Why understanding the nitrogen cycle is key to managing soil fertility
Hello, you're listening to Advancing Nitrogen Smart, the podcast series from University of Minnesota Extension. I'm Jack Wilcox at the communications desk here with Extension. Today, we're gonna go back to basics and talk about the nitrogen cycle. Here with me are Dan Kaiser, nutrient management specialist with Extension, and Brad Carlson, Extension educator.
Jack Wilcox:Brad, talk to us about the different ways that nitrogen will change after it's been applied to the field.
Brad Carlson:Sure. This has been kind of an important topic because as we we talk about our nitrogen recommendations, we talk about some of the environmental issues that are going on. Really, what underlies all of this is just basic understanding of nitrogen and where it is and and how it behaves in the environment. Because, you know, if you're gonna understand how nitrogen gets out of place or you're gonna understand how to best management as a fertilizer as far as selecting the right product and rate and timing and so forth, it's kind of imperative that you also understand, what these processes are. So we're gonna review some of that stuff here today, the process of nitrification, denitrification, volatilization, mineralization, and immobilization.
Brad Carlson:Let's start by talking about nitrification. So this is the process by which ammonium turns itself into nitrate. Now, you know, there may be some things that happen a little bit ahead of that, depending on what form the nitrogen starts in. But let's just say you're applying anhydrous ammonia. That product, the anhydrous nature, that means it's got no water, and so it finds water very quickly.
Brad Carlson:The ammonia turns itself into ammonium real fast that adheres to clay particles, but but the ammonium is a a cation, and it's gonna be held to clay particles in the soil. I I was gonna say, unfortunately or fortunately, I don't know what the what the actual that's just a fact of life that the ammonium turns itself into nitrate. So, it doesn't really turn itself into it, but bacteria in the soil actually, lead this conversion. And so this process happens relatively fast. But as with all, all things that are bacterial or microbial in nature, it is driven on moisture and temperature.
Brad Carlson:And so the warmer it is, it's it's gonna be the faster it goes. And we would expect, you know, if it's extremely dry, that's gonna turn itself off. And then when it's extremely wet, it actually, ends up doing something else, and and that's denitrification. So denitrification happens when the soil gets completely saturated, and then you've got microbes in the soil that are looking for oxygen. There's no oxygen there because it's flooded, and and, they are going to rob the nitrate molecule of its oxygen.
Brad Carlson:And so that process is taking the nitrate and turning it first into a nitric nitric or nitrous oxide and NOx gas. But if the conversion is complete, it goes all the way back to n two gas, which is the major component of our atmosphere and, of course, is not an environmental contaminant. And and so that's kind of the, end process where, you know, begin in the beginning, we've turned n two gas into into ammonia through the Haber Bosch process in a factory. Denitrification ends up in in it returning to n two gas and back into the atmosphere.
Daniel Kaiser:It's really the presence or absence of oxygen. So as Brad was talking, microbes are looking for an oxygen source. So when the soil becomes saturated, we know that then they have to find an alternative source. And usually, the the first step or the first source that they look for is nitrate in the soil itself. There are a number of other things like sulfate they can also use, but, typically, nitrate is is the first one.
Daniel Kaiser:So that's when we start looking at as an issue. Typically, it's gonna affect earlier than than some of these these other processes. And, you know, looking at just overall issues, too in terms of loss, I mean, nitrate, obviously, we have a leaching, you know, high leaching potential for that, since, you know, ammonium, they're the n h four, that initial step, since it is a positively charged ion, can be held on the soil's cation exchange capacity. You know, every once in a while, you'll hear some groups talk about cation exchange capacity, which is the the relative potential of the soil to hold positive charges, is higher in high clay soils versus, lower in, say, sandier soils. That we know that there is some holding capacity, but this this nitrification process happens relatively rapidly.
Daniel Kaiser:And it isn't uncommon, if we start looking at, say, late May to early June that, you know, may only take a week or two to fully nitrify the full amount of ant you've applied in the spring. With oxygen, with warm conditions, the process can happen relatively fast. The same goes on the denitrification side because one of the things that we know is it does take a few days, for this process to ramp up. So if your soils are wet and saturated, it doesn't necessarily mean that you're gonna see denitrification occur right away. You mean it takes, you know, about two to four days or so.
