Cover Crops and Nutrient Interactions
Alright. Well, good morning, everyone, and welcome to today's strategic farming field notes session. And before I introduce our featured guest today, I just wanna remind you of some quick webinar tips again for these sessions. Again, we're more conversational, more of a discussion type format. If you have any questions that pop up during the session, please just do put those in the q and a box.
Speaker 1:We like to reserve the chat for any technical issues. So again, if you have any questions, put those in the q and a box. If you're not sure how to get to that, just hover your mouse at the bottom of your screen and you should get a menu bar that pops up and you should have those options show up. And do, when you get off today too, we do have just a really short survey. We always ask for your feedback on that.
Speaker 1:It should take you less than a minute to do that. We appreciate your feedback on that. These sessions are being recorded, and we'll have this posted shortly, hopefully, by the end of the week or for sure by early next week too if there's anything you missed or other people that wanna listen to this as well. So, again, welcome to today's strategic farming field notes program. We do thank extension, of course, for sponsoring this and also the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council.
Speaker 1:And before I do introduce our guests, I do wanna say one quick thing too. I know on a lot of people's minds will be all the rain that some areas of our state has received. We've got crops underwater in spots too, and it looks like it's gonna take quite a bit of time in some of these fields. We will have that be the focus of our session next week, so tune in then. Again, it's gonna be so wet in some of these areas.
Speaker 1:There's not a lot you can do till things dry out too. So we'll put some resources in the chat here to help cover that. But with that, we have doctor Axel Garcia Garcia. He's our cropping system specialist at the University of Minnesota out of the Southwest Research and Outreach Center in Lamberton on today. And then Jeff Etch, he's a researcher with the University of Minnesota at the Southern Research and Outreach Center in Waseca.
Speaker 1:Both of them were at the Waseca Field Day yesterday, highlighting a lot of the cool research that they're working with. And so with that, I'm gonna turn it over to you first, Axel, if you wanna talk a little bit about some of the cover crop research you've been doing and and things you're seeing and so forth.
Speaker 2:Thank you, Liz. Good morning, everybody. As Liz said, my name is Axel Garcia Garcia. I want to talk with you about cover crops and practical decisions that our farmers face with managing this having this practice, things like seeding rates and termination, timing, water use, and those kind of things. And, of course, a little bit about weather conditions here in the Southwest part of of the state, specifically at the Southwest Research and Outreach Center near Lumberton.
Speaker 2:Well, first, when it comes to cover crop practice, this is not something that fits all size, you know, choices. You know, it cover crops mostly for our state depends a lot on on local conditions. That means weather and soil and management goals, and that's exactly what we are trying to find or to look at in our research. As Liz said, we were talking about our preliminary results of a two years project yesterday at the agronomy tour organized by in in Waseca. And I'm I'm gonna try to highlight some of those results today.
Speaker 2:And, yes, this year, weather has been really kind of weird if we wish to say. And we are, like, putting the test, you know, the test. You know? We started off a little bit warm early in the season, in the growing season, and a little bit dry too for conditions here, and then we turned cool and a little bit wet. And now we are heading to a hot and hopefully not too dry conditions again.
Speaker 2:It's been a season where timing and flexibility really matters. Well, overall, the current conditions tell us a lot of things. You know, this season, as I said, started a little bit warmer than average, and temperatures in April, basically, which allowed us for early, you know, field access and planting. I know some farmers in our region planted pretty early. But what happened after that is that we got cooler and a little bit wet.
Speaker 2:So the the point here is that at the end, crops started to grow and develop a little bit slowly. That's not the case for small grains. Small small grains, I've seen that they've been doing pretty well, actually. And that also applies for cover crops like cereal rye. Our cereal rye did well.
Speaker 2:Just a little bit of caution when we were about to terminate some of our our trials here in Lamberton because we had to terminate them a little bit earlier than what what we were expecting to avoid, you know, getting to what conditions or not just not to do what we had to do. Some key observations about our research. First, we have a trial across multiple locations in Minestora, and then we are learning several things. For example, termination timing drives biomass, and that's very important. It's not surprising, but this is striking how strong that relationship is.
