Soil Organic Carbon: The One Metric That Matters Most

0:06 What would you say was the most, if you would just measure one thing from the soil and he measured it, he mentioned it many many times, what would be the one thing that if you were just going to measure one thing and you saw whether it was healthy or not, what would be the one thing that you would measure? I'm talking about soil now. Okay, so the organic carbon level. What's sensitive? Okay, so about one single measurable factor that we're going to tell us the most about soil health, if we can only just measure one thing, it's going to be the organic carbon level.

0:43 And Jay mentioned why that was important. It's because this is actually going to be the key determinant of our water holding capacity. There were some questions that came up about you know what about the fact that a cover crops going to utilize moisture and in a dry year is this going to be an issue. And Jay said well you just have to really work through that. There could be some moisture deficits in the early stages, but if you start to build your soil carbon you're actually going to work through that and then you'll go on and on and on and things will get better and better and better.

1:10 We can't keep going with having bare ground because it's always going to exacerbate that situation and it can only ever get worse. So our water holding capacity is frequently the most limiting factor for crop production. So if we're really worried about moisture holding capacity in soils then we really have to be thinking about our carbon levels and it is also the key driver for the nutritional status of the plants and that's where your fertilizers come in.

1:37 Like if you have low nutritional or low nutrient availability in your soils then you're going to have to start spending money on fertilizer. If you've got high carbon active healthy soils you won't see any response to fertilizer at all. And we've had farmers around the world proving that you can actually get right away from your conventional fertilizers. So if you've got issues with soil moisture and you've got issues with fertility, in other words if you need to supplement the fertility with some kind of a synthetic fertilizer, then you really need to be looking at your carbon content, your soil biology, because those are the things that are letting you down.

2:10 And of course that nutritional status of your soil is going to be important if you've got grazing animals as well. How many of you, if you put your hand up, do you have livestock? How many people in the room have livestock? Great to see about half of you. That's great. And then it's going to be important for the nutritional status of people as well, because where are they eating the grain that you're producing or we're eating the meat from the animals that's grazing those forages that you're growing.

2:34 And that's going to pass all through the food chain. If you don't have active nutrient cycles in your soil and those trace elements particularly aren't getting into plants, then they're not going to be getting into your livestock and they're not going to be getting into the food chain. And if I had more time today we could go into all the downsides that we're seeing in terms of the food production system in terms of human health. I think the United States you have the highest health costs of any country in the world, but in terms of the health of the population you rank about number 17 in the world. So you're spending an awful lot on health care costs but you're obviously not doing so well in terms of human health. So you need to be looking at the food because you are what you eat.

3:17 So for all of those reasons, the organic carbon content of the soil is actually going to be the key driver for farm profit. And I'm talking about diversity for profit today. So I'm going to need to talk about how diversity impacts on soil carbon right, because it's a carbon that's going to be the driver of our profit, but that's in the soil and all we can manage is what's happening above ground. So what can we do as land managers and with our crops and our pastures? How can we somehow another channel the maximum amount of carbon into our soil that's going to be the most profitable for us and going to have a whole lot of other benefits in terms of the health of the population, the landscape function benefits that Jay talked about and other people.

4:03 Dale was just talking about there when he was talking about his book with you know the heavy rainfall and all that soil just washing off and forming a gully. I mean that's obviously going to be detrimental for the farmer that owns that land and also detrimental for the other people that end up with all that the mud and other things going into the rivers or onto the road.

4:24 When we look at the organic carbon content of most top soils though around the world, I'm speaking now not just here in the United States, it's 50 to 80 percent less than the original level. In Australia we could probably say it's mostly 80 percent less. A lot of the figures I see for the United States are probably more like 30 to 50 percent less. But I've noticed recently there was an article came out that your grassland soils, your mollisols, those rich black soils that were formed under the prairies, they've just resurveyed a whole lot of mollisols and found that a lot of them don't even I can't be categorized as mollisol soils any longer. So they don't have the characteristics of a mollisol which is a high carbon content. So even the classification of a lot of your soils have changed due to the way that they've been degraded. They've lost their carbon level.

5:12 So if we look at this like diagrammatically what's happened over time, I'm talking worldwide now, we see that in a landscape say prior to European settlement, whether it be Australia or North America, we had vegetation and it's a shame they didn't have flowers in there, because in our Australian environment the first thing that the first Europeans mentioned was that the grasslands were full of carpets of colorful wildflowers and they talked about big patches like the size of this room of brilliant red and blues and yellows and whites and all these different wildflowers that were. And in fact in a natural grassland as your.

5:52 Prairies would have had several hundred species there in a natural grassland, and probably about 60% of them are flowers. We call it a grassland because when you look across it that's what you see are the grasses because they're usually the tallest component and that's the way we characterize it, but it's a shame that we call them grasslands in a way because then we think if you want to have a forage or a pasture you just have to have grass. In actual fact it's going to be much better for the soil and much better for your animals, so much better for everybody really if it was 60% flowers.

6:25 Just keep that in mind that the original prairies had more flowers in them than they had grasses in them. But what happens is that when we lose that cover irrespective of what it was, and we get a reduction in what they call here net primary production, what happens then is that you start losing organic carbon. Because if you start losing ground cover it doesn't matter whether it was over grazed, whether it was tilled or burned or whatever the reason was, if you actually lose ground cover you start to lose soil carbon. And then when we lose soil carbon then we start losing moisture.

6:57 I like this diagram because it demonstrates very clearly what has happened over time in both North America and Australia: we've lost ground cover, then we start to lose moisture, and then we have an increase in aridity. In other words, lots of times we've created our own droughts. We've created our own moisture stresses in the soil simply because of the way we've managed ground cover. We've ended up with less carbon in the ground.

7:31 So we have to figure out if this is where we are now, how do we get back to where we were? And what are the important factors for getting back there? So what have we done, what's actually changed since the time of European settlement? Well, we've simplified the landscape. We've gone from those mixes of 300 to 500 species down to just a couple, maybe three or four in some planted pastures or monoculture crops. And we've reduced the amount of green definitely and we've reduced the diversity of plants.

8:03 This is the main thing that I want to concentrate on today. As a result of that, soil fertility has declined and it is now dry when it was once hydrated. In other words, in our Australian landscape in the middle of summer in areas where you really didn't get rain in summer, it was still green. It would remain green all summer even if it went for three months with not one single drop of rain and over 100 degrees Fahrenheit every day. That was one of the things that the first Europeans noticed: it's so hot and it's so dry and yet the ground cover is still green. How could it remain green?

