UW-Madison’s Dr. Matt Ruark discusses the benefits of incorporating legume cover crops after winter wheat in a crop rotation. Here is more information on what Dr. Ruark and his team are working on.
Hi, my name is Matt Ruark. I’m a professor at the University of Wisconsin-Madison, and also an Extension Specialist with the Division of Extension. This presentation is going to be on quantifying the benefits of legume cover crops falling winter, we’d like to thank my co authors, Chelsea Zegler, Jaimie West and Mike Ballweg. So the main thing when we talk about cover crops is well, what’s their potential benefit for crop production. So a lot of the cover crops that we promote are for conservation purposes, like the grass cover crops. But as we see in this review paper that evaluated the effect of using a grass cover crop on corn yield, so that would be the next, you know, this would be the corn yield following the cover crop, we see that we tend to have the most of the data skew slightly negative, implying that we’re seeing lower yields following a grass cover crop. But there’s certainly benefits to using that grass cover crop for erosion control that grows quickly. As well as trapping some nitrogen and preventing some nitrate leaching. On the flip side, or on the on. As an alternative, we can use legume cover crops now, legume cover crops, we have a low C to N ratio, so they’re pretty nitrogen rich. So when they decompose a supply nitrogen to that next cash crop. And so those sometimes we refer to that as green manures. Based on this literature review, you can see most of the data in the literature skews positive, implying that corn that follows a legume cover crop tends to have higher yields than following no cover crop. So legumes it’s possible for them to have that dual benefit of supplying nitrogen and helping improve crop yield. Other another recent meta analysis showed on the on the right here for crop yields the legume cover crop skewed positive 20% increase on average and in crop yield following a legume cover crop while the non legumes had a neutral to negative effect. Although on the nitrogen leaching side, the biggest benefit that’s the big benefit of the grass cover crops is for nitrate leaching. Okay, so the question then becomes Well, okay, legume cover crops are pretty great, pretty well quantify that they have these benefits. So how can we get more legume cover crops planted? Well, the problem with the legumes is they take a lot longer to get going and establish. So I would say I’ve broken this into sort of three categories of where they would fit into easy to get legume cover crops planted, if we frost seed into winter wheat, or plant after a winter wheat harvest in the summer. So it’s possible to get legumes established and going if we interseed them into corn that works on going in certainly more difficult to get them planted after corn or soybean to get that kind of establishment you need. So this presentation today will focus on the easy stuff. If you have winter wheat in rotation, if you have other small grains, if you have any crop that’s coming off. In the summer, we’d still have plenty of time for a legume cover crop to get established and put on a fair amount of biomass. That’s where we’re going to have the biggest benefit. So I’m going to talk about two things. One is frost seeding into winter wheat, talk about that process and show some study results. And then also testing some other legume cover crops that can be planted following winter wheat. So all the work that’s presented here, has been funded by the Wisconsin fertilizer Research Council. So we thank them for their funding. So let’s start with frost seeding red clover, so this is a picture in a in a field in the fall following you know, this is a few months after a winter wheat harvest. So you can see one of the benefits right away is we have a nice establishment of the red clover a nice thick stand and where we have harvested winter wheat we see that we do have a lot of volunteer winter wheat come up. So this is a system where you’re gonna like the wheat in the fall of previous fall, and you’re gonna come out in the spring, early spring we’re looking for conditions like this, these are perfect conditions. late March, maybe even into early April, the snows off the ground, soils pretty dry and that you can get on it. So here we’re just gonna, we’re just gonna overseed this red clover seed onto the winter wheat field. And so here’s another picture you can see so the winter wheat isn’t a is not really starting to take off yet but these are good soil conditions to get it planted. And this is also the crop previously that was soybeans we don’t have a lot of residue covering the soil. So when we when we seed we are still getting that good seed soil contact And even better, if you have a little bit of