Speaker 2:You know? So, basically, the later you terminate your cover crops, which makes sense, the more biomass you are going to produce. On the other hand, seeding rates seem not to be a big deal. Okay? Seating increasing the seeding rate will not always translate into more biomass.
Speaker 2:And that's probably from a practical point of view is important because it means that we probably don't need to put too much seeds, which means it's going to be less expensive for the farmer. Overall, from our first year of results, we can see where we found that around 30 pounds of cereal rye per acre is quite similar to applying even 60 or more pounds of seed per acre. So which that's a good that's a good thing. Yeah. And, yes, cover crops use water, but not much.
Speaker 2:During the fall, because cover crops don't grow too much, so, basically, we can just I can safely say that, you know, water use of coracros in the fall is not a big deal. In the spring, though, that's a different story. In the spring, depends on how in weather conditions. And if we produce a lot of biomass, they might use more water. And if it's if we are expecting to have a dry year, we should better take care of that and terminate the cover crop as soon as possible.
Speaker 2:Otherwise, it's it might, you know, affect the main crop results. What else I can tell you? We have some farmer questions. I'm going to just list them and give you a little bit of my my my thoughts about that, and then I will like to to pass this to Jeff for several reasons. The the first one is that Jeff knows much better than I do about, you know, plant nutrition and fertilizer specifically.
Speaker 2:And secondly, because yesterday, during the the agronomy tour speak, we we talked there in in Waseca. Jeff was giving some very interesting results about something that is going on right now in the research field about some of the questions that you guys are asking. For example, one of the question is how much nitrogen does a 12 inch rye crop sequester? Well, I can say from my research that it is about 20 to 60 pounds of nitrogen per acre. This depends a lot on biomass, and, basically, it's related to biomass.
Speaker 2:But this is the thing we had. We we had to be careful because from those 20 to 60 pounds, only about 10 to 20% maybe is available within the season. The rest is going to be released slowly. And another question is which let me see. Which cover crop is best for nutrient nutrient recycling?
Speaker 2:What I've seen is that cereal rye because it produces a lot of biomass and does well for conditions in Minnesota. It's a great nitrogen scavenging crop cover crop. I've read that radish or and turnip could do well for p and k, but I don't have that experience. And, obviously, some legume cover crops like clovers, let's say, creams on clover and red clover may add nitrogen through fixation. And for weed control, that's a kind of difficult thing for me to to to answer.
Speaker 2:But, basically, we've seen that we can have a good cover of the ground, you know, with CDRI, which that translate into width suppression. We don't have the numbers yet, but we are working on that. And the last question I have is should cover crops change nitrogen fertilizer plan? I would be a little bit careful with that because actually and Jeff is gonna jump into that. After right, probably, we even need to apply a little bit more nitrogen.
Speaker 2:And for legumes, we could consider cutting a little bit, but I don't want to give a number because I don't have those results ready yet. What about what do you think about that, Jeff?
Speaker 3:Yeah. I think those are all good that's all good input, Axel. The first question where they're talking about the 12 inch rye, I think one thing to remember is for cereal rye, typically, it's between two and a quarter and maybe two and a half percent nitrogen. So if you have an estimate of the amount of biomass, you can kinda calculate how much nitrogen's in there. I've seen situations where if it was very small, it might be even a higher percentage of nitrogen, maybe over two and a half, close to 3%.
Speaker 3:But if you don't have any idea what the biomass level is, I think there's some apps and some other other, insurance or things that you can use. And and I think a lot of times, if Axel would agree, 12 inches is probably about a thousand pounds of biomass, somewhere in that area, maybe as much as 1,300. So, yeah, I think the numbers you threw out there are just right on. As far as, how much is that available in that first year or for that crop, there was a really good study that I talked about yesterday at the meeting, an Iowa State study. And after a hundred and five days, they found that between 6077% of that end had been released from that cereal rye.
