Talkin' Crap

Revisiting the Yield Goal Method: Modern Insights on the Yield Goal Method

• Dan Andersen • Season 1 • Episode 15

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In this month’s episode, Dan Andersen and Luke Soko discuss the yield goal method for manure management in Iowa, which estimates nitrogen needs based on expected corn yield. They also look at the Iowa Nitrogen Initiative, which is generating yield response curves to improve nitrogen management. The discussion highlights the need for updated nitrogen use factors and the impact of weather conditions on nitrogen availability and loss.

CROP 3181: Pounds of Nitrogen per Bushel of Corn - Benchmarking Farms Against Local Averages

CROP 3140: Use of Late-Spring Soil Nitrate Test in Iowa Corn Production


Luke Soko:

Music.

Dan Andersen:

Hello and welcome to Talkin' Crap, a podcast by Iowa State University Extension and Outreach. This institution is an equal opportunity provider for the full non discrimination statement or accommodation inquiries, go to www.extension.iastate.edu/diversity/ext. In this podcast, we discuss insights into the science technology and best practices surrounding manure management. Our objectives are to build awareness about the challenges farmers and the broader agricultural industry face around manure and to demonstrate solutions in areas of innovation. Hello and welcome back for another episode of talking crap. I'm your host, Dan Andersen, and I'm joined today by Luke Soko.

Luke Soko:

It's always nice to be here, Dan. I am Luke Soko, and I am a PhD student working with Dr. Dan Andersen at Iowa State University in the agricultural and biosystems engineering department.

Dan Andersen:

Perfect. Thanks for joining me again today.

Luke Soko:

Absolutely.

Dan Andersen:

It's great to have you, and we're going to talk about, hopefully an interesting topic for you all. We're going to be talking about the yield goal method, essentially revisiting it. Most manure plant management plans in Iowa still use the yield goal method when determining manure application rates, to set the application upper application limit. And I think oftentimes it's used to help understand how much nitrogen a corn crop might need in the state of Iowa, and used to maybe help inform our rate. It is a method that around 2005 Iowa State stopped recommending. We went to the maximum return to nitrogen method. And we've continued to see that involved, maybe with the Iowa Nitrogen Initiative and where that might go, but for many of our manure planners in the state, I think it is still a method that they're really comfortable with. It provides maybe that first guess of where we should be at, and then we tinker from. And because it is used so much in manure management plans, I felt like it was justified for us to talk through it again and hopefully make sure that we're all understanding what's happening in when we're using it in the assumptions that we're sort of making.

Luke Soko:

Yeah. And Dan, can you kind of compare the maximum return to nitrogen approach with the yield goal? Why are they different? Why would we switch one to the other?

Dan Andersen:

Yeah, so I think that's a great question. So maybe a little bit on the history of the yield goal method first. So the yield goal method was developed a while ago, roughly in the 1970s there was a scientist named Stafford who did some some fundamental work on this. And he was really looking for what's a quick way to sort of guesstimate or gage how much nitrogen different crops might need. And he basically said, from a first order estimate, it's probably proportional to how much yield we have. And when you think about that, when he did his work, there's roughly eight tenths of a pound of nitrogen in a bushel of corn. And he said, Well, it looks like it takes about 1.2 pounds of nitrogen to grow a bushel of corn, to me, and that gets adjusted in different states based on sort of the risk of loss of nitrogen. So if you think about Iowa, from northwest Iowa to sort of their sort of southeast Iowa, there's a rainfall gradient, and we might only use nine tenths of a pound of nitrogen per bushel of corn as the estimate in northwest Iowa, where the risk of movement or loss is smaller, down to 1.2 for the majority of the state, because we're wetter and have more of that potential for nitrogen loss that doesn't make it into corn. And then he said, we have to take some credits for any legumes we grow, but it's really based on a mass balance sort of approach, trying to estimate some of those things and build them into the fudge factor of how many pounds of nitrogen I need per bushel of corn, and it has to account for things like nitrate leaching or denitrification. So he said, we're not going to get a lot of information. We can't develop a yield curve on every single farm, and in the United States, that's just as impractical. But people want this information. They want advice on how much nitrogen we think they need. And the algorithm gained a lot of popularity probably because it was reasonably simple. It feels correlated to what you're doing, and we know that there is nitrogen in every bushel of corn, so if we're removing that nitrogen with a bushel grain, we probably had to replace it somehow. And that was really the fundamental approach. And he recognized one of the limitations is it's not perfect. It doesn't account for all these things explicitly. And the Iowa State approach, when we switched to maximum return to nitrogen, it's really was an approach of, can we develop yield curve. So yield response curves, for every extra 25 pounds of nitrogen put I put on how much more corn will I grow when you do that, if you have that sort of shape of that response curve, knowing it varies a lot with different growing conditions.

