need to start thinking about those kinds of things. And like we said, avoid the temptation to just simply look at a yield map and turn it into a crop removal, yield goal based map that just simply that that just there's just no research data support that that works. And I guess the last thing is is don't think you're gonna just jump right into this. I mean, if you're going to if this is what you really wanna do is you wanna make some variable rate zones, but you've not been looking into it, the odds I would say your odds of coming up with good zones this winter are very poor.
Brad Carlson:You need to start gathering data, looking at it, evaluating over a few years before you actually start making some of those decisions like that.
Daniel Kaiser:Again, I'm gonna throw this out there is, you know, when I look at data, I'm looking at return to a given nutrient. So NPK, I'm looking at that overall return. I'm not looking at the maximum yield produced within a given area of the field to look at your overall profitability. I know that's where a lot of growers are really concerned about is, you know, looking at what yield do I need to essentially make this area profitable. So I mean, they're two different with that.
Daniel Kaiser:So with nitrogen, I mean, it doesn't matter if, you know, say the area would be a raise consistently 200 bushel versus 250. I mean, really what I'm interested in is what we call the marginal return or the return the difference between zero and that maximum yield just to make sure that it's covering the cost of the fertilizer itself because they're two different questions there in terms of of what you're trying to address. So when you're you're talking about, you know, variable rate, I mean, that's, you know, a good starting point too is, you know, is there an area of field that this isn't profitable to do anything? You know, maybe I just turn that into CRP or something else, you know, because I just can't make any money there. So that's kind of the thing when it comes to fertilizer is, you know, when we're looking at a lot of the data, we're not as necessarily fixated on maximum yield produced.
Daniel Kaiser:It's really essentially to the difference between zero and the difference between optimal yield with that at the optimal rate, and how much it took at that point in time to generate. And usually, we use what we call price ratios to kind of assess these things where you look at the price per pound unit nutrient versus the value of the corn just to look at overall return on investment. So I I mean, I used to said I wanna throw that out there when it comes to a lot of what we're doing is that's really what I'm more interested in is when it comes to zoning your fields, then you're probably going to be looking at it a different way looking at that maximum yield produced. And one of the things we've been trying to do with a lot of the nutrients is to provide growers with, you know, kind of a percent difference in yield should you not do anything versus the applied. Because that would help at least if you know kind of the average yield potential in those areas to make a decision on the return for a given nutrient.
Daniel Kaiser:But with nitrogen, it's easy because nitrogen, we generally get a nice clear response no matter what. I mean, there's certainly some field areas where we might see no response. I mean, usually there's there's a reason for that. A lot of times it's past winter history or something that's supplying a lot of organic N...
Brad Carlson:Coupled with perfect weather throughout the summer, which is impossible to predict.
Daniel Kaiser:So that's one of the things that, I mean, it's it's easy. With some of these other nutrients, a lot of times you can cut your rate back as long as you apply something, you generally get the majority of the increase you're gonna get within that given year. So, I mean, I said, I wish nitrogen was as easy as p and k because even if you over apply, then you can with p and k is generally you can bank it to some degree where you can you can take advantage of it in future years, but nitrogen, that's that's not necessarily the case. And if you over apply, I mean, the soybean crop, if you're in a corn soybean rotation, soybeans are gonna take it up that next year, and there just really isn't anything Yeah. Left unless you've got some sort of organic source that can be like I said, that's where mineral previous mineral history, it's amazing how how long that can impact crops into the future.
Brad Carlson:Yeah. I guess the last thing I'll just wrap it up with here is is we've said this many times before, if if you're looking at making some zones and you want, you know, another opinion, don't be afraid to ask us. I mean, we'd be willing to, you know, particularly take some of the meetings that we're speaking at this winter, you wanna bring a couple maps along and lay them on a table and say, I got this, this, and this, and what do you think? You know, we'll give you an opinion on what we think about it. We're happy to do that.
Jack Wilcox:Thanks, Brad and Dan. Let's just give out your email addresses while we're here. Brad Carlson's email is bcarlson@umn.edu. And Daniel Kaiser's is dekaiser@umn.edu. Thanks a lot for being here, both of you.
Daniel Kaiser:Thanks.
Brad Carlson:Thanks, Jack.
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.