Speaker 3:Not all of that necessarily is gonna go to the crop, but that's a pretty good idea. Two thirds to three fourths of it's gonna be released in a hundred and hundred days or approximately a hundred days. They found more when corn followed soybeans with a cereal rye versus when corn followed corn. And I think that kinda makes sense because of that, you know, some of the interactions with carbon to nitrogen ratio. One of the other really interesting findings from that study was the difference between carbon to nitrogen ratio of the shoots or the above ground material versus the roots.
Speaker 3:And they found the shoot biomass was 15 to 20 carbon to nitrogen ratio, which means that it should mineralize and should be mostly available. But the below ground roots was 45 to 50. So that's gonna be in that immobilization area where it's gonna tie up nitrogen, and that's gonna impact whether, how much of that n is gonna be available as that biomass decomposes and whether it has the potential to tie up nitrogen. My interest in my research in cover crops, being a nutrient management specialist, specifically being a nitrogen person, relates to I'd like to see if we can use cover crops to scavenge some nitrogen and minimize the amount of nitrogen that leaves the field in tile drainage water in South Central Minnesota or leaves the field in Southeast and ends up in ground and surface waters. So I'm very interested in these nutrient by cover crop interactions, and that's what I spent time talking about yesterday.
Speaker 3:No. As far as the best crops to recycle nutrients, I agree with Axel. I think when you think of recycle, are you looking at scavenging nitrogen? If you're really focused on scavenging nitrogen, then cereal rye with spring termination is gonna be the most effective. However, if the nutrients, you want them to be readily available to the next crop and maybe even enhance the amount of nitrogen or the nutrient availability of the next crop, then looking at a legume, as a cover crop is gonna be where you wanna be.
Speaker 3:But recognize that it's gonna take a lot more time to establish that. So the legumes probably are own are not gonna fit following full season corn or soybeans. They're only gonna fit following maybe canning crops or small grains where you have a much bigger window of establishment post harvest of the crop the previous year. And then the last thing
Speaker 1:Oh, go ahead. Sorry, Jeff.
Speaker 3:Yeah. The last thing I was gonna talk about was that question on how much should various cover crops affect end recommendations. And Axel alluded to this briefly, and I think it's really important that there's several factors that determine that. Axel mentioned the termination date, the seeding date, obviously, how much biomass. Those things those things determine how much biomass.
Speaker 3:Kind of the rule of thumb is if you're planting corn and you've got cereal rye cover crop, try not to let it get bigger than six to eight inches. You might be time to terminate it. If you wanna push it farther than that, recognize that the risk of it interacting with nitrogen in particular is gonna be greater. Also, the species of cover crop. There's some good research from, Wisconsin and other states looking at you know, every species of of cover crop is different.
Speaker 3:Syrro rye versus annual grasses versus radish versus legumes. If you are looking at the potential for tying up nitrogen and having the cover crop be a negative and maybe as as Axel said, maybe you need more nitrogen applied, that's probably when you're looking at something like cereal rye. The annual grasses that are gonna terminate during the winter probably aren't gonna have much impact on new nutrient availability the next year or nitrogen in particular. Radish, you know, studied by Matt Ruark in in Wisconsin showed that radish could impact nitrogen, needs the next year, and it did take more nitrogen to optimize corn production following a radish cover crop. And as I mentioned before, the legumes, if they have time to establish, they can actually provide nitrogen, and you could potentially reduce your end need.
Speaker 3:But as as Axel said, I totally agree. At this point, I don't know that we have enough answers and data to really put numbers to that. I think it's more of a this is kind of the the spectrum of options, and this is the things that we need to pay attention to to determine whether we're gonna need more in or whether we're gonna get in. And, obviously, Rye is at one end of that spectrum, and legumes are at the other end of that spectrum.
Speaker 1:Yeah. I think you guys are hitting on a lot of hot key questions that people have around cover crops. Like, you know, again, with the seeding rate, we know that we can reduce costs if we don't need to see that such a high of a rate. And it looks like, again, with our preliminary results, you know, maybe 30 pounds is gonna be enough, but also this whole nitrogen question. So right now, you'd say probably you know, what what would be your take home about nitrogen right now if people are wondering?