Daniel Kaiser:And with really warm conditions, we know that can, you know, really denitrify a lot if the soil stays relatively wet for about, you know, a week to ten days. So, you know, these issues are important when it comes down to the the availability. If you look at in Minnesota, the bulk of the nitrogen that's taken up by crops is going to be in the nitrate form, and that's just basically because of how quickly the, the conversion of ammonium to nitrate happens with this nitrification process. The plants can take up ammonium. You know, obviously, you know, if you look at plant utilization, the nitrogen they utilize, it's gonna mostly go into proteins, which are amino acids, which are akin to ammonium.
Daniel Kaiser:So even if it takes it up as nitrate, it's gotta be converted to back at some point. So, you know, the plant will take it up, but just the fact that, our soil is converted so quickly that that the bulk of the nitrogen is taken up in the nitrate form.
Brad Carlson:And one of the really the the key issues with the nitrogen cycle and nitrogen loss here is that the the two predominant methods through which we lose nitrogen and specifically nitrate to the groundwater, is leaching, where, as you mentioned, Dan, it's no longer held in the soil, and therefore, it kinda moves with the water. Some people say dissolved. It's not really actually dissolved. It's just more of a of a matter of it being free in the soil and and water that's moving through the soil profiles taking it along with it. And then also the volatilization process, both of these are in to the atmosphere, and both of these are really contingent on the nitrogen being in the nitrate form.
Brad Carlson:And so that process of nitrification is pretty significant when it comes to looking at the overall loss of nitrogen and to trying to keep track. And, you know, as I said before, it is temperature dependent, and so it happens faster the warmer it is. And so from that standpoint, while time is another factor, you can kinda keep track of when an application was made, what the temperature has been, and how long it's been, kinda get a handle on how much of it's probably nitrate.
Brad Carlson:Brad talked about denitrification and the form formation of nitrous oxide. That's you know, is there are some issues associated with that, particularly when it comes to greenhouse gases. However, if we can get a full denitrification to n two gas, if you look at our atmosphere, our atmosphere is about 78% nitrogen, which that's you know, bulk of that's as n two gas. So the bulk of our fertilizer and what we and nitrogen we get through, either chem or industrial or biological fixation comes from the atmosphere. If you look at what's available per every acre above your ground, it's about a 17,000 tons of nitrogen is potentially available.
Daniel Kaiser:So if we get full denitrification, it isn't as big of an issue. And we start looking at, you know, other things that, you know, we may have talked about already or will in the future on water quality. A lot of the, you know, the components which we are looking at trying to clean the nitrogen out of whether it's tile water or surface water is through denitrification. So if you can get full denitrification, isn't necessarily a bad thing if you get it back to n two gas other than the fact that it's nitrogen that's being lost from, your operation. But, you know, in general, that's one of the things, I guess, we don't talk a lot about since most of our nitrogen smart program is really geared towards water that we don't really talk too much about the atmospheric side of things.
Daniel Kaiser:But it can be, pretty substantial in terms of what we lose on a on a yearly basis when it comes through denitrification because there's always gonna be pockets in your soil that are gonna be saturated enough for some denitrification to occur. So it's, you know, something that you're likely gonna see in every acre every year. Some loss come through through denitrification just because, generally, the soil will be saturated somewhere.
Brad Carlson:And so like like you've already mentioned, Dan, the the process is dependent on be on, what the soil temperature is. And like all biological processes, things slow down significantly when we get to about 50 degrees Fahrenheit. You know, if you think about your refrigerator at home, you'd like it to be below 50. You know, probably in a lot of cases, it's just hovering right above freezing. The colder it is, the longer your food is gonna keep in the refrigerator.
Brad Carlson:Same thing applies to the nitrification process. The colder it is, the slower it gets. So that's one of the reasons why in parts of the state where we, recommend, that that fall application of nitrogen is acceptable, not to be doing it until it's, gets down to 50 degrees. And if you look at the curve on the rate of of nitrification of the conversion of the ammonium into nitrate, you see that it breaks right at about 50 degrees. And then when it gets above 50, it's actually going even more rapidly.
