Single vs. multi-species cover crops

Here is an interesting article that seems to favor single-species cover crops.

https://www.geneticliteracyproject.org/2017/02/01/monoculture-cover-crops-often-better-polycultures/

I am going to look into the article more to better understand the methodology used in the study. Gabe Brown has conducted similar experiments with opposite results that strongly favor use of multi-species cover crops.

In the middle of this article I found this line.

Whether it be crop rotation, cover crops, or the need to supply farm fields with inputs, agriculture is not like nature.

I think this should be rephrased to big ag is not like nature. As far as I can tell the whole permaculture movement is about reducing/eliminating synthetic inputs while maintaining adequate production levels. The best way to accomplish this seems to be by mimicking nature.

Adequate production levels are a subjective term that can only be decided by the individuals managing a piece of land.

When it comes to cover crops especially in mixtures the effects need to be measured in more than one growing season which is what the author of the article did. This is because a legume such as red clover which is very popular as a cover crop will pull phosphorus up to the soil surface, as well as fixing nitrogen, this will improve the next yield for the next growing season. One could try a simple mix such as red clover and rye grass, this would fix nitrogen and the rye grass would produce carbon. In the next growing season the carbon from the rye grass might not have broken down yet and the crop that is grown would be significantly less than what is grown on pure clover residue, however in the  next growing season the yield would be substantially substantially more than the crop grown on the second year clover residue.

The long term effects need many growing seasons to be determined.

Funny enough I agree with the authors conclusion.

I think that any cover crop can do some good. If you like planting polycultures, do it. But don’t let the appeal of the silver bullet, of the secret solution, cloud your judgement. Novelty entices the most sober-minded of us into thinking “this is it.” I still sometimes grow cover crop mixes, but also monocultures. Both are good, but as I found, and as science is confirming, cover crop mixes are not the restore-everything-to-as-it-should-be final solution we hope for.

Cover crop mixes are not the be all end all solution to people are looking for, even though right now they are getting a lot of attention. I think there are a lot of techniques and ideas that make up a real solution. These will be different for everyone depending on where they are and how much time they have to put into it. I have found this site to be chock full of great ideas.

I read several of the studies. Generally, very well done. The most recent one that they cited had no original data, it was a summary article only. But good stuff in there when you are planning cover crops.

MAJOR limitation, and I suspect why they are not supporting polyculture cover crops: ALL cited studies I read used tillage!!! Some less tillage, but Gabe Brown is no till! So this is possibly non-applicable in that system. My understanding on the benefit of cover crops is two major categories- increased biomass/nitrogen and increased soil health. With tillage you are down to one benefit- OM and nitrogen. You may get other benefits like pollen or forage but soil disruption is essentially going to make the soil start from scratch every year- you get a fermentation vat and not acres of compost pile. Gabe's contention is that over a modest period you have such an improvement in the soil biome that you can avoid further inputs. I have my suspicion that this is not true in all or even most cases if you are shipping mass minerals off your property (like hay), but intellectually it makes sense that the runoff (which is the bigger loss in most systems) is reduced hugely. I could be wrong, it may be that in a well-running system the calcium, sulfur and magnesium can be drawn from depth and make this unnecessary, but the macrominerals are lost in quantity in some crops. It may depend on your subsoil largely. I think Gabe knows more about this than I do by a lot!

I haven't met Gabe but if I ever have the honor I would tell him how much he has influenced my thinking. More than that but given the number of acres and calories his ideas can potentially be upscaled into, he is a bridge builder. I would suggest that Gabe is a model for Big Ag in a way the rest of us may not be, and I see that as inspiring!

A couple of thoughts - Google "multispecies cover crops" and you get loads of results, including scholarly articles.  I can't readily find the name of the cover crop specialist Gabe Brown credits with getting him started on multi-species cover crops, but I know Gabe talks about him in at least a couple of his presentations.


In other words, there's a substantial body out there showing multi-species cover crops as having greater performance than single cover crops. You can probably find research that looks pretty good to support any position whatsoever, if you look hard enough.

One must be judicious when reading most of the studies that are published.
I find very few published studies that are not funded by "Big Ag."
Universities receive a lot of funding for such research, all of this funding comes from companies Like Dow Chemical, Bayer, Monsanto, etc.
That means that funding is coming from people who want to see results that are favorable to their point of view.
When you are funded, the last thing you want to do is have results that are the opposite of what the funding company or companies or government expects to be found, because that ends the funds.
What we end up with are studies that have been slanted just enough so the results show want that fund provider wants or expects to see.

It isn't hard to prove the point you want to make when doing any study, all that is required is specificity by the designer.
If I want to show that mono cropping is good, I set up for yield per acre results.
If I want to show that mono crop cover crops are just as good as multi species cover crops, all I have to do is; test fields would be mono-crop and similar (competing) multi-crop plantings
Results would be via chemical analysis prior to and after turning under, thus the results would show no difference in viability for soil improvement.