cracking in that soil, that’ll help that seed to soil contact. So as that soil kind of what’s up, it’ll help, a little bit of that shrinks will help improve that contact with the soil. So these are the perfect conditions to do this. And then what’s gonna happen is you’re gonna that the winter wheats gonna take off, the clover then will also start to grow and it’ll just hang out in the understory. So that’s the nice thing that that I like about the red clover doesn’t try to do too much. Alright, it’ll get out of the ground. But that we kind of has that nice canopy, we’ll have that canopy closure. And it doesn’t try to overachieve. So just hang out until that wheat is harvested. And when it is, boom, it’s already established, and then it takes off. So the value of the frost seeding is you’re basically getting that jumpstart on the growing season. So here’s a picture of a nice field that was planted in in October, where we have a nice, thick stand of red clover that was grown. And then again, compared to the amount of volunteer winter wheat that can happen in these other plots. So I will say one more thing about this we in this system we have set up is that we’re growing so much biomass that we’re actually moving this back at least once to prevent, you know, a lot of disease from from taking hold. And we are going ahead and we’re going to go we’re going to terminate this in the fall. So we’re going to terminate this in the fall, we’ve we’ve grown enough biomass, we’re going to terminate it in sometime in October, where we feel we don’t have to worry about letting it grow into the spring. Certainly, if we let it grow into that next spring, we could terminate again, we grow even more nitrogen, so to speak. But here we’re kind of we’re hedging our bets a little bit, we’re going to terminate in the fall, so not to worry about operations in the field in the spring. So then what we’re going to do just like any study that I do is we’re going to follow to that into that next corn crop and we are going to conduct nitrogen rate study. So this is the first work here is from Janesville in 2010. This is work by Jim stute and Kevin Shelley. And we’re going to here they conducted a nitrogen rate studies on the on the x axis is nitrogen rate, and the y axis is corn yield. So in the red, the red dots are the corn yields following no cover crop in the blue are the corn yields falling or red clover cover crop. So when we conduct when we do this plateau analysis, basically where does the the yield start to level off at, right, and that point, where it starts to level off at is the the optimum nitrogen rate for that site. So the first thing we see is we’re seeing this yield increase. So we’re seeing 25 bushel, plus yield bump just from following that red clover. And we’re seeing where this where these yields plateau. You can see with the red clover, we’re maximizing yield with a lot less nitrogen, compared to compared to no cover crop. So when we use a linear plateau model, we’ve shown that we can get a nitrogen credit of 46, we use a couple different models, we actually saw a range of 41 to 82 pounds based on based on the statistics, but we do based on this, we’re saying 46 pounds. So in general, we like you know, we throw out that 40 pound nitrogen credit if you use a legume cover crop for the longest time, this was the really the only data we had to go off of. So we’ve continued some of this work at our Arlington Research Station just north of Madison. We saw some interesting effects. So in 2016, again, this is following a red clover cover crop in blue, no cover crop in the red. slight twist on this, we actually saw a slight yield decrease a little bit maybe more than slight in these high yielding environments. So there was nothing and we saw we maximize with 16 bushels less following red clover. Not clear why this was there was no indication in season that these crops were stressed at all, you can see that we’re seeing, you know, great yields here. So there’s something something in there that that prevented that we don’t have to do a little more investigation to figure that out. But what is clear though, is you can see especially like down here where we’re seeing much greater yields with no nitrogen applied that red clover is supplying nitrogen based on these response curves for say 92 pounds of nitrogen is what it supplied. So we’re growing a lot of nitrogen and we’re seeing this big benefit. But this is concerning. We don’t really know what what’s causing this, this yield drag. We conducted this again we skipped a year came back in 2018. We added an extra treatment in here and so this is in the Blue here is following a no cover crop. So we’re seeing that same thing where we see lower yields, with lower nitrogen rates and in that no cover crop. We also had in the orange here, that’s the red, that’s