Nutrient management & cover crops: A research update across Minnesota
Hello, and welcome back to University of Minnesota Extension nutrient management podcast. I'm Jack Wilcox at the communications desk here at Extension. Today, we'll talk about nutrient management and cover crops. We have four guests with us today to help us. Can you each please introduce yourselves?
Lindsay Pease:Hi, everybody. I'm Lindsay Pease, and I am an assistant professor and extension specialist in nutrient and water management at the Northwest Research and Outreach Center in Crookston.
Melissa Wilson:Hi, all. I'm Melissa Wilson. I'm the manure professor at the University of Minnesota Saint Paul campus.
Jeff Vetsch:Hi. I'm Jeff Vetsch. I'm a research supervisor at the Southern Research and Outreach Center in Waseca.
Bailey Tangen:Hi. I'm Bailey Tangen. I'm an extension educator focused on water resources and soil health based in Farmington.
Jack Wilcox:Let's start in Crookston, Minnesota with Lindsey Pease and then work our way southward here. Lindsay, can you please explain the cover crop research you have going and what you're seeing there?
Lindsay Pease:So one of the projects we have going on is looking at the effect of a rye cover crop, with strip till sugar beets. That's something that we've we've had, in partnership with Anna Cates for many years, and, we added this nutrient mineralization aspect to it a couple years ago just because we were curious how having that residue cover might be influencing how the nitrogen is cycling in the soil. So, basically, we go out every couple of weeks, and we take nitrogen samples, and we think about, you know, what the potential for for nitrogen to be mineralizing is throughout the growing season. So, yeah, we're a couple weeks into that. What's really exciting for 2025 on this trial is that we're actually gonna do a side by side strip till conventional till with rye cover crop and without rye cover crops.
Lindsay Pease:We're gonna get that side by side comparison that we've been missing up to this point. In addition to that, we've also tried, some interseeding of sugar beets. That one, unfortunately, we were never able to get interseeded cover crops as a sugar beets to really work. Some of that might be because we experienced a lot of drought, but the other piece of that is because about the time where you stop all of the herbicide sprays, in sugar beets that stop the weed suppression is during canopy closure. And it's really hard to get a rye cover crop to grow even if you have the temperature, if you don't have the sunlight to kinda help boost that rye cover crop to grow at the same time.
Lindsay Pease:So that was something we weren't able to quite get to work in the two seasons we tried that, but, you know, post season cover is is still something we're thinking about. And I'd say the third trial that we are doing that involves cover crops is our planting green trials. So this one, we are going from in Crookston, we have a wheat, a wheat crop that once that's harvested, we put down a rye cover crop. And then in the spring, we are planting a living soybean crop directly into the rye cover crop. And with that trial, we're seeing we're actually seeing that, you know, whether you do tillage or not before the cover crop planting, doesn't seem to be affecting the soybean yields at all.
Lindsay Pease:So that's a really positive, outcome of the trial is that the tillage piece doesn't seem to matter. We are seeing some influence of the cover crop on the soybean crop that follows. So that's maybe a less positive note. We're still trying to tease out where the biomass piece comes in that where is the where is that break point where that biomass is overcoming the soybean crop and and hurting it a little bit? But we're still working out those bugs, and we have another season of that trial. We get to go to help answer those questions.
Jack Wilcox:Just out of curiosity, what made you decide to do that particular rotation, wheat, rye, and then soybean?
Lindsay Pease:Really, they came up because of the rotations we see in Northwest Minnesota. Where is the easiest time in a rotation up here? The place that's easiest to integrate a cover crop is after a wheat crop because that spring wheat comes off a little bit earlier than some of our other crops that comes up earlier than the beets or the corn or even soybeans. So it becomes a really natural place where we were seeing growers experiment with these, soil health practices because you actually had time to get that rye cover crop out there and seeded. And so then along with that came a lot of other questions about what rates are you growing, how do I manage my nutrients, you know, all of these really practical questions.
Lindsay Pease:And so that's sort of how this came about was really because we were seeing growers start to experiment with this and we really wanted to dig into these practical questions of what do you seed, and when do you terminate, of course, as well-being a big question. You know? Because we're so cold over the winter, you get hardly any growth. And, and definitely what we're seeing is the tricky part about this trial is about the time that that rye growth starts to take off is about the same time the soybeans are coming up. So that timing question is really, really tricky and can be really hard.
