Why corn struggles with cover crops
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Jodi:
Cover crops are really taking off now, it seems everywhere. And you are doing some research, nationwide actually. Can you just kind of touch on what that's all about?
Alison:
Yes. So I am doing cover crops and I'm part of this nationwide project that is being funded by USDA NEFA, and it is being led by Chris Reberg-Horton at North Carolina State University and Steven Mirsky, who's part of USDA ARS. And the goal of our research is just to get more cover crops on the landscape because we realize the benefits of those cover crops. And so this is a really big proposal. It has lots of different components and moving parts. But I'm in charge of one part, which is called common experiment two. And basically what we are interested in doing is we are interested in looking at the effect of right termination timing on corn group growth and development, but also on pest management. So that would be insect pests, just beneficial insects, weeds.
Alison:
And then also I'm a pathologist so I'm interested in how termination of that cover crop affects diseases. And so this trial is being done in 16 states across the United States. And we have exactly the same treatments in all 16 states. And we are using a single cover crop, which is cereal rye. And the reason why we are using that is because it's the most popular cover crop, particularly here in the Midwest, and the north where it over winters. It establishes well in the fall and then it over winters and we have very good biomass production in the spring. So that's why we're using cereal rye. And then we are also growing the cereal rye before corn.
Alison:
And the reason for that is because corn can struggle following this cereal rye cover crop. Whereas from research that I've done, particularly as regards diseases, and then even from what we care out in the field, soybean is very resilient being planted into a rye cover crop. Corn struggles a little bit and so we're trying to understand why is that corn struggling?
Jodi:
Let's talk about planting corn into green. What are seeding dates and rates and so forth that you would recommend people to do?
Alison:
I'm going to talk about Iowa, because I've done a very similar experiment here in Iowa. And I'm going to take us back a few years. I was working with the USDA ARS scientist, Tom Kaspar. And occasionally when you plant corn after a rye cover crop, there's a yield decrease. And Tom wanted to understand why we had that decrease. And so one of the things he asked me was, do you think it could be seedling diseases? And so we did a lot of research where we looked at rye and we looked at corn. And we found that rye is a host of pathogens that cause seedling disease on corn, and that rye was acting as a green bridge. So what would happen is the rye would get infected. And then when you terminated the rye and planted the corn, the pathogens from the rye would just hop onto the corn and cause seedling disease.
Alison:
And while you might not lose stand to that seedling disease, you would get these chronic infections and so then you would get this uneven growth. And when you have uneven growth in corn, then you get barren plants, plants that end up being weeds and they don't produce an ear. And that's where the yield loss was coming from. So we did a lot of research where we were able to show that seedling disease, at least here in Iowa, is definitely playing a role in that yield decline. And so what we found is that if you can terminate that rye cover crop, and what I mean by terminate is just spray it with glyphosate at least 10 days before you plant the corn, that's a long enough window for there not to be the screen bridge effect. And so then the corn doesn't get infected with seedling disease, so we don't lose yield.
Alison:
We know that the date of termination makes a difference. So what we recommend here in Iowa is that you terminate the rye at least 10 days before the corn. I just finished up an experiment with Mark Licht, and a number other agronomists here at Iowa State, where we looked at seeding method. So we compared drilled versus broadcast seeding of the rye cover crop. And then we also looked at seeding rate. So we used the recommended seeding rate, which was about 50 pounds of rye seed per acre. And then we went at a lower rate and a higher rate. And what we found is that rate had no effect on corn growth and development, or on seedling disease. And the reason for that probably is because rye is a little bit like soybeans. If the neighbors are further away, it gets more bushy, right?
Alison:
Whereas if it's planted very densely, then it's a very upright plant. So that's why we think that seeding rate didn't have an effect. And then with seeding method, that had an effect. And so if you drill right too late in the fall, it doesn't have enough time to germinate and to come up. It will come up in a spring. So we found that out. But in our experiment it didn't establish well just because we got it in late. With the broadcast, if you've got enough moisture and because you are seeding it earlier, usually into that maturing soybean crop, then it gets established in the fall. So we would have some cover in the fall. And then in the spring we had more biomass production then with the drill. So seeding rate and seeding method, and timing and establishment is very important for that cover crop. And then what the conditions are like in spring.
Alison:
I mean, if we have an early spring, it warms up early, then that rye just starts growing like crazy. Whereas if it's cold right up into April, then we don't get a lot of biomass production in the spring. So it depends a lot on the year. But having said all that, we, Mark Licht and Tom Kaspar, who is now retired, and I, we really think that biomass plays a big role in what we are playing with. So seedling disease, and corn growth and development. And we know with weeds, the more biomass you have, the better that's going to suppress those weeds and it's going to affect insect populations. And so, yeah, we're still trying to work out this whole biomass thing. I think, and I know Mark Licht agrees with me, that there's a sweet spot. When the biomass gets so high, that's when you terminate it and then you should have minimal problems. But it's finding that sweet spot.
Jodi:
When you have all that biomass, you mentioned the glyphosate for the rye, but say we have a really nice spring with lots of sun, perfect rains, and the biomass is just out of control. What do you recommend for people regardless of what cover crop they've planted to get a handle on that biomass?
Alison:
That's a really good question. And we actually submitted a research grant last year to USDA. It didn't get funded, but we want to do it again. And it's kind of looking at managing this biomass. But one good way to manage it, if you have livestock, would be to graze it. I think that, that would be a good use of it. We always terminate our rye cover crop, or any cover crop, with glyphosate. But I know that there are other people out there who are using crimpers.
