SPEAKER_01 0:08

Welcome back to the Field Notes Like it's brought to you by Greenpoint Ag and Acufield. We discuss real-time agriculture problems and their solutions, trial results, and infield tips to share agronomic insights from leading industry experts. Each episode is catered specifically to you and your region. I am your host, Abigail Waller, and I am an ag technology specialist in South Alabama and a little bit into Florida. Today I have with me Mr. Curtis Fox. Carrie Webb and joining us again, Mr. Trent Roberts. So Curtis, if you'll start off by introducing yourself and then we'll go to Carrie and Mr. Shrimp.

SPEAKER_03 0:44

Hi, Curtis Fox. I am the area agronomist for Southeast Arkansas with Green Point A.

SPEAKER_00 0:50

Carrie Webb. I'm the Soul Agronomist for Mississippi, Arkansas, and Louisiana.

SPEAKER_02 0:56

So Trent Roberts, Soil Fertility Extension Specialist with the University of Arkansas. My office is in Fayetteville, but I primarily deal with the row crop production in eastern Arkansas.

SPEAKER_01 1:10

Awesome. Well, I know we talked a lot about the last episode in the micronutrients, but today we're going to kind of just focus on optimizing what we have in the soil. So our nitrogen, our phosphorus, and our potassium. We know that prices are high this year, and so we want to support you and your customers as best as we can. So I think, Chris or Curtis, if you'll just kick it off and just start what you got with.

SPEAKER_03 1:33

Okay. So like I said, I want to thank uh Trent again for joining us this uh on this episode. Um you know, Trent, when I when I think about the big three, the MP and K, um, you know, obviously soil testing is especially in times like these, where, you know, we've got high input cost of those products plus uh a depressed pricing for the crop. So, you know, every every producer we're working with now is looking at ways to not necessarily cut uh cut costs that cut production, but to be a little more wise with with how they see their these applications. And and uh, you know, when I think about soil testing, you know, there's so many ways, right? I mean we can we can uh grid, we can zone, you know, there's there's just lots of uh composite, you know, we we've got all the different ways of soil testing. Um you know, just briefly what's your thoughts on those those three ways. Um, and then after after after that, we'll go into maybe a little more specific of each nutrient.

SPEAKER_02 2:42

Okay, well, I'm I might get in trouble for saying this, but you know, one of one of the big issues I have with like grid sampling is so many people take grid samples just to look at the variability, but don't do anything else, right? And so I mean, yeah, it's great information, but if you're not gonna use that to make a management decision, to me, that gets that gets a little bit tough, right? So, I mean, it's great information to have, but if I'm doing two and a half acre grids and then I'm not trying to manipulate my fertilizer application, I still just do a broadcast. To me, it's kind of like, okay, well, you know, I'm not sure that that makes a lot of sense. Um the other thing that I would say is uh I am a huge proponent of grid sampling for variable rate Lyme. To me, that is one of the best tools that we have because when you look at a product like Lyme, and not necessarily the cost, but the impact that it can have on nutrient availability, we want to try to apply that as precise as possible. So, in my mind, you know, I kind of just try to think if I was a producer, what I would do. I'm I'm a big fan of like zone sampling. And there are a lot of different ways you can do zones, right? You could do a grid sampling and then identify some zones where you say, okay, well, this area is pretty consistent, you know, I'm gonna keep this as a zone. Um, this area is pretty consistent, or you could use soil textural changes. Uh, but I think that zone sampling is probably the best mix of the two, right? It kind of improves your accuracy and allows you to capture the variability in the field, but it's not overkill, right? Like a two and a half acre grid might be, but it's also capturing more variability than just a field composite would. But a lot of times I think you know, producers collect a lot of data, but they don't always use it in the best way possible. And so, for you know, once again, I'm probably gonna make some people mad, but I would never grid sample if I also didn't take my yield monitor data and put them together, right? Like, like, what are we doing? Every combine we have now is equipped with yield monitor data, and so if I'm gonna grid sample, why wouldn't I take my yield monitor data and overlay those and go, okay, what's going on here? Because I think a lot of times when we when we take all that information we're collecting and we put it together, we get answers to problems we didn't know existed, right? So a lot of times when I have a low yielding area of a field, I assume it's nutrient related. And then when I take the soil test map and I take the yield map, I find out it's compaction or it's salinity or it's drainage or it's something else, right? And so to me, it's about we're collecting all this data. How do we put it together effectively to make informed decisions?

