Nutrient management and sidedress considerations and small grains updates
Hello, good morning, and welcome everyone to today's Strategic Farming Field Notes program from University of Minnesota Extension. We have to thank our sponsors because these sessions are brought to you by University of Minnesota Extension with generous support from Minnesota farm families through the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. We're happy you've joined us for today's session focusing on nutrient management and small grains updates. And my name is Claire Lecan. I'm with our crops team at University of Minnesota Extension in sort of the East Central part of the state, and we welcome Jochum Wiersma, our small grains specialist with Extension, and Fabian Fernandez, our Extension nutrient management specialist, and thank them for joining us here today.
Claire LaCanne:So with that, I'll turn it over to Fabian to share his thoughts and nutrient management updates.
Fabian Fernandez:Yeah, so it's been kind of an interesting growing season, and we always say that of every growing season, I think. So when we talk about nitrogen management, I think it's good to kind of review a few things before we go into more of the management things. You know, we started this season with pretty much unsaturated soils. There was not a lot of snow cover or frost this last winter, and it was generally dry. And so with that unsaturated soil, what we have is quite a bit of a storage capacity for rain.
Fabian Fernandez:So the water will basically not drain out of the field. The soil is able to capture a lot of that water. And then the other part too, is that when you have unsaturated soils, air tends to warm up faster than water. And so the soils were a little bit warmer than usual starting this spring. I thought we were going to have a fairly early spring, and we did to a certain degree, but then we did get some rain that kind of slowed down planting at times.
Fabian Fernandez:You know, we always talk about water with nitrogen because they go hand in hand. And so these unsaturated soils allow us to basically capture water without very little drainage, and also very little nitrate leaching. And there was really not much of funding in the soil, where we are concerned about the other loss mechanism, would be denitrification. There was not much of either of those, you know, nitrate leaching or denitrification this year. So that means that if we apply nitrogen early in the season, it's likely most or all of it will be in the soil.
Fabian Fernandez:While the soils did warm up a little bit earlier than usual, they were not so warm as you say, well, we have a lot of mineralization going. We, if you remember this spring, we kind of went from, you know, a late winter to two days of spring and then full summer, and then it cooled down again. And for mineralization to take place, this is all done by bacteria in the soil, you need to have more kind of constant temperatures, or with warming trends. And so these ups and down, you know, they kind of get things moving, but then slows down again, kind of similar to what you see with a crop, you know, if you have heat, the crop starts growing, if it's cool and it starts, it's kind of stops. And so I don't think we have gotten to like full mineralization.
Fabian Fernandez:It's not full throttle yet. It will be, I suspect, because the days are long now. And as soon as we get some, some heat, we will start to mineralize pretty quickly, which will add nitrogen to what we already have in the soil. So I think we are sitting in a pretty good spot right now in terms of nitrogen availability for the crop. Of course, the question now in mind is side dressing nitrogen, and as soon as we warm up, because the days are so long already, the crop is going to take off.
Fabian Fernandez:It's going to start growing really quickly. And so this is where side dressing is important. The crop starts to take up quite a bit of nitrogen, you know, around V six is when the crop really starts to pick up the amount of nitrogen that will take quickly. And so applying nitrogen, if you need to apply nitrogen as a site rise application, because you haven't applied your full rate, or you haven't applied any nitrogen, it will be important to do it sooner rather than later, so that is there for the crop to take advantage of it. The, the other thing too, and especially as we look at, you know, especially the last few growing seasons that are a good example of what we are kind of seeing more and more, and what has been also forecast by climate models, where we will have wetter springs and then followed by dry summers.
Fabian Fernandez:And we kind of saw that in the last several years pretty strikingly. And so that's the other reason to apply side raised nitrogen somewhat early in the season is because if you apply nitrogen when the soils are dry, that nitrogen doesn't have water to get it into the root zone for the plants to use it. And so that can be a little bit of a problem. I always say that try to apply nitrogen before, between like the V4 to the V eight development stage is kind of a sweet spot, because that's before the crop really needs to take up a lot of nitrogen. And it also is kind of a time where the potential for nitrogen loss, it starts to diminish rather quickly.