Alison:
My understanding of using those roller crimpers is that the rye has to be at a certain growth stage so that when you crimp it you actually kill it, as opposed to if it's younger than you might not kill it and you'll get some regrowth. So when you have so much biomass, it can be very hard to plant into as well. So having row cleaners on your machinery can help just get that biomass out the way. And then I know that here in Central Iowa, there's a lot of growers who will do strip till I've heard. Of other, just getting that biomass away from where the corn is planted just to ensure that you have good soil to seed contact for that corn. And that biomass is not getting in the way too much.
Jodi:
So you've got the positivity of biomass, adding all those roots into the soil and providing aeration and nutrients and all that sort of thing. But there's also something called the disease triangle with cover crops. What is that?
Alison:
For us to get seedling disease, or any disease, do we have a disease triangle? And the disease triangle is basically the interaction of three components. That would be the pathogen. Okay. And we know that these seeding pathogens are endemic to the soils, they're everywhere. And the pathogens that we're talking about have a very wide host range. So they infect weeds, crops, cover crops, et cetera. So we have the pathogen there. The other side of a triangle would be the host. Okay. So the host in this case is corn. And I suspect that there is some variation in the resistance that corn has to those seedling pathogens. We haven't been able to do any work in that area, but for example, some corn hybrids have better emergence than others, right? I'd be really interested to look at, is that better emergence related to seedling disease resistance, or not?
Alison:
So we have a host, so pathogen, host, and then the third side of the triangle would be the environment. And so the type of environment that we are looking for is usually cool and wet. So we tend to see more of the seedling disease, more of a problem, when we have cool, wet conditions that occur after planting. And what happens is when we have those cool conditions is we slow down germination and growth of that corn seedling. Sometimes it even stops if we get below 50 degrees. If those soil temperatures are below 50 degrees, germination stops. And then that seed is just leaking all nutrients into the soil. And those nutrients are attractive to these soil borne pathogens.
Alison:
And so they'll sense these nutrients and go, ooh, rub their hands together, Thanksgiving dinner, right? And they'll find that seed or seedling and infect and therefore cause disease. So, in some years we can have a very warm spring, you can plant your corn. It can pop out of the ground within a few days, up to a week. You are not going to have problems with seedling diseases then. It's just when we get these cold fronts that come through the area where the corn sits and takes two to three weeks to emerge, that's when seedling disease can be more of an issue just because you have that disease triangle.
Jodi:
Are there any cover crops that can help reduce disease?
Alison:
That is a great question. So, yes. And we've been thinking about this, but for example, the brassicas. The brassicas can produce these compounds that can affect some of these soilborne pathogens like pyrethrum and fusarium. And so there's a chance that brassicas could help reduce this risk. And that's something that we kind of want to look at. The one thing that I'm a little hesitant there is most of the time with cover crops we just terminate them and then they just lie on the surface, right? With the brassicas, if you want to get the fumigant effect from those brassicas, you have to incorporate them into the soil surface.
Alison:
And I'm not sure that they're going to be very helpful at suppressing disease if they're just lying on the surface and those volatile compounds are not getting into the soil right and killing the pathogen. So, yes. I mean, I think there's a chance there. There's also lots of work going on, on the microbial communities. So we know that depending on the crop, you're going to have different microbial communities associated with that crop. And so it's possible that we could, with some certain cover crop mixtures, we could have different microbial communities that could suppress some of these soilborne pathogens. So yeah, I mean, definitely an area of interest, but not one that I've gone into yet.
Jodi:
It's really delicate, isn't it? It's such a fine line between hurting the crop, helping the crop and so forth. But is there a way to attract beneficial insects and keep the bad ones at bay?
Alison:
Yes. So as part of this national study that we're doing, we also put out cages in the cover crop in our different treatments. And in those cages we have of little wax worms that we put out as bait. And then we monitor those wax worms after 12 hours, and after 24 hours, I believe, and has it been eaten? And then that's an indication that there's been predators out there, right? Insect predators, like beetles and stuff like that. So when we have that biomass available, then those predators can come in and feed on other insects.
Jodi:
Let's go back to the project again. This has been underway for a while. When do you hope to have the results from the other states?
Alison:
This trial is going to be done over three years and we just finished up our first year. So the postdocs, we have three postdocs on the project and they've been gathering all the data. We meet once a month virtually to talk about our data. And the idea is that the end of this month, those postdocs are going to start sharing the data, and sharing some analysis of that data. So, hopefully, as we go into the summer and we get into our second year, we can modify some of our data collection points based on what we know from the first year. I would say that we can expect very rough results, probably starting towards the end of the month, and then monthly as the year goes on. But to get good data analysis and well informed results, well, good interpretation of that data, I would say, that's going to take at least another year, maybe longer than that. So we'll need a second year of data.
Jodi:
So it'll be probably pretty groundbreaking when you're all done and you have all the data here in a few years, we'll have to talk to you again.
Alison:
Absolutely. I was going to say I'm really excited just because I've done the work on diseases in Iowa, and that's the only place that's been done. And then the work on insects is primarily been done in Pennsylvania, maybe in New York state as well. And then there's quite a bit of work that's been done in weeds, but that's what's so exciting about this project is it's like, this is what we see in Iowa, but do we see that in Texas and Florida and North Carolina and Vermont, right? What's happening there, and just trying to get a much better under is standing of the system. So that's, what's really cool about this is that the diseases and the insects have been just researched in a very small location. And so this project is expanding that out to see, does this happen in other places too?
Jodi:
Alison, is there anything else that you'd like our listeners to know about?
Alison:
I could talk about cover crops all day. So, yeah, there's lots of work going on, on cover crops. And I think at the end of the day, all of us really believe in the benefit of cover crops. And so the goal behind our research is just to understand why there are these things that can go wrong. And if we can understand why things go wrong, then we are better able to come up with management recommendation for farmers to be successful as they use cover crops.