020 Relay Seeding Cover Crops
#RealisticRegenAg Relay cover cropping is simply deciding what we want to grow on the land rather than letting nature decide for us. Join me on this episode where I explain why I am convinced this is the best way to make cover cropping work in short growing seasons. To end the episode I'll go through an example rotation to help you get started while using existing equipment and inexpensive seed.
Hello! This is Scott Gillespie and welcome to the third season of Plants Dig Soil. In this podcast, you will learn how to think critically about regenerative practices as you work to incorporate them into your agricultural, horticultural, and home gardening systems.
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I have become convinced that the best way to pursue the goal of continuous cover of the land with a living root is to practice relay cropping. The concept of relay cropping is usually applied to cash crops in the areas with long growing seasons. One of the most extreme versions of this involves planting soybeans between wide row winter wheat, just prior to stem elongation. The soybeans establish slowly under the canopy and already have multiple leaves at wheat harvest time. When the wheat is harvested it exposes the soybeans to full sunlight, and then explodes in growth.
Where I first saw this concept applied to cover crops was in Wisconsin, Minnesota, and the Dakotas. Most corn farmers thought that it was too late to plant cover crops after corn harvest. Corn is harvested late into the fall, sometimes bordering on when the snow flies. It seemed impossible to have a cover crop, but then innovative farmers and researchers experimented with planting a cover crop between the rows just before the corn crop fills in[1]. It must be done after the last herbicide is applied and residual products can not be used, or must not target the cover crop species. The cover crop starts to grow but does not do much as it is shaded by the canopy of the corn. As long as it is a low growing plant that does not climb the stalks, it will not interfere with harvest, and the soil is already green once the combine has gone over.
Inspired by this and facing an even shorter growing season here in Southern Alberta, Canada, I decided to try it in my own garden. If you want to see some pictures of this, check out the transcript to my last episode of 2019,[2] which I link in this episode transcript. One of my clients was trying cover crops out for the first time and, as we were filling the drill, we realized the hoses had not been re-attached after it had been cleaned. It was not a lot of seed that ended up on the ground but, for a gardener, it was multiple years of supply. There was a little bit of soil and some crop debris in the bag, but it really did not matter to me because I would be seeding it by hand anyway.
In early June, all my vegetables were established. So, after weeding between the rows I spread some seed and lightly worked it in. It worked very well, better than I would have expected. The vegetables were not affected by it and, as early season ones were harvested (like garlic), it grew to fill in the space. For ones like parsnip, that are harvested near freeze up, there was not much growth, but it was also green all year long. It does not matter how long the vegetable crop grows, there is always something ready to take over as it matures.
Though the relay crop is hindered by less sunlight, it is not dormant. In a recent presentation by Dr. Mellissa Arcand[3] she put up a diagram from a study in 1937 that showed the roots and shoots wheat and wild mustard three weeks after emergence. While there was only 15 cm (6”) of top growth, there was 75cm (30”) of below ground growth. This would have been in ideal conditions with full sunlight and so rooting that deep could be expected in three weeks. Relay crops may need to sit under the canopy for six weeks or more so it is not unreasonable to think that more time would mean that they will be able to do the same.
This is why I am so convinced that relay cropping is the way to make things work in my area. We all know this lag period where you see the crop emerge and then it seems to just sit there not doing much until weeks later when it has explosive growth. When we do not see much going it is in fact growing rapidly underground; what we see above ground is like the tip of the iceberg. In the study from 1937 the roots were 5x deeper than the above ground height.
We also know how a maturing crop has a similar lag period near the end. While most of the grain has been filled, we just need to wait for it to mature for harvest. By overlapping these lag periods, we gain weeks, maybe a month or more, of growth in the fall.
If you are not convinced that this will work, think about harvesting a field and thinking it looked fairly clean only to come back in September and see it green with weeds. They did not germinate after harvest. They were there all along and just waiting for full sunlight. Relay cropping is simply deciding what we want to grow on the land rather than letting nature decide for us.
Below ground relay cropping also means a seamless transfer for the soil microbes. Plants are most actively exploring the soil and sending sugars to the microbes when they are in the vegetative state. At this point they are scoping out what resources they have and determining how many seeds they can produce. This peaks at flowering time and diminishes through seed set and seed filling[4]. Having a relay crop in the vegetative stage means fresh roots exploring the soil while the old roots are diminishing.
Recent research indicates that, with a healthy mycorrhizal fungi network, these dying plants may even give some nutrients to the newly establishing plants.[5] They will take care of the seeds they are producing first, the grain of your cash crop, but in their final stages of decay they may release nutrients and send them to the actively growing plants. I wonder if this could also help with maturity. It will remain to be seen but it is possible that by having the next crop ready to grow the existing crop may mature faster because it has a place for the nutrients to go.