Fabian Fernandez:And so we'll have nitrogen available for that crop. You know, one of the early conditions this spring, I guess some concerns I heard from folks was the dry spill that we have for a while, where folks apply like UAN left on the surface, and there were concerns about, you know, losses through volatilization. And certainly there could be some conditions where there was a little bit of nitrogen loss through volatilization of the urea portion of UAN. And that's an important thing to keep in mind is that UAN, you know, is 50% urea. So you were only really concerned about that 50% of the total that could potentially start to volatilize.
Fabian Fernandez:And there were a few days where it was dry and a little windy and you could have lost some of that. But again, I don't think it was like a huge concern, something that I would look at replenishing nitrogen because of that, it will probably be pretty minimum. Another thing that folks have asked is in terms of cover crops. If you have cover crops and you want to, you're planting corn now, when to apply nitrogen? And so in some of these situations, because we did have fairly nice conditions for cool season crops to grow in the spring.
Fabian Fernandez:Some of those kind of got big this year, some of those cover crops, and so the potential for immobilization, basically the microbes as they start breaking down the residue, take nitrogen from the soil, and then not available for the crop for a period of time. With that immobilization potential, then applying nitrogen sometime around this time would be ideal. The same thing, by the way, is true if you have like continuous corn where you have a lot of corn residue that has a high carbon to nitrogen ratio, you can get quite a bit of immobilization. And those are the situations where applying some nitrogen early in the season is important. We've done some research looking at, you know, applying something like 40 to 80 pounds of nitrogen.
Fabian Fernandez:And we noticed that there was no difference between the two rates. So even with a small amount of nitrogen, it's sufficient to get the crop going. There's not a lot of need for nitrogen by the crop early in the season. And you know, 40 pounds will do the trick, just to, to keep that crop going until you do the full side dress application a little bit later. Those are kind of the main things, you know, as we, as you look now at applying nitrogen, for side dress, the important thing is the timing.
Fabian Fernandez:I think again, V4 to V eight is kind of the ideal time to do that. If you're knifing in ammonia, anhydrous ammonia, it's also important to, to do it earlier because the roots start to grow into the middle of the rows. And so the more that you wait, the more that you will be damaging those roots as you go through with a, with a knife. And so applying that way early on is good. And in terms of when you, what you apply, you know, anhydrous ammonia is a wonderful source of nitrogen.
Fabian Fernandez:It stays in the ammonium form longer than any of the others. The other options of course are urea and UAN. If you do UAN, you know dribbling it on the surface or knifing it in or injecting it in the soil is good. It's a good practice. For urea, of course, you will have to leave it on the soil surface.
Fabian Fernandez:And that's one where if you're leaving urea on the surface, you have potential for volatilization losses. And so I would strongly suggest using a urease inhibitor just to protect nitrogen from volatilization until this rain to move it in. One thing you can do, of course, is look at the forecast. If you see that there was a very good chance of, you know, rain a quarter inch or more, you can apply without that and then get it incorporated with rain, you know, if you get about quarter inch or a half inch of rain, that's sufficient to move that application into the soil, so that you will not have volatilization issues. And then some folks have also asked about using other inhibitors, like a nitrification inhibitor for site dress application, and the reality is that plants use ammonium and nitrate.
Fabian Fernandez:So whether it's ammonium or nitrate, the plant is going to use it. So, a urease inhibitor, nutrification inhibitor, the only thing that it will do for you is keep nitrogen in the ammonium form longer, And so there is really not much of a basis to do that. You will be paying money for a technology, for a resource that is not going to make much of a difference at this time, because, again, the only reason we want to use a nitrification inhibitor is to protect nitrogen from transforming to nitrate that can potentially leach out or denitrify. But again, at this time in the season, unless we get radically wet conditions for a long time, the chance of nitrogen loss is pretty low at this point. And so you're not going to have a return on that investment if you use a nitrification inhibitor at this point.
Fabian Fernandez:So those are kind of the major things, I think, that we need to be thinking about right now as we look at side dressing.
Claire LaCanne:Yeah, I have a question that came in regarding side dressing anhydrous. How early do corn roots reach the middle of the space between rows when grown in 30 intros and also in 22 intros.
