Episode 67 | The Agronomics of N, P, & K

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The Illinois Nutrient Loss Reduction podcast explores efforts to reduce nutrients in Illinois waterways from agricultural runoff to municipal wastewater with host Todd Gleason and producers Rachel Curry, Nicole Haverback and Luke Zwilling with University of Illinois Extension.

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Episode 67 | The Agronomics of Nitrogen, Phosphorus and Potassium

Todd Gleason 00:00:00:00 - 00:00:32:23

This is the Illinois Nutrient Loss Reduction Podcast, episode 67. The agronomics of N P and K. I'm University of Illinois Extension's Todd Gleason. Today we'll talk with Jon Jones. He's an associate professor of agronomy on the Urbana-Champaign campus of the University of Illinois and the State extension soil fertility specialist. I spoke with him with just a week left to go in the month of October.

Todd Gleason 00:00:32:25 - 00:00:46:24

To that point, it had been up to three inches short of rainfall and was running about four degrees warmer than average. The soils were dry and they hadn't yet cooled down.

Todd Gleason 00:00:46:27 - 00:01:13:04

It is the fall: farmers will be finishing up if they already have not, with a harvest. They'll be looking forward to putting some fall fertilizers on. Let's start with nitrogen applications. There are a couple of rules of thumbs. One of them is third week of the October. The other has to do with soil temperature. Can you walk me through those and whether those are changing over time or not?

Jon Jones 00:01:13:07 - 00:01:45:28

Sure, Todd. So the the first week or the excuse me, the third week of October is usually a general threshold set related to soil temperature, a little bit to soil moisture, but really connected the soil temperature. And the reason we care about soil temperature when talking about fall applied or even, even spring applied nitrogen is that when the soil starts to warm up or is are already warm like that right now, the microbial life and biology within the soil is working , and will convert certain forms of nitrogen to nitrate.

Jon Jones 00:01:46:00 - 00:02:13:10

Specifically we're talking about anhydrous ammonia. There will be a abiotic transfer or a transition from ammonia to ammonium. And then our microbes will will work through biological processes to convert ammonium to nitrate. If the soil temperature is high enough, usually we put a 50 degree threshold on that, at consistently 50 degree threshold. And then if there's adequate soil moisture as well.

Todd Gleason 00:02:13:13 - 00:02:32:21

Yeah. So or above both actually or well above one and below the other one. So I think soil temperature is still a little bit too warm. And certainly the moisture has not been there. How important is it to get moisture in the ground so that these knife tracks seal.

Jon Jones 00:02:33:02 - 00:02:40:25

Yeah. So the importance of soil moisture is more related, as you just mentioned, to the the app, the physical application of the anhydrous.

Jon Jones 00:02:40:26 - 00:03:08:18

So getting a, a sufficient seal, with whether you're here and making sure that that the wing sealers and, and closing settings, whatever your system has are working properly, not cutting through dry clods that aren't going to seal and going to leave macro pores so that we can't get losses or simply get situations where soil moisture is and being contained, around that, that band of application.

Todd Gleason 00:03:08:21 - 00:03:33:23

And turn your attention now to N P and K across the board for corn and soybeans. There will be applications that are made, in the fall of for all three, I believe, and producers are in a tough spot because they really have to manage the input prices this year. And how much they're using. I suppose you can start with, the nitrogen.

Todd Gleason 00:03:33:25 – 00:03:39:29

That may very well just be the MRTN or the N-rate calculator to use. Can you tell me what your thoughts are?

Jon Jones 00:03:41:02 - 00:03:59:16

Sure. So right now if we kind of think about corn prices a little above $4, depending on what your local basis you're at or or what what markets you're working with or when you're contracted. But, in general, prices of nitrogen fertilizer again, around that, they've been slowly declining for a little bit.

Jon Jones 00:03:59:16 - 00:04:40:02

But anhydrous for example, is, is below below $0.50 per pound of N right now looking towards liquid formulations is a little higher than that. So when we think about the process of looking at an agronomic response, nitrogen and adjusting it for for price considerations, which is what the MRTN process does, looking at moving towards, that, that ratio of prices between nitrogen and corn, specifically that put you within that, that 0.1 ratio and generally that it's kind of in the middle of the the road for the ratios that we usually put out from the MRTN calculator.

Todd Gleason 00:04:40:09 – 00:04:52:32

When a person goes into that calculator, there are many things that they can adjust. What's important to you that they, they adjust properly?

Jon Jones 00:04:53:02 - 00:05:05:14

Well, a few things that are important to consider, because we do offer the options of selecting the region of Illinois, your previous crop, which we know affects the the coming corn crops, demand for nitrogen.

Jon Jones 00:05:05:17 - 00:05:28:25

So those those are two things that are baked into what... what we need to delineate between looking at, some are somewhat summarizing nitrogen, corn yield response to nitrogen, but especially the corn price and then the nitrogen price or something that that you also will add. And then there's, there's a context essentially that's that considers those prices.

