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Mike Howell (00:08):
The Dirt, with me, Mike Howell, an eKonomics podcast where I present the down and dirty agronomic science to help grow crops and bottom lines. Inspired by eKonomics.com, farming’s go-to informational resource, I’m here to break down the latest crop nutrition research, news and issues helping farmers make better business decisions through actionable insights. Let’s dig in.
(00:38)
Welcome back to The Dirt. Thanks to all of our listeners for tuning in. I think we’ve got a great program set up today as we begin our talk about the essential nutrients beginning with nitrogen. Previously, we’ve talked about our essential nutrients and looked a little closer at some of the non-mineral nutrients. So today, let’s dig in on the macronutrients, more specifically nitrogen.
(00:57)
To help us understand the role of nitrogen in plants, I’m pleased to have Dr. Hunter Frame with Virginia Tech joining us today.
(01:04)
Dr. Frame, welcome to The Dirt. Can you tell our listeners a little bit about yourself and what you do at Virginia Tech?
Dr. Hunter Frame (01:10):
Thanks, Mike.
(01:10)
So at Virginia Tech, I am the fuel crops agronomist and I work mainly in cotton and corn production, specifically on variety selection, but also in nutrient management. My program focuses on nitrogen management, potassium and sulphur management in cotton and corn systems, as well as focusing on enhanced efficiency fertilizers for the state of Virginia and throughout the US and mostly in the southeast.
Mike Howell (01:33):
Okay. Dr. Frame, we appreciate you taking time to be with us here today. Let’s get to The Dirt. Why is nitrogen such an important nutrient for crop production? What does it do within the plant?
Dr. Hunter Frame (01:43):
So within the plant, nitrogen is needed for protein synthesis as well as different pathways and photosynthesis, and it’s considered the most limiting nutrient in non-legume cropping systems. So that means that it’s needed in the greatest quantities or in the similar quantities as nutrients like potassium, especially when we’re talking about cotton. And it’s one of the nutrients that are mobile in soil solutions. So when it’s in the soil, nitrogen is more mobile than say phosphorus and potassium due to the states that it occurs in. And that’s why it’s such an important nutrient in terms of management and unique in that aspect of having to manage nitrogen to limit environmental losses.
Mike Howell (02:23):
Okay. You mentioned that nitrogen was important in the process of photosynthesis, and that’s the process where the plants are able to convert sunlight and make their own food, so that’s going to make nitrogen essential to the plant actually feeding itself. So Dr. Frame, you mentioned different fertilizer sources. What are some of the fertilizer sources of nitrogen? How can a grower apply nitrogen to a field?
Dr. Hunter Frame (02:43):
So there’s dominant sources throughout the United States. So if we’re talking about the Midwest, the Corn Belt, you’re looking at anhydrous ammonia being a dominant source in that growing area, as well as urea and urea ammonium nitrate solutions. Those are the, what I would consider the big three in terms of US crop production nitrogen sources out there. And they all have their unique handling aspects and unique management aspects of using those products and how they’re used in a growing system.
(03:14)
You have some minor nitrogen products and some specialty crops. You have some calcium nitrate products. You have ammonium nitrate, and then also you have some ammonium sulphate, which is mainly used as a sulphur source, but you do get nitrogen with that product. And then a lot of the specialty nitrate fertilizers, I mentioned potassium nitrate, but you have calcium nitrate. So those are some minor nitrogen fertilizers. But when we talk about row crop production, we’re really talking about urea based nitrogen fertilizers as well as anhydrous ammonia.
Mike Howell (03:44):
You mentioned the Midwest, and they’ve got an advantage that we don’t have. It’s not really a fertilizer source, but they’ve got another way to get nitrogen into that system that we just don’t have down here in the South, primarily because it’s too hot for us but talking about organic matter. So can you give our listeners a little bit of an idea how much nitrogen they may be getting from organic matter in their soils?
Dr. Hunter Frame (04:04):
Yeah, so when we talk about different growing areas of the United States, it’s very important to note that, because as you mentioned climate and temperature and history of our soils. Say we’ll start in the Southeast, soils are more highly weathered, which from warmer temperatures, they’re also in a humid environment, which means they have water, precipitation that has over millions of years weathered the soils. And so they have what we would consider low organic matter. So depending on what production system you’re in, if you’re in the coastal plain of the Southeast United States, you’re looking at organic matter 1% or less. And typically in mineralization, we’re seeing about 30 to 40 pounds of nitrogen become available throughout the growing season in those southeast soils with 1% or less. As you move into the Piedmont and into other growing areas in the mid-South, if you get into those alluvial soils, [inaudible 00:04:58] soils that hold more organic matter, so you could get 2% to 3% to 4% organic matter in some of those. The more organic matter you have in a soil, the more nitrogen’s going to be mineralized.