8:40 Now that we go back to some of the original records we had, we found that our soil carbon levels were up to 30% in some places, which there's nothing in Australia now that has soil carbon anywhere near that high. So we realized that it's no longer hydrated because it's lost carbon, and we have to figure out how to get that back.

8:56 We can't consider all of these things in isolation. We can't consider the plants and the soils, the microbiology, the hydrology in isolation. But when we go to a university what do we find? We've got a department of animal science and a partner plant science and a soil department and they're all separate and people aren't really talking to each other unless they play baseball together on the weekends or something like that. So we've tended to like just focus on these individual components of what really is an integrated landscape. And even with soils you have someone studying soil physics and someone studying soil chemistry and someone studying soil biology or whatever, not really realizing that it's an integrated whole.

9:33 The thing I like about what's happened with cover cropping and especially what I call multi-species cover cropping or multi-species forages is that we've actually started to reintegrate all of those things and look at them as a whole and how it functions as a whole. And in this case, very much so, the whole is far greater than the sum of the parts. And that's what we're starting to learn about diversity: you can never understand how the whole functions just by looking at one of the things in those mixes. And it would be like saying you could study hydrogen all of your life or you could study oxygen all of your life and not know the first thing about water, which is just simply putting hydrogen and oxygen together. So studying those individual components doesn't tell you very much about how it works when it's actually a combination.

10:21 All of these things are connected and plants do a lot more than influence the dynamics of the atmospheric water cycles. That group figure that I showed you was for how whether you've got plants there or not actually affects soil moisture levels and aridity and basically has a huge effect on the climate. What we do to our ground cover has a far larger effect on the climate than how much carbon dioxide is in the atmosphere. So in turn we can have a huge impact on reversing a lot of those changes that we've seen in the climate by managing our ground cover better, because it's not only about the hydrology.

10:59 Actively growing green plants—this is something I want to talk about now—is how they actually support the microbes that create our well-structured friable topsoil. How does topsoil get there? How did it get there in the first place? What is actually making that soil? It's not just silt and clay, is it? It's a whole lot of other things that actually give it structure and porosity and nutrient availability. And all those things require to be living. It's going to be a living ecosystem that we have to figure out how we're going to manage so that it does have high nutrient status and high water holding capacity.

11:39 This is just to give you an example. I'll learn how to drive this thing in a minute. What do you think might have happened there? A fence line and fields.

11:56 On both sides of that fence line have never ever been cultivated. This has been no-till for 30 years prior to this photo being taken. It's been no-till with high chemical use, high nitrogen use, and fungicides and insecticides and all the other things that go with high nitrogen use, because you just upset the whole balance and then you have to start using all these other things.

12:17 This is a drought year. The farmer, this is the first year that he'd taken this fence out because he just wanted to make these two fields into one larger field just to make it easier with GPS technology and everything. Amazing it didn't take the tree out as well, but anyway.

12:33 What that shows you is that in our Mediterranean type climate where most of our wheat is grown, we have a cool moist winter and the wheat is actually planted in fall, grown over winter and harvested in spring. All of our wheats are grown over winter and harvested in spring, so obviously our winters are nowhere near as cold as yours and it's much too hot in summertime and too dry to grow cereals.

12:57 But this fence line has just had weeds growing for any time of year when it rained. Any time of the year when it rained, the weeds would grow, and there's probably going to be a whole mixture of weeds there. And for the entire 30 years that this has grown wheat, the fence line has had a diversity of plants growing in it. And it's something growing there anytime that was able to grow here and it's just incredible.

13:21 We see this all the time where we take fences out in Australia. Originally people used to say it was because if the soil had been cultivated and it'd all been thrown up against the fence like with an offset disc or something like that, but now that we're not cultivating soil because no-till was adopted pretty rapidly in Australia in the 1970s, there's been no cultivation there. So this drought has been created. This man-made drought is what we're seeing there. And it all relates to the soil biology. Just by having some diversity along that fence line, those plants there have seen no drought. There's no drought.

13:59 So I think it's a great indicator. I think this photo tells us a lot about what we have actually done inadvertently to our source. The green presence of green plants is the most important factor for soil health.

14:16 I have never worked with one of these that was so sensitive before. So how can we use what we know about green plants to rebuild healthy porous carbon rich top soils? To answer that question, we first need to actually ask, you know, what is soil and by what processes does it form? And normally we would talk about this, but we haven't got much time today. So I just wanted to show this is the way that most people view soils.

14:44 And I'm sure most of you in this room probably think of it that way. I certainly always used to think of it that way, and that's because the soil is underneath everything that we do. Like it's under this building at the moment. It's underneath all your crops and pastures, and we think of it as being at the base of this pyramid where plants grow in soil and then the animals eat the plants.

15:06 So if our plants aren't performing as we'd like or our animals aren't performing as we'd like, we tend to want to take a sample of soil, send it off to the lab, have it tested, and try and find out well what's wrong with my soil. And if there's something missing, if we think there's something missing, if it hasn't got enough nitrogen or hasn't got enough phosphorus or potassium or sulfur or something, then we're going to go out and buy that and we're going to try and fix the soil.

15:28 We're going to try and fix the soil, see what's in it, see what's missing, and then try and fix it. And that is the way that we've been thinking about soil for decades. And the point that I want to make is that we've actually got that totally upside down, and that's why we're having problems trying to sort out what to do.

15:48 Because like I said, we're now crops and pastures aren't performing. We want to always want to be adding something to the soil to fix it. But what if it's not the base of the pyramid of life? And we've been directing our energy to the wrong things.

15:59 So if we look at a definition of soil, it's some combination of sand, silt, and clay, depending on what the parent material was. Those things, those weathered rock materials, are or have been in contact with plant roots. And so why are plant roots so important?

16:28 The reason that plant roots are so important is because they're joined to this bit here, which is the tops, which the plant leaves are actually going to be photosynthesizing, capturing light energy and carbon dioxide, which is a trace gas. As Jay pointed out, the atmosphere is 78% nitrogen, 21% oxygen, that adds to 99 percent. So all of the other gases are in that 1%—the hydrogen, helium, and argon, whatever. And carbon dioxide is only 0.04 percent of the atmosphere.