Speaker 1:Can I cut my nitrogen rates if I'm putting a cover crop, or should I put some more nitrogen on there? Do I need to make sure it's out there? Do just have some general comments around that, Jeff?
Speaker 3:Yeah. I think it goes from that spectrum to cereal rye to to the legumes. If you're planting cereal rye and you're terminating it in the spring and you've got biomass that's in excess of 750 or a thousand pounds, there's a chance that you may have immobilization of that end, and you may actually have to add additional end to optimize yield. Or you may see a small yield penalty, and it could be related to nitrogen. And some of my colleagues in in Indiana, which I talked about yesterday, showed that it could be related to sulfur immobilization and the need for sulfur.
Speaker 3:How you can manage that is maybe apply some nitrogen and sulfur near the row as a starter fertilizer at planting. If you're planting corn into a larger cereal rye cover crop biomass, if you've got annual grasses or brassicas or a blend of lots of different cover crop species, I don't think it's gonna have as much likelihood to interact with nitrogen. And then if you've got a very well established legume, whether it's a clover or a vetch crop or something like that, there's the possibility there that maybe you can reduce your nitrogen rate. And then I would recommend maybe just being on the low side of the recommended range when we look at the corn n rate calculator, not being at the highest recommended range for for crop rotation, but maybe applying at the low side if you had a very well established legume cover crop.
Speaker 1:Oh, that's a good good recommendations. And we we did a lot of talk about termination timing. Axel, I know you've done a lot of work with that, and that's part of the projects that you're doing now too. Are there any kind of key messages you wanna share about that? Because you've looked at this in both we've spent a lot of time here talking about corn, but also soybeans.
Speaker 1:What are your thoughts on that with with termination timing of cover crops?
Speaker 2:Well, yeah, as I said, termination timing really will affect the amount of, you know, the biomass that is produced by the cover crops. But this is the thing. Termination timing will affect no matter which seeding rate we are using, obviously. And as we mentioned previously, it seems like we should probably be using less seed, and we will be producing enough biomass at the end of the season at termination. But the problem is our there is a a trade off that remains in this thing.
Speaker 2:One is that if we delay termination for more cover crop biomass, we risk to delay planting or eventually to affect the main crop because too much water use or nitrogen tied up as Jeff was saying, those kind of things. But if we terminate if we terminate late early, so, basically, what is gonna happen is that we will have very little biomass. When I say early, I am saying that, you know, our regular rule of thumb, which is let's let's terminate ten days before planting the main crop, which for conditions in Southern Minnesota might be even around the April 25 or even earlier. So at that point, honestly, cover crops are just starting to regrowth for spring, and there is not much biomass yet. So that's the big thing.
Speaker 2:So when should I terminate my cover crop in a way that, on one hand, I'm going to have enough biomass so I have the benefits of the cover crop practice. And on the other hand, I am not going to affect my main cover my main crop. So that's something that we've seen in this in our research that is locally dependent and, obviously, management and several other practices that go into play. And, obviously, there is cover crop species, those kind of things. And but we are, how to say, we are hopeful that at the end of this three year project, we will have strong results that will help us to determine what is going to be better.
Speaker 2:We know that one size one doesn't fit all, and that we also know that we need site specific guidance, you know, for, you know, better results. So I just one more thing before I I pass I pass it to Jeff. This research we are we are having is supported by the Minnesota Environmental and Natural Resources Trust Fund, and I am really grateful with with their commitment to sustainable crop production in the state. I don't know if there are some questions in the chat that we could answer, but I will pass it to to Jeff right now.
Speaker 1:Okay. I I don't know if you wanna mention and say anything about the previous question, Jeff, or should we we do have a few questions here in the chat. I can throw those out here. One of them and I don't know which one of you would like to take this, but it's like, how is killing cover crops working in a rainy spring? So, which, you know, with our research trials, we have to deal with that too.
