Giles Oldroyd: Go fertilise yourself
Giles Oldroyd, Image Courtesy of Giles Oldroyd
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Temperature isn’t the only factor affecting how plants grow. Another big one is nutrients. And as we face a growing global population and a fast-changing climate, getting enough food into our food plants is a big issue.
Professor Giles Oldroyd is the director of the Crop Science Centre at the University of Cambridge, where he and his team are investigating how plants interact with microbes like bacteria and fungi to extract nutrients like nitrogen and phosphorus from the soil. To understand why that’s so important, I started by taking a step back and asking him to explain the scale of the challenge when it comes to feeding the world.
Giles: It's a real phenomenal scale of a challenge because we've got a continuing expanding population, so we're going to see probably another 5 billion people on the planet, stabilising somewhere around 12 billion. Associated with that is actually a growth in development as well, so an increase in the numbers of middle classes and as people increase their wealth, their diets naturally adapt and change and they tend to become more meat-eating than they historically were.
Giles: So you have the combination of more people, but then also more people with greater demands on the food production system. So for that alone, we have to double food production between now and 2050 to address just what we know is going to happen.
Giles: But you have to put that into context that over the next 30 years, we're going to be experiencing some pretty significant climate change. And one of the greatest impacts of climate change is our food production systems. And there are significant parts of the world that are actually going to become very prone to things like severe droughts, severe heat waves, flooding. That is extraordinarily detrimental to our food production systems.
Giles: So we need to grow our food production systems at a time when actually just tackling the consequences of climate change is going to be phenomenally challenging.
Giles: And I think if you add into that mix a desire to be more sustainable in our food production, such that agriculture has less of an impact on the environment and on greenhouse gas emissions, those three pieces individually, they're already significantly challenging. But meeting the demands of a growing population during a time of climate change and attempting to drive greater sustainability, it really is a phenomenal challenge that we have to meet to achieve those goals.
Kat: Yeah, I'm amazed that able to even think and do something about this rather than just hiding at home going, "Oh God. Oh God, just make it go away!"
Giles: Mm hmm. I think on a personal level, I'm very, very concerned about the future. What I actually think is that we need to get to 2050. In my mind anyway, that's the date where population starts to stabilise.
Giles: Hopefully we've got greenhouse gases emissions under control. My view is that once we get past 2050, things start to improve, at least some of the pressures come off the system. Now, climate change will be probably continuing and quite severe by that point, but things like the population maybe starts to stabilise and hopefully we've got some technologies in that just helps us tackle some of those challenges.
Giles: I am very concerned about the future. But I'm also a big believer in human ingenuity and our ability to solve problems using a variety of approaches. And I do think science and technology is one of those approaches, but it alone is not sufficient to tackle all of those challenges.
Kat: So let's hone in on the area that you are working in, which is on the issues of things like fertilisers.
Kat: And this may seem like a really dumb question to start with, but why do we need fertiliser? Why do farmers use fertiliser? And again, what sort of scale are we talking about here?
Giles: Yes, so plant nutrition is very, very different to animal nutrition. So we will have eaten a meal, and in that meal, it might be a combination of meat and plant based products. We break down the proteins into amino acids, we break down the DNA and RNA into nucleic acids. We break down the complex sugars into their more simple sugars. But we stop at that point, so we absorb the amino acids and nucleic acids as sugars, and then we use those as our building blocks to rebuild our own DNA, our own RNA, our own proteins and our own carbohydrates.
Giles: Plants are radically different. They start from the elemental basics. So they start not with an amino acid, they build that amino acid from its building blocks, and that's carbon, nitrogen and phosphorus principally, and then hydrogen and oxygen, which they're getting from water. So those core building blocks, they actually have to capture those nutrients from their environment in their most elemental form. So they get carbon from the atmosphere; they're fixing carbon dioxide from the air using the energy of light. They get nitrogen and phosphorus, which they capture from the soil, in the form of reactive forms of those molecules, so phosphate, nitrate, or ammonia, and then they use those molecules to build literally from scratch amino acids, nucleic acids, sugars, etc, which then forms a foundation of the totality of our own nutrition as humans.
