Nitrogen Cycle in Organic Farming w/ Greg Binford
Interview with Greg Binford, National Director of Advanced Agronomic Training at Wilbur-Ellis Company
In this episode, we welcome Greg Binford, National Director of Advanced Agronomic Training at Wilbur-Ellis Company. Greg breaks down the inner workings of the nitrogen cycle and explains how organic growers can better time their nitrogen usage. Wilbur-Ellis is the fourth largest ag retailer in the United States.
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#agriculture #farming #nitrogen #nitrogencycle #organicagriculture #organicfarming
INTRO: Welcome to Organics Unpacked, a podcast for the business-minded organic grower — an interview podcast where we hear from the top experts in the commercial organic industry, with a focus on the business elements of organic growing both in and out of the field. You will gain insight and grow your operation. This show is brought to you ad-free by Avé Organics, a Wilbur-Ellis company. To learn more about Avé Organics, visit our program notes. In the meantime, enjoy the show.
TOM: Hello, everyone. Thanks for tuning in today. Welcome to a new episode of Organics Unpacked, a podcast where we discuss organic farming from a practical perspective. I am your host, Tom Buman. Today, I’m joined by Greg Binford. Greg is the Director of Advanced Agronomy Training for Wilbur-Ellis. Greg, welcome to Organics Unpacked.
GREG: Hi, Tom. Thank you. I appreciate the invitation.
TOM: Greg, before we get started on talking about the subject matter today, which is nitrogen and nitrogen use, give us a little bit of background on maybe your education and your training and how you got to where you are today.
GREG: Sure, I’d be happy to. So I grew up on a farm, west-central Indiana, corn/soybean farm. I raised corn/soybeans and had a small cow calf operation. That’s what started my interest in agriculture. I’ve been in it as long as I can remember. I wanted to go to school in agronomy, and I did. I ended up doing an agronomy degree at Clemson University. And during that experience, I worked in a research laboratory and got very interested in research and just the whole education process. So I decided I wanted to go to graduate school and continue down the agronomy line. So I went to Iowa State University and did a master’s and PhD on nitrogen management. I worked on nitrogen management with Dr. Fred Blackman at Iowa State. Then, from there, I spent three years on the faculty as a soil fertility specialist with the University of Nebraska, out in Scottsbluff. Family took me to the east coast, where I actually spent four years working in the industry with Pioneer as a regional agronomist, and then had the opportunity to go back into the university world. The University of Delaware was looking for a soil fertility professor and extension specialist.
So I spent 12 years at the University of Delaware, and most of my research was on nitrogen — nitrogen management, working with nitrogen stabilizers — and also manure management. Delaware has a lot of chickens and a lot of issues with poultry manure. So I did a lot of manure management work and did a lot of extension education. About 10 years ago, I got a call from Wilbur-Ellis. They were looking for somebody with a soil fertility background to do training and education. That was an opportunity for me to actually come back to Indiana, and that was a dream that I’d had since I started graduate school actually. So I moved back to Indiana. I live about an hour from my dad’s farm, and I now, with Wilbur-Ellis, work primarily just on training and education around all agronomic issues. I train people on agronomic issues and, then, also about the science around the products that we have at Wilbur-Ellis.
Importance of the Nitrogen Cycle
TOM: Great. Definitely, you’re qualified to talk about today’s subject. Today, we want to talk about the nitrogen cycle, why it’s important. What are some of the misunderstandings about the nitrogen cycle and how we get nitrogen into our crops, and what are the different forms? And I know that you work both with conventional farmers and organic farmers. Today, we’ll focus on the organic side of that, obviously. So we’re really excited to have you here today. But I’ve got to just say, out of the gate, I don’t know how many times I’ve tried to learn the nitrogen cycle, right? It’s been taught to me in college and multiple times since then, and I find it very complex because we have nitrites/nitrates. We have ammonia, and we have ammonium. There are so many things that kind of sound alike, that I get those things mixed up. So walk us through the nitrogen cycle, and we’ll break it down so that a farmer that’s out there can really maybe have a better understanding of how they need to think about the nitrogen cycle. What’s important? What’s not important? What are some of the misconceptions?