Speaker 1:So
Speaker 3:Yeah. I've had challenges sometimes with, terminating a spring cover crop, based on climatic conditions. Glyphosate's usually really good at terminating cereal rye, but you need warm weather, and you hopefully need warm weather for a couple of days after the herbicide application. And maybe this question is referring to just really wet fields and can't get out there to do that, and that was a huge problem last year. And for some some growers, that could be a huge problem again this year because we we've had certain areas that had excessive rain and got a lot of drowned out spots and and ponded water, and you can't drive a sprayer through that very easily.
Speaker 1:Right. And that that's the thing we've kinda talked about too is if it's looking like you've got a stretch of rain and that cover crop's getting close to termination, I would on the side of terminating versus waiting. Right? Because you just don't want it to get because once we we really get that exponential growth when the when the heat starts to kick in here. We've got another question here from Shane.
Speaker 1:If people find themselves in a situation where a summer cover crop can be planted, which annual is best for soil compaction during that warm period? Sorghum Sudan grass would be one question. Axel, I'll throw this out to you if you wanna see. And and Jeff, you can add in too. But I know we've done a number of trials looking at different summer seeded cover crops.
Speaker 1:Maybe you have some thoughts on that you wanna share?
Speaker 2:Yeah. Sure. Yeah. Basically, sudangrass does much better than other warm cover crops. Actually, you know, we've been we did some we conducted some trials with you, Liz, here at the in Lumberton during three, four years and Southern Sudangrass was one of the treatments and it can produce more than 8,000 pounds of dry mass per acre in a short as less than two months.
Speaker 2:So and we did not check at soil conditions, but I remember we had a pit there and it was amazing how much root were in, you know, in the in the soil profile. So I will go with that if that's that's an option I I might have. But we have to be careful what for determination because it's just too much biomass. It's a lot of
Speaker 1:It's a lot of biomass. Yeah. Certain sedans. I mean, we have have proso millet out there, Japanese millet. All those kind of warm warmer grasses can do really well.
Speaker 1:But, yeah, like you say, if you need forage, it's a it's a great option. But but you also do gotta look at things like your herbicide option there too. But here's a question here. Do you have research about planting green and termination terminating the cover crop after planting?
Speaker 2:Yeah. I can jump on that as well. And maybe, Jeff, if you wanna chime in as well. Yes. We've been doing planting green for corn and soybeans.
Speaker 2:You know, in a shell, planting green for corn doesn't work very well. So you can have a heat in corn that is as much as 60% reduction on yield. Now for soybeans, what what we have seen and we have found is that soybeans do much better. So one of the better question is when to plant green. So we have been planting green, you know, let's say, planting the planting what is the name?
Speaker 2:The the main crop immediately and following by termination of the cover crop. What I what what do I mean with that is that I go ahead, plant my soybeans, and then terminate the the cover crop. And we have done that after five terminating the cover crops after five days, ten days, and I guess twelve day was the maximum. And the the the soybeans still doing well. Basically, there is no difference between the planting green soybeans at termination time or terminated the cover crops later.
Speaker 2:So it does very well. Corn doesn't do well. What do you think, Jeff?
Speaker 3:What what I would add is in my experience with some of our research, if your cover crops, say it's cereal rye, and you're planting corn and it's sparse or it's not very large and you decide to plant and like Axel said Axel said, you know, terminate it right after planting or within a few days, I think that's probably fine. But if you've got a significant amount of biomass already, I would not recommend planting green and corn. If
Speaker 1:No.
Speaker 3:If someone's considering that, I would recommend something like strip tillage where you till that zone and blacken it where you're gonna plant that seed and hopefully get rid of some of that root biomass, and I think that can help. And as far as planting soybeans green, I think the risk is a lot less, but there can still be some risk. And maybe it goes back to the thing that we just talked about, Liz, is that you get the wrong weather and you can't terminate, you know, within that five, seven days or you get delayed because of a really wet rain or really wet fields. And all of a sudden, you go a week or two weeks, and now you're gonna have a lot of plant competition. You're gonna have the potential for some, insects that are gonna form that green bridge from that, cover green you know, planting green cover crop to your crop.