Luke Soko:

Trying to find that optimal point, right, so that you're not over applying and you're saving some money on.

Dan Andersen:

That's right, you can figure out where that next bushel would next bushel of corn you grow, just takes as much nitrogen in terms of cost to produce it. So you're sort of at a break even. If you put more on, we're not going to make any more money because the nitrogen is not paying for it. And that was really the concept behind it. And if you think about that curve, there's something built into it about how much nitrogen we're losing given the growing conditions of that season. There's something built into it a how much nitrogen is released by the soil or mineralized by the soil that the crop can take up.

Luke Soko:

Would you argue that the maximum return to nitrogen can reduce over application of nitrogen? Or is that even a worry?

Dan Andersen:

It can, it's definitely a worry. We don't want to apply too much. We know that, if we know fundamentally, that as soon as we start applying more nitrogen than what our crop needs, losses start to go up exponentially, so we definitely want to try and avoid over application.

Luke Soko:

Yeah,

Dan Andersen:

But it's complicated, right? The amount of nitrogen that's released by soil is dependent on the soil you're using and the growing conditions that year, the amount of nitrogen you might be losing to leaching or denitrification. Again, it's dependent on how easy it is for water to move that through that soil, how wet that soil stays, and the growing conditions of that year. This is a really dynamic, complicated process. And I don't want to make it sound simple, right? It is complicated. And I think people are generally trying to make the best nitrogen application decision they can, but it's complicated. And I think the science bears that out. We've seen the yield goal be popular. We've seen the maximum return to nitrogen be popular and I think the Iowa Nitrogen Initiative, that's a relatively large, ambitious project where they're doing a lot of on farm research about if I put on x pounds of nitrogen and using this method or that method, and change my rate just a little bit, up or down, and up and down, they generate these yield response curves on every farm. And that's a lot of data, and it's really powerful, but trying to understand what that means in the context of the next growing season, or in general recommendations. We're still in the early days. That project has been going on for two years. I've seen some of their data. It's magnificent. It's more data than we've had before. So I think that fundamentally helps make a better decision. But there are a lot of challenges to do, because every growing season is a little different,

Luke Soko:

And that MRTN curve that's subject to the cost of fertilizer as well, right? So we've seen that jump up and down.

Dan Andersen:

Well, the curve that I think of it more as the yield response curve, is the fundamental curve in that and that one doesn't change with the price of fertilizer. Who kind of operates the Iowa Nitrogen Initiative, When you think about the curve that they're

Luke Soko:

Okay, generating from it, this maximum nitrogen rate, that curve is but the fundamental curve, to me is really that yield response curve. And once you have that yield response curve, you can think about, what's the price of corn, where does that impact where I should be on this? Where's the price of fertilizer? So it's run by Iowa State, and it's Mike Castellano over in the Where does that impact where I should be? But it's really based on that fundamental curve of that yield response. The yield goal method doesn't use that curve at all. Unfortunately, it essentially says we're some straight line up until the till we reach our maximum yield, and then we plateau. And we do see field yield response curves that look similar to that as a as a first approximation, if I didn't know what your yield response curve of your field looks like, man, that sort of assumption of a line to a plateau makes a lot of sense as a first guess. The problem is the devil's in the details, like you said, in terms of maximizing performance, that more detailed shape getting the curve right matters a lot about where we think we should be. For instance, when you think about where the maximum return calculator sort of spits out, or spat out, where we should be, it basically said you should be roughly 96 to 98% of maximum agronomy department, is coordinating that project. And yield in general years, right? And all of a sudden, that means we're not chasing that plateau, but we're just a little bit down on it, and we don't have the resolution in sort of using the it's a really great project. They've had it going on a couple yield goal method to show us that. So certainly, the yield response curve, I think, is great. I fundamentally like it as a better method, but I don't have the yield response curve in your field, and I don't have the yield response curve in sub parts of the field, so thinking about how to get that data definitely is a great strategy. And I think that's what the Iowa Nitrogen Initiative is really doing for us, letting us see years. I'm excited to see I'm excited to see how it's moving. Excited to see where it takes us in the future. But I think there's a lot of opportunities to really fundamentally understand nutrient management and nitrogen management better from that. It's just more data than we've had before. So getting back to that yield goal method, it really is just you take some nitrogen utilization factor per bushel of corn, multiply it by our expected yield, and then subtract off some nitrogen credits. And those nitrogen credits, we've often called them legume credits. That might be a misnomer. They're they're more of a rotation effect. I think there's a lot of great work that shows soybeans remove more nitrogen from the soil than they they fix, but there's still this impact of well, they they left some easier, more available nitrogen in the residue we left that that fundamentally, is a credit that the corn can take up the next year. Okay, and we've seen nitrogen use factors of around 0.9, 1.1, 1.2 how does that vary? How does the nitrogen use factor vary regionally, north to south, east to west land.

Dan Andersen:

So that's what in the manure plan. Those are the three factors that the state's broken up into. And that 0.9 factors really up in the very northwest corner, the driest part of the state. Okay, that 1.1 sort of mirrors where the Loess Hills of Iowa are and the rest of the state is buried in this 1.2 factor. And to me what it was really trying to say is what's potential for loss. We know that if there's less water, we probably have less risk of leaching, less risk of denitrification, and that probably means more of our nitrogen staying in the soil. So that 0.9, 1.1 are sort of in the drier regions of the state, the 1.2 is what we see as we move towards maybe some of the other parts of the state.

Luke Soko:

So are those factors kind of like empirically calculated?

Dan Andersen:

Yeah, I think they were. They were empirically calculated or empirically guessed at. I mean, I don't know that there was a lot of data that went into them. Certainly there was some, and you're making best guesses based on that. There is a new publication out. It's CROP 3181 and we released it in July of this year, so of 24 and it's called Pounds of Nitrogen perBushel of Corn, benchmarking farms against local averages. And fundamentally, what that publication did was compare county average yield to how much nitrogen we think you should be putting on if you were using MRTN, and develop sort of a scaled map of maybe what nitrogen use efficiency probably is, or what we'd as a first order estimated is based on some Iowa data on what nitrogen use is in different land regions for either corn soybean rotations or continuous corn rotations. And I think what's interesting there is, if you think about this yield goal method, most of the state's using about 1.2, a little bit of the states using 0.9, fundamentally from the data that they had there, and doing this analysis, we're in the range of what we saw in the state right somewhere between 0.8 all the way up to 1.2 in that continuous corn rotation. Maybe it didn't follow spatially as well as what you'd hope from from the Iowa DNR map, but there was at least some indication that that's in the ballpark range. Certainly there's places that are doing better. There's places that maybe didn't perform quite as well based on that. They did the same thing for a corn soybean rotation, and got somewhere in that 0.7 to maybe that 1.1 sort of range. And when you start doing maybe some math on what's the soybean credit that we were taking credit for in the yield goal, we're in the range of where it is. The numbers that we have today tend to suggest that maybe that nitrogen use factor is better than that 1.2 we were going to be estimating. And I think that's one of the reasons that it's time to rethink or reconsider how we're using the yield goal, right? We've seen this nitrogen use factor changing with time, hopefully improving with time due to production practices. Maybe we don't need that much nitrogen per bushel of corn, and it might not be the best approach for us. On the other hand, this is a couple years of data, but it's still still helpful for benchmarking. Maybe where we're at. I'd like to see some other years and how it varies, maybe by year as we move forward, but it's definitely a point of clarification and something to think about. And something to think about. And I mentioned there used to be eight tenths of a pound of nitrogen in a bushel of corn when the yield goal method was developed. These days, we're closer to six tenths of a pound of nitrogen per bushel of corn. So maybe you'd expect to have to put less nitrogen on because we're just not removing much as much with that bush of corn. Although the thing staying

Luke Soko:

is that what you'd speculate is related to the nitrogen use factor increasing or

Dan Andersen:

Decreasing, right? We need less, less nitrogen

Luke Soko:

Yes. So you had mentioned that the nitrogen today per bushel of corn than maybe what they did there. I definitely think that's a part of it. application array is equal to the nitrogen use factor multiplied by the yield goal minus the N credits from legumes or other resources or other sources. So how do how do I know my adjustments for nitrogen left behind by soybeans? How do I know that?