the red, the nitrogen spots on the red clover cover crop. And we added an extra treatment here in the gray. We actually had other plots where we harvested that red clover biomass. We said, Well, what if we needed a little extra forage, and we need to take that off. So two things here, well, let’s start with this one is we did see a little bit of a yield drag again, eight to nine bushels. So there’s something else happening at this site. Again, nothing that was clear in season, that would suggest that would have been a setback. But we are seeing about a 30 to 40 pound nitrogen credit. So yields are maximized with a lot less nitrogen compared to compared to without a red clover. So certainly, it’s applying some nitrogen, you could cut back on your nitrogen rates. The other thing that’s interesting is that we’re not seeing a difference between that the red clover where the entire biomass was returned to the soil in the harvested treatment, which means the above ground biomass was removed, but all the root biomass stayed. So this would give us some indication that it’s actually that root biomass that’s supplying the majority of the nitrogen, the above ground biomass may not matter as much. So So kind of an interesting effect that will, that we certainly need to need to study more. So you know, we always think about the stuff we can see, we can produce a lot of above ground biomass, that’s for sure. But there is still a lot of nitrogen in the roots below ground. That that’s that’s decomposing and returning nitrogen to the soil. So some positive aspects to this certainly, clearly, and every time we’ve done this, we’ve seen that red clover supply nitrogen, good, good amounts of nitrogen. And that’s why we’re seeing this slight yield decrease unclear what that affects all about. So um, so that’s one option. The problem with the Another drawback to it is that you got to get out and get that frost seeding happening at that right time and good conditions. There’s a window. All right, and if you miss it, then what do you do? Well, I suppose the good news is that there’s still a you have the option of drill seeding legumes in after winter wheat harvest. So the ones that we’ve tested are Berseem clover and crimson clover. So the trade off with this is that you can grow a good amount of nitrogen and biomass with those crops, berseem and crimson, but both of them will winterkill. And so then the benefits of that is that you don’t have to go out terminated in the spring or the fall works well, in no till systems. The trade off is are you maximum, you know, the question is, are you maximizing the benefit of that legume? You know, would it be better to have something grow into the spring can we get enough biomass to produce a good nitrogen credit? So um, we’ve conducted we conducted work across three growing seasons up in Northeast Wisconsin, mostly in Sheboygan County. On berseem and crimson clover, so I’ll take you through a few pictures and then I’ll show you a few years worth of data. So for the berseem clover and the crimson clover both both grew well. Berseem in our trials tended to have a little more consistency with its with the planting establishment Crimson sometimes had some skips in it depending on depending on the variation in the field conditions. The berseem tend to grow a little bit taller, a little bit wispier the crimson clover was didn’t grow as tall and was a little more dense in its biomass. So here’s what you’re seeing some weak spots, but then you have some spots where it Did you know up in here where it grew really well. Moving on to another year, the Berseem crop. Again, amazing amount of biomass can be produced with this proceeding crop grows pretty tall. Another picture with the crimson clover not too bad, not too bad with the crimson clover, just certainly not as tall but this this year was a great year for crimson clover, nice, nice, dense stand. And then when we compare them, you can see that there’s a fair amount, you know, we get much taller, much, much taller crop with the berseem clover compared to the crimson clover. So it will just look different even though they might produce somewhat similar amounts of biomass. The big trade off is that you lack the that residue control, you know, enough residue to control erosion in the spring. That said, if you can grow enough biomass, the question is, Is this enough dead biomass coverage for erosion control Maybe, maybe not. So in some years, it looks pretty good, right? Some years here’s this is with crimson clover doesn’t look very good that red crimson clover look like kind of fell apart pretty pretty easily on didn’t have as much biomass covered. So if you’re looking for biomass coverage, the winter killed legumes aren’t going to be the aren’t gonna be the way to go. Every year, we always dug them up to, we always had our