The smart solution to the global warming challenge involves the recognition that soil carbon is king in the rescue equation. We could cut CO2 emissions by 100% tomorrow morning, but it would not save us. In 200 years’ time, the CO2 in the atmosphere would be down to the levels we had in our atmosphere in 1975. That level remains too high and the oceans continue to acidify and heat. There are many knowledgeable commentators who would agree that we have less than 200 years left, so you might presume that it is all over bar the shouting. This is not the case.
There is a solution, and that saviour lies beneath our feet. When we build humus in our soils, we are sequestering the CO2 that would otherwise have returned to the atmosphere, as part of the carbon cycle. In this context, mastering the mechanics of humus building and applying that knowledge becomes a problem-solving contribution second to none. Over the following weeks we will look more closely at some of those mechanics, beginning with one of the most exciting research findings in recent years – the potential of cocktail cover crops.
Eight Reasons to Cover Crop
There is a common misunderstanding whereby growers fear competition from the cover crop for limited soil moisture. There is little evidence, however, to support this concern. In fact, the cover crop may provide the opposite outcome. Here are eight reasons to consider cover cropping:
Nature abhors a vacuum. Something grows immediately on bare ground to shade that soil, reduce erosion with living root mass and, most importantly, to feed and support soil-life. Plants gift 30% of their daily glucose production to the army of organisms gathered around their roots. The hungry subterranean hordes don't care if that food comes from a weed or a more valuable plant, but we do, and herein lies our opportunity to make this phyto-cafe really work for us.
Cover crops can serve to smother weeds. In fact, they can do more than that. Some popular cover crops like oats, rye and sorghum produce biochemical exudates that discourage the germination of weed seeds.
Cover crops can help to provide key minerals. In fact, this role involves three of the most important minerals – calcium, phosphorus and nitrogen. Most people think of legumes, for example, as a tool to deliver supplementary nitrogen. However, they do much more than that. They release acidic exudates that break the bond between locked-up calcium and phosphorus in the soil and make both of these photosynthesis essentials available.
Cover crops can protect against root knot nematodes, the world's most costly pest. Brassicas release root exudates called isothiocyanates, which are toxic to this invader. In addition, isothiocyanates can protect against some of the most destructive fungal diseases. For example, Mayton et al (1996) determined that the release of a specific isothiocyanate called AITC, by green manure crops, inhibited Fusarium in potatoes. Right back in 1937, Walker et al discovered that the AITC, produced by mustard, was toxic to a range of fungal diseases. Gamliel and Stapleton (1993) demonstrated that decaying cabbage leaves had a significant inhibitory impact upon Pythium ultimum and Sclerotium rolfsii.
Cover crops containing brassicas can also provide an allelopathic response and inhibit weeds. Isothiocyanates are also involved here, along with several unidentified compounds. The decaying residues of crucifers has long been known to inhibit the germination of weeds and some crops (particularly small seeded crops). Weed seeds are typically smaller than crop seeds and this is to their detriment in this scenario. However, growers must be careful with small seeded crops like lettuce, following a cover crop dominated by brassicas. The breakdown compounds from mustard as the leaves decompose are particularly effective against problem grasses. Rye, wheat and hairy vetch also produce compounds that inhibit weeds.
Cover crops feed the soil with the constant delivery of glucose from their roots to the surrounding microbial workforce. However, it doesn't stop there. When these crops are turned in, they provide a serious humus building opportunity, with all of the flow-on benefits that come from increasing your humus levels. There are well-researched improvements in soil structure following cover cropping, particularly when cocktail cover cropping is involved.
Cover crops seriously reduce erosion. Topsoil is a precious, life-sustaining medium (in every context) and yet, at our current rate of topsoil loss, we will have no food-producing soil in just 60 years. This grim fact should surely be a wakeup call in this, the International Year of Soils. Just 0.1% of rain events cause 75% of erosion. It was thought that the residues from no-till would help prevent losses from extreme weather, but it is not the answer. There is no comparison between the living mulch that is a cover crop compared to the crop residue involved in no-till farming.
Cover crops provide a habitat, along with nectar and pollen, for beneficial insects. They are becoming an increasingly important component of the IPM approach. In some instances, these crops can also host and feed insects that might otherwise damage the cash crop.
Putting It All Together – The Cocktail Effect
Hopefully, you have now realised that there are many potential gains from including cover crops in your fertility program – but what happens when you include them all together? Actually, an amazing phenomenon occurs, where the gains are greater than the sum of the parts.
The USDA were looking at why organic growers build more humus than conventional farmers. During this research, they came across a group of farmers in two states who were claiming tremendous benefits from cover crops involving multiple species. When seeking to ascertain the science behind these claims, the researchers were fascinated to find that, when seed combinations involving five species are planted, there is a synergy created. The roots seem to message each other and the root mass begins to exude phenolic compounds into the surrounding soil. We drink green tea for the benefits of phenolic compounds, but who would have thought that soil life would respond so dramatically to similar substances? On second thoughts, why not? A cell is a cell. These phenolic compounds seem to send the beneficial soil life into hyperdrive. The soil structure improves more rapidly and humus is created more efficiently.
The five species involved include grasses, cereals, brassicas, chenopods and legumes. A typical cocktail might include a dozen different plants, but the mix must contain all of the five species. Many people are unfamiliar with chenopods – this classification includes beets, spinach and the popular superfoods, quinoa and amaranth.