Dan Andersen:

Well, that's a really tough one, and I don't know that we know that. I think Iowa Nitrogen Initiative is giving us a lot of great data on that. The analysis that they've done from some of the ISU trials that are using the MRTN is really helping inform some of that. And I don't necessarily want to comment too much on maybe where that's going. Hopefully, we'll get one of the experts on that to come talk to us in a future podcast. Historically, though, Iowa DNR has had an algorithm in there that essentially said, for every bushel of soybean you grew last year on that field, up to 50, you can take one pound of nitrogen credit per acre. So if you grew 50 pounds, 50 bushel an acre soybeans, that'd be a 50 pound credit. If you grew 60 bushels of soybeans, that'd still be a 50 pound of nitrogen credit. If you only grew 30 bushels an acre of soybeans, 30 pound credit going to that next corn crop.

Luke Soko:

What if I planted soybeans following your plant corn? The following your plant corn again?

Dan Andersen:

Yeah. So the year that you had soybeans, the year before going to corn using that nitrogen correction factor, yeah, the next year you're using basically that continuous corn. We're assuming that there's no second year carryover of soybeans. If you had alfalfa in that rotation, a multi-year alfalfa rotation, then we would have that second year carry estimated in there. And then the DNR has some estimates of how to walk you through that. I think a lot of it's based on Wisconsin and Minnesota data, very little Iowa data in it. But it does give you an algorithm for how to sort of estimate what might be there.

Luke Soko:

What about cover crops?

Dan Andersen:

So we do not take account for cover crops in the yield goal method. John Sawyer was doing some work on cover crops with MRTN, and sort of the yield response curve overall. He said the ideal rate was relatively similar. And I think Richard Roth, a new scientist over in agronomy, continues to do some of that work, and has some really interesting data on cover crops causing tie up, and maybe some of the steps we can take to take care of that. And that's one of the reasons this can get really complicated really fast. We're all farming a little bit differently for good reasons, right? Based on our soil, based on our region, based on the equipment we have, and what we feel works best for us and it there are a lot of factors to consider, but I think both of these methods give you at least a baseline to sort of put in context, knowing that the yield goal method probably has an outdated nitrogen need factor for corn compared to at least what we're seeing today. But also knowing that there's some timing issues with manure gets applied maybe earlier in the fall than we'd see with other fertilizers, we know that MRTN tends to suggest a lower nitrogen application rate than what we saw with those yield goal methods. Well, the MRTN data all comes from spring applied fertilizer, not fall applied fertilizer, right? So there's some of these factors that we have to think about and work think about and work through. So certainly, I think that that publication CROP 3181 is a really nice walk through of maybe where some of those nitrogen use factors are today, or at least our best guesses of where they might be based on what people are doing. The Iowa Nitrogen Initiative will have plenty of data out soon, that sort of illustrates what people are achieving on their farms based on the actual maximum return to nitrogen yield response curve that was measured on their farm in that year. It'll be summarized so that it can provide some some data on where we're at. But I give think it'll give us a great point for that, that comparison to what we've been using in the yield goal method. The other part of the yield goal method that's important is, well, estimating what the yield is going to be in the in the coming season, right? And that's easy and hard, yeah.

Luke Soko:

How's that calculated? The yield goal?

Dan Andersen:

Yeah. So the yield goal, according to the regulations that we have here in Iowa, you can either take the average of four the last five years that you've had that crop in your field, average them together and get a number, or you can take the average of all five and multiply it by 10%. I've been looking into that data a little bit to say is that the best estimate that we can make, is that the estimate of how I would estimate how much corn yield we'd have the next year. And it turns out that plus 4% is probably really a more realistic yield of what I'd anticipate in the next growing season. So average, all five of them together add 4% to that, and that's probably better, but the truth is that just using trend line yield is a better estimate of maybe where we're going to end up.

