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  • You're listening to CowdScience from the BBC World Service, the show that drills down

  • into your questions about life, Earth and the universe. I'm Anand Jagatia and for this

  • episode, I've been doing a bit of DIY. In fact, I'm building a house for worms. This

  • consists of some plastic crates which I'm going to stack on top of each other. I've

  • drilled some holes in the crates for ventilation filled them with compost.

  • So what we got in here

  • smells disgusting.

  • Okay, so we got some bits of banana, bits of old bread, eggshells... And then, right

  • now I just need to add some worms.

  • Just gently spread you out.

  • This is kind of gross. I don't want to hurt them either.

  • There we go. just tuck them up. While I get accustomed to my new pets, let's hear from

  • this week's listener, to find out exactly why we're doing all of this.

  • My name is Dinesh and I'm from Tamil Nadu in southern India. I want to know how important

  • earthworms are for farmers.

  • How important are earthworms for farmers? Dinesh wants to know as he works on his parents

  • farm in Tamil Nadu, which is where he spoke to us sitting underneath a tree with some

  • of their animals in the background.

  • Right now we have goat and rooster, parrots

  • Parrot is a pet

  • Do you grow things in the in the earth as well?

  • Yeah, our primary farming is rice.

  • Do you notice that in the earth where they're growing that there's a lot of lot of earthworms

  • in the ground?

  • Yeah, we actually grow earthworms separately. Keeping the soil alive.

  • Dinesh’s farm is organic. They use cow dung as fertiliser and not really much else. But

  • he says that's not the case for lots of other farms nearby.

  • The others use chemical fertilisers. So that's the main question for me. What happens if

  • you use chemical fertiliser in the field? What happens to the worms?

  • Dinesh is curious about how inorganic or organic farming practices can affect earthworms and

  • how earthworms can affect his farming. He's noticed that the earthworms he cultivates

  • and adds to the soil do make a difference to how well his crops grow. But how exactly

  • and why? Now, I must admit that before building this wormery, the last time I picked up a

  • worm was probably as a kid playing in the garden making mud pies. But even though we

  • don't really see them, beneath our feet, the Earth is teeming with these subterranean annelids.

  • And while they're not exactly glamorous, they have the power to engineer entire ecosystems,

  • as we'll hear later in the show. Now, when it comes to being fascinated by the humble

  • earthworm, Dinesh finds himself in some pretty excellent company. Back in 1881, none other

  • than the great Charles Darwin published his last scientific book, which was devoted to

  • the behaviour and ecology of earthworms.

  • I became interested in them and wished to learn how far they acted consciously and how

  • much mental power they displayed. I was the more desired to learn something on this head,

  • as few observations of this kind have been made, as far as I know, on animals so low

  • in the scale of organisation, and so poorly provided with sensory organs, as are earthworms.

  • Darwin devised all kinds of experiments to learn more about earthworms, including what

  • their favourite foods were, whether they could sense light and heat, and whether they could

  • respond to sound, which involved playing them the bassoon, shouting at them - No, really

  • - and placing pots of the poor things on top of a piano. It turns out that earthworms don't

  • have ears, but he discovered that theyre extremely sensitive to vibrations. Some of

  • these experiments lasted decades, and in fact, a few of them are being recreated today in

  • the grounds of the house where Darwin lived and worked.

  • Charles Darwin studied earthworms throughout his life. And specifically used Down House,

  • the estate there, as an outdoor laboratory.

  • This is Kevin Butt, head of the earthworm research group at the University of Central Lancashire.

  • Earthworms are sometimes referred to as Darwin's plough and this is because their natural activities

  • in the soil turn it over. They bring mineral soil up to the surface and they take organic

  • matter down into the soil to act as food for themselves. So in doing so they actually mix

  • the soil layers. And by passing the soil through their gut, they create a really good quality

  • crumb structure to the soil, which is great for growing plants in.

  • It’s quite a long walk to Kevin's other experiments.

  • Kevin wasn't able to meet us in person, but luckily we were shown around by Jane McLaughlin

  • who volunteers at Down House and also works as a research assistant on Kevin's worm experiments.

  • This is Kevin's experiment set out in the field, to look at what Darwin observed with

  • the sinking into the ground.

  • What are we looking for?

  • We're looking for big flints.

  • Darwin observed this effect in action at Bucklands Meadow. Over 30 years he documented the disappearance

  • of large flint stones, some according to his notes half as big as a child's head, as they

  • slowly became covered with earth. This, he believed, was due to the action of worms.

  • As Jane explained to me standing at the same spot today.

  • He observed originally a layer of ash sinking into the ground. But then he said, Well, why

  • do Roman pavements sink into the ground? Why do buildings, old buildings sink into the ground

  • and it's all because he postulated because of the action of worms. This field was full

  • of big flints, but 20 years later, without doing anything, you could ride a horse across

  • the field, and the horse wouldn't strike its feet against any of the flint. So somehow where had the flints gone? This is why

  • earthworms are called Darwin's plough, because they have as much effect on the soil as ploughing

  • it would.