Fabian Fernandez:Yeah, so, you know, around V4 to V six, that's about the time where those roots start to connect, you know, reach their neighbors. And so, you know, a little earlier for the narrower roads, but yeah, around V4, V six. So it kind of is the, again, the perfect timing for side dress is really right now. I think a lot of crop as I've seen, it's kind of between, you know, before, and like I say, it's going to start growing pretty quickly here as soon as we get a little bit of heat.
Claire LaCanne:Thank you. Yeah, a few questions came in before our session here, just kind of on, like, sulfur, whether it is or when it is worth side dressing sulfur, and also, like, micronutrients. What are the critical values or, like, criteria for considering applying micronutrients?
Fabian Fernandez:Yeah, yeah. So, you know, sulfur first, if you need sulfur, any drive sources is fine, you know, ammonium sulfate is a really good source. It also has some nitrogen in it. So that's really good. It's a, you just need to make sure that you are applying something in the sulfate form, you know, don't apply elemental sulfur for instance, but anything that is in sulfate form should be fine.
Fabian Fernandez:ATS dribble on the soil surface also works well. Again, I would do it now rather than waiting much longer to do those applications. But again, kind of look at whether you need that, know, people apply every nutrient known to men, just in case, well, see if you really need it. If you don't really have issues with that, there is no point to applying those things. Same, same thing for micronutrients.
Fabian Fernandez:In fact, you know, when we talk about micronutrients, the main thing that we are interested in, or that we've seen response for is zinc, in corn is zinc, you know. And so the soil test is pretty reliable for that. The, so if you suspect that there is a zinc deficiency in your field, taking a soil sample, looking at where those concentrations are and then applying zinc. And zinc again, it could be just an elemental form like zinc sulfate, something like that, it's fine. Or you can also use chelated zinc that kind of keeps that element in plant available form longer.
Fabian Fernandez:But again, it's not every situation, every time. It's just like, you know that there are issues there, you can take plant samples as well to kind of have a second witness, guess, to whether you need that or not. The other one I would mention, sorry, the other one I would mention is boron, but it's very rare that that's a deficiency. Normally we see that more on like sandy soils with very low organic matter content, less than 1% organic matter content. And so if you, if you know that boron is a potential issue, that's where I would kind of keep my eye, but it's, it's pretty specific.
Fabian Fernandez:You know, there are no it's not a widespread condition where people should be doing these things everywhere.
Claire LaCanne:Yeah, good points. Thanks, Fabienne. I would like to do one last question here for you before we hand it over to Jokim. One came in in the Q and A here back to nitrogen, and it's, what is the latest to do side dress by fertigation? And in sandy soils, is there an advantage to small amounts of nitrogen around tasseling?
Fabian Fernandez:Yeah, so most of what I say is for dry land agriculture. For irrigated conditions, the best thing you can do is side rest applications and maybe doing multiple side rest applications. In my studies, I normally divide the application, the total nitrogen application in about three times, you know, I apply a small amount around V2, just to get the crop going, and then around V six to V eight, I apply a good amount of nitrogen, and then the rest I apply around V 10 to V 12. And so, the important thing with side, like corn doesn't care how long that nitrogen has been in the system. What it cares about is that there is nitrogen present.
Fabian Fernandez:And so, people kind of have this idea that if you apply just a little bit of nitrogen later in the season, it will help corn. Well, the reality is that the only reason we say address is to hedge against the potential for nitrogen loss. If you apply nitrogen, if you have the full amount of nitrogen there, and it's not going anywhere at this, you know, once the plant is past V eight or so, it's taking up so much nitrogen and water that is not going to move. We've done a lot of studies looking at nitrogen movement, it's in the soil, the plant will use it. And so, long as you apply the total amount of nitrogen needed by the crop, it doesn't really matter when you apply it.
Fabian Fernandez:So, I would not necessarily delay application. I mean, fertigation, you do have the option of applying with water, so it will move into the root zone. That's, that's a good thing. But you know, much past V12, I don't see really a benefit of being much longer than that, because you also don't want to limit the crop and setting the yield potential of that crop lower because of delaying applications.