(05:09)
So when we talk about nitrogen rates, especially on cotton, and I’m going to harp on cotton because that’s what I know, probably more so than some of the mineralization rates and things in other cropping systems. But in the mid-South, in Tennessee, Mississippi, Louisiana, Arkansas, a lot of times that amount of nitrogen that’s in the soil from organic matter and being mineralized is enough to grow a cotton crop. You may not see a nitrogen response, you may get 70, 80, 90 pounds of mineralization during the growing season from that organic matter.
(05:38)
As you move to the Midwest, we think of the Midwest as having these dark soils, and that’s because of the higher percent organic matter. You’re moving into what we call glaciated or glacial till soils, millimoles, which were covered by the last ice age, so they’re not as highly weathered. So when those glaciers receded, what you ended up getting is a younger soil with higher organic matter because once it was uncovered by ice, it was still like a muck or zen prairie it was in prairie grass. It was in long prairie type sod, and we know from research, even in the southeast, if we grow sod, those plant roots and that turnover of vegetation increases soil organic matter. And so you might have 3% to 6% organic matter in the Midwest and you’re going to have jet black soils and they’re going to be highly productive.
Mike Howell (06:25):
Okay, wish we could build our organic matter a little over 1% down here, it’d sure help, but seems like that’s about the maximum we’re able to get.
(06:32)
So you talked about different fertilizer sources. You mentioned ammonia and urea, and several others. The nitrogen in these different sources is definitely in a different form. So talk about the nitrogen that a plant can uptake. What form does it need to be in for a plant to be able to take it in?
Dr. Hunter Frame (06:47):
All right, so yeah, we’ll start with anhydrous ammonia, that’s the simplest one.
(06:50)
So anhydrous ammonia is 82% nitrogen and 100% of the nitrogen in that fertilizer is in ammonia form, which is NH3. Once you inject that underneath the soil surface, and they usually do it when the soils are frozen or very cold, it changes to ammonium in the soil solution. That’s NH4+. That ammonium is then converted through a microbial mediated chemical reactions to nitrite and then to nitrate, and that happens fairly quickly once soil starts to warm. And nitrate is N03-, and that’s the form of nitrogen that we associate with leaching or being high mobile in soils.
(07:27)
The predominant form of nitrogen used throughout the rest of the country, I would say, are urea based fertilizers. So that urea is a form that has to be first converted from urea to ammonium, and that’s done with a enzyme called urease that’s pretty ubiquitous in our soil environments and in crop residues.
(07:46)
And so urea gets converted to ammonium, and during that reaction, we can have an increase in pH, which results in ammonia loss to the atmosphere, and then that ammonium is then converted to nitrate. So when we use something like urea or UAM solutions, ammonium nitrate solutions, we really have to take into account that first reaction when we talk about losses and whether we’re applying them to the soil surface or whether we’re applying these fertilizers through with an applicator that we can get them below the soil surface. And that really dictates our management strategies when we’re working with urea based fertilizers, whether liquid or granular.
Mike Howell (08:25):
Dr. Frame, you talked a lot about the different ways that nitrogen is converted in the soil and go into that nitrate form. Tell us a little bit about the nitrogen cycle and let’s tie all this together. And this is something that touched home to me here recently.
(08:38)
My daughter is a freshman in high school and she came in the other day and said, “Dad, help me with the nitrogen cycle.” I said, “Well, let’s see what you’ve got.” And the teacher had done a rough outline of the nitrogen cycle. Not too terrible bad, but what really got my attention on there is in big, bold letters down at the bottom of the page, she said, “Manmade fertilizer is bad because it kills the fish in the Gulf of Mexico.” And that really got me thinking about the nitrogen cycle and just what our kids are being taught in school these days.
(09:05)
So help walk us through that and explain that a little bit to us.
Dr. Hunter Frame (09:09):
Wow. So not having a diagram in front of me, the simplicity of it, I guess, is that in the ecosystem in mother nature, we have a cycle of different uptakes and chemical transformations and depositions. So in the natural environment you have a few sources of nitrogen. One is through precipitations, so nitrates that are in the atmosphere, nitrous oxides that are in the atmosphere are converted to nitrates and they fall on the earth’s surface. You can also have, which contributes not a whole lot, but a small amount of nitrogen is through lightning strikes. Nitrogen can be converted and transferred to the soil. The biggest probably natural contributor to the nitrogen cycle are legumes. And legumes take atmospheric nitrogen N2 gas, which makes up 70% of our atmosphere. N2 gas is converted through a symbiotic relationship with a bacteria for different types of legumes, and that is converted to nitrates and then plants can take those up and grow from those nitrates that are generated from symbiotic relationship with the bacteria, and then plants are able to take it up.