Brad Carlson:It doesn't ever really quite get to zero, but the closer it gets to freezing, the the, closer it gets to zero, you know, to the point where it's quite insignificant. And and so, you know, the the kind of the both the factor of it being cold and then the the also the, fact that, as the days go on in the fall, it's getting colder still leading all the way up to the soil being frozen. And just simply that number of days is, you know, is fewer in number. All adds or contributes to to why we recommend not applying fertilizer until it gets down to 50 degrees.
Daniel Kaiser:And, you know, as Brad said, it's a there's a pretty significant temperature component to this. And that I mean, if you look at a lot of the data, as Brad said, if you, you know, kinda look at the optimal temperatures for nitrification to occur, it's it's somewhere between, we'll just say, 50 and, roughly about 70 degrees Fahrenheit. If you get above 70, then it does tend to I mean, high temperature will slow it down slightly, but it's not, it it's still gonna be pretty quick in terms of the the overall accumulation. So, you know, really, truly, we don't slow stop nitrification until the soils freeze. And at that point, then we know it's gonna be lower.
Daniel Kaiser:And one of the things that, also should be noted too with anhydrous ammonia in the fall is that with the anhydrous nature of that material, anhydrous means it's lacking water. It's gonna absorb water at the point of injection. On, you know, normal years where you have adequate moisture, you know, you might be seeing an injection zone around four or five inches somewhere in there. It might go out a little bit farther if the the soils are dry because it's gonna seek out water. And in that point, it's it's seeking out water since there's the microbes living in that water.
Daniel Kaiser:It's going to partially sterilize the zone of application. So that's gonna slow down your nitrification as well. I mean, it's because it takes a while for the soils to recover, and they will recover. I mean, it's I think one of the people that might not know a whole lot about some of these these reactions, you know, might say, you know, why do we wanna sterilize that zone? I mean, is it gonna permanently harm our soils?
Daniel Kaiser:And our soils, I mean, are really so active, the area that we're affecting is so slow that what you tend to see is is out of the fringe edges where you still have microbial activity. You know, once, you know, the pH and some of the other things become more more suitable in the zone of of application, they'll start to recover, and the microbes will start to multiply and move back inwards towards where that application is is applied. So it will slow it down a little bit as well in the fall, and that's why anhydrous, you know, tends to be one of the better sources, versus some of the other products like urea and even livestock manure. You just don't have the that anhydrous nature that impacts that accumulation. So you're you're more likely to see nitrate accumulation in some of those sources that aren't aren't in that anhydrous state like anhydrous ammonia.
Brad Carlson:Yeah. And, before Fabian was in Minnesota, he was in Illinois for a while, and and we've got some data from some work that he did in Illinois looking at comparing that fall application to the spring application. And the rate the rate of nitrification. And and some of the data is is pretty interesting, and I don't have the exact dates. And, of course, it's worth remembering that Northern Illinois is a little warmer than it is in Minnesota, but it's relatively close.
Brad Carlson:But a fall application with no inhibitor, and they were measuring then in late May what percentage of the nitrogen was converted to nitrate. And so a fall application with no inhibitor by late May was 97 nitrate. The conversion had been pretty well complete by that point of time. You know, it's worth noting, we've covered in previous podcasts that the majority of our nitrate loss and through tile lines is happening in May May and June. And so that's fairly significant that's happening.
Brad Carlson:By using a nitrification inhibitor, it was only 60% instead of 97%. The spring application was 65%. And so, you know, that's one of the reasons why, you know, in Minnesota, we'd look at making a recommendation of applying in a nitrification inhibitor with our our anhydrous ammonia because, you know, if you look at the data, the fall application with the inhibitor was very similar to the spring application without it. And, you know, and then conversely, if you look at a spring application with the inhibitor, it's 50%, which is, you know, less than the 65, but they're pretty close. And that's kind of also what we've said a lot is that that the inhibitors also wear off based on temperature.
Brad Carlson:So the spring application of inhibitor typically doesn't, isn't really effective as far as, doing much to prevent loss to water because it's kinda not happening at a time when when it makes a lot of difference. Then the conversion of urea is about 75% even from with the spring application. You know, that's slightly higher than the spring application of, anhydrous, which is because of the effect you were talking about, Dan, where it's kind of, punching the bacteria in the nose. And then, of course, the UAN solution that we're always careful about, was 80%. However, 25% of it was already nitrate when it was applied.