Seeding a relay crop can be as simple as putting seed in a fertilizer spreader and heading out over the field. The advantage to this is that you may already have a spreader or can borrow one from the fertilizer dealer. There will be crop trampling, but it should be no less than what is done with the sprayer. Ideally, you would use the same tracks as the sprayer but since most are self-propelled this is not likely. This will work if you are using tiny seeds, such as clovers, that can germinate on the surface with sufficient and frequent enough rainfall. This may not work every year, but it is a very low-cost way to experiment.
One way to increase the effectiveness of broadcast is to make a toolbar that scratches the surface and mixes the seeds in. On a field tour in August of 2019, I saw a toolbar that used a Valmar to blow seed to shanks that ran between the rows. There was a small harrow where the seeds blow onto and a chain that drags behind to cover them. This particular bar was used for inter-seeding covers between 22” corn rows and so it did not use a lot of iron. It was also being used on irrigated land so even if seeds are not too deep most will germinate. If you want to see pictures of this, check out the slides from a presentation, I gave this past winter called “Carbon Building: Realistic Expectations”[6].
On dryland, the most effective way is going to be to place the seed in the ground. Last year a client of mine, Josh Beck, used an old toolbar with some disc openers feed with a Valmar. The best seed is going to be a clover because it is so small and minimizes fill up time. By having it in the ground you do not need the surface staying wet to germinate. The discs cut and leave the soil mostly undisturbed. Even if the rains do not come for weeks or a month or more after seeding it will be ready to grow when they do. If you would like to learn more about his system and how it worked in the first year of operation check out an article that was written up about him this past winter in Grainews call “No such thing as failure, it’s all a learning experience”.[7]
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Let us now shift to an example rotation and how you can integrate relay cropping to maximize the amount of living roots you have in the soil over the growing season. I am going to use the rotation that I talked about in episode 018[8] of the podcast when thinking through nutrient exports. You would have all crops growing every year at different points in the rotation but for simplicity I will just start with the peas.
Peas can be planted very early. Ideally, you will have cereal stubble and ideally there will not be much nitrogen leftover. Since peas are great at fixing their own nitrogen, we may as well be maximizing the amount that they take from the atmosphere.
You are harvesting the pea seed and, contrary to common sayings, you are not getting free nitrogen left in the soil. The plants do not give because they are feeling generous. Nitrogen fixation reaches its maximum at flowering and seed set time. When you see the yellowing in the field the plants are taking every last bit of nutrients they can to give to their seeds. Since you are exporting the seeds, you are exporting most of the nitrogen.
Soil tests after peas and most legumes will show very little nitrogen leftover. The common myth that there is a nitrogen leftover comes from corn and soybean production in the United States. Planting corn after soybeans require less nitrogen because less is tied up in the breakdown of the soybean residue. When corn follows corn 30-50 lbs. of nitrogen is needed to breakdown the corn residue. When corn follows soybeans, the residues already have a good C:N ratio and so nothing extra is needed. In my experience it is better not to count on a nitrogen credit to the next crop. Even if there was a small credit our season length is so short the next crop may not see the nitrogen in time.
Since peas are harvested so early the next crop would ideally be winter wheat. There will be a gap where there is no living root, but this is less of a concern to me as I know winter wheat will germinate and grow. Most of the cover crops are very slow to germinate and struggle to get going in the heat of August. Winter wheat seeding is not until late August or early September. This gap in having a living root in the ground could be an opportunity for dealing with hard to control weeds such as perennials. A burndown in early September near or just after a light frost will maximize the amount of glyphosate that gets down into the root of thistles and dandelions.
Coming around the next spring, there is an opportunity to plant your relay crop within the winter wheat using only a spreader. There is sometimes a period where clover seeds can be broadcast onto frozen ground and through the day as the surface thaws and then refreezes at night the seeds are drawn in. In the cold temperatures of March and early April, the ground will stay moist longer and may get them growing. As long as there are not many weeds this will work. Otherwise, you will be better off spraying out the weeds and using the interseeder later.
After winter wheat harvest, you should see the field green up as the clover gets sunlight. With some fall rains and the cooler temperatures more conducive to its growth you should see a nice green field in September. Moisture will need to be monitored in case you want to terminate it early, or if it gets too weedy and you want to prevent seed set. The advantage to a legume over a cereal as a fall cover crop is that it can produce nitrogen for you and does not use as much water[9].