Jack Wilcox:Art imitating life instead of life imitating art.
Lindsay Pease:Exactly. Yeah. Definitely definitely like a a art imitating life kind of a trial.
Jack Wilcox:Next up is Melissa Wilson here in Saint Paul. Melissa, we've been hearing about a lot of cover crop research in the past, and now we're starting to see some of that research coming into regulations around manure management.
Melissa Wilson:Yeah. It's been great to see a lot of the cover crop research that's been going on in the state recently, even in the past decade, really. And we're actually starting to see more and more of that coming into our regulations with manure management specifically. There are new permit rules. This is only for facilities that have a state permit or a national permit.
Melissa Wilson:So the n e d e s, which is a Nash National Pollution Discharge Elimination System. So if you have one of those kinds of permits, these new roles are coming into play, starting even this upcoming fall, I believe. And there's gonna be a couple different options for trying to use best management practices with manure fall application, but one of them is cover crops. And I think what it is because you'll always have to talk to MPCA. I'm not a regulatory person, so I'm just trying to summarize what I've learned.
Melissa Wilson:But it sounds like if you're going to be applying manure anytime in late summer through October 14, they wanna see a cover crop growing. Or for in vulnerable groundwater areas, and MDA and PCA all have their maps determining where these vulnerable areas are. And if you are in a nonvulnerable area, then between October 1 and October 14, you could use a cover crop, you could use some other active growing crop, You could apply, like, liquid manures especially with a nitrogen stabilizer. There's a couple different things. Or the soils could be a certain temperature or below, for consecutive two days.
Melissa Wilson:So there's a couple of different options there, but the use of, cover crops kind of being one of the options, I started getting a lot of questions about how that looks with manure application. Because typically, we wanna get manure applied late in the season because that's when soil temperatures are cooler and then you don't have the biological transformations happening in the soil nearly as rapidly. Whereas cover crops are kind of the opposite. We wanna get those growing as early as possible in the growing season so that they actually get time to grow and get roots in the ground. And typically people are worried about, well, if I'm growing a cover crop, why would I wanna apply manure into it then, which could potentially damage or destroy the cover crop.
Melissa Wilson:So that's where I've been working with Jeff actually with some of some research plots where we've done down in South Central Minnesota as well as West Central Minnesota, looking at manure application into cover crops and what that looks like. So in these cases, we planted cover crops first, got them in usually August, September, sometimes October. We tried a couple different methods for planting, whether it was interseeding into a standing crop or drilling after the crop was harvested. And then, did some manure application usually in earlier fall after harvest, right after harvest when soil temperatures were usually still a little warmer, and also did later fall application as well, which is when our standard temperatures are cooler and that sort of thing. In our case, we use, like, minimal disturbance tiller tillage to get the manure injected underneath the cover crop, and that worked pretty well.
Melissa Wilson:Down in our heavy clay soils where Jeff works, the clay the injection did cause kind of the bigger clumps to come up. It was a little bit wetter, those falls that we got manure applied. So it wasn't quite as minimal disturbance as we would have liked, but it did leave kind of these nice tilled strips where the cover crops were a little disturbed, but then had these nice areas in between that weren't disturbed. So the cover crop coverage actually, ended up still being pretty nice even though we did get a little more disturbance than we liked. So that's one thing I've been talking to farmers who have and manure applicators, commercial manure applicators who have had these questions like, what does this mean with the cover crops?
Melissa Wilson:Does the cover crop have to be planted and growing? Does the cover crop just have to be planted? Do we have to plant it after the manure? Do we have to plant it before the manure? And from what I understand, again, this is something you have to take up with your MPCA staff, But it sounds like as long as you're getting it planted that fall before or after application is fine.
Melissa Wilson:Recommend they're recommending doing it before if you can because we have seen that we can apply manure into a standing cover crop is good. If you're going to be doing a surface application with a cover crop, definitely keeping it a little lighter rather than going with really heavy rates is good just to, make sure that that cover crop is going to be able to grow through it. Although I guess with the permitted facilities, they probably do have to incorporate. So in that case, that might be a good reason to have the cover crop seeding after application.
Jack Wilcox:Does the type of cover crop matter at all?
Melissa Wilson:Yeah. Well, so for the rules, from what I understand, it does not matter what cover crop. We used a couple different cover crops. We did rye. We did, annual rye grass.