GREG: Sure, Tom. Happy to do that. And you’re not alone, from the standpoint that I’ve given probably thousands of talks on nitrogen over the course of my career so far. And I’ve had many people tell me — I remember one time a guy came up to me at a Wilbur-Ellis meeting and said, ‘I’ve heard you give that talk five times now, and I’m finally starting to understand at least half of that nitrogen cycle.’ So it is a complicated process. There are really six processes, I would say, within the nitrogen cycle. And those are mineralization, which is the release of organic nitrogen into inorganic nitrogen. There’s immobilization, which is basically taking inorganic nitrogen and converting it back into an organic form of nitrogen that’s going to be unavailable to plants. Then there’s nitrification, which is the conversion of one inorganic form of nitrogen — the ammonium form — into the nitrate form. Both of those two inorganic forms are available to plants. A lot of times, people have the confusion that nitrate is the only available form of nitrogen, but ammonium and nitrate are both plant-available forms.
In soils, ammonium doesn’t tend to last very long because there are microbes that want to, basically, get energy from taking oxidizing ammonium into nitrate. So, because of all those microbes that are in the soil, ammonium just doesn’t last that long in the soil. It tends to convert to nitrate, so that is the form that’s most often taken up by plants. But unfortunately, when it’s in the nitrate form, it’s susceptible to loss. And that’s the three other words that I wanted to mention, and that’s: leaching, denitrification and volatilization. And those are three ways that nitrogen can be lost from the soil, either up in the air or movement down through the soil. The challenge is that all of this is controlled by Mother Nature. It all depends on temperature/rainfall. All of these factors come in, and they control, especially with mineralization. Mineralization, as I said, is basically taking organic nitrogen and converting it into an inorganic form.
Different Forms of Nitrogen
TOM: Greg, let me stop you there. So I kind of think of, ‘Okay, we have this plant system, right? But it’s not using organic nitrogen. It’s using inorganic nitrogen.’ And is that exclusively? A plant only uses inorganic nitrogen. Is that right?
GREG: That is correct. That is correct. Nitrogen has to be either in the ammonium form or the nitrate form, which are both inorganic forms. And I think that’s the source of confusion, sometimes, in organic agriculture. You put on organic nitrogen, thinking that the plants can take up organic nitrogen, but they can’t. When it’s an organic nitrogen, it means that you have carbon and nitrogen molecules bound together. And that’s really what the mineralization process is: breaking apart the carbon and the nitrogen so that the nitrogen now converts into an inorganic form, of which that first inorganic form is the ammonium mile.
Organic Sources of Nitrogen
TOM: Then, from an organic standpoint — I’m just trying to unravel this. From an organic standpoint, that’s really important to have that carbon and nitrogen together that breaks down because, then, you have the carbon leftover that really adds to soil health?
GREG: Absolutely. That’s the beauty of organic sources of nitrogen. If you look at soil health, which is extremely important in organic production, I would challenge you that soil health is important in all soils — whatever you’re doing, if you’re trying to grow plants. And one of the things that influences soil health the most is organic matter, and that’s carbon. So, anytime we can add carbon to a soil, we tend to have the potential to improve soil health because we have that carbon there that can form soil organic matter. And that soil organic matter helps the soil because it helps improve soil structure. Soil structure helps improve water infiltration, improves rooting. It gives you better soil properties. It improves water-holding capacity. Organic matter helps improve nutrient-holding capacity. Then that organic nitrogen also serves as a — actually, I shouldn’t say organic nitrogen — that organic matter serves as a source of nutrients. Because every year, part of that organic matter breaks down, and it gives off plant-available nitrogen. It’ll give off plant-available sulfur. It’ll give off plant-available phosphorus. You get nutrients from that organic matter. But yes, Tom, carbon is an extremely important part of soil health.
Building Soil Health
TOM: So, Greg, in organic farming, we’re putting on that carbon with manure or cover crops or some other type of fertilizer. In a more of a commercial or traditional standpoint, we’re putting on anhydrous and stuff. Where do we get that carbon from, then? Is it that we just don’t build soil health as fast? Or do we have to think about it in a different way? How does organic and traditional farming maybe differ in building soil health?
GREG: So organics, I would say you have a better opportunity for building soil health, just because you’re adding. Well, cover crops can be used in organic agriculture. It can be used in normal agriculture. And cover crops have been shown to be a benefit to soil health because you’re adding carbon back to that soil, and you have just more biodiversity/microbial diversity. But it’s also because, in organics, really, most of our sources of fertilizer are organic. They’re manures that have been processed. They’re plant materials. There are all kinds of different things that we use for organics, but they’re always nitrogen and carbon bound together. So organic matter is a hard thing to build in soils, though, if you look at long-term trends. As soon as you take a soil in its native condition and plow it up — and you introduce all that oxygen into the soil, and all this microbial activity starts occurring and breaking down organic matter until there’s a large, quick depletion — it’s difficult to bring it back, to bring your organic matter levels up. And what typically happens — and I would say in conventional situations, we kind of reached that steady state, where you take soils. For example, on the farm that I grew up on, our soils ranged from probably about 2½ to 3½% nitrogen. And they’ve been that way since my dad started farming it, and they’ll probably continue to be that way.