Giles: Now, a natural ecosystem, like if you think of a permanent grassland or a woodland, there's a system whereby there's a slow degradation or a breakdown of plant products. Nutrients are released in that process, but those plants are capturing those nutrients; a very, very, very slow release system. Very little loss of nutrients in those systems; it's continuously cultivated, so there's always grass, there's always trees growing in that system.
Giles: Agriculture is radically different, because we grow our crop, we harvest that crop off the land and we take all of that harvest away. Now, in that harvest is nitrogen, is phosphorus, is iron and other components, and if you don't put those back into the soil, you're actively mining those molecules out of the soil and moving them off to some other place.
Giles: Over time in agriculture, we deplete these nutrients in the soil and as a result, our productivity declines. So in the agricultural system, you have to intentionally return those nutrients back into the system in order to maintain productivity. And that's why farmers use fertilisers.
Kat: And what kind of scale are we talking about?
Kat: Because I'm thinking about my own garden, you know, hopping along with a little can of Miracle Gro. I don't think we're talking about that kind of scale, are we?
Giles: If you were in a, driving a big tractor through your garden with a tank full of Miracle Gro, it's not dissimilar. Farmers are doing what you're basically doing with your Miracle Gro.
Giles: Miracle Gro is exactly that; nitrogen, phosphorus, potassium, principally, in an inorganic form. And so, it's just a massive version of that. But if you imagine that most farmers, at least the high income parts of the world, are covering their fields multiple times with a version of Miracle Gro across the whole landscape.
Giles: And then you think of that across all the arable areas of high and middle income countries and it's a massive global impact, or global release, of, in particular, reactive nitrogen and phosphorus. And so, we as humans have had a huge impact on the global nitrogen cycle. We put as much reactive nitrogen into the system as naturally gets into the system every year.
Giles: I said we have to double food production. So if we just take a business as usual, we're going to quadruple the global nitrogen cycle, putting three times as much nitrogen into the system than would naturally be there. So we are having profound impacts on global systems because of that use of fertilisers.
Kat: I certainly remember seeing things like lakes that have all turned green, the runoff from agricultural land, these fertilisers, getting into lakes and rivers and places where they're not needed, and then boosting the growth of algae and all these things. The problem is you want the right amount of fertiliser to get your crops to grow but in the right place and also this stuff's incredibly expensive as well, I can imagine.
Giles: Yeah, so the system's not very efficient, right? As you can imagine, if you're just spraying the whole field with fertiliser, only some of it is captured by the crop plants and a significant amount of it is lost into the environment. That can be lost, as you say, in runoff. It can also be lost as volatilising nitrogen, conversion into nitrous and nitric oxide, is something that bacteria during the soil, and that is a very potent greenhouse gas.
Giles: Most natural ecosystems have very low nutrients, particularly aquatic systems, but also most of our natural terrestrial ecosystems; a chalk grassland is naturally a low nutrient environment. If you have a lot of agriculture around that chalk grassland then nitrogen gets into the system, the whole system becomes more nutritive, and you lose a lot of the specialised species, which are actually the very reason that chalk grasslands are so important; the locally adapted, rare species of plants that are adapted to that environment. And we start to lose those species. And then in aquatic ecosystems, it's really detrimental to have high nutrients in these aquatic ecosystems.
Giles: So agricultural pollutants, nutrient pollutants from agriculture are extremely detrimental to biodiversity and pretty bad news for greenhouse gas emissions as well.
Kat: So clearly we need a better way. What's the way that you're proposing? What are you working on to try and solve this problem?
Giles: If you look in the natural ecosystems, plants actually get their nutrients mostly through engagement with microorganisms. And that's pretty common across the whole plant kingdom.
Giles: Most plants are associating with a group of fungi that we call a arbuscular mycorrhizal fungi. And they are colonising the root of the plant very extensively and then ramifying out into the soil. And they create an enormous surface area of contact with the soil, much more than the plant root alone can do.
Giles: And these fungi are really good at taking phosphates and nitrates, but also water and micronutrients from the soil, and they deliver it to the plant in exchange for carbon. So it's a beneficial interaction. The fungus gets a source of carbon, which is delivered as lipids. And the plant gets a source of phosphate, nitrates, water from the fungus. So it's a mutually beneficial interaction.
