Cover crops are generally user friendly and successful with little stress, but there are a few things that shouldn’t be overlooked...
“Prairie Creek Seed, who do you give such a wide range for recommended seeding rates on your cover crop blends?” Good question! Different seeding rates have their place. Want a thick, full stand to achieve maximum forage for livestock? You better stick to the higher end of our scales. Looking for a cover crop that will not be harvested? Then it is more economical to stick to the lower end. There is such a thing as too low of a seeding rate, and that is the first way cover crops can be sabotaged. A seeding rate that is too low will result in not enough cover to establish and will not gain you any benefits.
Another way to mistreat your cover crops is not giving them a proper seeding method. While there are many cover crops that can be broadcast, not all of them can take that! Many large seeded cover crops need to be drill or incorporated in some way to have a strong establishment. Taking the extra time, and sometimes added expense, of drilling your cover crop will pay for itself. The establishment of many cover crops will be sped up by around 2 weeks when drilled. Getting seeds in the ground also makes them more tolerant of weather extremes by having a healthier established root system (this will be important later).
If you are planting a cover crop without the goal of harvesting, then this point is not as critical, but is still important! Growing anything desirable with low fertility is next to impossible. If you want your cover crop to get large enough for forage (or even just large enough to provide adequate erosion control) it does not hurt to provide some fertility as it fits into your operation.
Remember how cover crops that are drilled have a stronger root system to handle weather better? This leads us to the ways that good ol’ Mother Nature can sabotage cover crops. The same way that drought and heavy rain effect your cash crops, those events can also be damaging to your cover crop. While this point is out of your control, it is important to remember that cover crops are not indestructible.
Keep these points in mind to set your cover crops up for success!
Wikipedia tells us that the carbon to nitrogen ratio is “a ratio of the mass of carbon to the mass of nitrogen in a substance,” but what does that mean in the cover crop world? I like to think of carbon to nitrogen ratios as the length of time plant residues take to break down for different cover crop types relative to each other…
Keep in mind, this information is based on the development stage of the plants and can vary within each category.
There are many types of grass residues that we observe breaking down in cash crops and cover crops. Corn stalks, as an example, would be a very mature grass. As you can see in the photo below, corn stalks from the previous season are not all the way broken down the following spring. Corn stalks have a high carbon content (high C:N ratio) and take the longest to break down relative to other types of residue. Circled in blue in the photo is the spring remnants of oats in the cover crop mix planted the previous fall. The oats would have been in a less mature stage (lower C:N ratio) when they winter killed so their breakdown has gone much quicker than the corn residue.
Another common grass that we think of with cover crops is cereal rye. Early in the spring, cereal rye would be a young, immature grass with low carbon and high nitrogen (low C:N ratio). When terminated in this early stage, cereal rye breaks down very quickly which acts like a starter fertilizer releasing nutrients it sequestered. Cereal rye that has been terminated later when it is more mature has been shown to cause nitrogen deficiencies in crops planted after. This is because the mature cereal rye has a higher C:N ratio which takes longer to break down. This ties up existing soil nitrogen as the soil biology works to break down the high carbon residue.
Brassicas like radishes, turnips, and rapeseed have the middle breakdown rate compared to legumes and grasses. As you can see in the photo above, the bottom green circle is where a radish was growing the previous fall. If you were to dig in that area, you could find some structural remnant of the tuber, but no top growth remains. Tubers take longer to break down compared to the very low C:N ratio of the above ground foliage. This is a benefit of the brassicas as a cover crop because over the winter the radish slowly breaks down to release nutrients brought up from deep and held in the taproot. The quick breakdown of brassicas is a large reason we do not often seed them alone as a cover crop and, instead, include them in a blend.
Legumes are low carbon and high nitrogen. This is what makes them have such high protein content, as the nitrogen is stored in the plant as protein. Even when legumes are mature, they tend to break down much quicker than the other categories mentioned, which is why legume residue cannot be seen in the photo above. There were legumes in this blend, but no residue is visible from the previous fall. This is another great example of why diverse blends are important. If you are wanting to control erosion or build soil, having more than just legumes in a blend is necessary.
Of course there is much more to the science of carbon to nitrogen ratios, but all of this shows what C:N ratios mean for your residue. How have you seen the breakdown rate of different species vary?
If you plant a cool season cover crop, odds are it has some kind of grass in it. When you think of grass, you may think of perennials, but we are going to focus on cool season annual grasses planted in the spring or fall! Cereal rye, annual ryegrass, oats, barley, and triticale are all examples of the cool season grasses we are talking about below. What can these grasses do for you?