16:58 So that point zero four percent of the atmosphere has to be captured in the process of photosynthesis in green leaves. A plant can't do this unless it's green and actively photosynthesizing. And it's going to convert light energy into biochemical energy, and that's going to basically drive all the terrestrial processes that we think of, including ourselves.

17:25 You've all just eaten lunch and you've had an afternoon snack, and what you were eating was actually the products of photosynthesis. So if there wasn't green plants photosynthesizing, we wouldn't be able to be here. In the process of converting light energy to biochemical energy and growing and feeding animals and feeding us and feeding the soil, they're also converting water into oxygen. So they're creating an oxygenated atmosphere as well as growing topsoil and feeding us.

17:54 So green plants are absolutely extraordinary what they do through this process of photosynthesis. And they can turn those weathered rock minerals of sand, silt, and clay into fertile topsoil. But they cannot do that if we're interfering with the process. And when we're using high analysis fertilizers, we interfere with that process and we prevent green plants from.

18:16 Building topsoil because they're not going to excuse carbon from their roots. And if we don't look at how plants work in communities, then we're also interfering with the process and it doesn't work as well as it could.

18:28 So what does it look like when plants are exceeding carbon from their roots and feeding the microbes in the soil? Why are the plants excluding all this carbon from their roots and feeding that biology around their roots? Why are they photosynthesizing? They photosynthesize enough to grow themselves, to grow their green leaves, and they also punch a whole lot of carbon out as exudates out of the roots. Why are they doing that? They're just giving away all that solar energy that they've just converted into biochemical energy?

19:01 Yes, so they're receiving you so that they can. Plant roots that are just sticking down into weathered rock materials—there is no way that they can, well there is some ways that they're not very efficient that they can actually extract the nutrients that they need from the soil. So if you think of all the things that plants are going to need, they're not just floating around in the soil as pure elements. There's not just pure calcium or pure magnesium or pure salt or pure phosphorus just floating around in the soil. It's always going to be bound to something else—like because one thing will be positively charged and the other thing will be negative charged and they're bound together. They're fixed in the soil as soil minerals and plants can't extract those things, but microbes can.

19:47 The bacteria and the fungi that can produce enzymes that can release those nutrients and make them available to plants and also transport them back to plants—they're going to need there to get energy from somewhere, and all of their energy comes from the Sun just like ours does. So we basically package sunlight as our plants and as all of the things that live in the soil getting their energy from the Sun transferred through photosynthesis. And when plants are supporting the biology in the soil, you can tell by looking at the roots because they'll have lots of soil sticking around them like this because the exudates that come out of plant roots are feeding the microbes that can make sticky substances and joint or particles together.

20:27 And if we look at that, if I can press the right button—yeah, honestly I just touched that. Doesn't want to show you, does it? This is the plant root here and these are soil particles out here. And if we look under high magnification—this is 300 magnified, 300 times—we see all these exudates that are there. There's the hyphae of fungi, beneficial fungi all around the plant root, and there's little drops there of exudate actually coming out and feeding all of the things that live around the plant roots. So they're all getting their energy from that plant in the form of exudates.

21:10 And if you lower magnification, that just shows how these particles of soil are all being stuck together with all this sticky stuff. And that's what we're looking for when we just like with the naked eye—when we get a spade and dig plant roots up, we want to see that all the soil is stuck around the roots like that. Now it doesn't want to go at all really.

21:31 Okay, so what are those? Those riser sheaths or those aggregates around plant roots? What do they look like? This is a fine feeder root of a plant and there's the root hairs that are too fine for us to actually see with the naked eye. And this is what's called a macro aggregate, which is one of those lumps that stuck around a plant root. When we have these forming around roots, we know that the plant is actually building soil. So what you're looking at there is new topsoil formation. This is new topsoil, and it's a combination of a whole lot of things that the microbes have brought together to actually convert. These are the minerals here. These are grains of sand, for example, into topsoil.

22:09 So we have the hyphae of mycorrhizal fungi coming out of that plant root. We've got all these little colonies of bacteria, and some of these are fixing nitrogen. And every plant can form a relationship with microbes that can fix nitrogen. You don't need legumes to do that. And in fact, the more we're learning about legumes, the more we realize that we can build soil carbon much faster without them than we then with them. So some of these will be solubilizing phosphorus and making software available and a whole lot of other things. And they're all living in this protected environment inside a macro aggregate or in a riser sheath around a plant root where they're getting—there's plenty of moisture in there, which is why it's shown as being blue. There's lots of energy, all those sugars I showed you before, coming out of the plant roots, and there's a low partial pressure of oxygen.

22:55 And there needs to be a low pressure of oxygen in there. Even though you want the rest of your soil to be well aerated, and the more macro aggregates you have, the more porous that's going to be and the more oxygen there will be around the outside of the aggregates. But on the inside of the aggregates, you want to have a low partial pressure of oxygen. Any idea why you want low oxygen levels inside those macro aggregates?

23:13 All right, therefore fixing nitrogen. So there's a little guys in these yellow ellipses here that are nitrogen-fixing bacteria. The enzyme that they use, nitrogenase, is inhibited by oxygen. So they can't fix oxygen in the presence of—they can't fix nitrogen, sorry, in the presence of oxygen. So if you think about the nodules that are on legume roots, then they've got high moisture content, lots of sugars inside them, and a low partial pressure of oxygen because there's a membrane around there that's stopping the oxygen from coming in. So the only way that you can fix nitrogen is in that special little factory in the soil, which all plants can do this provided that they're forming riser sheaths around the roots or macro aggregates around the roots. So that's why you'd be looking—if I just step back again to that photo before—that's why you'd be looking like this to see where the soil was sticking around the plant roots because inside those structures there, this plant, although it's not a legume, is fixing nitrogen inside those riser sheets.

24:14 Okay, so that's why you're looking for those. And when you see those on your plants, you'll know that you don't need to have.