Giles: Some plants have also learned how to engage with nitrogen fixing bacteria. And that is really useful because there's actually a lot of nitrogen in the air. 70% of the air you're breathing is nitrogen. But the only organisms on the planet that can use that form of nitrogen are bacteria.
Giles: And some plants - peas and beans; legumes - have learnt how to engage with those bacteria and then have, the same as with the fungus, a mutually beneficial interaction. The plant gives the bacteria a source of carbon, the bacteria give the plants a source of nitrogen. And so in many examples we can see that actually the plant gets virtually all of their nutrient needs through these beneficial microbial associations, but these are really underutilised in agriculture.
Giles: I believe that if we can bring these beneficial associations much more into our agricultural systems, we can reduce or even eliminate our dependence on inorganic fertilisers.
Kat: What's the deal with peas and beans with legumes and things like clover's in there as well, isn't it? Why can they get these nitrogen fixing bugs and other plants can't?
Giles: The simplest way to answer that is peas and beans had diverged from cereals evolutionarily before they evolved nitrogen fixation. So on the evolutionary tree legumes have already diverged from cereals long before they learned how to engage with nitrogen fixing bacteria. So as an evolutionary trick, it happened at one part in the plant kingdom but that didn't include cereals.
Giles: Now that's the simplest explanation. It doesn't say why, right? Why is it that peas and beans do it and cereals never bothered to evolve it? And I think the answer to that, we have a very anthropogenic view of the importance of nitrogen because the way we've structured our agricultural systems is such that we're actively mining the soil for nitrogen, as I said before.
Giles: There is no natural ecosystem that's like that. All natural ecosystems have these nutrient cycles, which are actually preserving a lot of the nutrients in the system. So although in agriculture nitrogen is a be all and end all to productivity, in most natural ecosystems that's not the case, actually. In contrast, the way we've structured our agricultural systems, it becomes much more important and makes us think, "Why can't all plants do this?"
Giles: But I think that's an anthropogenic view of the nitrogen cycle rather than a natural view.
Kat: There truly is no such thing as a free lunch. Let's come back to these mycorrhizal fungi. Again, my whole reference point for this is my own garden. I've been planting a load of trees and shrubs and little packet and a little scoop and I scoop these little fungi into the hole when I put my shrubs in and they say this is good.
Kat: So what are these fungi and why aren't farmers just putting them into the field when we do agriculture? What's the challenge with harnessing the power of these fungi to use in agriculture and in food production?
Giles: Well firstly, it's great to hear that you're using the mycorrhizal fungi and particularly in the context that you said, planting trees and shrubs, that has been demonstrated that's the most effective use of mycorrhizal fungi.
Giles: And actually in agriculture, the most effective use is for establishment of orchards; fruit orchards. That's where you really see an impact of an inoculum of mycorrhizae. Now actually mycorrhizae are everywhere. They're present in all soils. So even though you're adding the sachet, it's just increasing the number of mycorrhizae close to the plant root and it helps that plant get established in your garden. And for perennial plants that are going to live for a very long time, that's a really useful thing for them.
Giles: In an arable farming system where we're using annual plants that we're cropping every year, our soils are very low in mycorrhizae. When you add all the nutrients with fertilisers, the plants don't bother engaging with them.
Giles: So even if we add inoculums, if we're fertilising, the plant recognises there's ample nitrogen and phosphorus around, it doesn't bother engaging with the fungus and it doesn't matter whether you inoculate. So we actually have to breed or adapt our crop plants. They have to be a little bit rewired in an agricultural system to make the mycorrhizal system work for the crop.
Giles: And that's not unusual: when you go from a natural plant, you domesticate it to make it better for use in agriculture. And during that domestication, we've not thought about mycorrhizal fungi. Now we're thinking about it because it's a sustainability issue. But we have to think about a domestication of that process in our crop plants to optimise that association in an agricultural context.
Kat: So it isn't literally about just chucking loads of fungus in there and hope they sort it out. We actually need to teach the plants, and by teach I mean some kind of presumably genetic tricks, that they can really harness the power of these fungi. How do we do that? What are you trying to figure out to make that work?