  • It's difficult to think of earthworms, pink fleshy squishy things, as a force of nature.

  • But acting in large numbers over decades that's exactly what they are, as Darwin's experiments

  • recreated by Kevin and Jane are now showing.

  • Earthworms are considered to be ecosystem engineers because they change the very nature

  • of the material that they're living within.

  • Can you kind of talk me through how this actually works? So how that helps to improve the quality

  • of soil and how it changes the soil? The type of worms that live in organic matter, are

  • taking that very raw material, usually waste vegetable, plant material, and they're passing

  • it through their gut, and within their gut, there are microbes that act upon that material

  • plus their own digestive enzymes, and they change the nature of that material and make

  • it more available more usable by other organisms within the soil. But also they change it chemically

  • so that it becomes more available to other organisms. Horizontal burrowing worms, the

  • ones that live just below the soil surface are geophagus, they eat their way through

  • the soil. So what they're doing is utilising organic material that is found within the

  • soil that's been brought down into the soil, and then mixing it with the mineral soil,

  • actually creating a better physical and chemical structure to the soil that then is much more

  • available to plants.

  • And then what about the third category of worms, ones that live slightly deeper in the soil?

  • The deep burrowing earthworms provide lots

  • of ecosystem services in the soil, they produce what are called macro pores, large holes in

  • the soil, extending down a metre, perhaps down to three metres at a time. This allows

  • water to enter the soil. This allows air oxygen to enter the soil, and so improves the quality

  • of the plants that are living there. In addition, of course, as they feed, they gather organic

  • material from the soil surface, things like dead leaves, and they drag that down into

  • their burrows. And by doing so, they increase the fertility of the soil and make that material

  • available to the other types of earthworms the ones that live just below the soil surface.

  • So the fact that our listener Dinesh finds lots of earthworms in his paddy fields in

  • Tamil Nadu means that his soil is probably nice and healthy. Those incredible natural

  • engineers he's introducing on his farm are not only mixing up the soil, they're refining

  • and improving it making nutrients more available to the plants. But it's not just Dinesh that

  • this is relevant for, this is something that could potentially affect all of us.

  • Because crops need to feed the world and we are increasing in population. So we would

  • need more food. And if earthworms can increase this crop yields, so more crops, that will

  • be a very good thing.

  • This is Ingrid Lubbers from the University

  • of Wageningen in the Netherlands. She studied the potential impacts that earthworms could

  • have on food production.

  • Weve looked into crop yields, so the market crop. But we've also looked at above ground

  • biomass, so that's the entire plant. They all increased about 20 to 25%.

  • Wow. Okay, so that's a pretty big increase. Actually, I'm quite surprised at how big of

  • an effect the worms can actually have. How exactly do you think that is happening? What

  • are some of the ways that they could be increasing the size and the output of the plants?

  • Yeah, scientifically, that's, of course a very interesting question. How do they do

  • it? Well, by being active in the soil, what they do is that they increase the availability

  • of nutrients for instance, nitrogen. Nitrogen is really essential for all living things,

  • but also for plants. So to increase the availability of nitrogen for plant uptake.

  • You might be wondering something here. Nitrogen makes up about 80% of the air in our atmosphere.

  • So why do plants need help from earthworms to get hold of it? Well, pure nitrogen in

  • the form of a gas is pretty inert and isn't much used to living things. It has to be converted

  • into other forms by bacteria, first into nutrients like ammonium and then into nitrates and nitrites.

  • It's this form of nitrogen that plants can make use of to grow. Earthworms seem to speed

  • up this process by their action in the soil, making more nitrogen available for the plants

  • to use. Although Ingrid says that this effect is more helpful for some crops than for others.

  • We found it to be more helpful for let's say, grain crops and pasture grasses, and less

  • helpful for legumes so peas for instance.

  • Our questioner Dinesh he lives in India, and

  • his farm is organic, and they don't really use any kind of, you know, artificial fertilisers.

  • But what does using large chemical fertilisers do to soil does it add nitrogen in the same

  • kind of way that earthworms do?

  • That's the thing. It doesn't. So if you use

  • inorganic fertilisers, which include nitrogen then it's already fertilised in a way that

  • plants can take it up immediately or very fast. So if you are an organic farmer and

  • you use organic fertilisers or you leave the crop residues out of your land, then the earthworms

  • they eat it, they mix it into the soil, and in this way, make the nitrogen available to

  • the plants. And that's a slower process. But also, the effect of earthworms is used to

  • a maximum really.