If I were to plant clovers, daikon radish, brassica, alfalfa and let it all go full term then turned it under, it would destroy my desired results.
So I would not use those types of plants as one of my multi-species cover plantings.

Clovers are nitrogen fixers, daikon is a soil loosener/ tilth improver, brassicas build useable shallow minerals and alfalfa is a deep mineral miner plant with tall straw stalks.
Using this mix, the results would have shown better soil conditioning, increased humus and mineral content, thus skewing the results away from mono-crop cover planting being as good as or better than multi-crop planting.

Any time you read someone's research study, it is important to read what they are studying and how they conducted their study. Usually this is listed specifically after the overview (abstract).
Once you understand what they were trying to find out and how they went about gathering their findings, you have a much better understanding of what they report in their paper.
Rarely does a scientist start a research study with out an idea of what they want to find out, by that point they have already written the thesis and grant proposal.

Redhawk

It all depends on the soils, species, and goals as to how many multi-species crops a soil can carry. A rich high carbon and nutrient rich fungally dominated soil that receives a lot of rain or run-off will carry more than another that is low in carbon and bacterially dominated. It doesn't surprise me they saw annual monocultures outperforming multi-species, especially if the soils were also tilled. There is a recent paper[1] on soil networks showing that as restoration progresses those networks become more connected and sequester more carbon despite no appreciable increase in soil biomass. It's the connectivity that makes the entire soil food web more efficient and able to share resources for higher productivity. Building a community of microbes and plants that work together makes a big difference, but that can take time that big ag simply doesn't have, but is something people like Gabe Brown do recognise.

I've seen a large study on native grasslands that showed for up to about 4 grass species the results were a linear increase in biomass at best, with lesser gains all the way up to 32 species. Another flood study showed 16 native species reduced soil bulk density the most and reduced flooding.

I've also seen low count multi-species lab and greenhouse studies showing wildly varying results with researches scratching their heads as to why.

[1] Soil networks become more connected and take up more carbon as nature restoration progresses : Nature Communications http://www.nature.com/articles/ncomms14349

In my experience which has been 42 years of farming, I have never seen a monocrop of any kind out perform variety. It does not matter if we tried replanting old fields into pine trees, hackmatack or oak, or in planting one species of grass in a field. Each time we reverted back to a variety of species, things went VERY well.

In this case, I can see where they got the results they did. Permiculturists use cover crops for a different purpose than row crop farmers. It is still a VERY good thing they use them however and they are getting good results compared to what they had before. They are getting green manure, nitrogen fixing and less soil erosion, but this is nothing new. In the 1970's cover crops were HUGE and it was well funded by the USDA. The silly part was that they stopped funding the cover crop program.

I watched a few Gabe Brown videos and like what he is doing. We are seeing similar results as him, but do it differently just because we do not have thousands of acres of wide open prairie that he has. He does it through grazing, but we do it another way, through the spreading of manure mechanically. It is the same thing only our way costs more, but due to the land base here, have no alternative.

He is seeing amazing results where he is at because his neighbors are dependent upon synthetic fertilizers, on my farm we never were, nor have we ever. We have enough sheep and cow manure so we get similar results, with high worm counts, deeply rooted crops, and vigorous growth. It is that organic matter going on the ground that does the work. He is doing it by having his cattle and sheep walk about his fields, but we simply haul our manure to a field and spread it by tractor and manure spreader. Same thing, just done differently.

As for our crops, we have never went with 100% alfalfa fields simply because our climate could not support it like Gabe Brown's neighbors. Because of the cold here, high winds, and elevation, we would get winter kill. We can put a percentage of it in the mix, but it is VERY field location dependent. But this is also New England where we have the greatest pastures in the world. A very short growing season to temper that greatness, but the topography and terrain, weather and rainfall are very good for the grass we grow, which is a mixture of cool season and warm season grasses. This is much better then native prier grass which is rather poor grass. That is why Gabe Brown is constantly tweaking the grass he is growing.

So in conclusion, to me the report is accurate, its just not really comparing apples to apples.

It is kind of like the three sisters method of growing those three crops. Without a doubt that method combined can grow abundant crops in comparison to those same crops grown in a mono-culture system, but since it is impossible to harvest mechanically, it does not do much good for putting food on the national food chain. The abundant crops would rot in the field by the time they were harvested. To me it just does not make much sense to argue whether or not the three sisters method of raising crops is better, and slamming big agriculture for not doing it; the intelligent thing would be to try and conjure up a mechanical harvester for the three sisters method to make the crop raising method work so more food is put on the national food chain. And so it is with cover crops. I am just excited to see so many neighbors of mine referring back to using them again.

Genetic literacy project is a pro gmo shill science advocacy group... nothing to see here. Plant poly cultures.