Well, I will take that back. My dad did change his system, now that I think about it, because there’s one thing that will help build organic matter faster. And that’s a lack of tillage. If you till that soil and introduce all that oxygen, you tend to really break down carbon faster. My dad did change to a no-till system back in the mid-1980s. And no-till systems can build organic matter levels up, probably faster than anything, because of that lack of tillage. If you would have taken that and included cover crops, included organic sources, you could have potentially seen even more organic matter build up. My father doesn’t farm that farm anymore. It’s being farmed by a stepbrother, and he has done some tillage. So my guess is that their organic matter levels have probably dropped a little bit, but that’s the biggest thing that we fight against organic matter buildup. Whether you’re organic or whether it’s inorganic, that tillage process makes it very difficult to build organic matter. Then the other thing that comes into play is climate. It’s a lot harder to build organic matter in the southern part — say, Texas, where it’s hot for a great period of the year versus Minnesota, where you freeze up and have, really, no microbial activity going on for a portion of the year. You tend to build organic matter faster in those colder climates.
TOM: Right. What’s really important in organic farming is that you can’t necessarily compare yourself against somebody that’s three states away or has a different rotation or a different tillage system. Because, it seems to me, all those things influence how much carbon you’re going to build up and the nitrogen cycle and what’s going to happen. But getting back to the nitrogen cycle: we put on, typically in organic farming, we put on a product that’s got a good carbon-to-nitrogen ratio. What is that? What is that? What is a good ratio of carbon to nitrogen when we’re putting on something like manure or we’re adding cover crops or something?
GREG: So, in general, soil organic matter has a carbon-to-nitrogen ratio — native soil organic matter — of somewhere around 8 to 1. 8 parts carbon, 1 part nitrogen. It’s more in that 8 – 10 to 1 range. And when you talk about animal manures, they’re usually somewhere less than 15 to 1. There’s a critical point at about 20 to 1. You get 20 parts carbon, one part nitrogen. As you go above that, you tend to have more carbon than you do nitrogen. So, when those microbes are breaking down that organic material, they’re getting energy from that carbon. They have to have nitrogen to support them, in their bodies, to do what they do. Let’s just say you have a material that has a 10 to 1 carbon-to-nitrogen ratio. As that microbe is decomposing, there’s enough nitrogen in that material to feed what the microbes get or what the microbe needs. So, as it breaks that carbon down, it actually releases nitrogen into the soil because there’s more there than what the microbes need. Now, let’s take something that’s 30 to 1, and you put that into the soil. Microbes start working on that. That doesn’t have enough nitrogen to meet its needs, and so it’s going to use all the nitrogen in that organic material. And it’s actually going to take inorganic nitrogen in the soil. If you’ve got nitrates sitting around in the soil, it can actually consume that and tie up that nitrogen, and it will outcompete the plant. And the higher that carbon-to-nitrogen ratio goes, the more tie up, the longer that tie up occurs because those microbes have to break that carbon down. And they have to have nitrogen to do that.
That critical point is, I would say, 20 to 1. If your material is 20 to 1 or less, then it will tend to mineralize and release nitrogen in the soil. And the lower it goes, the more nitrogen it will release faster. It’s been shown to be a pretty good predictor of how fast you can get nitrogen out of an organic material. But if you put something on the soil that’s, let’s say, 30 to 1, it’s actually going to probably decrease nitrogen for a while. If you had plants growing out there, you could start with those plants for a period of time. I’ve seen it happen before once. I’ve seen it happen several times, but I remember one time in particular. A gentleman out in Delaware had these trees that he planted, and he put this compost out to feed those trees. But this compost hadn’t been composted properly. Had a lot of straw in it. And the trees actually just started turning yellow a couple of weeks after he put the compost on. He’s thinking he’s feeding it, but, literally, he’s not feeding it. He’s taking nitrogen out of the soil and started starving plants. And that’s something that you have to be aware of whenever you’re using an organic source, to make sure that it has a carbon-to-nitrogen ratio. Putting on something that has a high carbon-to-nitrogen ratio before the crops need it and it has time to break down can work. But if you put something on or you’re expecting to get nitrogen out of that material right away, and it’s a high carbon-to-nitrogen material — 30 – 40 to 1 — it’s not going to release nitrogen immediately. It’s going to take time for the decomposition process to occur.