24:18 Any use any nitrogen fertilizer now it doesn't want to work and what we're building inside there is the holy grail of humus, which is once you actually form humus it compounds in the soil, they can be there for hundreds of years or even thousands of years. And the humic molecule is about 60% carbon and 6 to 8 percent nitrogen, 1 to 2 percent phosphorus, 1 to 2, 1.5 percent sulfur. And why am I giving you those amounts? So you know, so to be so rigid and that is because it doesn't matter where humus has formed, anywhere in the world under what kind of vegetation, in what kind of soil, what kind of climate, it always has the same combination of those elements in it. And if you add those things together they come to about 70 percent. Well, what's the other 30 percent? Well, they're the minerals and you saw like aluminum, I think you call it something different, aluminum or something, and iron, which are actually an important part of that humic molecule. So it is an organometallic complex that's formed by biology in the soil. It's not able to be extracted from soil. You can pull out humic acids and fulvic acids but they're not humus. It's the same as like a tree is photosynthesizing, it's got green leaves, it's converting carbon dioxide into liquid carbon compounds in its sap, into sugars and things, and then the tree biologically, it's combining all those carbon atoms together to form wood. So the formation of wood by a tree is called lignin. It's taking very simple carbon compounds said it made during photosynthesis and turning them into much more complex ones. It's a very similar process that takes place in the soil where things like grasses and clovers and brassicas and like all the kinds of forage things that we looked at today, taking atmospheric carbon dioxide, photosynthesizing, creating sugars, but instead of creating wood they're actually stimulating the biology in the soil that's going to turn those simple carbon compounds into humic molecules which are quite complex molecules. They're very stable and they're very, very important for the soil structure, for water holding capacity, for hanging onto nutrients. They've got high cation exchange capacity. It's actually much more valuable in your soil than clay. Jay mentioned this morning that there's sand, silt, and clay and that clay is the most valuable fraction of those three kinds of weathered rock materials. But your humic component is actually even more valuable than your clay and it has a higher cation exchange capacity and higher water holding capacity than clay. So even if you've got sand, if you can build humus in your sand then you can improve its productivity enormously.

27:04 So this is what we're aiming at is that we want to build humus. So the liquid carbon pathway by which we're going to build humus always starts with photosynthesis. Then those compounds have to be translocated to the roots, they have to form aggregates, and then humus can only take place inside an aggregate or inside a rhizosphere. So this humus tumors rich topsoil that we're building is actually a product of photosynthesis and microbial resynthesis, and it's photosynthesis not soil that forms the base of the pyramid of life. So our pyramid actually looks like this. It's upside down to the way that we normally think of it. So we've got photosynthesis on the bottom with green plants like carbon dioxide and water. Then those plants have to have roots and well grown roots, and well we'll talk about roots in a minute, and all the microbes that are associated with those roots, and then, and only then can we form soil. So if we limit this, and Jay was talking about in North Dakota where he grew up in an environment where a summer fellow was very normal, so you've just got bare soil over summer, so you're basically cutting this in half. Or if you cut this bit of the triangle in half, well of course you're going to have a huge effect on how much soil you can build and how much soil you can maintain. So while ever we're reducing the amount of photosynthesis over a 12 month period, then we're reducing the productivity of our soil. And that word photosynthesis basically, photo means light, synthesis putting together, so it is making life from light. That's the literal translation from that work for that word, making life from light.

28:42 So what's the difference between this liquid carbon that I'm talking about and organic matter, which tends to get those terms get used interchangeably in the literature but they're actually not the same thing at all? Yeah, that's me, not. So there's two pathways for carbon in the soil and one is the well known decomposition pathway where we talk about organic matter that breaks down, and then there's the less well known, the liquid carbon pathway. So the decomposition pathway ends in carbon dioxide. If you take some mulch, some organic materials, some leaves, some manure or whatever it may be laid on the soil surface, it is going to decompose and it's going to go back to be CO2. It's never actually going to stay there in any kind of a permanent form, whereas the liquid carbon pathway is the one that's going to produce this stable humus in our soil.

29:30 The decomposition pathway also starts with photosynthesis and we saw some examples of that this morning where the stock had just trampled material down onto the soil surface. That's going to give you good soil cover, protected from erosion, protected from evaporation, reduce temperatures, temperature fluctuations, but that organic matter on the surface of the soil is going to decompose and go back to be carbon dioxide. This is what it looks like when you're looking into the soil, sometimes you'll see all this white, separate fungi, which are very beneficial for your soil, but they're just decomposing, in this case roots, and turning them back to the atmosphere. Or this kind of material, we know is beneficial for the soil surface, but it's going to decompose and go back to CO2. And this is what happens when organic matter decomposes, you just go back to the mineral soil whatever that may have been. We now know that photosynthesis and plant root exudates are considered to be the primary pathway for soil building and there's lots and lots of literature on that these days. In the last two years even there's

30:34 There's been a lot of material come out, almost every day there's something new comes out. We've got a green plant here and some roots. We've got root exudates. Those root exudates are processed by microorganisms and finally they end up in this stable soil carbon pool. No one is actually sure what happens in this bit here except that it requires fungi and bacteria working together. This is the little mystery box—a bit like we don't really know how a tree forms. We just know that it's got green leaves and it grows the trunk and it's making wood, but the actual process of joining those carbon atoms together to make the wood we're not really sure about.

31:12 In our bodies we eat food and we make things like bones and teeth. Here, like, we don't actually know how our bodies make bones. We can make a ceramic that's got very similar properties to human bone, but in order to make that we have to fire it at 1,200 degrees centigrade. We can't make bone at normal temperatures and pressures, and yet our bodies are doing that all the time. We're always replacing the atoms in our bones, and so it's really amazing what biological systems can do and we don't understand the details of how the biology actually does that. But we know that in the soil, if we create the right conditions, the biology in the soil is able to produce this stable soil carbon pool, and what actually happens in there is a little bit of a mystery.

32:01 The main pathway is the one that comes down through the root exudates, and we know that the decomposition pathway is also important in that particularly the fungal metabolites—they've got lots of fungi in the soil, the secondary compounds, the byproducts of decomposition—stimulate the humification process as well. So it is important to have organic matter in your soil and it's important to have living plants. You want to have both of those things, but of both of those things, living plants are really the ones that are the key factor because we now know that root inputs like your root exudates build soil carbon at least five times faster than the carbon derived from above-ground biomass. And some of the studies have actually shown that root exudates can build carbon 30 times faster.

32:49 So it's those living plants, and I think that's why when we've got cover crops between your crops or we're starting to look at how does grazing management affect how much photosynthesis is going on, it's really through the photosynthesis which is going to be the process that fixes that carbon in the first place. Like, how do we manage that photosynthetic process to get as much exudates out of plant roots as possible so that's when we really start to build soil? We're going to put organic matter on the surface to protect it, but that's not really going to build soil carbon at depth.