(10:12)
You also have some weathering of some minerals that have ammonia in, small amount in the nitrogen cycle. But largely, and in soil organic matter decomposition, we just mentioned, that can mineralize quite a bit of nitrogen in different soils that aren’t as highly weathered as some of our Southeast soils. And then because of cultivated crops and our need as humans to have enough protein in our diets to survive, we’ve invented a process called the Haber-Bosch process, and that takes atmospheric nitrogen and hydrogen gas and reacts them at high temperatures and pressures to create ammonia. And then that ammonia is further reacted with carbonic acid to make urea or different sulfuric acid to make ammonium sulphate or phosphoric acid to make your MAPs and your DAPs, your ammonium phosphate, and then your diammonium phosphates we use for fertilizers.
(11:01)
Once these fertilizers are applied and they’re in the soil, nitrogen can be transformed in a multitude of ways. I mentioned urease transforming it to ammonia. That ammonia can then be lost from the soil system via ammonia volatilization to the atmosphere. It can be transformed into nitrate, and then nitrate and the nitrate by a bacteria species, you have nitrosamines, and then you also have nitrobacteria species that do that transformation process.
(11:27)
From nitrate if we have a lot of rainfall, nitrate can be leached from the soil environment below the plant rooting zone and be lost in the groundwater or can run off into surface waters. And that’s when we start talking about algae blooms and the Chesapeake Bay where I’m close to or in the Gulf of Mexico or in Lake Erie even. We talk about nutrient losses. Now the other input that you have for nitrogen that I didn’t mention is manure, animal manure.
(11:53)
So you can take hog manure, chicken manure, dairy manure, and we even use what we call bio solids, which is human manure. It’s been treated, but those are also sources of nitrogen. But once nitrogen gets to nitrate, it can be leached or in anaerobic conditions, they can be deified into the gases. So that’s N02, N20, NO, and those are what we consider the highly reactive gases for greenhouse gases in terms of retaining heat within the atmosphere.
(12:24)
What’s interesting though is farmers don’t want to lose that nitrogen. They don’t want to see the algae blooms in the Gulf of Mexico or Chesapeake Bay or Lake Erie because that means the fertiliser that they’ve bought or the manure that they’ve applied that they wanted for crop uptake has been moved out of the system and they’ve lost that. Farmers and the fertiliser industry in general, they don’t want to hurt the environment.
(12:45)
We have to grow food in the environment and without these inorganic fertilisers. One statistic that I’ve heard here in the past few years, and now I use regularly is 40% of the dietary protein of humans across the world comes from the Haber-Bosch process, comes from in synthetic inorganic fertilisers. And if we remove that because it’s bad for the environment or society deems that it’s bad, then we have to really look at where are we going to get that 40% of our protein in our diets. And that’s something that not just agriculture has to look at, but also human civilization across the board because we rely very heavily on these fertilisers and growers and producers and industry are really trying to use them as efficiently as possible in these agricultural systems.
Mike Howell (13:33):
That’s exactly right, Dr. Frame. We’ve got to manage this nitrogen and make sure it stays in the field where we want it applied, and that’s the only way the crop’s going to be able to take it up, is if it stays in that field. Any nitrogen that we’re losing, we’re not just losing that nitrogen, we’re also losing income, losing yield on that crop that it was intended to be on.
(13:53)
Dr. Frame, thanks for being with us today. We talked a lot about nitrogen, the importance of nitrogen, why it’s needed, and different forms of nitrogen. We also mentioned a little bit about nitrogen loss, but there’s a lot more we can talk about on nitrogen loss.
(14:09)
Listeners, if you want to hear more about nitrogen, how it can be lost, and different ways we can protect nitrogen fertilizer, join us again next week when Dr. Frame and I will talk about the different loss pathways and how to prevent this nitrogen loss from happening.
(14:25)
As always, I want to thank our listeners for joining us today. For more information on nitrogen, you can go to www.nutrient-ekonomics.com.
(14:37)
Finally, I would like to ask our listeners to pass along a link to our program, to your friends and neighbors. Also, please rate our show and leave us some comments. We’re always looking for feedback to improve this program and make it more beneficial to you.
(14:53)
Until next time, this has been Mike Howell with The Dirt.