Melissa Wilson:We also did mixtures where we had, oats and rye and, mixtures where we had, oats and rye and, like, a turnip added in, and they all seem to work pretty well. Just based on some of my colleagues' work that they've been doing, like, out on Michigan, they found that red clover doesn't seem to like manure application that much. So that one hasn't been working as well. But so far, a lot of the stuff we've tried is seems to work decently well with it.
Jack Wilcox:Where should our listeners go if they have questions about these kinds of details?
Melissa Wilson:So questions about the new permits, definitely talk to your MPCA staff. I'm actually looking at I just went to my favorite web browser and typed in MPCA new permit rules, and they have a nice web, like, news release, and it takes you to an information session. And they actually have the recording posted of their talk about this as well as their presentation. And then you can it also links to the actual new hermit language too. Definitely check that out, and it's a link we can share as well.
Jack Wilcox:Thank you, Melissa. Jeff Vetch in Waseca, Minnesota. Can you describe some of your research there at the Southern Research and Outreach Center?
Jeff Vetsch:So we actually started a study about nine years ago, and that study was initiated to look at cover crop interactions with nitrogen and nitrate losses in tile drainage and the impact of cover crops on nitrate losses. Because throughout all the Midwest, using cover crops is a is a common practice that's part of nitrate reduction strategies in surface waters and groundwaters. So we wanted to see what was the potential in, Southern Minnesota for for cover crops to reduce nitrogen losses in tile drainage water. So this first study started in, 2017, it ran through 2020. And it was a bit disappointing because really only in one of the four site years did we get good establishment of cover crops.
Jeff Vetsch:And that year, it did have a nice reduction in nitrate concentration in tile drainage water. And that cover crop was, as most would expect, cereal rye that was seeded in the late summer. And this was, simulated aerial seeding where we seeded it into a standing crop right before senescence and tried to get it established in the late fall and then terminated it about two weeks before planting corn again or planting the next crop in the spring. So that was our initial study. So when we had less than ideal success with that, we decided that we wanted to answer the question is, what can we do?
Jeff Vetsch:Similar to what Lindsay mentioned, let's find let's find situations where our cover crops are more likely to thrive, and that's after these shorter season crops. And that could be field peas or peas that are harvested for canning. It could be sweet corn. And what we chose to do is look at corn silage. And corn silage has, in Minnesota, about the eight and a half million acres of corn that's planted.
Jeff Vetsch:About 350,000 are typically harvested for silage. So it's not a huge amount, but it is enough that it's justified to take the look at this. And it's a good situation where you can establish, cover crop after that. And as Melissa said, a lot of times, these fields are gonna get manure too. So that's kinda phase three.
Jeff Vetsch:But so what we do is we establish our cover crops after corn silage harvest. And the corn silage harvest in Southern Minnesota usually occurs around September 10, and that we try to get the cover crops seeded immediately. We use two species of cover crops. One is cereal rye, which is not terminated until right before planting the next year, and the other is a blend of of annuals that terminate with cold temperatures. And we use oats, forage peas, and tillage radish.
Jeff Vetsch:And they all are good ones to establish in the fall after cover or after silage harvest. They the oats grows very fast. The tillage radish and the peas also provide a different species. But usually when you get to about December, you get good cold temperatures and they will die, and you don't have to worry about terminating them in the spring. But clearly, they don't have the impact on water quality that is what we expected, and that's what we found.
Jeff Vetsch:So after that establishment, we do strip tillage, and then we come out in the spring, and we harvest the cover crops for biomass, and we look at the carbon to nitrogen ratio. And we're not getting a tremendous amount of biomass, you know, 300 pounds. Actually, in the spring of twenty twenty four, we had almost 700 pounds of dry matter in our cereal rye. So that was our biggest biomass. But we're looking for just enough to get that to be a good scavenger for that nitrate and keep it out of the tile lines.
Jeff Vetsch:So in the fall of twenty one, the first year of the study, we had good establishment of both the cereal rye and the annual blend, and we terminated the the cereal rye in the spring of twenty twenty two with planted corn. The fall of twenty two was extraordinarily dry, and we had very poor establishment, not only germination getting it germinated, but it just didn't grow. We kinda learned from that in the fall of twenty three. It was also very dry, but we waited to seed until we got about a half inch of rain. And then we seeded right after a day or two after that rain, and that helped our establishment considerably.