Brad Carlson:You know, so that's the main reason why we're not recommending applying UAN solutions, specifically in the fall, but even pre plant because it's already 25% nitrate when it hits the ground.
Daniel Kaiser:Yeah. And once it's nitrate, you can't do anything to inhibit that. You know, one of the things about inhibitors I think that's important is the fact that they can reduce leaching by delaying nitrification. They delay it. They slow it down.
Daniel Kaiser:They don't completely stop it. I mean, it's essentially like, if you'd kind of have a hose, you know, with water flowing through it and you'd kink the hose. You know, over time, we know that the activity tends to wear off or the the flow or the conversion will will get to be more and more, and that effect is going to be greater of the wearing off of the inhibitor, the especially the warmer it is because they tend to especially the inhibitors, they tend to work better with with cooler temperatures. A few other things too, high clay soils, high organic matter soils can help increase persistence, particularly of nitrification inhibitors. So, I mean, if you're in a sandy soil or something like a silt loam, you're not gonna see the the general effect that you would see as you might get with a with a clay loam soil.
Daniel Kaiser:But that data that Fabian had from Illinois is interesting because it, you know, it speaks to a lot of kind of some of the things we're talking about, especially if you look at the inhibitor versus, you know, the anhydrous in the spring without versus in the fall with us seeing similar accumulation of of nitrate at that point in time. You know? And then if you look at the spring anhydrous with and without, you look at the the general delay or the inhibition, it's it's far less than it is in the fall with that. So it speaks a lot to how quickly that's that's wearing off. And then urea kinda being, you know, higher than anhydrous ammonia without that, it's kind of what I mentioned before is that anhydrous nature of the anhydrous ammonia really, you know, can knock back.
Daniel Kaiser:It's not an inhibitor itself, but it does act as a, you know, pseudoinhibitor at least of of slowing or stopping things for a short period of time, before the bacteria get going again. The big thing about this with any of these inhibitors is the fact that they disrupt the nitrifying bacteria. So there's two of them, nitrosomonas and nitrobacter. One of them is responsible for the conversion of ammonium to nitrite or n o two, and then the other one converts the nitrite to nitrate. And that conversion of n o two, which is, know, somewhat toxic to plants, is relatively quick.
Daniel Kaiser:So you don't really ever measure any nitrate in your soil. I mean, it's a it's a relatively quick process. They don't affect the fertilizer, since they're disrupting the bacteria, there's there's several of these that are labeled as as pesticides, and you need a commercial pesticide license, which becomes kind of tricky, which, you know, looking at their custom manure handler, haulers across the state. I know that's one of the challenges for them to use a product like Instinct in with the manure that we know that there's there's some benefit to doing so is the fact that they have to carry commercial pesticide licenses to do so. So, you know, you're again, you're disrupting the bacteria.
Daniel Kaiser:So some of these products, like Instinct initially, some of the product claims is that you could just spray it on the soil itself and get some of the activity. I I wouldn't recommend that because I think it dilutes it down too far. But, you know, theoretically, what you're, again, you're trying to do is you're affecting the the bacteria, not the fertilizer itself.
Brad Carlson:Yeah. It's it's important to, to also make the distinction, Dan, that that requirement for that commercial applicator's license to use, nitrification inhibitors, at least the ones that are licensed as pesticides, is kind of a Minnesota deal. They are they are classified as general use products. However, Minnesota requires a commercial license for any pesticide, whether it's general or restricted. However, a farmer can use those products with or without a license because they are general use products.
Brad Carlson:As far as what might be required in in a different state, I'm not an expert on that. So, check with your own state regarding some of that kind of stuff. The point you make about it, not affecting the fertilizer though, I think is also a very important one. Some people feel like, you know, that that something's happening with the fertilizer when in fact what's happening is is in the soil. Because of, as you said, the concentration of the product in the soil is very important for its performance.
Brad Carlson:It's very important not to simply dilute it or spread it out because all of a sudden, there isn't enough there in order for it to be functioning. You know, one of the things that I say frequently about nitrification inhibitors and people say, well, do they work or do they not work? Well, the the there's some known ingredients, like nitropyran and and DCD and so forth. We know they work. And and I guess I would say they always work in terms of, you know, do they delay the conversion to nitrate?