TOM: So, Greg, I’m an organic farmer, and I’m looking and weighing my different options for manure, maybe, and I can get it from different sources. So I want to make sure that I have that carbon/nitrogen ratio. 8 to 1, 10 to 1 is what I hear you saying. How do I know what different sources are? Are there tests for it? Are there book values for it? Can you give me some guidelines of what I should know?
GREG: I would tend to lean towards book values. It can be tested. It can be tested for nitrogen content, and it can be tested for carbon content too. But in general, you can look at book values of different types of materials in terms of what the carbon-to-nitrogen ratio is. If you’re taking a compost, something that’s been composted — and particularly if it’s something that you’ve composted or you’ve gotten it from a neighbor or somebody that’s composted it — it’d probably be worth doing a test on that because it can be tested to see what the carbon-to-nitrogen ratio is. That’s the challenge with organic. One of the challenges with organics is just how fast that nitrogen is going to become available.
TOM: Right because it becomes available, even if you have an 8 to 1, 10 to 1, right? It’s not like it’s metered out in a certain amount every week, every day, every hour or something. There are things that influence how that’s breaking down from the organic matter and combine with the carbon/nitrogen to just the nitrogen that becomes inorganic and is available. What are those different things that a farmer needs to know about? How fast does that nitrogen become available? What are the factors?
GREG: That’s what makes it such a challenge when you’re dealing with organics because it depends on Mother Nature, and it can vary each year. And it can vary based on soil types. Sandy soils connect differently than heavy textured soils. But the biggest driver, I would say, is temperature — what the temperatures do — and then also what the soil moisture is like, if it’s kind of an ideal soil moisture. If you get extremely dry, that slows down mineralization. If you get extremely wet, where we don’t have as much oxygen in the soil, that slows down mineralization. But the biggest driver is going to be temperature. We typically think of mineralization as being fairly insignificant below 50 degrees. We think of nitrification as being fairly insignificant under 50 degrees. So temperature is the biggest driver. Then, from that standpoint, again, that carbon-to-nitrogen ratio. If you have something that’s 18 to 1 or 20 to 1, it’s not going to release as fast as something like seabird guano, I think. It’s something that they use in organic agriculture. That tends to have a very low carbon-to-nitrogen ratio. That’s going to release a lot quicker. But that’s where that challenge is. And sometimes it just takes experience to figure that out in terms of how that’s going to be released. You can take soil samples. You can always measure how much ammonium and nitrate are in your soil to get a feel for what’s actually happening and how that mineralization is occurring.
Nitrogen Sources in Organic Farming
TOM: It’s, to me, one of the challenges. Let’s say we put on manure as a source, or we’re counting on our cover crop releasing nitrogen. We get one of those cold, wet springs. We know that we’re low in available nitrogen, just because it hasn’t been mineralized or released from that carbon. But then what do we do? We only have so many. In organic farming, we only have so many sources of nitrogen available. It’s not like we can run out and give it a shot of urea or anhydrous or something like that.
GREG: And that’s one of the challenges in that. And what we typically have done in the past is you have to put on, really, more than what the crop is going to need. If you have more out there, you’re going to have more available at any point in time. But we are starting. There are some materials now — protein hydrolysates, for example — that are readily available sources of nitrogen. And as we go forward, I think we’ll see more types of nitrogen like that. They come from natural products, and they are basically available when you put them on the soil. It helps in that type of situation, as long as you use them right. It’s very similar to fertilizer in conventional agriculture. If you put too much fertilizer into conventional agriculture at a point in time, and Mother Nature brings in a lot of rainfall, or you put on too much irrigation water or whatever, you can take that nitrogen out of the soil and leach it or denitrify it. The same thing can happen in organic agriculture using a more soluble source. But if we spoon-feed it, really, whether you’re talking organic or conventional, to me, one of the best ways to manage nitrogen is to spoon-feed it. You’re going to have a small amount out there at any point in time. That way, if Mother Nature does bring us a lot of rainfall, then you have much less out there that’s susceptible to loss. So that spoon-feeding technique can be a really valuable way to do that, and some of these types of products are becoming available in organic nitrogen. So spoon-feeding can be really good because, again, if you put on too much organic nitrogen just so you make sure you have enough, then when that crop comes on, more than likely you’re going to be adding nitrogen into the environment because of that mineralization. You’re not going to stop the mineralization. It’s going to just continue to occur if you’ve got that organic source out there. And now, there’s no crop out there to grow unless you’re in an environment where it never rains. Then you’ve got the potential to leach that nitrogen into the ground.