Jeff Vetsch:Now it delayed the seeding a little bit, which isn't ideal, but helping get good establishment is critical. So as I mentioned, we had decent cover crop growth in the fall of twenty three. The blend actually grew better than the cereal rye, but we did have about almost 700 pounds of cereal rye, biomass dry matter in the spring of twenty four. So when we looked at silage yields, what we find is that we have two nitrogen rates, and our hypothesis is that there's this interaction between nitrogen rate and cropping system. And then we also wanna look at how does the cover crop help mitigate the nitrogen loss potential of this corn silage system.
Jeff Vetsch:So what we're doing is something unique that I have never found in the in the literature. We actually have some corn grain plots that are planted corn at the same time as the silage, but we're harvesting them for grain. And we don't have a cover crop in those, but then we have silage plots with no cover crop, silage plots with the cereal rye that's terminated in the spring, and silage plots that are terminated or we plant to the the annual blend and they terminate in the winter with cold temperatures at two different end rates. So the core is like eight treatments. It's a factorial between two end rates and those four cropping systems with and without cover crops.
Jeff Vetsch:The key conclusions that I've seen so far, and this is after three years of this study, 2022 through 2024, is we've had good cover crop growth in the fall of twenty twenty one and 2023, poor cover crop growth in the other year. The 80 pound treatment has typically optimized corn silage yields, but our corn rain system needs more n, probably two twenty or maybe even in some years more than that. Our nitrate concentrations in tile drainage water, I have the first year 2022, we reduced 37% by the cereal rye cover crop and by 21% with the annual blend. In the second year where we had poor cover crop establishment, we did not see any effects of the cover crops on nitrate concentrations in the tile drainage water, which is understandable. If you can't get the cover crops to establish and grow, they're not gonna scavenge any nitrogen.
Jeff Vetsch:They're not gonna mitigate those losses. In the last year, 2024, we had a 31% reduction with cereal rye in the silage system compared to the no cover crop silage system that was in that year. When we look at in the silage system alone, our nitrate concentrations averaged about 18% greater where we had the 220 pound nitrogen rate versus the 80. And that's been shown in a lot of other studies. Typically, when you increase nitrogen rate, you're gonna increase nitrogen losses in tile drainage.
Jeff Vetsch:It's pretty much a given. And the other thing that was very obvious was 2022 and 2023 growing seasons where we had rain in the spring, we had tile flow in the spring, and then the summers and early falls were very dry. And 2023 was actually a pretty severe drought year. Twenty twenty four was just the opposite. It was extraordinarily wet in the spring.
Jeff Vetsch:It stayed wet all through July. And then in aug August, we had more rainfall, but then the very late fall was dry. But we had almost 20 inches of tile drainage in the 2024 crop year, and our nitrate concentrations in tile drainage water in that year were almost two to three times as much as the previous two years when it was relatively dry. And that did not surprise me, but one of the things that did surprise us or at least is interesting to talk about is in this system, we apply a small amount of nitrogen fertilizer at planting as a starter, and then we side dress the rest. But where we saw this rapid increase in nitrate concentrations was in May of twenty twenty four.
Jeff Vetsch:Our side dress application or the majority of our nitrogen wasn't applied until June. So all that n that we saw that spiked out of that tile system in May and late April primarily came from n that was still in the soil profile from the previous cropping years or it was mineralized in that spring of that growing season. The last thing that I would say is our nitrate concentrations and our losses have been less with corn grain than with corn the corn silage cropping system in the last two years. That was not the case in the first year, but that was kind of our hypothesis. And that makes sense because one is we don't think we need as much n with the corn silage system as corn grain, and we our data is showing that.
Jeff Vetsch:And it also goes back to when you harvest silage, you're taking away a lot of carbon. You're leaving the soil bare. You're taking away a lot of potential immobilization of of nitrogen because of all that carbon, especially in the corn stover residue. And you're also leaving this fallow period in September and early October where you can mineralize a fair amount of nitrogen, and that fallow period then can feed that potential nitrogen for loss the next year. So this has been a really interesting study.
Jeff Vetsch:It's gonna continue for one more year. And then we'll probably, give it a a break and then probably take some similar treatments and put manure on in the fall and see how that goes. And I Melissa and I are gonna work on that together. So that's what I've seen so far in our studies.