All grasses are known for how much nitrogen they require. Grasses are very good at taking up as much plant available nitrogen as possible. This is the same for cool season cover crop grasses such as oats, annual ryegrass, cereal rye, and more. What is the benefit of this? That available nitrogen is stored in the plant’s tissues instead of washing away or volatilizing. As those plants break down after being terminated, the nitrogen they were holding is released to be taken up by the next crop planted.
Cool season grasses do not just help you hold on to only nitrogen, however. Water-soluble nutrients like calcium and potassium can be brought up from the soil and stored in plant tissues until they are terminated and break down. This protects them from washing away in the same way as nitrogen.
Interested in how to manage manure with cover crops? Read on that here!
Fibrous Root System
The physical attributes of the root system make cool season grasses an important part of a cool season cover crop mix as well. The dense, fibrous layout of the root system is made up of millions of fine roots and root hairs resulting in a high root surface area to come in contact with the soil. This conditions soil physically by growing throughout the soil and creating channels. When the roots break down, those channels are left for air and water to move through. Grass root systems also have a substantial amount of rhizosphere area where the roots can excrete sugars to feed and interact with soil biology. This builds glomalin in the soil which is how soil structure is improved.
The growth habits of grass root systems explained above physically hold soil in place with their structure. This reduces erosion while the plant is actively growing and while the residue is breaking down. Even after the grass breaks down, the infiltration and structure improvements that grass cover crops make creates a soil that is more resilient and less erodible.
How do you use cool season grasses in your cover crops?
Various grass species and varieties have different growth habits. Some are rhizomatous or sod forming. You can see in the picture below that rhizomatous grasses spread from the original plant through underground structures that send up other plants. This is a very effective method for the grass to spread throughout an area providing solid ground cover, much like a lawn.
What are the benefits?
Since sod-forming grasses create a dense stand with the rhizomes safely underground, they are very traffic tolerant. This is useful for areas that have a lot of mechanical traffic as well as livestock traffic. These types of grasses generally have low growing points on the plant making them tolerant of very close grazing. For those of you with horses, this may be what you need since they can chew stands down very low when given the chance. These sod forming grasses can bounce back from that when given time to recover from their rhizomes. On the cattle side of things, set stock paddocks can benefit from having sod-forming grasses. These species can recover from frequent grazing. This is the same reason lawns can handle being mowed regularly during the growing season.
What are the downsides?
With all of those benefits, you may be wondering “Why don’t I use sod-forming grasses in all of my pastures?” There are a few negatives to these grasses. With their low growing habit, many of these species will not get very tall. This makes them difficult for mechanical harvest and also not very high yielding. As more durable grasses, they also do not provide very high forage quality for grazing.
Sod-forming grasses do have their place if the benefits outweigh the negatives for your situation!
The word “rye” gets thrown around a lot in the ag world, specifically when talking about cover crops like cereal rye and annual ryegrass. When you are choosing cover crops, make sure to get the right rye to meet your goals.
Let’s start with the technical differences between cereal rye and annual ryegrass:
Cereal rye’s scientific name is Secale cereale and it is a cool season, winter annual cereal grain. In order for cereal rye to switch from vegetative growth to reproductive growth and produce a seed head, a vernalization period is required. This means cereal rye is a fall planted cool season that will not head out until the following spring.
Annual ryegrass’s scientific name is Lolium multiflorum. Pretty different from cereal rye, right? Also different from cereal rye, annual ryegrass is a bunch-type grass that does not require vernalization in order to produce a seed head and does not always overwinter. We have seen annual ryegrass overwinter in the Midwest depending on the type of winter season we have.
Cereal Rye: We have a full post on cereal rye here, but to summarize, cereal rye can be used as just a cover crop to reduce erosion and sequester nutrients, as a forage to be grazed or harvested, or it can be harvested as grain and straw. In the spring, cereal rye is going to be the first of almost any grass species to green up and begin growing. When it is mature, cereal rye has a higher carbon to nitrogen ratio than annual ryegrass.
Annual Ryegrass: This “rye” can also be used as a cover crop or as a forage. As a fall planted cover crop, annual ryegrass is quick to establish and has an aggressive, fibrous root system that will go to work on conditioning the soil and improving structure. Like we said, it may overwinter and continue to grow in the spring. At that time, it can be terminated, grazed, or harvested in the spring. Contrary to cereal rye, annual ryegrass can work well being early or late interseeded into standing corn. Annual ryegrass will begin to green up later in the spring than cereal rye and cannot be harvested as grain.