Nitrogen in Cover Crops
TOM: So, Greg, I understand where nitrogen is coming from when I’m putting on manure or something like that. When I use cover crops, where’s my nitrogen coming from? What’s the source from cover crops?
GREG: So it depends on the cover crop. If you’re using a rye cover crop, for example, the nitrogen in that rye cover crop comes from the soil. It takes up nitrogen, and that’s one of the nice things about cover crops. They can be a scavenger, so it can take up nitrogen in the soil when there’s nothing growing there, when you don’t have your crop growing, and therefore prevent loss of that nitrogen. Basically, it’s just taking it out of the soil. Now, if you have a legume as a cover crop, then that actually has the potential to take nitrogen out of the air. Our atmosphere is 79% nitrogen — N2 gas. And that’s how we make fertilizers. We take that N2 gas and convert it into an inorganic form. Well, the legume crop plants have the ability to take nitrogen in a process we call nitrogen fixation, where they take nitrogen out of the air and convert that into a plant-available form of nitrogen. They can feed themselves, and if they’re a high nitrogen-fixing crop, they’ll leave extra nitrogen in the soil. When you destroy that cover crop, you’ve added nitrogen into the system because of that nitrogen fixation. If it’s just a rye cover crop — something that’s a non-legume — you don’t really add it into the system, but you’ve captured it, kept it from leaching out.
TOM: A little like a storage tank, maybe, if you will. It’s pulling that free nitrogen that would probably be lost to leaching or something else — denitrification — and it’s storing it in the plant. So, when we have the nitrogen stored in the plant, whether it’s a legume plant or something like rye cover crop, is it in the organic or inorganic form? And then what has to happen to get it into the growing plant?
GREG: So it’s primarily in the organic form. It’s nitrogen and carbon bound together, and it has to go through the process of mineralization, like I was talking about. And again, this is where the carbon-to-nitrogen ratio comes into effect. If you take rye, for example, as a rye crop or pretty much any crop. As any crop grows and gets bigger, it tends to produce more carbon relative to nitrogen. The nitrogen concentration tends to go down. You can have a cover crop that you plow under, which is one of the things that can make organic farming challenging. Although it can be challenging if you’re using cover crops in conventional too. But that nitrogen, again, the release from that cover crop is based on that carbon-to-nitrogen ratio. So, if you take rye, and you plow it into the soil, and it has a carbon-to-nitrogen ratio of 30 to 1, it’s not going to release nitrogen immediately. As a matter of fact, it’s going to tie up some nitrogen for a while, until we get some decomposition and we’ve broken down and basically reduced that carbon-to-nitrogen ratio. So, to answer your question, that cover crop is really just like an organic source of nitrogen. It is an organic source of nitrogen.
Escapes in the Nitrogen Cycle
TOM: So, when I think of the nitrogen cycle, you look at a circle. So we talked about how nitrogen comes into the process, right? We can bring it in animal manure. We can have roots growing that are scavenging the nitrogen. We can have legumes that are fixing the nitrogen from the atmosphere into the root system, but what is the escape of nitrogen in a nitrogen cycle?
GREG: There are three primary ways that nitrogen is lost — I guess four, if you count runoff. But generally, in organic nitrogen, I don’t think that would be an issue. But leaching and denitrification are basically the loss of nitrate. Whenever we have nitrogen in the nitrate form, we have the potential for it to either leach, which means it moves downward in the soil. And the reason why it moves downward in the soil is because nitrate is a negatively-charged molecule. It’s NO3 with a negative charge. Our soils are negatively charged. Organic matter particles and clay particles in the soil have a negative charge. So you put a negatively-charged ion in there. It’s not attractive in the soil particles. It fades out in the soil solution. So, if we move water through the soil, it’s going to leach some of that nitrate down. The more nitrate you have in the soil solution, the more potential there is for downward loss or leaching. Now, if you have heavier soils, where they tend to hold water, and your soil pores have more water than they do oxygen, there are actually microbes in the soil that are denitrifiers, and they can actually live off the nitrate. They basically get energy from nitrate, and they convert nitrate to nitrous oxide. If they take all the oxygen off of those nitrate molecules, it literally converts back to dinitrogen gas, and it goes back up into the air. So leaching tends to be more of a problem on soils that are well-drained. Denitrification is an issue on heavier soils. Denitrification is going to be a temperature-dependent process.