seed treated with an inoculant. Is that necessary? Not sure. But if we want to really make sure that it’s it’s fixing a lot of nitrogen and growing well, that we always we always invested in that. And we always check that legging nodules were forming. So it was fixing nitrogen in that biomass. But a quick, quick aside, so the fact that these clovers or legumes, fixed nitrogen, they have that symbiotic relationship with the soil bacteria, where the bacteria then lives inside those root nodules and they can convert nitrogen from the atmosphere into usable nitrogen for the plant, the plant then feeds the rhizobia bacteria to to keep it alive, so there’s that it’s a symbiotic relationship. Now, that helps bring new nitrogen into the system, and helps the plant grow and prevents you know, allows this plant to do well in low nitrogen environments. But the benefit from this nitrogen credit does come from the fact that the C to N ratio of the biomass is low. So it’s about the decomposition patterns of that biomass. So it’s gonna it’s a nitrogen rich crop, it breaks down when it decomposes. There’s there’s a lot of nitrogen leftover after that decomposition process that can be available to that next. And just always, for comparison, we have this the no cover crop control, where we see you know, a lot of exposed soil, some volunteer winter wheat coming back. So in 2015, you know, we planted the covers in on August 15. Sorry, this is a this nitrogen rate study was in 15. So in 14, we’re setting it up planting the cover crops, August 15. seeded both at a rate if about 15 pounds per acre. And then 2015, where we plant corn, and then we put out a bunch of nitrogen rates are looking for this effect. So the main conclusion from the first year then was that crimson clover provides a nitrogen credit, and both crimson and berseem clover provide yield benefits. So for crimson clover here, we can see that crimson clover is in red with this red response line. Berseem clovers in green, and the I’m sorry, I’ve mixed that up already. The no cover crop control is in red. And this is the response curve. So this would be your standard response curve to nitrogen. For corn that didn’t follow cover crop, then the Crimson clovers in blue. So the first thing is we didn’t see that big effect for that crimson clover at these lower nitrogen rates. But at once we started applying nitrogen we are seeing this this yield bump. And when we look at where these yields start to plateau, we are seeing ultimately a four a four bushel yield gain, but look how much less nitrogen that it required. So based on this, we’re saying 160 to I’m sorry, 168 pounds of nitrogen, you can maximize yield, with 168 less pounds of nitrogen. Now you probably aren’t putting out you may not be putting out nitrogen all the way at this level, but that’s what that calculation is. So certainly it would indicate that it is supplying nitrogen and in that year, we only had 46 pounds of nitrogen in that above ground biomass. So when we’re doing these calculations, we’re collecting the above ground biomass only so even even a fair amount of biomass that’s grow a fair amount of nitrogen is still producing that that benefit. So what about Berseem clover, so Burstein clover, he grew 75 pounds of nitrogen this year. So we did grow more biomass and more nitrogen, a little bit odder of a response curve where but the main thing is to look at there’s a couple things to look at here. Generally always seen this yield benefit across all the end rates or sub greater yield. Second is we saw this big bump when we’re not applying any nitrogen this huge yield benefit. So just from the this alone is showing that the Berseem clover is supplying nitrogen. Exactly how much we have some estimates based on some other things but anywhere between, you know, 40 to 60 pounds of nitrogen in this case as well. The problem that we saw is that we always struggled with is that so we we always collected pre plant nitrate tests, not the best way to evaluate these in season. These these legume nitrogen It’s here we would use a pre-sidedress nitrate test. And in case you know, following the no cover crop, the Crimson we’re seeing, we never saw that flush of nitrogen from these clovers at the pre-sidedress nitrate test wasn’t helpful for us. So that was a that was a little bit of a bummer we normally do promote that for its use. But it may not be it may not be as helpful as we think in these in these conditions. We continued to study again at a different location here we planted the clovers on August 12. Again, at 15 pounds per acre, we also applied a P and K to that field as well. So low in P and K. And we are and then we ended up sampling about November 5th. So in reality, we get maybe a you know three months of growth in these conditions, maybe two and a half months of growth depending