Take a look as some real life testimonies about the use of annual ryegrass here!
Seeding Rates and Dates
Cereal rye and annual ryegrass vary in seeding rates and when they can be planted. Annual ryegrass can be spring seeded or fall seeded up until Mid-September in the Upper Midwest. Cereal Rye is a fall seeded species and cannot handle the summer heat if planted any earlier. We have seen cereal rye be planted very late into the winter and still establish well, however, if your goal is a full forage stand or you plan on harvesting the grain, then it needs to be seeded earlier in the fall.
A full seeding rate for annual ryegrass is 20-25 lbs alone, or about 10-15 lbs in a cover crop or forage mix. Cereal rye as only a cover crop can be seeded at 50-60 lbs per acre, or if you are using it as forage or to harvest as grain the rate would be higher at 80-120 lbs per acre.
Make sure you are using the "rye" that is right for you this fall!
What kinds of brassicas can you plant right now? All of them for a few more weeks! (If you are wondering what in the world brassicas are, we have that answer for you HERE!)
Now that we are into September, our time left for brassicas to have a great benefit in the Upper Midwest is coming to an end. Our usual “cut-off” date for seeding brassicas in a mix is around September 15th. After this point, there is not enough growing season left for the brassicas to develop enough to give you the full benefits that we are about to tell you about…
The brassica we get the most questions about is the famous radish. We would almost say this is the most famous brassica because it is known for its deep taproot. The largest section of the radish tuber can reach up to 9-12 inches deep (or even deeper if planted early). This large root does help loosen soil in the immediate root area; however, for soil conditioning and compaction relief we prefer a grass with a fibrous root system mixed with the brassicas. What’s even more interesting is there is still a thinner section of the brassica taproot that can tunnel several feet into the ground to reach multiple layers sequestering many deep nutrients.
Speaking of capturing nutrients, all brassicas do a great job of this in the fall. Radish, turnips, rapeseed and others can readily take up available nitrogen, phosphorus, potassium, sulfur, magnesium and more/ These nutrients could otherwise be lost over the fall and winter until your next crop goes in during the following spring.
Brassicas aren’t greedy. They release those sequestered nutrients back into the soil as they break down throughout the winter. Brassicas are not winter hardy and will not require spring termination to melt into the soil. The photos above are great examples of what brassicas look like growing in the fall vs. what they look like in the spring. A few holes in the ground here and there along with active soil biology where the brassicas were makes for great planting conditions. As you can see, there is very little residue left of the brassicas. That is why we always recommend brassicas in a mix with some kind of grass that will break down slower and provide some additional soil cover and erosion control.
What brassicas are you using in your cover crops this fall?
Too tall, too short, or just right? What is that “perfect height” to leave pastures going into winter? It can be useful to vary your pasture heights depending on how the paddocks will be used over the winter and in the spring.
We are defining a tightly grazed pasture as having a residual height of 3-4 inches after the final grazing pass in the fall. Why would you want to graze the pastures this low? Areas grazed to 3-4 inches tall will be slightly stunted in the spring compared to areas left taller. This can be an advantage if you are planning on frost seeding in February-March. This can also be a good height to interseed in in the fall. The shorter grass will work well to drill into and its slowed growth will allow extra time for the new seedlings to get up and growing in the spring. We do not recommend doing this to all of your pastures as it can cause some stress to the stand
A “medium” height pasture would have a height of 4-6 inches after grazing in the fall. This is the preferred height for most pastures going into winter. This leaves enough residual that the grass will not pull from all its reserves going into the winter. The ground will be sufficiently covered to go through the winter and it will have enough height for spring growth to be jump started. Plan on leaving pastures that will be grazed late spring to early summer at this medium height this fall.
We would call a pasture that has 6-8 inches of remaining stubble “tall.” After the final pass of grazing in the fall, we do not recommend many pastures be taller than this unless you are stockpiling certain paddocks. If an area is taller and is not grazed before snowfall, air can be sealed out and cause snow molds. Areas left at 6-8 inches can kick start their growth quickly in the spring providing your earliest grazable paddocks.
Every pasture and management system is different, but consider these various heights as you get through your last passes of grazing this fall.
Looking to add cool season legumes to a cover crop this fall? Now is the time to get legumes planted in a cover crop, but don’t wait too long!