Luke Soko:

Trend line of five years?

Dan Andersen:

Well, I was using trend line of all the data we had at county level to do that, you probably want at least five years in your trend line.

Luke Soko:

How far back does that go? All the county level data?

Dan Andersen:

I went back to 1950 it goes back further than that, but I went back to 1950 and if I had five to 10 years in there,

Luke Soko:

Yeah>

Dan Andersen:

I like more than five. Five to 10 was probably the minimum that I want. Trend Line yield was a better estimate of what I'd have coming up in the next

Luke Soko:

You do that in Excel and trend line, that's how I did

Dan Andersen:

I mean, you can use whatever statistical method it. Yeah. you want, but some sort of trend line yield. And we know that trend line yield is really powerful. I was been gaining about two bushel of corn per acre per year for a long time. Now, every county is a little bit different on that. Some counties might be up to 2.4 some might be a little under two, but that trend line yield estimate tends to be a pretty good direction of where we're heading and what we might anticipate next year. Knowing that growing season holds a mystery for us, right? Some years, that's really accurate some years, maybe 1993 when we had a lot of flooded fields, or the drought of '88 or 2012 trend line yield missed by quite a bit, but it does give you a pretty accurate guess of where we might be falling in terms of yield. And I think that that brings up a couple things when you think about using the yield goal method as a regular regulatory tool for how much nitrogen can I apply as a maximum? Maybe that 10% isn't bad, if I'm using it as a fertilizer guideline, how much fertilizer do I need? Well, that's not the yield I probably should be anticipating next year. I should probably be more towards whatever trend line yield tells me I'll be adding that 4% instead of 10% and that's really maybe what I should think about fertilizing too. And then, you know, making sure we're getting that nitrogen use factor dialed in as close as we can is probably a better approach than saying I'm still at that 1.2 number, knowing that we've improved nitrogen use efficiency

Luke Soko:

Makes sense.

Dan Andersen:

It does. And I think you can make this as easy or complicated as you want to be, right? I mean, in some ways it's nice to just say this is an algorithm. That's what I'm going to apply. That's the number, and I'm going to just trust that number. But trying to think about, what do different growing seasons mean? What do I really think I'm trying to get here? What am I trying to do? I think it's useful for it as a tool.

Luke Soko:

Yeah, and you wouldn't want to, you know, overestimate your yield every year and constantly be disappointed.

Dan Andersen:

That's right. So, I mean, there is an algorithm to give us, hopefully, a somewhat useful yield number.

Luke Soko:

Yeah.

Dan Andersen:

But I think it depends every growing season is a little bit different. The other thing about the yield goal method and why I started thinking about it more deeply, I mean, when I first graduated, I was like, that's that's the method. I like it. And then I was like, MRTN, that's where Iowa State's at. I'm just going to use that. And you start thinking about the nuance here of MRTN, all being spring and a lot of manure getting on in the fall, I had to think about, how do I adjust for that? Or, if I'm collecting yield maps, and I want a variable rate, apply nitrogen, what? What's my approach there? If it's MRTN, it's the same over the whole field. That's essentially the assumption that MRTN is making, right? Because we don't have yield response curves in different parts of the field generally, we could, could generate them, but we don't have that data, or if you're yield goal, you're just saying the high yielding parts of the field need more nitrogen. The low parts of the field need less nitrogen. And I think within a field, that doesn't always bear true, the better yielding parts of the field are probably better for a reason. They have better soils, maybe more nitrogen mineralization and more nitrogen supply from the soils in the worst part of the field. So when you start thinking about some of those nuances, that method doesn't always work.

Luke Soko:

Yeah, it's complicated fast.

Dan Andersen:

Yeah. So thinking through maybe what some of those things are telling us about our nitrogen management practices and how to how to work on this problem is extremely useful. And that's, I think, what the Iowa Nitrogen Initiative is really doing. We know we need a lot of data and data driven information to make sound decisions on this. And I think that's why that project is so powerful. We've often been trying to do this with limited sites, or limited site years of data to make our best inference. And all of a sudden, having lots of data is extremely powerful.