SPEAKER_01 5:57

I've done a lot of that. Sorry, Curtis. I've done a lot of that just let's say in the past two years of trying to be more site-specific on where we're putting fertilizer, and we have, like you mentioned, we have so much heel data coming in, and if we're not gonna use it, then what's the point of getting it? Um, I think that's a big tool. And I've even had some more growers going into this year saying, hey, next year I really want to look at doing some zone sampling or just zone sampling because then we've done fertilizer or planner maps off of it. There's just endless possibilities with it.

SPEAKER_03 6:33

Yeah, Trin. I don't think you're making any bad man. I I think our sellers, I think our sellers would would 100% uh love for that to be heard by all of their growers. They uh they know that that the only way that they can really help these guys is when there's some transparency and and being able to uh you know put those two things together. What the little bit of grid sampling that I've I've been a part of, it seems like in the end, it really never saves us any money. It ends up we like you said, we find that spot that uh you know, I I've got a a great example that I give to a lot of people is that you know, I was working with a grower several years ago and he wanted a grid. And when we when we pulled up the specific field, his highest yielding spot in the field was his lowest fertility spot in the field. And you know, and it and it I was like, you know, it makes complete sense, you know, and and based off of that, you know, we changed his entire fertility program and and made it more specific to his high yield dairy. And I mean, and it ended up costing him more fertilizer, you know, just because that's what it took. And so yeah, I think there's a a a huge disconnect when when we don't overlay or at least lay those two things side by side for sure. Um so transition into into something else, you know. We know that when we talk about like cotton or rice or corn, you know, we know that that nitrogen is the huge yield driver in those. Um you know, thinking about soybeans is potassium, and and and I'm sure there's a little bit of potassium as a driver in the cottons. I I just I'm not super familiar with that. But um you know, when we think about you know, when we're having these conversations with growers and we're talking about, you know, hey, if there was an area that I could pull back on, so like let's I'm just at the moment just thinking of say soybeans specifically, right? So, you know, we we go, we we get our test results, we see that we have a pretty adequate amount of phosphorus in the soil, but our potassium levels are questionable. Um you know, is is that do we have a potential to possibly just use potash, or do we need to continue to use the the O-grade mix of a of a P and K? Um you know, just you know, and then even you know, we might just we might stop and and talk about that one specifically right now, and then transition that same question into, you know, what do uh what do potash applications in season look like, Trent, versus not? You know, how could we could we use a tissue sample to make that decision in season if we didn't want to put it out pre-plant? And you know, not even that, but I I even think about a lot of times, you know, I I don't know how common this practice is, but a lot of times we do the same thing with our phosphorus in rice. You know, we'll we won't necessarily put all of our phosphate out pre-plant. We may make that that DAP application, say along with our uh flush, you know, our first flush, or or not necessarily wait till pre-flood, but you you know what I mean, in front of a rain or something. And just curious what your thoughts are on you know more in-season timing versus pre-season timing, maybe.

unknown 10:09

Okay.