33:27 So it doesn't matter whether you're producing grain or milk, beef, lamb, wool, cotton, whatever it might be—you're first and foremost a light farmer. You're harvesting light and you're turning it into a saleable product as well as using that light energy to build your soil. So there's two rules for light farming and it's all about photosynthesis. One is to build photosynthetic capacity and the other one is to enhance the photosynthetic rate, and these things are quite different.

33:53 Photosynthetic capacity is basically going to be—well, how much green leaf have you got there that can intercept light as the first stage of that process? It doesn't matter whether that soil has been cultivated or whether it's been no-till—without cover crops, how much photosynthetic capacity is there? So in Australia, what happened when we converted to no-till—these photos are obviously from Australia—when we converted from cultivation to no-till, we really did nothing about photosynthetic capacity because no one told us about cover crops and we thought that we had to have a summer fallow to store water to grow to be able to grow our winter crops. And in fact, now the official advice is still that this is best management practice in Australia. And if for some reason we get some rain over the summer and some green stuff appears in there, then you go out and spray it because if your neighbour's driving past and they see three weeds in that paddock, they'll be ringing you up and saying you've got some green stuff growing in your paddock, and that's going to form a green bridge, it's going to take the pests from one crop to another or it's going to use up all your soil moisture or it's going to use up all your soil nutrients. And you've got to keep that looking like that, and while ever we've got that as best management practice, our soils are always going to be going backwards.

35:19 So I think I got this photo from JSI here. I think that's yours, isn't it, Jay? So from Innoki farm, I'm pretty sure you sent me that, but a long long time ago. You know, instead of that, obviously we can have one of our multi-species summer covers or we can have pasture cropping, which I don't have much time to talk about that today, but this is another alternative to just having bare soil over summer.

35:47 How did you manage this thing, Jay? Did you have as much trouble with this as I'm having? I'm just touching it and it's flicking over two at a time. But again, in our dry climate in Australia, we have people that just honestly graze everything into the ground over the summer when it's totally unnecessary because same animals, same climate, they can have something that looks like that. But when it comes to grazing, our grazing management really does matter.

36:11 About half of you have got livestock, so I just want to touch on this really quickly. This is actually American data that I'm using, and it was from an article called 'Great Grass Farmers Grow Roots,' and it's all about how much of the solar panels you remove. There's going to have a really big effect on the root systems. And if it's all about root exudates, you don't want to be losing your roots into the soil. If you take 50% of what's the green leaves, you will have no effect on plant roots, and that's what you want. If you take 70%, you're going to have about 50% of the roots.

36:49 Going to stop growing and if you take 90 percent which is what commonly happens in New Zealand in their dairy pastures like all the dairy is is pasture pasture dairy but they graze their pastures right down all the time because they're told and they're still being told by dairy in New Zealand that every leaf that's not grazed is wasted so if you leave a paddock when it's still looking like that you've actually wasted all that that's what people are being told. In actual fact what happens is when they graze it right down like that they've pruned a whole lot of roots into the soil which may be beneficial in a way except that that organic matter is only going to decompose and form carbon dioxide.

37:23 Remember if they had living roots and they'd still be building topsoil and if you leave 50 percent of your solar panels when you come in and graze again this is going to require good management tightly-packed mobs short amount of time in there you're going to have to be able to control the grazing to just take 50 percent out but that will regrow far more quickly and in a growing season you can produce something like 50 percent even a hundred percent more biomass in a hole in a growing season by only taking 50 percent out of each grades because this you haven't lost any of the roots this one has got a regrow roots. It'll regrow some roots and then regrow some tops and regrow some roots and it's it's like using a lot of energy to replace those roots that you've lost through grazing.

38:09 And I think this is the same data that's just put into into a table form this is the percentage of leaf area removed down to 50 percent leaf area removed you have virtually no effect on the roots and then once you get over 50% you start having a massive effect on how how many roots you're taking out and you don't want to be you don't want to be are this is a very famous photo that's been around the world 500 times some pretty short was it's a Canadian photo but again how much of the leaf area is available for photosynthesis is going to have a really big effect on root systems and remember it's going to be the root chips that are going to be actively exerting carbon and building top soil.

38:48 So if we want to start building really deep soils obviously these are perennial grasses but you want to have those roots down really deep and building soil down here because that's you're really going to get and being effect on landscape function and the fertility of your soil if you could build soil to double the depths that it currently is on your farm it's almost like having twice the amount of land you know if you're if it's and it's can hold more water and it's going to have more nutrients available to your plants it's going to be easier all the operations that you perform on that farm are going to be easier everything's going to start working better and you'll find that things like you know weeds almost magically disappear because they're often a symptom of certain can't be called scenarios in the soil that simply aren't present once the soil becomes healthier.

39:37 The other thing about your grazing management is that if this happened to be a weed and the plants don't eat that then your grades everything else really short like if you graze grasses short they will have short root systems there's no other way that they can't possibly maintain a large root system like this if your grades them short then the weeds that they're not eating more and that could be anything that could be a thistle or something it doesn't have to be another kind of grass it will get it's more than its fair share of the water and the nutrients so you're giving a competitive advantage to your weeds all of the time if you graze your pastures short so that's photosynthetic capacity was like how much green stuff do you have there what about photosynthetic rate.

40:15 So let's just assume that we have got green stuff from one fence to the other it's all green so what is the photosynthetic rate then what is that a measure of we've got plenty of photosynthetic capacity there what are we measuring when where what are we actually looking at and when we're looking at photosynthetic rate and why would why would one plant photosynthesis faster than another one so if I had two plants that were exactly the same say two wheat plants for example knew I've got them growing in pots here and that soil is exactly the same the soil moistures are saying they're getting the same amount of light that's the same variety of wheat it's the same age everything is the same but I could have one photosynthesizing ten or twenty times faster than the other one why would it be photosynthesizing faster what would make it photosynthesize faster.