Luke Soko:

So how is this correlated with our manure management plans?

Dan Andersen:

So the majority of manure management plan, still you'll use yield goal to figure out what that maximum allowable rate would be. And I think most of them are still using that maximum allowable rate to say that's how much manure I'm going to put on, and that's what I'm really using as a fertilizer recommendation. And I think the point that I want to make here is that's probably not maybe the best use of nitrogen, and that's maybe not how we want to think about nitrogen from a fertilizer recommendation standpoint, looking towards some of those newer tools, like maximum return to nitrogen, or the tools that the Iowa Nitrogen Initiative are using, or towards this benchmarking procedure to say, maybe I don't need that 1.2 maybe I'm closer to this number now in my county, for how much nitrogen I need per bushel of corn, to be forward thinking about, how do I make the most use of that manure? How do I get the best value from my manure.

Luke Soko:

Okay, now that makes sense, and I remember, I believe it's one of your fun facts, that all the swine manure in Iowa applied accounts for roughly 25% of the nitrogen needed for all the corn grown in Iowa.

Dan Andersen:

That's right, so I think that's that's a slightly outdated fact. Now, we just had the new Census of Ag, and it's up to about 30% of all the nitrogen we need, it comes from all livestock manure over Iowa.

Luke Soko:

Okay.

Dan Andersen:

So just a little bit higher than that these days. So manure definitely is an important fertility source. And if you think about if we have almost a third, 30% of all the acres potentially being fertilized from manure, if we can dial that down just a little bit, maybe towards more of what we see for these nitrogen use factors, rather than that 1.2 we could stretch that nitrogen a little bit further.

Luke Soko:

Yeah.

Dan Andersen:

Maybe we get up to 35% of our acres instead of 30, right? So shooting for that third, and I always think about this as incremental steps, right? Certainly there are years where we'll have weather conditions that we're prone to loss and we'll need more nitrogen than maybe what this recommends on average. Certainly there'll be years where it needs less nitrogen than what this recommends on average. And I think the future is trying to figure out which one of those years are we in, and how do we adjust accordingly, but working towards this average and thinking about what it means in terms of my manure plan, the rate that I should be picking are critical to addressing some of those water quality concerns, but also critical in terms of making sure that we're being as circular as possible and taking best advantage of that manure as a resource for our state.

Luke Soko:

Okay, yeah. So, speaking of weather conditions, what if we have drought or excessive rain? How does that impact, you know, nitrogen availability.

Dan Andersen:

So in terms of availability, if we're really dry, that might from some of our salad manures, like poultry manure, cattle manure, delay mineralization and release. In terms of swine manure since most of that nitrogen, 80, 85% of it is an available form. When we put it on it's not adjusting availability of the manure necessarily.

Luke Soko:

Available, how so?

Dan Andersen:

Yeah, so available. In order for a plant to take it up, it has to be in a mineral form, right, either nitrate or ammonia. So we use the term availability. That's generally what I'm thinking of, is that nitrogen cycling into one of those forms, either when we put it on or after we put it on, you're thinking maybe more of nitrogen supply in terms of what does the soil provide? How much does that manure provide? And the weather conditions matter a lot. In sort of warm, moist years, we probably have the best opportunity for mineralization of soil organic matter in really dry years, if we get to water limited, the microbes aren't going to be as active. And if we're cool, they aren't going to be as active, releasing nitrogen, right? So that's sort of a supply factor, and the other part of that was loss. We know that in those wet years, especially when we have a fair amount of water movement in the spring, maybe, like we had this spring, more of that nitrogen is going to be lost to leaching to the tile lines, there's more potential for denitrification, and how do we balance sort of that happening with how much nitrogen we actually needed? And it's tough, because we don't know. There's no right number for the nitrogen supply from a soil. It's dependent on the soil. It's dependent on the rest of the growing conditions. We don't maybe have great insights into estimating how much nitrogen is going to be lost in a specific year. We know what averages are, and we know maybe this year looks more prone to loss because of the weather conditions we've had. And if you think back to the MRTN tool, one of the helpful things they've done with that is they had a bracket on each side right where you'd make roughly within $1 profit per acre of what you're doing. And if you're in a high loss year, one of the things you could say is maybe that year I should be on the higher side of MRTN. So if I applied MRTN, I've had that higher loss. It gives you sort of a range to say that, Well, maybe I should be more of that higher range. If we were on a dry side where it impacts corn yield, maybe we should have been more on that low side. Or if leaching losses were looking lower that year, because we were on the dry side, maybe I could have been on the lower side of that MRTN range. And it's complicated. I think there has some great work going on again, there's a lot of modeling to supplement some of that data from the Iowa Nitrogen Initiative that I think is going to provide a lot of insight into where we're at and maybe the directions that we're moving for new tools. But I think where we're at today is, is sort of, we still see a lot of people thinking about that yield goal method, especially in manure plans and and I think we should be thinking about what yield do we really want to use? Is that 1.1 or should we fertilizing maybe to 1.04 or something that the data says is where we've traditionally been more prone to hitting. Is that 1.2 factor still right? Or should we thinking about it maybe little a little bit different. Should we referring back to that 3181 Benchmarking Nitrogen Use Tool, and the two maps that they show for the different counties in Iowa there on what we were capable of hitting in those different rotations in terms of nitrogen use efficiency and pounds of nitrogen per bushel that that is actually needed, rather than this, maybe older factor.