Jon Jones 00:05:28:25 - 00:06:03:05

So for example, if we're looking at around a little over $4 a bushel, corn looking at let's say 40 to $0.50 and generally that that should give you, let's say in northern Illinois, around 195 to 205, pounds of N per acre, up to a minute rate, following corn in around 165 to 178, following soybeans. That's going to be a little bit different in central Illinois when when we're talking about, around 491 to 200 pounds of N per acre following corn, and then about a 173 to 181 following soybean.

Jon Jones 00:06:03:07 – 00:06:08:33

And then that those those numbers are coming off of being updated from the 2023 growing season.

Todd Gleason 00:06:09:00-00:06:15:11

Do you need to look at that and say, that's my anhydrous application pounds per acre, or is that total pounds?

Jon Jones 00:06:16:22- 00:06:33:16

That would be considering total pounds of nitrogen that's been applied to the corn crops within those data sets. And so if there's going to be spring applications, if, you know, those are going to be happening with the plant or with herbicide application, please consider those when setting your fall nitrogen rates of those are going to be going out.

Jon Jones 00:06:33:19 – 00:06:40:15

So those nitrogen rates are considering all applied N to a given corn crop from the fall before spring and in season.

Todd Gleason 00:06:41:12-00:06:59:14

Now talk about the other plant nutrients that producers can think about as it's related to cost savings this fall. And which crops they can, think about not or holding back on PNK, I suppose.

Jon Jones 00:06:59:16 - 00:07:24:12

Sure. Well, the conditions are a little bit different for, for phosphorus and potassium. Phosphorus fertilizer prices have been same fairly strong potassium maybe fluctuating a little bit more similar to nitrogen. But in general, setting yourself up by having a recent soil test does pays dividends for understanding what are the potential for prioritizing specific nutrients, cutting back, or looking at different fertilization strategies.

Jon Jones 00:07:24:15 - 00:07:58:02

So using those those immediate soil tests is really valuable. Now we're in a year and fall 2024, where perhaps the last soil test was the fall of 2022. If you did have dry conditions that year, it's important to really put that into context as well, because we may have two years or two to soil test two years in a row if you're skipping every year or if you're going over maybe every four years, that you only have dry conditions for soil test data, and that can bias number specifically in potassium and pH, it shouldn't affect phosphorus as much when thinking about prioritizing nutrients.

Jon Jones 00:07:58:04 - 00:08:26:28

You can look at potentially only applying crop removal or a little under crop removal if you're going to be getting in a situation where you're don't need to build because your soil test levels are high enough for PNK. So that's an opportunity that usually comes when one of the important concepts, though, is that even though the, the prevailing, we want to consider that prevailing yield of a given field or system when planning for removal for, let's say, next year, if that's what you're considering.

Jon Jones 00:08:26:29 - 00:08:56:29

Depending on what what seasonality you're using for your PNK applications. It's important to note that even though the net returns to PNK are going to be lower and a little unpredictable at some low prices, the agronomic home soil test levels doesn't change. And so if we're if we're really focusing on attaining or maintaining those agronomic optimum soil test levels, that also gives you a little bit of buffer when you have a need to to back down on some inputs.

Todd Gleason 00:08:57:07 – 00:09:06:09

You mentioned a couple of times that, if your soil tests were taken during dry years, do you suggest not taking the soil test this year?

Jon Jones 00:09:06:16- 00:09:20:00

I don't suggest not taking them. If if indeed some showers come up where they do get, let's say, a few days of consistent moisture back in the soil, taking our soil samples will be just fine and probably provide you with, with adequate results.

Jon Jones 00:09:20:02 - 00:09:41:17

You can always delay to spring sampling. In most recent years we have had some really dry periods into September, October and November, and the soil moisture is a little more consistent in the spring. So there are options. And that's, that's actually part of my, my ongoing research is to look at providing fall soil sample interpretations and spring soil sample interpretations.

Jon Jones 00:09:41:19 - 00:09:54:03

But in general, if you can get out there and grab samples, especially if you're dealing with maybe a four year time span since when you last took them, it does. It will have benefits picking up those areas that might not need fertilization for PNK.

Todd Gleason 00:09:54:23- 00:09:55:08

Thank you very much.

Jon Jones 00:09:55:25- 00:09:56:02

Thanks a lot.

Todd Gleason 00:09:56:15- 00:10:22:26

You're welcome. Jon Jones is a soil fertility specialist for the University of Illinois Extension and an associate professor of agronomy on the Urbana-Champaign campus. You've been listening to episode 67 of the Illinois Nutrient Loss Reduction Podcast. It is produced in conjunction with Rachel Curry, Nicole Haverback, and Emma Eldridge. Like me, they all work for University of Illinois Extension. I'm Todd Gleason.