Claire LaCanne:Thank you. Yeah, we do have one more question that came in for you, Fabienne, but I'm gonna ask that maybe you look at the Q and A and answer it in there or in the chat. It's about whether alfalfa needs boron. So if you could, answer that on the side here while we hand it over to Jokim, just to keep us on track for time.
Fabian Fernandez:For sure. Thanks for Thank you.
Claire LaCanne:That's your cue, Jochum.
Jochum Wiersma:That's my cue. Well, I better have some coffee. Well, my questions were all about what's gonna happen next. And is there gonna be diseases? Is there gonna be insects?
Jochum Wiersma:And so I'm gonna I'm not very good at predicting the future because if I was really good at it, you wouldn't be looking at me in my office. I'd be on a beach with an umbrella drink right now having breakfast in this you know, with my toes in the sand because I would make smarter investments a long time ago. So in small in the world of small grains, and it's not the only one, sugar beets, etcetera, we have very robust weather based models that help us understand the risk for disease development. In North Dakota, those have been available almost for twenty years. And in the valley, the Minnesota site, they've been available for just about as long because of American crystal sugar.
Jochum Wiersma:Thankfully, MDA has now stepped up and is expanding the North Dakota Agricultural Weather Network into Minnesota. It's called the moon, Amman, whatever it is. But I'm over the moon because of it, because they're very robust models. I'll go to, for instance, Becker, and we say the winter wheat is flowering. The address is here on top, agndsu.edu//cropdisease.
Jochum Wiersma:But if you just do n d s u small grains diseases, this page will pop up. And we say we're reaching flowering, you'll get a table, for the risk for fusarium head blight for the last ten days. And depending on the variety's rating from very susceptible to moderately resistant, it will calculate a likelihood that you would have an economic loss. If you scroll a little bit down, you'll see three diseases listed there, tan spots, septoria leaf blots, and leaf rust, where rather than reporting a high risk for economic loss, a moderate risk of economic loss and a low risk, we only report whether or not we have a day that was favorable for infection or not favorable for infection. And basically, and this is where the crux comes in, if you go to weather, the things that matter is basically the range of the temperature and how long there was free water on the plant, what we call leaf wetness duration period or wet period, number of hours where there was free water on the plant.
Jochum Wiersma:That measurement there determines all of what you see above it. And so this is your guideline for determining how risky it is for disease development. Why the difference between fusarium head blight and those other three diseases? Well, the difference is in the case of fusarium head blight, it is what we call a monocyclical disease. It goes through one life cycle basically to infect the crop.
Jochum Wiersma:And so we need to basically assume there's gonna be spores around, and there always are because Fusarium graminearum, the fungus that causes Fusarium head blight, has a very wide host range, including corn. And so we pretty much assume there's always gonna be Fusarium spores floating around in the air. And so then after that, you start looking at how many days consecutively you are, depending on your varieties rating for the disease, you're at moderate risk and high risk. By the time you accumulate probably five, six days prior to heading and you're in that moderate to high risk, you are gonna probably spray a fungicide. It is that simple.
Jochum Wiersma:Now why don't we do that with tan spots, septoria leaf blots, and leaf rust? Well, those are what we call multi cyclical diseases. They go through several generations in a season, and they need to be present in your field to be able to go through those generations, which allows you to actually scout. In the case of tan spot, the way the spores disperse, they don't fly very far. The same for Septoria, those are generally have to be in field, the spores for really for the disease to get going.
Jochum Wiersma:The case of leaf rust, the spores have to blow in all the way from basically Nebraska and South Dakota for us to come get the disease here. In each of these three cases, we could trap the spores, but it really doesn't tell you much. If I catch them here in Crookston, it doesn't say anything for a field and fisher, or Becker for that matter. And so we cannot use the same approach as above for fusarium head blight where we have to actually look at the field and see if we find the disease. In the case of TANSPOT, again, by the time you get to six to eight days of consecutive yeses, it's time you start looking for the disease.