Brad Carlson:Yes. They do. The question is if your definition of working is, did they improve yields or did they reduce the net amount of nitrate loss? That really gets down to what the environmental conditions were that they were subject to. And so, if it's too warm or they're out there too long, the product worked and then it broke down and in the end, it didn't make any difference.
Brad Carlson:And so that's really kind of the distinction there. So, you know, just simply using these products is not a guarantee that you're going to have some yield increase or you're gonna reduce the amount of nitrate lost to water. They also you also have to be very careful about applying them right and at the right time in order to hit that magic window where they're gonna be effective at both of those objectives.
Daniel Kaiser:So we talk about a lot of these products and, you know, nitropyrin's been around the longest. We've got a lot of data on it. I mean, Nserve has been researched for quite a while with, anhydrous. I mean, there has been some changes in terms of how it's being handled, which we do have some questions in terms of the efficacy, you know, initially with, you know, the answer of being mixed within the tank, versus now where a lot of the the equipment essentially is injecting it in the lines, because one of the the problems with nitropyrin is that it's highly corrosive. So I know that's when one of the complaints, particularly from a lot of the retailers and those, you know, managing or have a lot of tanks is some of the issues that it can cause, with this corrosiveness.
Daniel Kaiser:Instinct, that's been around probably since I started in Minnesota. It's probably been a good share about fifteen years or more. It was initially being tested. I know around the time, you know, kinda around just before 2010 when I started here. The the difference between Instinct and and Nserve is that Instinct is microencapsulated.
Daniel Kaiser:The issue with nitropyrin is that if you apply it on the soil surface, it's highly volatile. So it will volatilize relatively quickly, if it's not protected. So that's why it needs to be injected, especially in the in the case of N Serve. But instinct being encapsulated, what that does is that limits the volatility, and it also somewhat limits the release of the product over time. And I think that's been one of the challenging issues with that particular product.
Daniel Kaiser:Why we've seen some performance issues from at least with urea is that it might not be releasing a high enough concentration to inhibit the, the nitrification process because, you know, like any other ag chemical that you're using, there is an optimal concentration for these things. They just don't work at any concentration that that you apply to the soil. The other products that are out there are are dicyandiumite or DCD. The issue, predominantly with DCD has been the fact that DCD will have some mobility in the soil. Nitropyrin will tend to stay put.
Daniel Kaiser:It won't tend to leach, but DCD can move throughout the profile, which works okay because the rate at which it moves is pretty similar to what urea would move. So with urea, technically, DCD would be better. However, there's there's some issues with it, and a lot of it has to deal with the concentration. It needs to be, I think, at least over one or 1.2% of the total end in eating protection needs to be as DCD for it for it to work. And there are several products out there that, you can buy that they'll mix at the point of sale, you know, AgriTain Plus, and then the products like Nedge, Guardian.
Daniel Kaiser:There's a there's a few others that are DCD products. The issue with those is getting a high enough concentration where it won't turn the urea to soup. And that's kinda one of the challenges with any of these that have to be coated. I mean, Instinct is another one that if you're using Instinct, since nitropyrin is a rate per acre versus a rate per ton. If you're variable rating your urea or your your nitrogen source with, instinct that you may not be getting the same, rate per acre, if you've got it coded at that point.
Daniel Kaiser:There's some things to kinda consider. Generally, a product like SuperU is better, especially with DCD. The SuperU is DCD plus, NBPT, which is a urease inhibitor, which we're not talking about today, but that's blended or they actually mix that in at the point when the urea is hot when they're it's a liquid and they're granulating it. So it works better in those regards because you can get to a higher percentage of, you know, DCD. The, you know, interesting about DCD is it's a nitrogen source itself.
Daniel Kaiser:If you look at the end content, it actually is higher percentage of end than urea. The issue is though it's it's toxic at high concentrations. So the low concentrations you put in the material tend to work as an inhibitor, and they don't have that effect, but it is something that's kind of interesting. The other product that's out there right now is pronitrogen. That's, called Centuro.
