Carbon Farming Part 2: Cover Crops and Carbon Sequestration

The Carbon Farming series addresses one of the more erroneous activist claims: that agriculture contributes heavily to climate change (and the activist tactical deception that abandoning conventional farming in favour of organic or agroecological solutions will help solve the climate challenge). This chapter will examine how cover-crops are contributing to more sustainable conventional agriculture and reducing climate stresses. It includes excerpts (indented) from interviews with eight farmers on cover cropping written for my 2018 column in European Seed.

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This autumn/winter, if you pass a field covered with green vegetation, it is probably not a winter crop enjoying the last days before the frost. It is likely a cover crop, grown to help prepare the soil for the coming crop next year. If you look closely you will see a variety of plants serving a wide range of services to soil, environment and farmer. What’s going on?

There’s a revolution going on in the ground below us. A growing group of passionate farmers have been experimenting with complex combinations of cover crop seed species which may have as much influence as cash crops on the future of sustainable farming.

A cover crop is any vegetation grown outside of the growing season or apart from the main crops to provide cover that protects the soil. As any farmer will tell you, their soil is the most important asset they have. Pioneers in the last decade have shown how cover crops are not just necessary to prevent soil loss, but also to develop biota, rejuvenate biodiversity, “sweeten” the soil and literally grow the earth. Weeds, pests and disease can be managed with the correct cover varieties. Cover crops are also increasing yields. Together with no-till farming, this revolution has become known as “conservation agriculture”.

The benefits of conservation agriculture are many. By protecting and developing the soil, farmers are protecting their land from wind and water erosion. Water tables are protected as runoff is reduced, the soil becomes richer, more porous and penetrable. As soils are fed a wide variety of nutrients, organic matter increases, nitrogen levels improve, and farmers can fertilise less. With less tillage, more CO2 is sequestered in the soil and less diesel emissions are released into the atmosphere.

So the first step in sustainable carbon farming is to reduce tillage to avoid releasing carbon that binds in the soil (article on that to follow). The next step is to load more CO2 in the soil through increased varieties of cover crops. As plants take in carbon, it is stored in the soil via roots, biota and soil organisms. A diverse cover crop field is not only restoring the nutrients and protecting soil, if managed properly, it is also serving as a carbon sink. See the US EPA-funded SARE pamphlet for more information.

But how much CO2 can cover crops sequester?

The film Kiss the Ground seems to suggest all climate problems can be solved with cover crops (which I feel is a bit too heavy on the KoolAid). A study recently showed that covers could remove 0.22 US tons of CO2 per acre per year. Given the soil saturation deficits, the US could conceivably sequester 0.17 to 0.35 gigatons of carbon per year in the soil via cover crops. Compared to trees (which store most of the carbon in the wood and leaves), this is significant.

While I’m not suggesting just to plant radishes rather than trees, I think we need to tone down the single-minded activist rhetoric in trying to blame conventional agriculture for all of the ills of the world. Our farmers are our best solution to climate concerns and if they can do that while feeding a growing and increasingly affluent global population, then we need to further embrace the best available agrotechnologies.

When organic-industry-funded campaigners talk about the climate impact from conventional farming, they signal their ignorance about how farmers are reducing their footprint with no-till farming and the use of complex cover crops. But they have always put politics before science. When organic farmers and their agroecology consultants talk about cover crops (without the use of herbicides) to regenerate soil, they fail to tell you about how they are unable to combine a wider mix of seeds to provide further cover benefits; they fail to acknowledge how they are limited in low CO2 termination strategies; they don’t show you how they are emitting more diesel into the atmosphere. Agroecologists would be more efficient and sustainable if they used a substance like glyphosate to terminate crops before spring planting. Their religion clouds their thinking so they just don’t say anything.

Cover crops are not an agroecology concept and factions who limit farming approaches to naturopathic dogma and social justice politics are doing a disservice to the the environment.

The next Carbon Farming chapter will be a “Monger Review” of the film Kiss the Ground to show how their orthodox concept of regenerative farming would succeed in its objectives of improving soil health, promoting sustainable farming and addressing climate issues if they would only drop their cultish rejection of modern technology and embrace the best scientific practices.

What seeds are best for cover?

This is early days in cover crop research and debate on the best seeds to use keeps farmers busy over the winter months. Add the question of which cover seeds are better for carbon sequestration, pollinator support or pest avoidance, and the pioneers light up.

While some farmers would say: “the more seed variety, the merrier”, others want to have deep rooting plants, fibrous roots and those that can survive into colder winter weather. Time and cost are important. If farmers are planting covers in August, a larger investment may be justified. A faster growing plant that has a quick uptake is important if farmers can’t manage to seed until well into the autumn. Strategy also varies if cover is combined with manure and grazing.

As farmers get better at combining cover crop species, some, like Jake Freestone, vary seed varieties according to the next crop in rotation (or if there is certain weed targeting or companion cropping planned). Jake was involved with the NIAB and Kellogg’s Origins project assessing farmer trials in cover crops. They produced a ‘cookbook’ style menu cataloguing the strengths and weaknesses of the different cover species entitled: Cover Crops: A practical guide to soil and system improvement, 2016/17.

There are of course certain cover seeds that are better for carbon sequestration in soils (particularly at deeper levels), but it also depends on the types of soil, the climate, growing seasons…

There is debate about how soil depth and saturation levels can influence the volumes sequestered. Research though has not caught up with the objectives of carbon farming and regulators have yet to fully see the light to provide recommendations. This is a serious fail in Brussels where von der Leyen’s Commission seems more interested in posturing to the activist crowd’s “Organic to Fork” strategy rather than listening to their scientists.