41:06 Now the lights the same the moistures the same everything's the same well no it's the same they look the same I've got two plants that look the same cause it's looking at them I wouldn't be able to tell you which one was photosynthesizing faster than the other how would I know how fast they're photosynthesizing we looked at that this morning and you remember what JD this morning yeah okay so we used a refractometer bezier Brix levels and what are we measuring with Brix measuring the sugar content and the dissolved or the mineral content so we're actually looking at the dissolved solids in the sap like we're looking at how much light is refracted when it passes through the sap of that plant if we put distilled water in there the refractive index is going to be zero we're going to get zero on our Brix meter so if we put something that's got lots of sugar in there it's going to have a high reading something that's got lots of minerals and trace elements is going to have a high reading so you want a high number and a really fuzzy line which is going to tell you that that high number is the result of having lots of minerals and trace elements in there.

42:13 So we're going to use the refractometer we're going to measure the Brix levels of these two weak plants and I could have one actually photosynthesizing in other words have a much a Brix level that was ten or twenty times higher than the other one why would it have a higher Brix level what would what would cause it to photosynthesize faster what what is it what a plant's photosynthesizing for if photosynthesizing to grow themselves so they're going to make some.

49:17 This is a whole lot of flowers. Through here I mean, so this is pretty much a native prairie that these stockers on, but when you look closely into it, it's not just grasses. There's a hole he doesn't have another guy. Try pointing it back to it. Okay, so when we're standing on that soil, we actually like to just go back to that prairie again. Do you want to have a go? Can you like, what am I doing wrong?

49:50 Alright, so I just want to see, when we're standing on that soil, so next one, what we have to understand is that we're actually standing on the rooftop of another world. I did it all right. I'm going to stand over here, not going anywhere near that thing, and it's your fault if it all goes wrong.

50:12 All right, let's so what we have is that this is prairie. I'm sure many of you seen this slide before, but it just goes to show you that all the different kinds of plants have different kinds of roots. We know that a diverse system like that always produces more biomass than if you just had one of those kinds of plants. You had a hundred of one thing will never produce as much biomass as when you've got like say a hundred different kinds of plants. We know that from trials all around the world, and we thought it was because of the difference in the root architecture, it's what they called niche complementarity. So some plants that have got those deep tap roots that go right down, you've got other plants that have got branched roots that are closer to the surface. We think well, they're all occupying different parts of the soil profile so they're not competing so much, and that was why we thought that a diverse mix was actually more productive than a monoculture.

51:04 And although some of you aren't going back to prairie mixes now, you'll be doing things like having these kinds of like the sorts of things we saw this morning, you know, with the plantain, the red clover, chicory, peas, rye grass, Wilson beets, fescue, dandelion, cocksfoot, like all those different kinds of plants. If you start putting those together, you're going to like Jay was talking about, like mimic what would happen maybe in a prairie. And again, we've got different kinds of root systems so that we have this niche complementarity. Well, that's what we thought was the reason why those mixtures were giving us more biomass, but now we know that's a whole lot more goes on.

51:36 Because these plants, even if they're not considered to be, some of them would be considered not to be mycorrhizal, and like the beets may be, but they once they're in a mixture, they actually do become mycorrhizal. So when they all join together into what's called a common mycorrhizal network, and what happens in a common mycorrhizal network, it's, you can I haven't got a pointer now, but you've got flax on the left and then saw them to the right of that. And you've got the root system, which is the brown bit, and then those little blue lines that are shown there, that's the mycorrhizae that are all linking up, joining underground.

52:17 So what a common mycorrhizal network means is that plants each have their own mycorrhizae that are associated with them with the mycorrhizae actually linked up underground, and they start exchanging water and nutrients and all kinds of things. They send messages. Messages between plants get exchanged along these mycorrhizal networks. They're actually the highway and the Internet of the soil, and when we get, we're in this example what they were looking at was that the sorghum they've got carbon investment, which is the green, and then you've got phosphorous uptake, nitrogen uptake. What they've found is that the grasses in this case sorghum actually usually do contribute a lot more carbon to the soil than some of the other plants do, and that your broadleaf plants or your herbs or your dike ox or whatever word you want to use for the things that aren't grasses, they often have higher mineral and trace element contents than grasses.

53:06 So if you've, if you're looking at a forage again, if you have those things in together, you're going to have better nutritional status for your animals if you've got some broadleaf plants in there. But what they found in this experiment was that when they put those things together, they had a monoculture of flax or a monoculture of sorghum, and then you look to see what happens when you put them together. They found that in a mixed culture, the sorghum grows seven percent more and the flax actually grew 300% more, and they put that down to this common mycorrhizal network.

53:39 Just some examples of what that might look like in practice. This was in Ontario where they had a demonstration, a bit like what you saw this morning with there, something's grown in monoculture and something's grown in mixture. This was radish grown in monoculture, which even though the whole area had been fertilized with a base fertilizer, was looking quite nitrogen deficient. And next to that is radish just grown with oats and phacelia and some sunflower and a couple of sunflower plants. So there wasn't much else in that mix. And if I just put those two photos side by side, if we put those just splice the photos and put them side by side, you can see the radish is nitrogen deficient there, but there's no nitrogen deficiency showing at all when it's in that mixture. And it's not even with legumes, so it's got some oats and phacelia and sunflowers, and it's not showing any nitrogen deficiency. So everyone could see that on the day. It was really quite spectacular, the difference.

54:38 But there's more to it than that, because when we start looking at diverse plant communities, we realize that we've got multiple plant hosts now, and then we've got multiple fungal partners, so it's not just one mycorrhizae that's joining all these things together. These are the spores of mycorrhizal fungi, and you can see that like people who are good at this can identify what kind of mycorrhizae they've got from the different shapes.

55:05 And colors and things of those sports. Thanks Keith, and that's another one of like fungal spores in the soil. So we have to start realizing that once we get a whole lot of different kinds of plants in there, we're going to have a whole lot of different kinds of bacteria and fungi and viruses and protozoa and all the different things that are going to be associated with those plants.

55:23 The viruses are actually incredibly important. We used to think bacteria were bad because we associated them with diseases, and now we know that like 99.9 percent of them are beneficial. And we think of viruses as being bad because there's the flu virus and other things like that. We now know that there's beneficial bacteria and beneficial fungi in the soil that actually can't function unless they have viruses. They themselves have to be colonized by a beneficial virus to actually function, like mycorrhizal fungi. On their own, with beneficial viruses in them, actually can't work. So viruses are the smallest things that we're aware of that live in soils, but they're very, very, very important and they're probably going to be the next frontier in soil science.