on when we’re sampling. And then the next year we’re following with a with a nitrogen response study. Okay, so we’re gonna throw this all together. In this year crimson clover had the clear nitrogen benefit and berseem had the clear yield benefit. So what I like to do here is just so the same, it’s the same the red is the no cover crop crimsons in blue, I suppose which put Crimson crimson, but and berseem is in green. And then we have this these lines represent the yield plateaus yields go up to this level. So basically, this line is the where the average yield, once we stopped increasing yield, so no cover crop, we max out at 210 bushel. crimson clover , following crimson clover maximize with two away but we did see a nitrogen benefit 46 pounds of nitrogen again, with crimson clover, we saw a bigger yield bump Here we see a 13 bushel yield increase, but a smaller nitrogen credit in this case, only 15 pounds. So that was a little bit variable in terms of the crimson clover produced 70. With this was a great year, we had a lot of biomass, 70 pounds of nitrogen in the above ground biomass, 81 pounds nitrogen, and the above ground biomass with a Berseem clover. So there’s a lot of nitrogen, we’re adding back to the soil. And with the response curves, we can get 40 you know, that round that 40 pounds, we got it with crimson, we didn’t necessarily get as big of a bump with the berseem. But we are seeing a yield benefit. Okay, so we’re getting a lot of a lot of mixed results, which can happen. And again, we go back to that pre-sidedress. If anything, it tells us that maybe this site wouldn’t have been that responsive, we sell at a pretty high sidedress, you know, high nitrate conditions in the in the side dress treatments, I’m sorry, in the no cover crop treatments, based on a pre sidedress nitrate test. You see, we see 19.6 as the as the value in that upper foot. But we didn’t we’re not seeing this big flush of nitrogen being in the crimson and berseem plots when we sample it in in early, you know, late May, early June. So when we put all these numbers together, we put all these numbers together, here’s what we get. So we have two years of red clover data. Two years of crimson data two years of berseem data, we see this big range anywhere between 15 to 168. On average, we calculate about a 68, Pound nitrogen credit from legume cover crops regardless of regardless of species or when it’s planted. But you can see that the there is quite a bit of variation, on average than too we see anywhere between the 27 bushel yield bump to a 16 bushel decline on average, we’re seeing an eight bushel yield increase. So in general, we’re seeing it be positive, although certainly we did this doesn’t include that that second year at Arlington. But we do see on in most cases, we see a positive benefit. However, most of the positive benefit does seem to has been shown in the crimson and berseem studies in Sheboygan rather than the frost seeded studies in Arlington. So I will say this, these are unofficial numbers we’d like to we have a couple more years of data of years of numbers to crunch, apply some more rigorous statistical approaches to this. But at the end of the day, then what is what does this mean that the legume cover crops do what we think they’re going to do they have that they add they add nitrogen and cut back on your fertilizer nitrogen when you use them, and it’s likely you’re going to see a yield benefit with using them. So they apply meaningful amounts of nitrogen to corn. When planted after winter wheat I should really just say when you enable it when you’re able to plant them in August, on average supplied about 60 certainly was variable from year to year. I think that then Using a book value of 40 is probably is pretty good. Our biggest challenge in is like, what’s that assessment to let you know if it’s going to be year where it’s probably going to only be 20? Or it’s going to be that year where it’s 60? Is it above ground biomass? Is it a soil test? Is it a tissue test? It doesn’t seem to be clear quite yet. So, um, you know, even though we have a lot of, you know, we spent a lot of time doing these nitrogen response studies, you know, in the end still gives us really only 6,7,8 data points to work with. So we certainly do need to expand this, this work and work with others to figure out how best to assess it. I would say if you’re going to do it, start with a 40 pound assuming a 40 pound credit and work from there. So especially if the stands goes your stand, isn’t that great? then then then cut back from there but might maybe worth testing out on your, on your phone, so that if anyone has any questions down the road, feel free to feel free to contact me anytime. M D R u a r firstname.lastname@example.org wisc dot Edu. All right. Thanks, everyone. And hope you enjoyed it, bye.