Luke Soko:

Would you, would you factor in future weather predictions in this and I know it's very tough to predict the weather long term, but also 2024 and our technology is.

Dan Andersen:

Well, I think we still struggle to predict the weather long term. And yeah, I think it depends. I think that's one of the reasons why side dress applications, spring applications, can be helpful. Having that information of what the growing season is looking like is extremely powerful to us. Like I said, we put a lot of our manure on in the fall. We're making fertilizer decisions in the fall. And I'd like to tell you that when I sit in the fall, I can tell you something about the next growing season, but generally they all look average to me. I just don't have enough information to make a better statement than that. I think last year, if you would have made me guess, I would have said maybe I need a little less. It's been dry. I think the chance for leaching going into next spring is low. And then it turns out we had a wet spring, right? So if I would have made that prediction the two years prior, that's probably a good prediction. If I made it last year, it was probably a poor prediction. So I think trying to maybe think about split applications, trying to get more information into the growing season, to make that informed decision gets at what you're you're sort of pointing at the weather is really important. We can predict climate well, but predicting weather in any given growing year is tougher than that, so trying to get what actually happened and use that information to help us make a more informed decision is important.

Luke Soko:

Okay? And isn't it true, if it is dry outside and we do have a large rainfall, we'd have increased runoff because soil is less saturated. Crusting or not necessarily,

Dan Andersen:

Not necessarily. It depends.

Luke Soko:

Okay.

Dan Andersen:

It depends. I mean, you could have a situation where that happened and you had a crust, just like you said, and that might make us more prone to runoff. Okay? And I know you had mentioned in the past. You know

Luke Soko:

Okay.

Dan Andersen:

You could have a situation where that rainfall is you could refine these nitrogen estimates by using soil tests a nice, slow, soaking rainfall. So maybe I'd worry somewhat and in season monitoring. What kind of what kind of test is about what our soil conditions are, but I'd also worry about, what's that rainstorm look like? We'll talk about soaking rains that? What does that look like? Who does that? or really intense storms, right? And that soaking rain will move So I think what you're referring to is when we do the late spring it into the soil more. So it depends. Sometimes those soils can be more prone to runoff. Sometimes they're not. Certainly, if we've had those conditions, getting that water into the ground, if we've been dry, extremely important. We know that the rain makes grain, right? So we need some of that water to get into the soil. So we don't want it to have it, to have it, have it run off and but the way that water moves or partitions is really important to how the nitrogen is moving or partitioning, and maybe what some of our potential loss mechanisms are. nitrate test, yeah, and there's a publication about using the late spring nitrate test. I've made you do it for me in the past. Send you out there to get some soil samples on some of the plots we work on. So anyone can do it. You send it off to a certified lab get it measured for ammonium and nitrate to see, sort of what levels we have in the soil currently, and that is a potential indication so of where our nitrogen supply is at, and you can use that information to try and adjust where your rate is. I think the ISU publication provides some guidance on if nitrogen levels in the soil are below such and such a number, you should think about applying x pounds more, like 30 pounds more. If they're above this level, that probably means we're sufficient, right? And I think that's sort of how I think about that tester would use that test is I still have a fundamental plan of where I wanted to be before that, and I'm using that more to understand what nitrogen and the weather has brought this season, right? Where is my nitrogen supply currently, and how do I think I want to adjust?