SPEAKER_02 10:10

Well, so I mean, just to start, I think the one thing I wish all producers like really had a good handle on was the law of diminishing returns, right? So when you look at like a yield curve, you know, it increases and then it kind of plateaus. And the first little bit of fertilizer that I put out, I get a huge yield response, right? And then the more fertilizer I put out, the less yield return that I get. And so what I always try to tell producers is that that last few bushels you're trying to get is the absolute most expensive ones from a fertilizer nutrient management standpoint, right? So if you if you look at like a crop like soybean, that last five percent of yield that you're chasing is losing you money, right? If that makes sense. If I'm trying to go from say 75 to 80 bushel beans, the amount of fertilizer I've got to put out to try to get that five bushels, I'm usually losing money on it, right? And so to me, that's the first thing. So when we start talking about like tight years with high prices and low commodity values, if you understand that law of diminishing returns, you can kind of say, okay, is that last four bushels of soybean worth 15? You know, um, well, maybe not 15 if we're talking about potash, is it worth $30 worth of potash? Right? And you've got to kind of make that decision. Um, and so I think in years like this, you can kind of say, okay, I can shave a little bit off my fertility program and probably not see like drastic yield declines, right? And so it's all kind of about balancing that that return on investment. But when you start talking about timing, I do think it's nutrient specific. And so if you look at all the work we've done in potash, right? So corn, cotton, rice, soybean, you have a huge window of opportunity to put out potash and maximize yield. And what I mean by that is across all these crops, you know, we've delayed potash applications well into reproductive growth and still maximize yield, right? So take rice as an example. You can go all the way out to boot and still maximize yield. You take something like soybean, depending on the level of deficiency, you can wait till R4 or R5 to put out your potash and still maximize yield. Some of the recent work that my colleague Dr. Dresher is doing in corn, you know, you can wait till VT in corn and still maximize yield with potash. So if if we think, okay, I've got this huge window to put out potash, then to me it comes down to okay, what's my fertilizer rate? So if I'm looking at like 90 or 60 units of K2O per acre, I'm just gonna put it out all pre-plant, right? Because that's the easiest that makes the most sense. But when I start getting high rates, like you know, 120 or 160 units of K2O, that's when I'm gonna say, okay, let me put out the 60 pre and let me come back in season with some type of tissue test to make an adjustment. Right? Does that kind of make sense? So for lower rates, let's just put it out and and go with it. But when we start getting these really high rates like 90, 120, 160, all of a sudden I want to put out a little bit preplant. And then for something like soybean, I want to come back at R2 and take a tissue sample and then make a decision about additional needs. And one of the nice things about soybean is we just finalized a program where if you know the days after R1 and you know your tissue analysis, it will tell you the exact amount of potash fertilizer you need to maximize yield. Now, in the other crops, we don't have it refined that well, but for something like cotton, we would say, you know, pinhead square, anytime after pinhead square, you could take a leaf sample and know whether or not you needed additional potash. Similar for corn and rice, right? Any time for something like rice, I would say anytime after PI or green ring, uh, for something like corn, anytime after V6, right? We could take a leaf sample and determine those. So I think we've got the ability with potash to take tissue samples in season and make it make adjustments.

SPEAKER_03 15:07

I carry out is there anything over there? Well, yeah.

SPEAKER_00 15:12

So the big question I've been getting is on phosphorus, of course, phosphorus prices are high, and phosphorus it takes a while to be available in the school. So some of what you're putting out this year is for next year, and the guys are trying to cut back, how how bad is that gonna affect them in the future by skipping a phosphorus application this year?

SPEAKER_02 15:36

Um, so that that's probably one of the most common questions that I've gotten this spring is you know, one, how much can I cut? And when I do cut, what impact is that gonna have on next year? Um, I always start with the soil test P concentration, right? So if I'm like medium soil test P, um you can cut and it's probably not gonna be a big issue, right? Because you've got a fair amount of soil test phosphorus, maybe not enough to maximize yield, but there's some there. The problem is it's when you start getting into those low and very low soil test categories, you know, what that's telling you is there's not much phosphorus availability in the soil. And so when you start cutting in those categories, that's something that's going to catch up to you in the subsequent years. And I think really what it all comes down to is just trying to balance nutrient removal. And so in all of our production talks this year, what we've really been emphasizing is okay, if you can't afford to put out, say, 90 units of P205, try to at least put out crop removal, right? So if I'm cutting a 180 or 200 bushel rice crop, I'm gonna remove 45, 50 units of P205. So if I can't afford to put out that 90 that the soil test recommends, try to put out you know 45 or 50 of what that crop is gonna take out so that when I come back next year, my soil test hasn't fallen even farther because I've mined phosphorus out of the soil. And so that's kind of the approach that that we went to is you know, if I can't afford to put out the soil test rate, look at crop removal and try to get as close to crop removal as you can.

SPEAKER_01 17:36

Yeah, I'd say that's something we've been doing in the the East region a lot is having those conversations and just giving them alternatives. Um, for us, we've been playing with the the different lab equations we have too, in addition to the removal only source. So I know you've talked a lot a lot about tissue samples. Could you kind of briefly just tell us the best way to pull a tissue sample in order to get accurate results and to stay on top of what we're needing to apply based on them?