56:11 These are some spores of different kinds of fungi in a soil. When we've got a whole lot of different kinds, what we're starting to realize is that suddenly everything changes. We reach a critical mass of having enough different kinds of things in the soil, and somehow through the signals, the communication signals that everything that's living in soil is sending out. Everything is sending out signals all the time, just like if you start thinking of it as a living organism. Just like we're a living organism and we've got heart, liver, lungs, spleen, kidneys, adrenals, hypothalamus—all these different parts of us that are functioning as a coordinated being. You're digesting the food that you've eaten, and all of those things that are going on in your body right now without you really thinking about it, because of all the signals that the different organs in your body are sending to each other. So there's a whole lot of messaging going on there all the time, and that's how you function as a whole, as a living thing.

57:26 When we start realizing that the soil needs to be living as well, we realize that there's a whole lot of signaling going on there too. And all of these things—like plant seeds—are all the time when they're sitting in the soil. They're very aware of what's going on outside. They know whether it's the middle of winter or whether it's the middle of summer or whether it's just rained or it hasn't. They're picking up on temperature signals and moisture signals. They know whether there's other seeds of their own kind close to them or other seeds of different kinds of plants close to them, because everything's putting chemicals out into the soil. So a seed actually knows a lot about how close it is to the surface, how much light is there, how deep is it, how cold is it, how hot, how dry, what other plants are around it.

58:15 And these things that live in the soil like fungi and bacteria, they're even more aware than seeds are. We think of them as small, but they ain't stupid. They can detect through all these signals when all of a sudden you reach a threshold where you've got a plant community. And when you've got a plant community above ground rather than just a monoculture of one thing, then the soil microbiome responds and it suddenly changes to do some quite incredible things.

58:59 One of these was photos that Jay sent to me a while back from the breakthrough that he talked about earlier, where they had one-way, two-way, three-way up to seven-way mixes, and everything up to seven actually failed in that drought. And then in the eight-way mix it was like, what drought? We see this repeatedly, and for some reason it seems to be the number eight. I don't know what it is about the number eight.

59:30 This is from Alberta in Canada, July 2015—very hot, dry year. This is triticale. So there's some monoculture. This was on a demonstration farm where the farmers have an input into what they plant. The farmers wanted to have a cocktail mix in one corner. So this is the same triticale sown across the whole paddock, and then it was oversown in that corner with nine other things. And it's like this is drought. If we look into the actual cocktail mix itself, you can see the heads on the triticale that's like what drought? And there's sunflowers and radish and oats and I can't remember the names of all the things that were in there, but nine other things were in there.

1:00:22 You'd think if you had all those different kinds of plants that it would actually be more drought if moisture is limiting. So what's going on there? How can it look like that where it's just going as a monoculture at a fairly low plant density, and then be looking like that right next to it? It's the same soil, all planted at the same time, same amount of moisture, everything's the same. So what's going on? And this is what we're starting to see—that there's this tipping point when you get over a certain number of plants that it just changes everything. And it's got to be something to do with the soil microbiome. There's quite a lot of research going on now about what is going on underground, what is the signaling that's going on. How can all of a sudden these things get more water? It's got to have something to do with mycorrhizal or fungi, because we know they can bring water from a long way. But why had they suddenly been activated just because?

1:01:16 We've got more different kinds of species. Well, now we're starting to look at this in a bit more detail. This is an experiment that's been running in Germany for 15 years. It's called the Llena biodiversity experiment. So what they've found some really interesting things. One of the things was the effect of plant species richness on the need for nitrogen fertilizer. They looked at one, two, four, eight, or 16 different kinds of plants in those plots with either none, 100, or 200 kilos per hectare of nitrogen per year. It's a multifactorial experiment. They had like just one kind of monoculture with none, 100, or 200 pounds per acre right up to 16 different kinds of plants with 100 or 200 pounds per acre.

1:02:02 What they found was that if they had 8 or 16 plants together with no nitrogen fertilizer, they actually grew a lot better and produced a whole lot more biomass than having one or two different kinds of plants with up to 200 pounds of nitrogen per acre per year. So if you've got a monoculture, you're almost forced into a situation where you're going to have to put fertilizer on it to get it to grow. If you want it to be really productive, because it just can't do what a diverse mix of plants can do.

1:02:32 The other thing that they found, which I found was even more interesting than that, was that the soil carbon increased with increased species richness and it was almost a straight line. So the more species that you kept adding—because they went actually right up to 60, even though it was 1, 2, 4, 8, 16, and then they kept on going right up to 60 different kinds of plants in the mix—they found the higher the number of plants they had in the mix, the more soil carbon that was fixed. That's because the plants in the mix were actually excreting more carbon out of their roots. So above ground they look pretty much the same, but there were more plant exudates coming out of there. And they found that on the monocultures declined over time. So their high diversity plots where they had 8, 16, or 60 different kinds of plants accumulated over 20% more carbon compared with the ones that were low diversity—one, two, or four.

1:03:30 If you're thinking about this in terms of how quickly can I improve my soil, what do I really want to have—8, 16, or 16 plants species? It looks like as long as you've got over 8, you probably don't have to go all the way up to having 60, or you may not even have to go to 16. And they don't all have to be big, bulky sorts of things. Like some of the plants that we saw today—like the flax and the lentils maybe—they're not high biomass plants, but they could be doing an incredible amount for you underground when they're linking up with all of the other plants in some kind of a mix. So it doesn't have to be something like sunflowers or whatever with great big leaves that are photosynthesizing heaps. In fact, it's what they call subordinate species—those plants that are small but they're an important part of a mix.

1:04:20 If you go back to thinking what the prairies were like and why we call grasslands—well, you've got some of those really tall warm season grasses, for example, in your tallgrass prairies. Well, I suppose they would have been over my head, but they're the most obvious things that you see. But the reason I showed you those photos from Birdwell and Clarke is that if you get down under there, you'll find there'll be little things in the prairie that might have only grown this big or some things that only just crawled around on the ground. They would have had nearly always flowers—little flowers on them. So they would have attracted lots of beneficial insects and predators and that kind of thing. So they're very important for a whole lot of reasons but also for carbon building.