Luke Soko:

Okay? Is that practical for most farm. Or so is it very, you know, maybe expensive to send soil samples to a lab.

Dan Andersen:

Well, it's about$10 per soil sample to get it analyzed, plus a shipping cost. So I don't think it's that expensive.

Luke Soko:

Yeah,

Dan Andersen:

Relative to I mean, nitrogen today is 25-30 cents a pound, so depending on the fertilizer decision you're making, it can be a very value adding piece of information.

Luke Soko:

And peace of mind if you know.

Dan Andersen:

yeah, so I think getting more information is generally better if you're collecting it just for fun. And I'm sure sometimes it feels like I'm having you collect it just for fun, because we're not adjusting fertility, but we're trying to understand where nitrogen supply is. It can feel expensive because it's not helping me do any better, but it is a helpful calibration tool to see sort of where we're at and to understand fundamentally is, does it look like I'm experiencing a nitrogen shortage for my corn because I had a cover crop or because I did this or that? So it can be a diagnostic tool to help inform future decisions.

Luke Soko:

Yeah, and that's typically done with a soil probe.

Dan Andersen:

Yeah. Sample, soil samples with a soil push probe, especially in situations where we band like with injected manure, you have to take several samples spaced evenly from row to row to make sure you're not getting just a band sample, or just sampling from where the manure wasn't placed right with other fertilizers. So that that publication walks you through the steps mix the soils together, taking composite sample. And that composite sample is really what we're sending off to the lab. Which publication is that? That's a great question. I don't know the number off the top of my head. I'd have to look that one up, but it's the late spring nitrate test. So if you go Iowa State late spring nitrate test, it'll come up with that publication from the ISU Extension Store. All right, just to recap, we've seen a few changes in time. I think the data bears out that that 1.2 factor that we use in the yield gold method has tended to be improving with time, potentially because of some of that change in how much nitrogen is a bushel of corn, we've seen it go from roughly eight tenths of a pound of nitrogen when that yield goal method was created to closer to six tenths of a pound of nitrogen per bushel now. And I think that gives us some some pause or reason to reconsider, how is that yield goal method working? Should those factors be recalibrated, or should I really be looking to some of those more modern tools, like maximum return to nitrogen, or the tools that they're proposing in the Iowa Nitrogen Initiative to help make a better yield, or, yeah, a better estimate of how much nitrogen I need. The other part that we're using in the yield goal method is, what's corn yielding? And certainly we've seen that change drastically with time. And are we using the right number? Certainly, from a regulatory standpoint, having some leeway so that the farmer can make the best decision for his farm, his field is important. But if I'm estimating what my yield is going to be next year, that 10% tends to overestimate how much corn I'm going to actually grow. So while it might allow us to think about a maximum amount or a maximum amount of nitrogen need, that might not be the best approach for thinking about how much nitrogen do I need for that crop that's actually out in the field, and adjusting those factors accordingly, I think is important. So certainly, nitrogen is a complicated topic. Manure nitrogen, even more so when we factor in some of that availability discussion or the potential for loss discussion relative to some other fertilizers. And hopefully we'll have some more discussion with some members of the Iowa Nitrogen Initiative with that in the future. With that said, thanks for joining me today, Luke, it was great to have you well.

Luke Soko:

Thank you.

Dan Andersen:

And thank you to all of you for listening. Hopefully you found this informative, and we can get some of your questions again in the future to try and address some of the things that are on your mind. Thank you. Thank you for joining this installment of Talkin' Crap. Be sure to take a look at the show notes on our website for links and materials mentioned in the episode. For more information or to get in touch, go to our website, www.extension.iastate.edu/immag/. If you found what you heard today useful or it made you think, we hope you subscribe to the show on your podcast app of choice, signing off from a job that sometimes smells but never stinks. Keep on talking crap.