How to Design a Cover Crop Mixture for Multiple Goals
Researchers from the “Cover Crop Cocktails” research project at Penn State highlight the main benefits that different cover crop mixtures (3, 4 and 6 species) can provide and how to design one.
- Hi, my name is Jim LaChance.
I work with a group of researchers and farmers here at Penn State who are interested in using winter annual cover crop mixes in organic systems.
And so we work in a corn, soy, wheat rotation here.
We're in central Pennsylvania at the Rock Springs Agronomy Research Farm, and I'm standing in a strip of cover crops that were planted after wheat in that rotation.
And so these were planted in about mid August, and now we're here in December to show you a bit about some of our research here at our research station.
We have a variety of mixtures that we've been planting as well as monocultures.
We use six main species to make up our monoculture treatments, and then those six species come together in all of our mixtures.
The species are two legumes, red clover and Austrian winter pea, two brassicas, canola and forage radish.
And then we also use two grasses, so winter hardy cereal rye and then oats that winter kills here in Central Pennsylvania.
When we started working with mixtures here in Pennsylvania, and we started talked to farmers, we realized that a lot of the work they were already doing on their farms using mixtures aligned with some of the general ecological theory and knowledge that was kind of already out there.
We knew that farmers wanted to get more out of their cover crops by using mixtures.
They wanted to achieve different goals or get different benefits for their farm.
And so what we saw in some of the research that was existing specifically in natural grasslands was that as you added more species to a field, you increased the amount of a certain function.
And so you can think of that function as a benefit that you get out of your field.
So it could be anything from weed suppression to nitrogen supply or nitrogen retention, beneficial insects and pollinators that you can attract to your farm, so that's what we really wanted to research is what kind of functions and goals can we get and then what are some of the trade offs or challenges to using these mixtures?
To give you a bit of a context of where we're working in central Pennsylvania, we have a average January temperature of around 20 degrees.
In December now we've already had several very hard frosts.
Our low temperature of the year in the winter is usually around five to 10 degrees below zero.
That's a plant hardiness zone of around six.
And so that gives you an idea of where we're working and maybe now I can show you a bit about each of the individual mixes and tell you a bit more about the six species that make up those mixes.
So this is our three species weed mix.
This was designed to suppress weeds and then to retain and to supply nitrogen.
This is made up of our oats, which you see here.
Then we have our cereal rye seen here.
And then we have red clover.
Together these three species are planted at 127 pounds per acre.
They're drilled in mid August, and now you see what they look like in December.
So here we have our three species nitrogen mix.
Now this mix was designed to both supply and retain nitrogen.
It's made up of our red clover, Austrian winter pea, and rye.
And so the rye is in there because it's a very aggressive scavenger, and it's kept at that low 20% rate also because of that aggressiveness.
We don't want it to crowd out either of the legumes, the Austrian winter pea or the red clover.
So let me show you those real quickly.
This is our Austrian winter pea, and this is the red clover.
Now the Austrian winter pea does come on a little bit more aggressively for us in these mixes than the red clover.
So you see it at a bit thicker establishment here.
But it can be, if planted too early, susceptible to winter kill in some situations where the red clover is a bit more winter hardy.
Then here you see our cereal rye part of our mixes.
Again very winter hardy and can be very aggressive.
So this plot here is of our four species mix.
Now this mix is made up of canola, red clover, Austrian winter pea, and cereal rye.
Those are all from those six monocultures I mentioned before.
Here this is planted at about 78 pounds an acre and that comes out to about $77 an acre.
This is our most expensive mix.
And that is because the canola, which we added, is for our primary goal of this mix which is to additionally attract pollinators and beneficial insects for biological control.
So we know that of the six species that we're studying in this project, the canola is gonna be the first to flower come this spring.
So by adding that to this mix, we hope that in the spring we'll be able to attract more of those beneficial insects to the field.
Here you see our four species in the mix together.
This was planted in mid August and now it's early December.
And so you see here we have some of our canola in the mixture.
We also have our Austrian winter pea, and then we have small amounts of red clover, and we have our cereal rye in the same mix.
So here we have our six species mix.
And so we thought of this mix as our insurance mix because it includes each of the six species that we're also looking at in monoculture cover crops.
We have them all here.
We think of it as an insurance mix because if one or two of the species doesn't perform well in a particular year, we still know that we'll have a solid mixture of at least four or five species or at least we hope to have at least four or five species that do perform well and to keep whatever benefit or function that we're thinking about and that we want to achieve to keep that at a high level.
And so I'll show you the six species here.
They're at smaller rates obviously because there are so many different mixes.
But this is our oat again which is in the process of winter killing now in December.
This is our other grass, our cereal rye, very winter hardy.
We also have one of our brassicas here, canola.
And then our other brassica, which I have to look for over here, is our tillage radish.
Let's see if I can get a good one.
So here is the top of that tillage radish.
That's a pea.
The top of the tillage radish, and then you see where this is about where it met the ground.
Then in addition to the brassicas, we have our two legumes in this mix, again, the Austrian winter pea vining, usually winter hardy but can winter kill a little bit more easily than our other legume which is the red clover right here.
So in working with winter annual cover crop mixes in organic systems, there are four key takeaways that we really want you to be able to take home from this research.
So first when thinking about weed suppression, we suggest it's best to have one or two species that you know are going to come on very aggressively in the fall and that's primarily to be able to suppress weeds in the fall.
We've see that if you can suppress them in the fall, then you'll have better spring suppression for your cash crop.
And so once you have those one or two species picked out, then you can think about adding other species to the mix for additional goals.
Our second key takeaway has to do with insects.
So to attract beneficial insects and pollinators to your field, we found that it's most important to have a species in the mix that will flower early, or just about flower at all before you terminate your cover crop.
And so once you figure out what that is for your area and your fields, add that in and then think about adding other species for additional goals.
The third key takeaway is for managing nitrogen.
We suggest that you start off with one or two species of legumes that are well adapted for your area and that will help to make sure that you're supplying nitrogen to your fall and cash crop.
Then once you choose those couple of species, then you can think about adding a grass or a brassica which is winter hardy and is good at scavenging to retain nitrogen.
And then finally our overall fourth key takeaway is that when you're designing your mix and you see how your mixture establishes and what it kind of looks like in your specific farm and climate, what you really want to aim for overall is a balance of the different species that you have in the mix.
That might take some kind of tinkering or tailoring over a course of a couple years to figure out what's gonna be best to get that even expression of each species in the mix on your farm.
So those are our four key takeaways.