Clover may or may not over winter. If it does, you will want to be ready to kill it in spring. In areas of the Eastern United States and Canada, there are opportunities to plant green and kill it later. They often have more time for it to grow and they generally deal with excess moisture in the spring. Here in Southern Alberta, we need to hold onto our moisture supplies as we do not have a long shoulder season to get a little extra growth. Most of the time we are seeding as soon as the ground thaws. There may even be a little frost still a few feet down when seeding. I covered this more in depth in an episode last season called “010 Plant Green? Plant Brown?[10]”
The next crop to grow will be canola. It is non-mycorrhizal and so it will not work with the fungal networks that colonize your soils. They will not die off completely, but they will go dormant if nothing is there to feed them. This is where your interseeder will work well. Just like with the winter wheat you can interseed a clover after the herbicide applications. Since canola is a later crop to establish the demands of the interseeder will be spread out as the winter wheat will have been done many weeks prior to the need to be in the canola.
To complete our four-year rotation, let us look at using spring barley or wheat. If you have the legume the wheat may benefit from a mid-season nitrogen release and increase the protein. Barley may be easier to grow as it can be planted a little later than wheat if there is spring growth to control. Since peas will be the next crop in the rotation planting a legume relay crop may not be the best option. An option here is simply to rely on the volunteer growth harvest. A light harrowing will plant these seeds and likely some weed seeds too. The goal is to use up the additional nitrogen so that the peas will fix as much as possible.
As you can see, getting into relay cover cropping does not have to be complicated. It can be as simple as using existing equipment and small, cheap clover seeds to get going. Existing equipment may be able to be modified to shift half a row width over or you may be able to make something out of scrap equipment and a little ingenuity as many other farmers have done. Ease into and learn from each year and, in time, you will be able increase your sunlight capture and the amount of sugars going down into the soil to feed the microbes.
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Remember to get local advice before acting upon this information. If you do not know who to talk to, get a hold of me and I will help you find someone. If you are in my local area and need help, contact me. It is always free to chat. If we get to the point that the scope broadens to consulting work, we can work out a plan that fits your budget.
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If you are still listening, you are probably like me and like to know what the catch is. Why am I putting out this information for free? The reason is that I love to learn, and I love to share the information. My knowledge has been built up from experiences in my own garden, advising clients in my consulting business, and from reading the latest books and articles on agronomy and regenerative agriculture.
I have a B.Sc. (Agr.) with an agronomy focus and a M.Sc. with a focus on Plant Science. Beyond my formal education, I have attained, and maintained, my Certified Crop Advisor designation and am a member in good standing with the Alberta Institute of Agrologists.
Nearly everything I talk about is from free resources posted to university and research organization websites. Books that used to be hard to track down are available to buy or borrow for nearly anyone with an e-reader. The information is out there – sifting through it all is what takes the time.
I make my living entirely from consulting. I do not sell any products, software, or systems. I strive to be as independent and as unbiased as possible so I can provide the best advice to my clients and help as many people as possible move from conventional to regenerative agriculture.
[1] University of Wisconsin Integrated Pest and Crop Management. 2015. Interseeding cover crops into corn in Wisconsin: Can it work? https://youtu.be/ipw2lsyYZ0E
[2] Scott Gillespie. 2019. 006 Lessons Learned in 2019.
https://www.plantsdigsoil.com/podcast/006-lessons-learned-in-2019
[3] Melissa Arcand. 2020. The Root of the Matter: Why Crop Roots are Important to Soil Organic Matter and Nutrient Use Efficiency. https://aia.in1touch.org/document/5719/ArcandM_AIA%20Workshop%20-%20Dec%2017.pdf
[4] Clain Jones et al. 2020. Cover Crop Management in Semi‐Arid Regions: Effect on Soil and Cash Crop.
https://acsess.onlinelibrary.wiley.com/doi/10.1002/crso.20065
[5] Michael J. Goss et al. 2017. Functional Diversity of Mycorrhiza and Sustainable Agriculture:
Chapter 3 - The Roles of Arbuscular Mycorrhiza and Current Constraints to Their Intentional Use in Agriculture.
https://www.sciencedirect.com/science/article/pii/B9780128042441000034
[6] Scott Gillespie. 2021. Carbon Building: Realistic Expectations.
https://www.plantsdigsoil.com/s/Carbon-Building-Realistic-Expectations-slides.pdf
[7] Lee Hart. 2021. No such thing as failure, it’s all a learning experience.
https://www.grainews.ca/features/no-such-thing-as-failure-its-all-a-learning-experience/
[8] Scott Gillespie. 2021. 018 Three Pillars Propping Regen Ag.
https://www.plantsdigsoil.com/podcast/018-three-pillars-proping-regen-ag
[9] Adityarup "Rup" Chakravorty. 2020. Cover crops can benefit hot, dry soils.
https://www.crops.org/news/cover-crops-can-benefit-hot-dry-soils/
[10] Scott Gillespie. 2020. 010 Plant Green? Plant Brown?
https://www.plantsdigsoil.com/podcast/010-plant-green-plant-brown