What is the perfect cover seed?

Farmers are more concerned about stronger roots than tops, letting in more light and less flower. A fibrous root helps open the soil, increase organic matter and promote biota. It’s about creating a “below-ground biomass”. Certain crops might work as vaccines to prepare the soil to better resist diseases. Cover crops should also repel pests that may threaten harvests.

Termination is an important topic. As Tom Jewers said: “We don’t want cover crops to become a weed, so ideally, they need to grow rapidly, but never set any seed!”.

George Hosier uses a ten species cover but also enriches the soil by grazing on his cover crops (so an ideal plant should be palatable for sheep and cattle). Frost resistance is important. With a wide mix, George has managed to keep different cover working through the winter.

As research attention is directed to more efficient cover crops, especially for carbon storage, one can imagine seeds being bred to feed more nutrients back into the soil, require fewer inputs and promote more carbon sequestration. Of course this would entail European regulators having a more open mind towards technology, gene editing and herbicides but I am hoping some climate campaigners will drop their chemophobic cousins and embrace such innovation. Just imagine the impact from the introduction of a deep-rooted cover crop seed that could reduce fertiliser use, hold more water and store vast amounts of carbon while easily being terminated at planting time with a small dose of glyphosate.

Some issues

Not everyone agrees on the virtue of cover crops. Any farmer will tell you every soil, every climate, every crop is different. Not every farmer can or needs to use cover crops in the same way – this practice is anything but a one-size-fits-all. Some are blessed with ideal conditions without the need to actively intervene or have mixed farms with ample manure; others with early winters or wet conditions would not benefit very much. A lot more research needs to be done on this subject.

Several farmers raised the issue of the cost of seeds, noting how natural off-season growth (volunteer re-growth) can be sufficient to regenerate soil. Seed merchants often offer complex blends many farmers find unnecessary (some are blending their own). Farmers also need to acquire extra machinery to allow planting through dense cover without disturbing the soil. This is prohibitive for smaller farmers. Then there is the demand on time (usually just after combining) and diesel fuel.

While farmers agree cover crops are beneficial, there is much debate on the “what” and the “how”.

If climate mitigation strategies were to seriously be considered, then better cover crops would become an important tool in the policy strategy. Farmers should be given incentives to plant carbon-sequestering covers and research should be done on the best types of climate-friendly covers that also support yields and soil. This makes much more sense then some journalist telling them to stop farming and rewild their fields at a time when population growth is putting pressure on food security.

But to promote cover crops as a means to fight climate change, regulators would also have to promote certain vital technologies.

Glyphosate is vital

Complex cover cropping has been made possible with inexpensive glyphosate-based herbicides, allowing an effective termination process once the crops have done their job. Four years ago, I was given a tour of George Hosier’s conservation agriculture farm in England and I was sold on the sustainability of glyphosate. (See my video series from that visit that includes his discussion on his ten species mix of cover crops.) Many farmers standing up for the environmental benefits of conservation agriculture could not imagine the losses to biodiversity should the activists have succeeded in banning the herbicide.

The biggest challenge for cover cropping is the continued regulatory pressure in Europe to ban glyphosate. The organic lobby rejects conservation agriculture as farming with a chemical plough. Organic farmers are not able to protect their soil with multiple seed covers without access to effective herbicides. Since the lobby will not allow organic farmers to use synthetic herbicides, there will likely be more pressure to fully ban glyphosate in the EU.

And that is more pressure than what the soil, farmers and consumers can handle.

What would happen though if European regulators actually put facts first, ignored the organised outrage of the single-minded chemophobes and put the environment and agriculture first? They would see how cover crops provide a service to the soil and water tables, reducing the need for fertilisers and insecticides, capturing and storing more carbon while reducing diesel emissions through a more sustainable farming practice. This though would only be fully beneficial (and provide the needed increase in crop yields) with the use of herbicides like glyphosate and could be more enhanced by better designed cover crop seeds.

I went back and talked to some of the British farmers last year to see how the progress had been since my visit (and article) and I am afraid I have some sad news. Most farmers accept that conservation agriculture practices are better for the environment, their soil and the climate, but there are some costs incurred in switching over to no-till farming (eg, buying the drilling equipment). As there is uncertainty whether glyphosate will be renewed in the coming years, many farmers are not ready to risk making the investment and then have no means to terminate their cover crops.

So kudos to the chemophobes in Brussels and Paris – they are winning the campaign against glyphosate but destroying the environment by preventing farmers from adapting more sustainable approaches. I’m sure that doesn’t really bother them. And shame on the cowardly EU policymakers for not sending farmers a clear message that they will support the environment and sustainable farming by committing to keep vital herbicides on the market.

It is time to stop listening to the cosmopolitan zealots and dogmatic activists and embrace science and innovation. It is time to harness agriculture to protect the environment and fight climate change (rather than to protect some idealists’ anti-chemicals campaign).

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A special thank you to the following farmers for their support in researching this subject in the original article: Jake Freestone, George Hosier, David Butler, Tom Jewers, Tom Sewell, Laurent Van Arkel, Marcus Höltkotter and Terry Daynard. Your work for farming has been precious.

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2 Comments Add yours

  1. Dr Robert Johnston says:

    As usual, a totally brilliant summary of the latest science and a devastating critique of the mindless eco-extremists who care more about their bonkers, out-of-date political objectives than farmers OR the planet!

    Like

  2. Good article – much appreciated.

    Like

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