Giles: We have field trials right now where we've got barley plants and we've broken the connection between the plant's perception of nutrients and its decision to engage with the fungus.
Giles: Normally, if there's lots of nutrients around as you would normally have in a fertilised field, the plant recognises ample nitrogen, phosphorus. Why bother paying for that from the fungus because it's a more expensive way to get it? It's a mutualistic engagement; the plant's paying with carbon for nitrogen and phosphorus. If there's unlimited supply in the soil because we've fertilised that soil, just take it straight from the soil. So it doesn't bother engaging with the fungus. That's unfortunate because the fungus is a much more efficient route to take those nutrients and means that we would lose less to the environment and probably need to put less on in the first place. So what we've done is broken that connection.
Giles: We've stopped the plants from limiting their engagement with the fungus to only times when there's no nitrogen and phosphorus around and we force the plant to engage with the fungus anyway when there's ample nitrogen and phosphorus around, and that's what we've got in field trials right now.
Giles: The other thing is that the actual benefits the plant gets from the fungus is variable. There's a genetic component that underpins that actual benefit from mycorrhizal fungi, and that segregates in all of our crop plants, and it's something that we've never bred for. There's not been an intentional breeding for optimising mycorrhizae.
Giles: So we are trying to force the engagement with the fungus constitutively, independent of the nutrient concentration, and then bring the genetics in from a breeding perspective that ensures that they get also maximal benefit when they do engage with the fungus.
Kat: So are you achieving these characteristics through breeding or are you bringing in elements of genetic engineering as well?
Giles: So it's a combination of stacking breeding for optimisation of the benefits from the fungus, but with that, currently we use genetic modification to override this nutrient suppression of the engagement with the fungus. Our field trials at the moment are using genetically modified material. But we have actually achieved the same thing in the lab using gene editing and we're setting up in order to actually test a gene edited approach in the field as well.
Giles: Gene editing doesn't leave foreign DNA in the plant; it achieves a genetic change in the plant that's identical to what you would get through conventional breeding, it's just a very targeted way. And the recent legislation, the Precision Breeding Bill in the UK, means that a gene edited crop is no longer treated like it's genetically modified, it's treated like it's a conventionally bred crop. So it's actually preferable for us to have a gene edited crop. There's more public acceptance of that, much easier to have impact, it's much cheaper to release a gene edited product.
Giles: The one thing I would say is that, although I can optimise the fungal association with breeding and gene editing, the nitrogen-fixing association with the bacteria has got to be genetic modification. I have to take genes out of legumes and put them into cereals. So my crop plans for the future will be far more sustainable, they'll be cheaper, I believe there will increase productivity for all the world's farmers, not just high and middle income farmers, but they would be carrying biotechnology traits.
Kat: Taking all this together, what do you think the future of farming is going to look like if we have these modified plants that are able to engage with the fungus and are able to take more nutrients out of the soil? What can we hope for?
Giles: My future for agriculture, my vision of a future for agriculture, is one where our crop plants are engaging proactively with the mycorrhizal fungus and we've broadened the engagement with nitrogen fixing bacteria beyond simply peas and beans, but now move them into many more crop plants, particularly our cereal crops.
Giles: If we can achieve that, so basically you get all of your nitrogen from the air through the engagement with nitrogen fixing bacteria and then you optimise the capture of phosphate from the soil and potassium and other micronutrients, you optimise that through the fungal association, it means we don't need to add reactive nitrogen into the system because the bacteria is doing that for us.
Giles: And we can minimise the amount of phosphate we're actually putting in. You probably always have to put a little bit of phosphate into the system. But it can be much less than we're currently doing and done in a way where actually the fungus is really capturing it so we're not losing it out into the environment. It's a much more efficient capture of the phosphate that we apply.
Giles: So much less inputs go into the system, way cheaper for the farmer, economically more viable, it's much easier to deliver because you don't have to have a huge tractor pumping vast amounts of fertilisers on the fields on a frequent basis and way better for the environment because it's a much more efficient way of getting those nutrients into the plant, less loss to the environment.
Giles: So, in my view, it's win, win, win, win, win.
Thanks to Giles Oldroyd.