Daniel Kaiser:It's a derivative of DCD, and what they've done is tried to eliminate some of the issues with the corrosiveness of nitropyrin, but also eliminate the mobility issues of DCD, and that's kinda where pro nitrodine or Centuro comes into play. And we've had some testing on it. You know, that's been in, you know, last ten, fifteen years. You know, just like anything, it hasn't been a given that we get any benefits from these these inhibitors. You know, if you look at nitropyrin, disandamide, or DCD, or the the pronitrodine or the Sentura, the three that we have, I think, that are decent.
Daniel Kaiser:There's one other one, over in Europe that I know is being used used over there. But the challenge really with any of these is some of the regulations that some of the companies have to go through in terms of getting these things marketed and and registered. I mean, it'd be similar to some of your commercial herbicides, so there isn't always as much money in it. So I, you know, I don't know if we're gonna see a whole lot of development of of new nitrification inhibitors just because of some of those issues. But, I mean, those are the things to watch out for.
Daniel Kaiser:Just if something claims that it's a nitrification inhibitor, just know that, you know, those these three, nitropyrin, DCD, and the pernitrodine are the I'd say the three that we have good data on that show they actually do delay nitrification. There's a lot of other products out there when you look at tests in the lab, you know, looking at delaying nitrification. They don't do anything, even though their their labels claims they should.
Brad Carlson:Yeah. And because of the nature, particularly the nature of nitropyran with as volatile as it is, as corrosive as it is, In general, that product is really only available from your fertilizer dealer. Like, they're going to put it on with a commercial application, a custom application of anhydrous. We don't typically see that product sold directly to farmers. Technically, it could be, but it generally isn't.
Brad Carlson:For the most part, for most farmers, though, your use of these products is going to be kind of bound by whatever your fertilizer dealer has chosen to use. I guess it's worth having a conversation with them about that. But probably your choice is gonna be do I use it or not use it? It's not probably gonna be between products. So let's, let's kinda wrap this up by talking about what's either the front side or or the backside of the nitrogen cycle, and that's mineralization.
Brad Carlson:So our soils are very high in organic matter. And so mineralization is just simply the decomposition of that organic matter and the release of nitrogen in the soil. Immobilization is that reverse process. And so, for instance, if you're plowing down a lot of cornstalks, that's a very high carbon source. It's going to, actually rob nitrogen out of the soil, The the microbes doing the decomposition, of the of the, residue are gonna take that nitrogen away.
Brad Carlson:It's not lost from the system. However, it's also not free in the soil and plant available. So these processes are important. Mineralization is the process by which we are naturally supplying large portions of the nitrogen to our crop beyond the commercial fertilizer. You know, our research has shown that, for the most part, for our corn and soybean rotation, we're able to get about 75% of yield without applying fertilizer.
Brad Carlson:So that is strictly coming from mineralized nitrogen out of soil organic matter. We're we're not really focusing on the data right now, but but if you look at other states, that number drops precipitously, and it has a lot to do with just simply having lower percentage of organic matter, the farther south one goes than the farther east one goes. But, mineralization is a very important process, as it is microbial, in addition to the the rest of the nitrogen cycle. It it also will continue to happen after the growing season. And so we continue to see nitrogen mineralized into the soil post physiological maturity of the crop.
Brad Carlson:Typically, our crops gonna mature right around Labor Day ish. However, the soils aren't gonna cool down to 50 degrees until probably the October or so. And so mineralization keeps on happening, and we end up accumulating a lot of nitrate in the soil after those annual crops are done growing, whether we applied fertilizer or not. We still see mineralization and nitrate accumulation in the soil, from soybeans and from from corn, we applied no nitrogen to. And so that's really important to kinda keep track.
Brad Carlson:Really kind of the, you know, the the magic wand here would be is if we could actually control mineralization and turn it on and turn it off. You know? But but that's, that's some space age technology that's not there yet.