Leaching is just the volume of water, but denitrification: warm, wet soils/lack of oxygen. Denitrification can occur very rapidly. If it’s really cold out, it’s going to be very slow. So those are two ways that you lose nitrate. You can also lose ammonium if it’s sitting on the surface of the soil in a high-pH environment. So, when I say ammonium, I’m talking about NH4, which NH4 is the ammonium ion. It has a positive charge. Ammonium is actually held in the soil by the cation-exchange sites, the negative charges of the soil. But if you have ammonium ions on the surface of the soil in a high-pH environment, they tend to convert to ammonia. So, in other words, they lose a hydrogen ion. It becomes NH3. NH3 is ammonia gas. I’ve smelled ammonia gas. If it’s sitting on the soil surface, it can go up in the air. And that is something that we have to be aware of. Whenever we’re using organic sources of nitrogen, if they have some ammonium in them, we can volatilize that, and manure can have some ammonium in them. It depends on how they’ve been handled. If you take something that’s been really well composted, you usually have gotten rid of the ammonium. But if you’ve got something that has a significant quantity of ammonium, that should be in the analysis of the material. You can test for that. You don’t want to put that on the soil surface and leave it on the soil surface if you’re in a high-pH soil, in particular. But in general, those manures are often high-pH anyway, but that’s how you lose. That’s the third way, what we call ammonium volatilization, where you have ammonium ions on the surface of the soil in a high-pH environment. You can lose the nitrogen that way.
Environmental Effects of Nitrogen Loss
TOM: So, on the loss side of it, Greg, I get anytime we lose nitrogen. We’ve worked to get nitrogen in the soil through cover crops, through manure, whatever. Losing it is bad. What are some of the environmental implications of losing nitrogen?
GREG: With nitrate, the concern is — at least with, I should say, nitrate leaching. With nitrate leaching, moving down into the groundwater, there’s a concern about food and health, how much excess nitrate. The EPA limit on groundwater is 10 parts per million of nitrate/nitrogen. We shouldn’t consume water that has greater than 10 parts per million of nitrate/nitrogen. Now, from an environmental standpoint, we don’t want to send nitrogen up into the air — for example, nitrous oxide. We can get concerned about greenhouse gasses. We hear a lot about the greenhouse gasses that build up in the atmosphere. Well, nitrous oxide is actually a much more potent greenhouse gas than carbon dioxide is. That’s a negative for the environment, just the impact it can have on the atmosphere.
TOM: So, whether the nitrogen goes up in the atmosphere or it goes down with water, those loss mechanisms are really important for us to control. Not only from an efficiency standpoint, from an environmental standpoint also.
Understanding the Nitrogen Cycle
TOM: So, again, it’s making more sense to me. We have all these different forms of nitrogen. I think that’s the hard part for me. It’s not just like a linear process, where this turns into this and turns into this, because there are feedback loops based on what’s happening too, right? So it’s important to really understand that nitrogen cycle. Especially for organic farmers who have limited options of what to do, it’s really important, I think, that they understand this feedback, and it makes sense to them. So they understand, going into it, what the risks are and what the opportunities are.
GREG: Yeah, I agree completely. It’s important in any kind of agriculture, but it’s especially important in organic agriculture, just to understand what you’re dealing with. I can recall being called out to a field probably 10 years ago, where an individual was positive that they had a nitrogen toxicity because an agronomist had come in. They had a couple of different people look at it, and their corn was turning yellow. And I went in and looked at it, and the first thing I said to them is this is not a toxicity based on the symptomatology of that plant. I think you have a deficiency. And the whole reason he had a deficiency is because he didn’t understand nitrogen volatilization, and he didn’t understand immobilization. He put all his nitrogen on top of the surface of a very, very high-carbon material, a corn residue. He put it all on that surface of that soil, and it was all getting tied up due to immobilization. His crop was starving. But it’s even more important to understand those processes in organics, just because of the nature of what you have to use for your sources. One thing, Tom, I wanted to mention, too, that I thought of when we were talking about environmental issues — and one thing we need to be aware of — is phosphorus from an environmental standpoint.