When in South Africa recently, I checked out a cocktail cover crop on the farm of a dear friend, Dick Isted, in the Drakensberg mountains. I pointed out that they should be making kale salad with the healthy young kale that was part of his mix, and we did. It occurs to me that you could formulate a cocktail that was largely edible, harvest some of it and sell it in bags for salads or green smoothies. Incidentally, you can tenderise kale and make a truly delicious salad by massaging the leaves with lemon juice and letting them stand for 20 minutes before consumption.
I recently toured South Africa with the head scientist from Brookside Laboratories in the US, Dr Luke Baker. Dr Baker cited his own research, where he had monitored single species cover crops and their impact on a poor, compacted, clay and gravel soil. There was always a response with the single species crops, but within weeks of turning in his first cocktail cover crop he reported a dramatic change in this unforgiving soil. He described driving a spade into a soil that was like pushing a warm knife into butter. This is a major breakthrough, to the point that governments should be subsidising the inclusion of these crops whenever possible.
Here is part of a recent email, along with some photos, from NTS client Adam Oaten from South Australia (reprinted with his permission). Adam describes his experiences with cocktail cover crops:
"The productivity of the pastures is unbelievably good, farmers and agronomists alike have been stunned by the amount of grass we grew last year and this year there is more than last year but we have added more variety of seed.
Last year we used a composted chicken manure at 5 T/ha and 2 T lime/ha. I also brewed up your Azotobacter (Nutri-Life Bio-N™) and my own fish hydrolysate mix and sprayed that out at 20 L/ha over 2 – 3 applications. This year has been similar, but we used gypsum instead of lime (and less chicken manure) and with seeding we coated the 60 kg/ha of seed (I'll elaborate on the mix) with your Seed-Start™ and Rhizobium inoculants. Then, we dusted the seed in a mixture of your Soluble Humate Granules™ and your mycorrhizal powder (Platform®) right before seeding. Thank you. Your products are amazing! I bought all this from your agent, Bio-Tech Organics in Virginia SA.
I am in SA (Adelaide Hills) in a 650 mm rainfall region. Some of the seed was purchased off farm and are "older" varieties.
The seed mix is a little different to the standard and I received a lot of negative criticism from farmers/agronomists because of my choice. However, I was working on Gabe Brown and Elaine Ingham's principles of "diversity".
We used Adrenalin Annual Rye, 2 types of Perennial Rye including Barberia, Fescue (warm season variety), Australian Phalaris, Porto Cocksfoot and the legumes we used included Balansa Clover, Persian Clover, winter active 9 Lucerne, winter active 6 Lucerne, Namoi Vetch. Then to add some more bulk, we added a forage Barley, Wintaroo Oats, Lupins and Fenugreek Herb just for fun into the mix. The cereals, (oats and barley), and lupins were added for forage and bulk organic matter but I also read that oats are exceptionally good at proliferating mycorrhizal fungi.
The cereals amounted to approx 10 kg/ha and the grasses and legumes amounted to the balance. This was a heavy seeding rate but I worked on the principle of leaving no room for weeds.
Then, I decided to extend Gabe Brown's ideas of cover crops (and this is where I get howled down by the agronomists and seed merchants). I am sowing a further seed mix into the same pasture come spring, consisting of: 2 types of Millet, Sudan Grass, Cowpea, Lablab, Buckwheat, Leafy Turnip, Chicory, Sunflowers and possibly Mung or Fava Beans; Sainfoin and Stylo, if I can get it.
I grew a partial mix of these last year on some land that wasn't overly productive in the past and, to our amazement, it went nuts. So I intend to expand the "experiment" over most of the property. The aim is to prove that we can have green pastures all year round with only using rainfall and zero irrigation. We successfully grew pasture 5 ft tall right through summer with just what fell from the sky. Plant diversity is the catalyst for plant growth and that area of land that grew the sudan/sunflower and warm season mix over summer is now in the middle of winter as productive as the rest of the farm (see pic with winter grasses browned off but sudan/millet/sunflowers thriving). The attached pic was taken at the end of Summer, March 2015.
The winter grass has browned off but the cover crop is thriving
I'll stop going on, but all in all, I'll sow close to 30 species of grasses, legumes and herbs.
Over 80 acres we used 4 L of MCPA (broadleaf spray) and basically spot spray capeweed, it sends the brix plummeting and the insects attack en masse, leaving the beneficial plants pretty much alone.
Herbicide usage is minimal, we don't get all the capeweed, but what we don't get, the bugs soon clean it up. The pic is a little blurry but on the capeweed is 3 different bugs munching away whilst the grass looks lovely and healthy in the background. The pic with the quad bike was taken yesterday to show the growth of the oats/barley and how well the grasses/vetch combine with these. The last pic shows how thick the grass is, no sunlight is hitting the soil surface and hence the fungal growth over the entire surface of the soil.
Insects eating the capeweed but ignoring the cover crop
Oats and barley powering with grasses and vetch
Healthy diversity at the height of winter when the pastures have frosted
As part of the "food web" we have had a flock of resident finches (small black birds) that have been gorging themselves on bugs/insects etc for close to 3 months now. Every day they are hovering over a different part of the paddocks cleaning up the insects. I took a small video as it’s fascinating to watch. The birds would easily number in excess of 100, they are so thick they look like flies. Cheapest insecticide I have ever used!!
I always read your blogs with interest and love the sharing of knowledge. Thank you."
Thank you Adam. You are doing a great job and I hope we can have a field day on your farm sometime soon.
Mayton, H.S., Olivier, C., Vaughn, S.F., and Loria, R., Phytopathology, 86, 267, 1996
Walker, J.C., Morell, S., and Foster, H. H., Am. J, Bot., 24, 536, 1937
Gamliel, A. and Stapleton, J.J., Phytopathology, 83, 899, 1993