Jochum Wiersma:In the case of tan spot, you would really have to be weed on wheat for a disease to really get a chance. So historically, tan spot was kind of the canary in the coal mine because we have used fungicides extensively at, early season, basically very cheap tank mix, we see less and less tan spot across the landscape. Septoria tends to come in, and leaf rust right now hasn't made it past Nebraska as has stripe rust, and so I do not expect to see any leaf rust or stripe rust in the crops right now. The incidents across Kansas and Nebraska has been very, very low for both stripe rust and leaf rust. And so right now, if I have to make a prediction since you asked me, I think we're relatively safe for stripe and leaf rust this year.
Jochum Wiersma:Hand spot giving where the temperatures have gone and the precip have gone, I think we're gonna stay for a for a while in this on off scenario in Southern Min. If you go to the North, there's gonna be a lot more nose because we're relatively dry. And that's where we probably have some weed on wheat. I doubt there's any weed on wheat South Of I-ninety 4. So there too, not a lot of risk.
Jochum Wiersma:As far as insects, aphids like leaf rust have to come from the South. We've had very little word of problems with aphids in the Central Plains. So there are two for now, the risk is low. Army worm, Anthony is on. I don't know if people have started trapping army worms.
Jochum Wiersma:I have not heard of any. Normally, by now, armyworms oftentimes have will have made it all the way up to Rose Oak County in the grass seed industry, and I have not heard of any. So that's about it. It's relatively quiet right now. Enough predictions for now?
Claire LaCanne:Yes. Thanks for the predictions, Jokim. And I think kind of what I'm hearing you say, this is a really good tool, and then of course, scouting for assessing risk in your own fields, right, because sometimes we get asked, like, should I just throw a fungicide in when I do my herbicide passes, right, and hearing you say that, no, you really need to figure out if there's risk of disease or disease present to make a fungicide application pay off.
Jochum Wiersma:You know, it's very tempting because a half a labeled rate of a generic tilt, propiconazole, is literally cheaper than the bottled water you get at QuickTrip. But there is a flip side to that equation, and that is we do have in greater risk that we're gonna eventually select for resistant of fungal populations for tan spot, for instance, that are resistant to that active ingredient. We are not anywhere close to that scenario compared to where they are across Europe, where tank mixing different AIs is pretty much mandatory to overcome problems with resistance in two specific fungicides. We haven't noticed it. There's both for tan spot as well as fusarium head blight.
Jochum Wiersma:There is monitoring in The US for for that event. And so far, even though we find genetic differences for sensitivity to fungicides, none of them of the populations and the genotypes we've or races, whatever you wanna call them, can be labeled as truly insensitive to the fungicides at the labeled rates.
Claire LaCanne:Yeah, thank you. Thanks for that information. We're here at the end, so I'll just quick share that, Angie Peltier, who's in Northern Minnesota, said that armyworms have made it to Roseau, not in the Yay. Yeah. Not in the numbers as in past years, so also yay for that, not not your flight I
Jochum Wiersma:like it when the world makes sense. Army worms should show up in Rose Oak County because they they they really their flight patterns are along the beach ridge. Army worms like to fly over wooded areas for some reason, And so that's always a telltale sign if they've made it to Roseau County. And it should be the May, first week of June.
Claire LaCanne:Oh, right on track too. There we go. Yep, Bobby, and did you want to share at all about boron and alfalfa? And then we'll wrap up here.
Fabian Fernandez:Yeah, I put something in the chat there. There's a huge wonderful resource there from the University of Minnesota talking about boron for all crops in Minnesota, including alfalfa. And certainly alfalfa is one of the ones that is most susceptible to boron deficiency, and this is typically in sandy soils where you will see more of that. The tricky thing with boron is the range of sufficiency, insufficiency and toxicity are very narrow, so you don't want to go overboard with the application, because you can actually cook your plants if you apply too much boron, but the resources there, there's a lot of great information, and so I would encourage people to go there.
Claire LaCanne:Yep, well, thanks to Joakim and Fabienne, our residents Stetson and Waldorf here today for your thoughts. And I just wanna thank everyone for attending this University of Minnesota Extension Field Notes Program. We wanna thank our sponsors again, the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. And reminder that we'll be back here again next week, same time, same place to talk about weed management with Debalin Sarangi and Ryan Miller. So thank you and take care.