I spent 15 years out in the Delmarva Peninsula, where they deal with the Chesapeake Bay. They’ve been looking at nitrogen. They’ve been focused on improving nitrogen management since the mid-1980s, to try to keep nitrogen and phosphorus out of the Chesapeake Bay. And whenever we’re using organic sources of nitrogen, we typically are using a lot of phosphorus to put something on. Let’s say you put on a 4−3−0 fertilizer — 4% nitrogen and 3% phosphorus. If you put that on to meet the nitrogen requirements, you’re going to put on way more phosphorus than what you need. And if you continue to do that year after year after year, you can really build up phosphorus levels into your soils, where, then, that phosphorus can move off that soil relatively easily. And if it gets into surface water, then we have issues with algae blooms, like they have in Lake Erie, issues that can cause fish to die. There are all kinds of issues with algae blooms. So, just again, it’s something to be aware of. When we’re using these organic sources as a nitrogen source, and it has a lot of phosphorus in it, you can build those phosphorus levels up to the point where you start to run into issues.
Animal Manure as a Nitrogen Source
TOM: It would seem to me that this is especially important for organic farmers that are using manure, right? Because with commercial fertilizer, I can blend my nitrogen and phosphorus to a level that is good for both. But with manure, to me, it’s a little like a multivitamin. You get what you get inside the manure. And if you get manure that has high phosphorus, for some people that might be good. You might need to build your phosphorus levels in your soil. But for people like, maybe, in the Delmarva who have used manure a lot, and that phosphorus level is really high, you might have to look at other alternatives other than manure. Because you might have gotten that phosphorus level higher than you expected, and you could be causing some water quality problems.
GREG: Exactly. Any place where they have high concentrations of animals. Up in New York, where they have lots of dairy cattle, they have issues with too much phosphorus in their soils. In California, they have lots of dairy cattle. Again, too much phosphorus. And it all comes from the standpoint of taking that animal manure and using it as a nitrogen source. And when you use it to meet the nitrogen requirement of your crop, typically you’re over-applying 3, 4, 5, 6 X more phosphorus than all that crop needs. And it’s not that big a deal if you do it once or twice. But if you do it every year for 20 years, all of a sudden you look at your phosphorus levels, and you’re like, ‘Wow, how did I get such high phosphorus levels?’ One of the problems that you have is that phosphorus builds up in soils. It’s very difficult to pull it back down. Inorganic nitrogen doesn’t tend to build up in soils because it’ll leach out like the processes that we talked about, but phosphorus will just keep building up. It’ll get tied up in that phosphorus, and the soil will actually start to become saturated. And when it becomes really saturated, that’s when you have a problem because then it starts to release easily from the soil. And as water moves across the surface of the soil, it can take the phosphorus with it. And one of the issues with phosphorus relative to nitrogen is that the concentrations that it takes to have an environmental impact are very, very small. It doesn’t take much change in phosphorus concentration. All of a sudden, you’ve got these major algae blooms and all kinds of environmental issues. So it’s something to be aware of because you want to try to prevent that from happening. It just makes it a headache to deal with after the fact, if you build those levels up too high.
TOM: Probably a topic for another episode is some of the new forms of nitrogen that are coming out that are readily available. Maybe it helps you to balance out your phosphorus/nitrogen levels a little bit better in an organic system.
GREG: Absolutely. That’s a benefit from those types of sources. Not only can you use them to spoon-feed the crop and help with the nitrogen, but you can help eliminate building up the phosphorus level.
TOM: So I want to go back to one word here: mobilization. You talked about mineralization, the breaking apart of carbon and nitrogen. You threw another word in there: mobilization. Tell me what that is.
GREG: Immobilization. Basically, the easy way to think about it: mineralization is you take organic nitrogen and convert it into plant-available nitrogen.
TOM: Which is inorganic nitrogen.
GREG: That’s inorganic nitrogen. Even if you’re in organic agriculture, the plant’s taking up ammonium nitrate, which are inorganic forms. Now, immobilization is taking that inorganic nitrogen and converting it back into an organic form. How that happens is the microbes consume that nitrogen, and so that nitrogen now becomes part of the microbial biomass of the soil. It’s now an organic form, and it has to, basically, mineralize again to become available. So that’s that issue that I was talking about. If you put too much carbon relative to the nitrogen, the microbes want to take that nitrogen out of the soil, and they will outcompete a plant every time. If you put a high carbon-to-nitrogen material out in the soil, and you expect nitrogen to go into the crop, it’s not going to because the microbes will outcompete it. You can take a soil that has very high concentrations of available nitrogen, and if you put a lot of carbon out there, you can basically convert all of that available nitrogen into an unavailable form because it’s immobilized.
TOM: All right. It’s not going anywhere. It’s stuck there.
GREG: It’s an advantage. You don’t have to worry about losing it. It’s protected in the soil. But if you want it in the plant, that’s not going to happen for a while. So that can starve your plant if that occurs.