Speaker 3:And it it there's some challenges there, and there are some nutrient interaction challenges as well. And I talked about those yesterday too and earlier.
Speaker 1:Yeah. Yeah. I think that's a great thing to add. Just Angie Peltier has done worked with a lot of on firm trials and other people with extension as well too, but she's got a little comment in here too that, yeah, they've had on farm trials where they did see a yield hit with with soybean. I think drought conditions were part of that too, but that doesn't always necessarily is not always the reason.
Speaker 1:So, yeah, there's there's less risk, but there's not no risk.
Speaker 2:Yeah. So Well, quickly just quickly. I I saw Angie's comment and well, Angie Pertz, we've seen that here in Lumberton, and, also, we are doing the same thing in Grand Rapids, in Waseca and here again this year. And I've seen results from other states, you know, our neighbors that, you know, planting green soybean does pretty well. And that's a good point.
Speaker 2:If we have a dry year again, planting green might not be a good choice.
Speaker 1:Alright. Well, I see we are getting up on our time. Are there any closing thoughts that you either of you might wanna add quick here?
Speaker 3:Yeah. I mean, I
Speaker 2:Yeah. Go ahead.
Speaker 1:Yeah. Go ahead, Jeff.
Speaker 3:My main thing is is that, you know, being a nutrient management specialist, you know, one of my, summary comments yesterday was cover crops, especially cereal rye, will interact with nitrogen and sulfur. And, you know, if you're planting corn the next year, you need to be thinking about that and terminating at the right time. And as Axel said, terminating, is really about your biomass. It's in and which goes back to how much biomass you get. Depends upon your seeding rate, your your, species that you planted, and and the type of weather that you had and how fast it grew.
Speaker 3:So there's lots of factors. And just picking, like, a date on the calendar and say, well, I'm always gonna terminate on this date might not be the case. You're gonna have to adapt to each individual year and to the conditions that you have and maybe the forecast for the next couple weeks to before you determine when to do that.
Speaker 1:Well, excellent points. How about you, Axel? Any parting thoughts here?
Speaker 2:Well, basically, I couldn't agree more with what Jeff said, and I just wanted to add that cover cropping is really big deal, and and it's really a very interesting practice. And I do realize, and I accept that for conditions in the Upper Midwest, specifically Minnesota, This practice is not really very simple. We have to be very, very thoughtful on how we are going to do it, but I truly believe that it is possible to have cover the cover crop practice in the conservation rotation in several other crops in the state. We we just have to figure out the best way to manage those cover crops. This is an interesting topic, actually.
Speaker 1:Right. And and we because we know there's a lot of benefits we can get out of a cover crop. We just gotta figure out the best way to fit this into our system. We can't just plop it in there and expect everything
Speaker 2:That's correct.
Speaker 1:To change.
Speaker 2:So Probably, should say quickly, Liz, that there is something that is lacking for the cover crops here in the state and for conditions similar to Minnesota and is, you know, breeders breed cover crops that are tailored to our conditions. We need cover crops that get established as soon as possible and that are fast growing in the in the in the spring. So we do not put our main crops, you know, in pedal. And if we have if we are able to do that, we should be really good in terms of sustainability.
Speaker 1:Yep. That's an excellent point. Well, thank you everybody too. And I do know we did have a question that popped up about armyworm as well. We do have resources online about that as well too because that is something that can be an issue when you're planting green.
Speaker 1:Maybe we can pop that link into the chat here. But, yeah, I do wanna thank Axel and Jeff for joining us today and all of you as well. And of course, our sponsors, the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. Just a reminder, when you jump off today, there's just a really quick short survey. We do appreciate your feedback on that and hope you'll join us next week, same time, same place.
Speaker 1:And one of those focuses again will be all the moisture that we have gotten. For more resources on cover crops, you can check out our cover crop website at z.umn.edu/cover-cropstwo. And we do have an upcoming field day at Lamberton on June 26 too. So, hopefully, we'll see a bunch of you there as well. So thank you.
Speaker 2:Thank you, everybody.