Daniel Kaiser:So this is one of the things too with mineralization that, you know, you look at some of my higher yielding fields. They always tend to be fields that seem to mineralize a lot late in the growing season. So that's always one of the things that I you know, you do tend to get some questions now in terms of late season and applications. And, you know, we know that if you go over time, particularly get beyond tasseling, the uptake of nitrogen tends to slow down, but those are also times when our soil should be wet enough and mineralized enough where likely you're gonna see, much of the demand that the crop needs for nitrogen being met through mineralization. Now the opposite of mineralization is a mobilization, which is the actual tie up of nitrogen by which if, say, you have something like a corn a lot of corn stalks in your field that nitrogen can actually be removed from the soil by the microbes as they're decomposing those corn stalks.
Daniel Kaiser:If you look at, you know, what's important to this is what we call the carbon to nitrogen ratio. This is the, you know, the typical ratio. If you look at organisms and the the ratio of nitrogen to carbon they have in their their tissues is around eight to one. Now we know that all organisms, it comes to this immobilization process, they aren't a % efficient. So, you know, generally, for every one carbon incorporated into their structure, about two of them are are lost through, just processes through the decomposition process.
Daniel Kaiser:So, you know, typically, when we're talking about carbon to nitrogen ratios, which you can measure, I mean, if you're interested in never looking at that, that the magic number is around 24 to one. 20 four parts carbon to one part nitrogen by which it drives whether we go if that number is is smaller, we get a mobilization. If it or if it's smaller, we get mineralization. I should correct myself. Or if it's larger, you know, if it's greater than 24 to one, we'll get a mobilization.
Daniel Kaiser:And that's one of the things that I still get a lot of questions on from growers that there's still people recommending applying UAN solutions to cornstalks to break them down in the fall. And the the thing I would say about that is in Minnesota, we have a thing called winter that tends to stop the process by which this residue will break down. So it is an absolute waste of money to start looking at trying to put nitrogen on to break down corn stocks. Because if you're looking at situations like continuous corn production, that's why we recommend more nitrogen for continuous corn versus corn following soybean because that additional nitrogen is what's needed in that immobilization process. So, you know, spring application is fine.
Daniel Kaiser:And really, the big thing for you, if you're looking at breaking down your corn stalks more is sizing them down. So chopping corn heads or something that's going to make them into much smaller pieces are really the best option. Spraying nitrogen on them. I mean, it's just you you're just gonna add more nitrogen, especially nitrate that's not gonna be utilized. That's gonna be flushed out in the spring when we start getting the majority of our our rainfall events.
Daniel Kaiser:So I just wanna throw that one out there because that one does come up from time to time because we know this immobilization is real, and that's why we account for it with the additional nitrogen in the the corn nitrogen recommendations. So, you know, we also get this question of, you know, how much do we effectively mineralize, based on soil organic matter? We know that for every, per percent organic matter, we have roughly around a thousand pounds of nitrogen, and that's in in the the top six to seven inches. So, I mean, if you look at annually, if you look at, around 1% organic matter, are we we okay. We say annually about one to 3% of the organic and will convert to plant available, and there's really no way for us to track this.
Daniel Kaiser:You know, we give good good years, we probably get close to 3%. We get really dry years, it's probably more closer to 1%. So it it's really hard to model this. You know, if you if you look at kind of what that would mean is for every percent organic matter annually, you'd get about 10 to 30 pounds of n mineralized and available for the crop. So, you know, if you've got about a three and a half percent organic matter soil, that would account to about 35 to a hundred and five pounds of end per acre per year, which is a pretty wide range in value.
Daniel Kaiser:So that's why if you look at that wide range in that value, it's really hard to account for that in your nitrogen guidelines. But we know it happens because we know that if you put no nitrogen on, you're you're still gonna get 65, 70 five percent of your maximum yield. And where does that come from? I mean, part of it's coming from say, majority of it's coming from what's likely being mineralized from your soil. I mean, there's there's certainly some other sources with that.
Daniel Kaiser:So, I mean, you could pencil this out all you want. I mean, really, challenge, though, is when it gets in the field setting, we just really don't know what to make the this calculation. And in effect too, you might have some low lying areas that are saturated with water that may have 6% organic matter, but the denitrification potential and the fact that their waterlog would slow the mineralization process down where you you wouldn't get that same rate of mineralization. So there's some challenges. I mean, while we could we could account for a lot of this, but, you know, effectively doing that to make adjustments to your nitrogen guidelines becomes really, really difficult.