TOM: So, if I were going to have nitrogen in my soil, from your standpoint, what would be the best? I know that it moves from one form to another. But if I could keep it in one form, what form would I try and keep it in?
GREG: If I could keep it in the ammonium form, that would be good from a standpoint that the soil would hold it because it’s positively charged and the soil is negatively charged. The problem is you wouldn’t want to keep building it because it could get too high. So it’s a hard question: just pick one. Really, in my opinion, you like a balance between organic and ammonium. Nitrate is the one that has more chances of getting away from you. But unfortunately, you can’t stop the microbes in the soil. The ammonium-oxidizing bacteria are prevalent in all soils, and that ammonium is going to convert to nitrate.
TOM: We haven’t found the secret bullet for nitrogen yet, have we?
GREG: Not really. In conventional agriculture, we have these materials called nitrification inhibitors, which basically slow down that conversion of ammonium to nitrate. It can only last for a certain period of time, and then they’re gone. They decompose in the soil, and so they can protect that nitrogen for a while. But we still haven’t found that. Ultimately, Tom, the ultimate secret to nitrogen is if we could have all crops be like legumes, where you don’t have to put any nitrogen out there because it takes it all out of the air and converts it into a plant-available form. There’s a lot of science going on developing microbes, for example. Microbes in the soil have the ability to take nitrogen out of the air and convert it into a plant-available form. So, if we have this conversation again in 20 years, I’m sure we’ll have new technologies because there are already those types of technologies becoming available, and they’re just going to continue to get better as we go forward.
TOM: So is it possible to think that some of those technologies — I know we’re kind of looking into the crystal ball — can overproduce nitrogen that a crop could need? So, if we’re in the Midwest, and we have a corn crop, is it possible to think that we could fix so much nitrogen we’re kind of in the same boat we are? I know that we’re not making it out of petroleum and putting it on, but I’ve heard that some legumes can produce more nitrogen than the next year’s crop can utilize, and we still have the risk of losing that into water. Is that correct or not correct?
GREG: So, when I think of the really best nitrogen fixers that I’m aware of, one of the very best is alfalfa. Alfalfa fixes a tremendous amount of nitrogen. It utilizes a tremendous amount of nitrogen. But because it fixes so much nitrogen, when you plow that alfalfa crop under, there’s a tremendous supply of nitrogen for that next crop. And typically, we plant that next crop in the Midwest as being a corn crop. You may need a small amount of nitrogen early on to get that crop off to a start because of that nitrogen in the alfalfa. It’s still organic, and it needs to mineralize to become available. But there is enough nitrogen to feed that crop. It’s possible that you get to the end of the season. It could continue to nitrify and release nitrogen. In any soil that has organic matter in it, you can’t shut down mineralization. If Mother Nature gives you the right conditions, you’re going to be releasing inorganic nitrogen into the soil. And if you don’t have a crop growing there to take it up, then you’re potentially losing it to the environment.
TOM: Well, Greg, I appreciate your time. I want to be cognizant of your time, too, and your schedule. I appreciate you taking the time to talk to us. I feel like I only need to hear about the nitrogen cycle another five times, and I might get it down.
GREG: Well, thank you, Tom. I appreciate the invitation. I always enjoy talking about nitrogen, and I certainly enjoyed our conversation here today.
What Farmers Should Know
TOM: Okay, so I have one last question, Greg. You’re in a room with a farmer, right? And you’ve got two minutes to discuss the nitrogen cycle with the farmer. What is it, at the end of that two minutes, you want that farmer to understand about the nitrogen cycle in organic farming, to make them a better farmer?
GREG: I would say to just make sure that you really understand the mineralization process. Understand the carbon-to-nitrogen ratio of the material that you’re using as a nitrogen source so that you can have your best chance of matching that mineralization — that release of nitrogen — with when your crop is going to need it. And realizing that you can’t be perfect because Mother Nature is going to control it. But just making sure you understand that nitrogen is not available immediately. It’s going to become available at a given point in time, and you want to try to match that time with when your crop is going to need it. But Mother Nature is really going to control it. At least understand it. Understand the process.
TOM: Greg, thanks. Thanks so much for getting on, talking about the nitrogen cycle. I know it’s complicated, but you definitely simplified it. So, to the listening audience, we hope that you enjoyed today’s episode with Greg Binford of Wilbur-Ellis. Be sure to tune in every week when we’ll talk about another facet of organic farming. Thank you.
GREG: Thanks again, Tom.
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