Q: An interesting debate came up in the No-Till Farmer Advisory Board meeting this morning revolving around this research paper from 2020. The authors analyzed 27 studies comparing the performance of a single species of cover crop to diverse cover crop mixtures (defined as at least 3 species). According to the paper, the single cover crop performed just as well as the mix 88% of the time and did better 10% of the time. 

Several of No-Till Farmer's farmer board members disputed the conclusion of the paper, saying they've seen better soil health results on their own farms with diverse mixes. What has been your experience with using a single cover crop species vs. a multi-species mix?

I think additionally you have to ask where are you located and when will you be planting. Here in Southeast Minnesota, if I am planting a cover following the removal of forage oats for hay, I always choose a multi-species mix. My feeling is the more diversity of roots below and plants above ground, the greater soil health and pollinator happiness is achieved.

With cost in mind, my goal is to plant the most varieties with the highest seeds per pound at a cost cap of $50 per acre adaptable to my location. That said, by the end of October or into November, planting after corn harvest I would, for economics and establishment success, lean to single-species winter rye. I have in the past added radish, turnip, vetch, rapeseed and winter camelina but never saw enough spring growth to justify the cost. The one exception was a mistake of sorts as I added turnips to winter rye planted in November that did not germinate until mid-summer in my corn crop. I had a beautiful undergrowth of huge red tops but still have not figured out how they escaped my Verdict pre and Status post sprays.

— Robert Christie, St. Charles, Minn.

We have a demonstration plot that compares rye vs. a multi-species mix vs. no-cover in a no-till situation. Last year, we did a rainfall infiltration study, and the multi-species mix performed more poorly than the rye plot at infiltrating rainwater. In general, we don't get great growth on the plot any year, but rye tends to provide more biomass than the multi-species mix. Yield performance per trial has varied over the last 8 years, but in general, the multi-species mix trial has had a lower yield relative to the adjacent plots more than it has a higher yield. The 2022 report can be found on our website: https://farmerledwatershed.files.wordpress.com/2023/03/2022-horse-creek-watershed-council-test-plot-report.pdf

— Tara Daun, Chippewa Falls, Wis.

We could certainly spend an eternity debating the finer points of this and reach no conclusion, scientific or otherwise. First, "performed," someone had to define what that meant in the study. Pretty sure it was pretty subjective. For example, did the mix have something that grew through the winter or just all winter killed — the variants on this are endless. The results quickly become meaningless given the multitude of non-controllables — just my opinion.

For our farm, "performed" means "did it do what we intended." Under that scenario, the single species virtually never performs as well as a diverse mix since we intend different things for different fields, even different pixels in our VRT management system. Just today we planted a mix of cereal rye and oats after corn. The rye always performs in cornstalks going to beans, science on it is indisputable. Why add the oats? We wanted to create a few tons of fibrous roots and soft leaves to feed the earthworms and their friends. Will the mix perform better than the rye alone? Probably not in their test, but 100% of the time, it will be for our "intended purpose."

Also, just today planted 200 acres of oats, radishes, clover and rapeseed into bean stubble. Do we need all 4? It is expensive? Well, part of this is just managing the variability of a biological system dependent upon nature for its inputs. What I mean by that is pretty simple. Some years the oats get 8 inches tall, once they didn't even winter kill, some years they get 2 inches tall, once they germinated the following spring, and we had a glorious spring cover crop. 

The point is, that we plant a mix to better manage the variability of life. We always try to add in the rapeseed so that we have something growing in the spring to capture and hold the fertility so it doesn't leach into the creeks. Did their "performed" standard include nutrient leaching studies? Doubtful.

I'll end on my initial point, the variables are endless as are the outcomes. I'm pretty sure I could statistically blow up their claims if given 10 minutes and a calculator.

— Ken Rulon, Arcadia, Ind.

I agree with Ken’s comments. We have been using mixed covers after wheat and manure (1,800 usg/a liquid poultry) on our heavy silty clay for 23 years. CSW fixed rotation. Depending on the weather, different species in the mix (we are currently 41 days without any rain since most cover planting), and differences are obvious. Only the first field had rain after planting. At about $20 per acre, costs are not excessive. Manure (and seed) is and must be incorporated with shallow cultivation to avoid n and p loss and keep surrounding neighbors happy. That is the only tillage we do. All crops are planted no-till. While my observations are mostly subjective, our soils are much “friendlier." Crop yields are more consistent. Planting is easier. Rutting is non-existent. Compaction was virtually eliminated. Erosion is virtually ZERO. We have no intention to change drastically. Only fine-tune with current conditions.