SPEAKER_02 18:08

Yeah, so with any type of tissue sample, I think what you want to do is look at what you're gonna use to interpret it, right? So you need to start there. So for instance, anything that you would use University of Arkansas guidelines to interpret, you know, we have real clear definitions of what you need to sample. But for instance, if you're using another state's recommendations or interpretations, you need to go look at their guide and see exactly the growth stage and the plant part that needs to be sampled, right? So to me, that's the first thing. What are you gonna use to interpret the data? And then you have to sample based on that data set because for all of our crops, the growth stage, the crop, and the plant part are very specific. So typically for something like soybean, we're gonna sample the uppermost fully developed leaf. So that's pretty consistent, right, across all the states. Um, typically that's gonna be two or three nodes down from the top of the plant, right? But that fully uppermost developed leaf. Now, here's where it gets tricky. Like for our recommendations, we just want the three leaflets, we don't want the petiole, right? So you would separate the leaflets and just send those in. We don't want the petiole, but other states, they just want the petiole, they don't want uh the actual leaflets. So to me, that's where it's like look at the source that you want to use to interpret the data, or if the lab is going to do the interpretation, right? You need to know what plant part they're expecting to get that interpretation correct. Um, cotton is another one, right? Some states they want the petiole to do the interpretation, some states they want the leaf blade. But in general, with almost all of our nutrients, we're gonna want the uppermost fully developed leaf. The only one that gets a little bit tricky is gonna be corn. So for corn, we typically do that uppermost collared leaf until the earleaf is identifiable. And once we can identify the earleaf, then we switch from that uppermost collared leaf to the earleaf. But that's just kind of some general rule of thumb. But like I said, to me, it's about um looking at who's going to interpret the information or what source you're gonna use, and then make sure you sample so that when you look at that data table, you collected the right plant part so that interpretation makes sense.

SPEAKER_01 20:55

That's great.

SPEAKER_00 20:56

Speaking of the corn, um like on a corn and somebody misidentifies the stage because they didn't cut the stalk, how bad will that throw the sample off?

SPEAKER_02 21:09

Yeah, that's that's a great question. And once again, it's it's nutrient dependent. So for something like nitrogen, it really doesn't matter. And what I mean by that is from essentially like V10 through like R1 or R2, the magic number is three percent. As long as we're three percent or above on nitrogen, we're good. When you start to look at other elements like potassium, the number kind of changes as the season progresses. So with potash, typically the earlier in the season your critical concentration is going to be higher, and then the later in the season, your critical concentration tends to decrease. And so it's not a real big deal, but You know, you just kind of have to remember if I was shooting for like a V10 stage and I actually sampled at V12, my critical concentration for V12 is probably going to be a little bit lower than it was for V10. And so to me, that's kind of how you make the adjustment is by saying, okay, if if I don't have a V12 number, right, like in my table or how I'm using to interpret, what I can do is say, okay, well, if my V10 number was, let's say, 2% potassium, if my V12 number is slightly less than that, I'm probably okay. Right now, if it's a half a percent off, then I'm in trouble, right? But unfortunately, it just it's so complex that interaction of like concentration and growth stage that it gets really hard to interpret if you don't have you know like growth stage specific numbers. So my last little plug, right, is you know, most often fertility is the largest single input cost for a producer, but it's also the thing that people want to cut first. Um, and I understand that, but I also think, especially like in irrigated production systems, producers need to realize that if I'm spending all this money on seed and herbicide or you know, pesticides and irrigation, the last thing I want to do is is cripple myself by cutting my fertility too hard. Because I've got all these other input costs, and I don't want you know cutting fertility too hard to essentially waste the money that I've invested on all those other input costs. So there's flexibility in fertility, but it's one of those, you know, we don't want to to to cut a leg off, you know, trying to save money on fertility when we've got all these other expenses out there. Sure. I think that's great.

SPEAKER_01 24:08

Very true. Well, guys, thank y'all so much for being on here today and taking the time. Um, I think this was a really great, like Mr. Curtis said, great, great and timely uh material to talk about. So for now, this is the end of our Field Notes podcast, but we will be back. Um, and maybe we can twist Mr. Trent's arm to come back and and keep educating us. So thank you all again for being on here. I really do appreciate it. And um just stay tuned for our next episode.