Melissa Wilson:I have a question, Jeff. Are the years that you had the most losses and I don't know. Are you looking at just concentrations in the tile water, or are you looking at load too? Yeah. We're looking at concentration times water.
Melissa Wilson:Okay. So, like, would you say the years that the cover crops grew the best are the years when you had the most losses in the non covered crop plots? Like, is there a correlation between when cover crops do well and when you see the most leaching? Like because I would think that wet conditions, it will help with establishment. If it's nice and warm, that helps with mineralization, but it also helps the cover crop grow. Do you see what I'm getting at?
Jeff Vetsch:Yeah. So I think that there's two factors that that are influenced there. One is, as you mentioned, the fall establishment is critical. So having just the perf climactic conditions after you seed, Seeding in some moist soil, getting some rainfall, and then obviously with, no matter when you're seeding it, the sooner you seed it, the more likely you are to have good fall growth.
Jeff Vetsch:We did not have great fall growth in the fall of twenty twenty three, but we did get good establishment. But we had excellent growth in the spring of twenty twenty four of the cereal rye. And I think that was just because we had a very mild winter. We had a fairly mild early spring, and we had decent, you know, plentiful, but not excessive rainfall up until this May period when we started getting May, June, July, and early July was so excessive rainfall. So, yeah, I think it I don't think that cover crop growth is necessarily related to excessive losses, but clearly, the more rainfall you have, the more nitrate drain or more drainage in the tiles you're gonna have and the more loss you're gonna have.
Jeff Vetsch:I think what peaked or increased our concentrations in the spring of twenty twenty four was the fact that the previous two years were relatively droughty, and we probably had some carryover n that was in the profile in the fall from the previous corn crop that was then lost in the next growing season, which happened to be an extraordinarily wet year. So it was the majority of it was flushed out.
Melissa Wilson:I can't remember. Did you say the cover crops did help reduce nitrate losses in that really wet spring?
Jeff Vetsch:It did. Not as well as in the 2022 year, but it did by about 20%. It was over about 30% less in the other year.
Jack Wilcox:Bailey Tangen, you were involved with some important cover crop projects and events. Talk to us about those, please.
Bailey Tangen:Yeah. So the Great Lakes cover crop project, we're working with a lot of farmers across Minnesota, Wisconsin, Michigan, Illinois, and Indiana and Ohio. We really wanna figure out what cover crops are working in different conditions. And if you're growing overwintering cover crops this season, we want you to be part of this exciting project. So it's pretty easy.
Bailey Tangen:Just fill out a quick survey this winter. Get signed up at z.umn.edu/greatlakes cover crop project. We'll have you take a couple photos and some height measurements in the spring right before termination. And in return, we'll give you a custom report with biomass and nutrient estimates and $50 per field, so up to three fields. And it's a chance to make a real difference and get some cash while you're at it.
Bailey Tangen:If you wanna sign up for the Great Lakes cover crop project, you can visit z.umn.edu/glccp.
Jack Wilcox:Bailey, how are we doing with cover crops at a state level here in Minnesota?
Bailey Tangen:We wanted to learn more about changing agricultural practices in Minnesota. So we looked at remote sensing data, the USDA agricultural census data, and state reported cost share, and we compared data that we saw from 2017 to 2022. And we saw some really interesting trends across Minnesota. Overall, we saw that farmers are reducing tillage and increasing soil cover. We saw more residue cover on the field, nearly doubling from 36% in 2016 to 64% in 2020.
Bailey Tangen:We saw that more farmers are no till, and no till practices increased by 16.7%, and more farmers are using cover crops. Cover crops, increased by 24% since 2017. But I think it's really important to put these numbers in perspective. You know, only 5% of Minnesota cropland uses no till, and cover crops are only used on about 2.28% of acres, and fewer than half of the planted cover crops successfully emerge in the fall. So the takeaway is that farmers are adopting soil health practices.
Bailey Tangen:We're seeing a rise in these, but we still need you to work on really scaling these up across the state.
Jack Wilcox:Thank you. Lindsay Pease in Crookston, Melissa Wilson and Bailey Tangen here in Saint Paul, and Jeff Vetch in Waseca, Minnesota. We appreciate you being here.
Jeff Vetsch:Thank you.
Melissa Wilson:Thanks for having us.
Bailey Tangen: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:We'd like to thank the Agricultural Fertilizer Research and Education Council, or AFREC, for supporting the podcast.