Nitrogen Fixing Legumes
What is pictured above? Insects? Fungus? Nope, nodules! This is where the magic happens that allows legumes to fix atmospheric nitrogen and turn it into a plant usable form. That whole process is explained here! When planning what to put into a cover crop blend, legumes are often a first choice due to their ability to fix that nitrogen for the following crop.
Why does this matter this time of year? Late summer and early fall can be a great time to get cool season legumes established. Some cool season legumes such as lentils, crimson clover, and balansa clover will grow this fall and begin fixing nitrogen and taking up other nutrients and then they will winterkill. Winterkill legumes will break down throughout the winter releasing that fixed nitrogen back into the soil to eventually be taken up by the following crop (See the image below). Other legumes like medium red clover, winter peas, and hairy vetch can overwinter and continue growing in the spring. These legumes will need a spring termination plan, but can supply high amounts of nitrogen credits from that spring growth.
Like we said before, do not wait too long this fall to plant your cool season cover crop mix that includes legumes. These cover crops need adequate time to establish to get you the best bang for your buck. Specifically the legumes that you want to overwinter need to be well established in order to build root reserves to survive the winter. In the Upper Midwest, Mid-September is a general timeframe to get diverse cover crop mixes seeded by. In any area, it should be at least 6 weeks before a killing frost.
You know that stockpiling your cool season pastures is a great way to stretch the grazing season of your perennials. What about stockpiling your warm season annuals? Forage quality and overall tonnage are just a few benefits to this practice.
Extending the grazing season is one of the most profitable tactics livestock owners can use. Aiming for the longest grazing season possible minimizes the amount of stored forage you have to grow, harvest, haul, and feed, which saves money all around. Also, livestock are able haul their own manure for you, saving the time, labor, and fuel it takes to move it from winter feeding areas.
These monetary benefits can sometimes pale in comparison to the power that grazing livestock can have on soil biology and their activity. Grazing warm season cover crops allows for residue and manure to be recycled directly back into the soil for microbes to start their part in the process. Above and below ground livestock stay well fed further into the winter.
If the warm season annuals are planted early in the summer, one to two cuttings could be taken before beginning to stockpile. If planted later in the summer, it may be best to let the mix grow and only be harvested by grazing once it is stockpiled. What exactly do we mean by “mix” in this situation? We recommend a blend of annual grasses, legumes, and brassicas for a stockpiling situation. This is usually some combination of sorghum sudangrass, sudangrass, millet, cowpeas, mung beans, clovers, and forage brassicas.
A similar mix is pictured above. The grasses in the mix will have a lot of growth in the summer heat and create structure in the mix to hold snow at different layers. We recommend using BMR varieties so that even at this more mature stage, they maintain better fiber digestibility. Legumes add protein to the mix earlier in the fall and winter and brassicas hold their quality longer into the winter. Livestock are able to make their own TMR combining the high protein brassica foliage with the digestible warm season grasses.
Now, don't let the name deceive you; alfalfa cannot be seeded the same day as trick-or-treating in the Midwest. However, late summer into the beginning of fall can be a great time to establish next year’s alfalfa fields.
One benefit is having this time available. Generally, this seeding window will land after spring and mid-summer seeding work is done and before harvest of other cash crops gets into full swing. It is important to finish planting at least six weeks before a hard freeze when there is moisture available (this will be important later). Another positive is there is usually less weed pressure for this new seedings in the fall. With summer annual weeds dying out as temperatures lower slightly, the new seeding will have less competition than spring seedings where those aggressive weeds can be your worst enemy. This helps establish a strong stand and takes away the requirement for a nurse crop, saving a little cash to spend on Halloween candy!
Remember that point about moisture early? Sometimes August to September can be dry unlike the ample rain available in the spring. If your alfalfa seeding happens to miss some of our fall showers, there can be trouble getting the seeds to germinate and plants to establish. However, if you pay attention to the forecast for seeding times, and Mother Nature works with us, the gentle fall rains can be perfect. The colder side of Mother Nature can be your other battle for fall seedings. If your hard freeze arrives sooner than expected, you could have some winter kill in areas where the alfalfa seedlings were not able to establish a hardy root system.
To summarize, general guidelines would be as follows:
Timing is key – seed alfalfa early enough to get established enough to survive the winter.
Pay attention to the forecast – moisture can be a critical factor in the fall for new seedings.
Skip the nurse crop in low weed pressure areas.
Utilize a window of precious time available to establish these seedings in the fall.