Brad Carlson:And this is one of the fascinating areas of research right now in the whole soil health field is trying to look at this whole organic fraction in the soil and what its triggers are and how it behaves. One of the topics that we've been talking about a lot here lately is the potential soils have to produce yield, particularly when there's no nitrogen that it seems like there's some really close correlation between lower yielding sites with no nitrogen versus ones that end up, as you said, getting up towards 75% with no nitrogen applied that in a lot of cases, we're kind of feeling like potentially these areas that need higher rates of nitrogen beyond what's kind of recommended could possibly be fished out through that. And all that really goes back to the soil's ability to supply nitrogen to the crop. And so while we're really not quite there yet, you mentioned that we don't really have a way of predicting it or even probably even measuring it for that matter, beyond some some fairly, complicated methodology post harvest. It it is important, and it's something that's going to be worked on through research in the in the years or maybe decades to come.
Daniel Kaiser:That's one of the things to think about with this too is, you know, some people would talk with some of the the biologicals and the and some of the like that are out there that we could access more of this this total nitrogen. But the thing you need to remember is that there's a cycle going on, and that cycle is highly dependent on what kind of cultural practices, including tillage that you have and your cropping rotation because there's an input and output to this that tends to affect the cycling. So, you know, just going in and mineralizing more in may not be the best idea because that means you're likely essentially reducing your overall nitrogen or your organic matter pool quicker on a needle basis. I don't even think it's possible at this point. You know, really, what's gonna affect things maybe if you go to no till over time that you increase your pool of organic organic, and you might be able to boost this a little bit.
Daniel Kaiser:But, you know, just going in with a lot of the biologicals right now, and actually, the biologicals that are on the market aren't even looking at anything like this. What they're trying to do is fix the atmospheric n two, not affect this this organic pool. You know, our soils are really productive here. I mean, it's why if you look at from, you know, where we're at to, you know, Southern Iowa and into Illinois, why we likely have a lower nitrogen recommendation is because of the fact that we have a greater pool of potentially available end through our organic matter. So it's a good thing.
Daniel Kaiser:We need to maintain this over time as much as we can, and it isn't just as simply as we can unlock things and, you know, get all of our available in from the soil itself because that's likely going to have some consequences. There needs to be some sort of cycling back into that pool. And if you look at our nitrogen, the fate of the end we apply on an annual basis, we know there's a certain percentage. You know, maybe 30% of what we apply for our end goes essentially into it's effectively mobilized through microbial action, which in effect can be returned through this mineralization process in future years. So it's more of a stabilizing agent for a portion of that nitrogen fertilizer.
Daniel Kaiser:So this again, it's a cycle. And just, you know, one of the things that we don't really know is if you start trying to change your outputs on one end, how that may affect things in the long run. So it, you know, may not necessarily be a good thing to try to get to a point. I don't think we ever will be able to get to a point essentially where we, you know, save, you know, getting, some sort of rhizobium inoculation on corn where we don't have to apply some nitrogen because all these these pools do supply something, but it isn't gonna be enough to apply the the full rate of n.
Brad Carlson:Kind of the last thing here is is also a warning, you know, is kind of the unintended consequence, Dan, that, you know, we've shown that of the nitrate that's lost through tile lines is if you're doing best management, about two thirds of that is probably from mineralized nitrogen when there's not a crop growing out there. And so from that standpoint, if we greatly increase mineralization, we'd probably also increase that fraction. And so it's possible that doing that and reducing commercial fertilizer, if you really boosted mineralization, it probably would also be not necessarily well timed with the crop that's out there. And we could actually increase the amount of nitrate lost to water. So, you know, it's very complicated and it's something that's, I guess, as I said, it's going to be the source of research for the next years to decades as we kind of investigate the nitrogen cycle in this way.
Jack Wilcox:Dan Kaiser, Extension Nutrient Management Specialist, and Brad Carlson, Extension Educator, thank you both for the information.
Daniel Kaiser:Thank you.
Jack Wilcox:Do you have a question about something on your farm? Just send us an email here at nutmgmt@umn.edu. Thanks a lot for listening and we look forward to seeing you next time.
Jack Wilcox:Advancing Nitrogen Smart is proud to be supported by the farm families of Minnesota and their corn check off investment through Minnesota Corn.