1:04:59 Not because they themselves photosynthesize a lot and not because they themselves build a lot of carbon necessarily around their roots, but what happens is that once you get over that certain threshold for plant diversity, you can trigger a whole change in how the whole soil microbiome works. I think we need to think pretty seriously about that because we're seeing that if you had livestock and you were grazing, the same thing applies to ruminant nutrition. But if we have a whole lot of some of those little subordinate kinds of plants in that mix that the animals are grazing, and again it's not that they're not big dry matter so they're not going to produce hugely how much dry matter animals they're actually consuming in a day—but those secondary plant compounds that we knew there was a little bit of talk today, like things like condensed tannins that are in some of your legumes, for example, they can actually stimulate the rumen to function more efficiently and the animals can digest their food better and their feed conversion efficiency is greater.

1:06:00 Let's say that they're getting a certain amount of dry matter from a monoculture of oats or something like that and then the same amount of dry matter from a mix that's got like 15 different things in it. They could actually gain a lot more weight from this, even though the dry matter, the metabolizable energy, the protein content and everything could be the same, because this one has got a whole lot of secondary plant compounds that actually improve their feed conversion efficiency. So we've got this thing where we want to measure dry weight and convert it to—we think that something high is going to be better than something this high. But in actual fact, you could get sometimes better average daily gain from something this high if it's going to have higher nutrient density, right, and it's going to be a mix of a whole lot of different sorts of things.

1:06:51 We've got to get out of our heads thinking when we're thinking livestock that it's all about dry matter and a big bulk of stuff. And the same with soil building—we have to—it's not necessarily going to be the big, bulky things that are going to be the little things that produce that build the most topsoil. We've got to think about how many different kinds of functional.

1:07:12 Groups actually you have in that mixture. So when they're looking at different functional groups you want grasses in there, you want some tall herbs in there like your chicory and your sunflowers, but you also want some short herbs in there and I think he thinks like your flax, anila, maybe the lentils or chickpeas, even those kinds of things, probably could be short herbs.

1:07:42 Okay, so we've got experiments around the world now that show that plant diversity builds soil carbon and because it built soil carbon, it can—that's the reason it can replace fertilizer, insecticide, fungicide. And we know it can also display sweets, not because it's building soil carbon but I'm just because it's physical.

1:08:04 So then I was just going to show you one example now from New Zealand, which is one that I just saw just a couple of weeks ago. So this is what's called a pumice soil or an ash tile—it's a result of fairly recent volcanic activity in the North Island of New Zealand, which is a fairly new landmass. And it's a very light-colored, really soft kind of soil. It's a bit like the ash that you just—if you have a fire and you just take all the ash—that's what they call an ash tile. Blows like crazy if it's not covered.

1:08:36 So in a bare area like that where there wasn't much plant cover, this is basically what this soil looks like. Traditionally they grow ryegrass. This is on a dairy in New Zealand pasture, pasture-fed dairy, so they grow ryegrass for the dairy cows because it's high in sugars. And they just—it's basically rye grass with a bit of clover and that's basically it. That's a rye grass plant that's been dug out, but I know it looks upside down. So if we turn the photo upside down, just to give you a mix. Yes, so you've got your perennial ryegrass and it produces about this much black or darker-colored soil on top of the pumice. So this is what farmers used to—they only ever see this much soil in there, like what you call topsoil in there, pumice, when they grow ryegrass.

1:09:23 So this particular farmer, this is his son, but I've been talking to him for years now about getting some diversity. And six months ago he put in a five acre crop. It just goes from here down to where those cars are. That was a twelve-way mix. You can see mostly chicory and plantain and prairie grass and whatever in there, but there were twelve species. And the rest of his farm is ryegrass. And we just went out to look to see whether the red clover was nodulating. I said, ah, let's go and have a look in your multi-species mix to see whether the red clover's nodulating. And he started digging holes and he couldn't believe. So this is prairie grass in here, which grows really well in New Zealand, and chicory, of course.

1:10:06 So the next one. He couldn't believe it because this pumice soil was totally transformed. And this is a little bit of pumice soil—there's been some in the bottom there, but he basically had this much topsoil where they've only ever been able to grow this much with ryegrass and clover. And he dug about fifty holes and I said, the rate you're going you're gonna dig the whole five acres up. He just couldn't stop digging holes. And then the next morning I rang him up again and I said, oh, you know, we should really go and look at the paddock next door, and you know, just to make sure that it really was just that particular paddock and it hasn't just happened over your whole farm. He said, I don't worry, I've already been out this morning and I've dug another hundred holes. And he said every single spade just come up like that. He said, I just I can't believe it.

1:10:49 So the only thing can be that he's just putting more diversity there. And it just goes to show you those really infertile pumice soils—they just load them up with nitrogen and everything all the time. So one of the other things that he did do was stop using all the synthetic fertilizers. So there was no fertilizer on that. And I said, what are the cows think about it? Said, well, you know, I can hardly keep them out of that paddock. You said they break down the fence to get in and then when they're in there I can't get them out again, like compared to having grown grass all the time.

1:11:58 All those hills in the background have been cleared of trees. Look how deep they are. It's just amazing. That's fine forestry for you. That's what the New Zealand government does—they clear those really steep hills and then they'll actually put pine trees back on there again. But what he wants to do now is have the whole—so this is his multi-species paddock and the rest of his farm is ryegrass. And he just wants to have it all like that as soon as he possibly can because he wants to build soil carbon.

1:12:25 So I'll finish there, but it was just interesting the things that we see around the world in terms of drought tolerance, the nutritional changes, like plants not being deficient in nutrients anymore, and then like incredible examples of soil building. And it really does come down to diversity. And I know that lots of people will recommend—look, if you're just getting into cover crops and multi-species forages and things, just experiment with a few simple mixes because it gets too complicated if you try and put too many things in. But you don't have to manage all the things that are in them. And even just looking at that, it looks like it's just chicory, plantain, and prairie grass and red clover really, but there are twelve things in there. And it's not necessarily going to be the big things that are going to make all the changes.

1:13:13 So I guess from what I've seen and from what I read in the literature, I would really encourage people to probably go to make more work for the green coast people. But even just to slip in some of those lower dry matter plants. The good news is right now we're running a special on our sixty plant species mix. It's called remix. It's all the stuff we spill throughout the year and then we just rake clean and mix it all together. So we actually have that and it's on sale now. We spill a lot of this. We have quite a bit of that.

1:13:54 So can we take some questions and answer that?