— Eric Kaiser, Napanee, Ohio

Eric, it sounds like you have a great system. If we really wanted to ramp up our system, we would add beef cattle grazing into the mix. That of course is a specific skill set that no one has in our operation, so we will just not damage our joints further at this point. When you are already $150 per acre better than most, why do we need to be $300 per acre better?

 — Ken Rulon, Arcadia, Ind.

I did spend some time on the data from the Horse Creek Watershed. So, just a couple of thoughts:

1. The work to obtain the data is substantial, and they should be admired for putting in the effort!

2. The tighty whitey test does a great job illustrating how rudimentary our understanding is of soil biology. Once we get a test that actually tests how the soil is working, we will leave the dark ages behind. Using an underwear test kind of proves you don't know what is going on.

3. The "performed" definition was not stated. It seems that it was all yield, but then throw in some data on erosion and infiltration that doesn't look like it flows to yield performance. This is what I was getting at, if performance was reducing erosion all the covers would have been equal since the mix still had rye in it. Really tough to define since everyone's goal is different. In my view, the results just confirm what most already know.

Even in the northern belt in Badger Land, no-till with covers reduce or eliminate erosion and leaching, cost less. and yield the same, or even more... and yet less than 5% of the U.S. acres are farmed this way. Incredible.

4. We would never put wheat in a mix following corn going to beans. Wheat mats as it dies and reduces early season temps, thus increasing seedling soybean diseases is the thought. Same thing on the clovers, never in front of beans. Producing N in front of the bean crop is almost always bad for bean yields. So, what is in the mix becomes very important. Some of the clovers could easily be a host for SCN or SDS, whereas the Rye is disease-suppressive it seems. Also, I just couldn't tell if the mixes were the same following corn as well as soybeans. If so, that is probably a cause for concern.

5. We don't live in Wisconsin, so I'll say they know more than me. In Indiana, we only plant covers, aerial seeding (including a Cyclone Bag Seeder) is just far too erratic in terms of seed spacing, emergence, etc. We want the covers to have roots touching 100% of the surface area, not leaves above ground, roots. We need some leaves in the spring to stop erosion but not a mat. To do that, we have to plant in 10-inch rows with an excellent piece of equipment. Just took delivery this year of a Horsch Maestro 60-foot wide seeder to plant the covers within 10-inch rows. So far it is fantastic. Similar results with our Horsch corn planter by the way.

6. The crusting seems pretty severe for that type of soil, especially in long-term no-till situations. I'd immediately take a sub-one acre grid soil test and focus on Mg., Mn., Ca. and S. Something just isn't clicking in this plot. Also, really need to see the tile drain layout vs. the yield results. Again, something just isn't right and so far I can't find out what it is, just being honest. There is a lot of data missing that just leads to questions, for what it's worth.

Lastly, and I do have to get to the combine, or I'll be getting a call from the crew, there are spots in fields that just don't yield as well. We have found many of those spots to be high in salt (often less than 1/2-acre spots that just kill yield averages. Hundreds of reasons — road salt is a big one, tight white clay that had flat rates N, P, K for years before we took over the field. Also, some spots always outperform. In our area, they are the soils just outside of where water can pool at the base of a slope.

The hill above it seeps its water in a dry year and since there is no ponding there is zero root restriction/damage from too much water in the spring. Since this field has 2 to 6% slopes, it probably has some of these types of conditions. Since the plot systems do not move, the mixes maybe just in the wrong spots in the plot. So maybe the wrong mixes are in the wrong spots and you get data that is misleading, especially if the Mg base saturation was not managed by pixel before the plot was created.

OR the mixes just don't work, which is also a possible outcome.

— Ken Rulon, Arcadia, Ind.

I agree. What works for you works for you. Remember that; you don’t have to achieve goals set by others.

Essentially (with a couple of degrees and several years of field time), I am an ecologist. I strive to see the above/below-ground interactions flourish. There are so many nuances to establishing a CC system that works for you and the soil. It's well known that plant diversity supports soil diversity and vice versa. Rye CC is king for a single species, but the structure and function of each plant in a diverse mix play an important role.

It takes time. That study is 8 years in and we don’t know the baseline conditions, but can assume it was severely annihilated by conventionally tilled soil. I have decent data from many years ago that revealed it takes 7 years after a plow to start recovering function in the soil. That has stuck in my head and come out of my mouth many times and have never had anyone dispute it. So, just being year 8 it's plausible that it's just getting to a real transition point.

 — Michael Stephens, Nebraska