  • Artificial fertilisers are great for boosting plant growth quickly, but they can also cause

  • nitrogen pollution when they leach into water systems, disrupting natural ecosystems and

  • they can make soil less healthy in the long run. Using earthworms to help fertilise soil

  • is slower, but they can boost yields by up to 25 percent, and they have the greatest

  • effect when the nitrogen availability is already low. So they could help organic farmers like

  • Dinesh to increase crop yields in the absence of artificial fertilisers while being kinder

  • to the environment. But it doesn't stop there. In fact, if farmers leave their crop residues

  • on their fields after harvesting, the earthworms can actually help to lock up carbon in the

  • soil.

  • It's said that earthworms can store carbon in the soil and they are supposed to be able

  • to do this by just feeding themselves with litter and mixing this litter. So, I mean,

  • that's plant remains, they mix that with mineral particles in the soil and excrete that as

  • their cast - so earthworm poo, and within these casts, the carbon is less available

  • for microbial decomposition, which would mean in the end that there's less co2 coming out

  • of the soil.

  • You're listening to CrowdScience from the BBC World Service, where this week we're looking

  • at how worms affect our soils - thanks to a question from Dinesh in India. Dinesh wants

  • to know how worms can help him to grow crops on his farm. And I'm also trying to harness

  • them here in my garden. It's been a few weeks since I set up my wormery with some worms

  • I was sent in the post. And I have to say, I am totally over my initial sense of slight

  • disgust. I'm looking at them now and they are basically amazing. I've been feeding them

  • bits of kitchen scraps over the past couple of weeks, and they are slowly but surely turning

  • it into a really rich, nice compost. Earthworms are like a small army of underground workers

  • that engineer the soil, aerating it helping it to drain increasing the availability of

  • nitrogen for crops and locking away carbon preventing it from entering the atmosphere

  • as a harmful greenhouse gas. It kind of sounds like it's too good to be true. Right? Well,

  • unfortunately, it is. This is the point in our story where we find out that the worm

  • has turned.

  • Worms do have lots of amazingly positive effects on ecosystems, but they have

  • some negative ones too. It's something that scientists like Ingrid called the earthworm

  • dilemma.

  • We have just discussed the upside that they are good for crop yields, so their activities

  • in the soil increased nitrogen availability, but the same mechanism can increase greenhouse

  • gas emissions.

  • So while earthworms can help store carbon

  • in the soil by locking up with minerals in their poo, they can also indirectly increase

  • the release of greenhouse gases. One of these is nitrous oxide, which is produced naturally

  • in the soil by certain microbes. But it turns out the earthworms just by going about their

  • business can rapidly accelerate this process.

  • Yeah, so the microbes produce nitrous oxides in the soil. And the earthworms are working

  • the soil, they're moving about into soil and while they do that, they dig their burrows

  • and make the soil more porous. And these pores, they can function as a little chimney. And

  • through these little chimneys, nitrous oxide gas can leave the soil from deeper in the

  • soil towards the atmosphere.

  • The role that earthworms play in greenhouse

  • gas emissions is complex. It turns out their activity may simultaneously increase and decrease

  • carbon dioxide or nitrous oxide. So Ingrid wanted to know when you tally it all up, which

  • of these effects wins out in the end?

  • If you look at the main effects, we found nitrous oxide emissions can be increased by

  • 42%. So quite a lot. CO2 emissions can be increased by 33%.

  • Wow. Okay. So this is compared to soils where there are no earthworms.

  • Exactly.

  • Yeah. So we found these quite big main effects. But what I would need to add to that is that

  • most of these studies for highly manipulated laboratory studies so that means no plants

  • growing and also the experimental maturation of these studies. Yeah, 30 days, 100 days,

  • but not very long.

  • Okay, how do you think the figures would be different if you were able to study them in

  • a sort of real world situation? I mean, would it be that the worms cause a release of more

  • co2 from the soil, but because they're also stimulating plant growth and the plants will

  • capture some of that co2 and then relock it back into the soil?

  • Yeah, that's exactly the right question to ask because in real life, so not in the laboratory,

  • but out in the fields, you will have plants growing. So nitrogen will be taken up by the

  • plants roots, nitrogen can leave the system by leaching and less will be available for

  • the formation of nitrous oxide emissions, for instance.

  • In terms of overall global warming, then, how much do you think that earthworms, if

  • you did take these figures as being what's emitted by them, would contribute towards

  • global warming compared to other processes that happening on the planet?

  • You can make a very, very rough estimate, really a guess, you could say that perhaps

  • a maximum of 1% of global warming could be attributed to the activities of earthworms.

  • So it seems even though earthworms have a positive effect on soil fertility, which is

  • surely good news, this same mechanism could lead to an overall increase in greenhouse

  • gas emissions, which isn't such good news. It is worth pointing out though, that even

  • Ingrid's worst case scenario is still a tiny fraction of manmade greenhouse gas emissions.

  • Still, it's kind of hard not to marvel at the ability of the lowly earthworm to engineer

  • the soil under our feet and the atmosphere above our heads. The fact that they can increase

  • emissions from soil by 30 or 40% just shows how important they are for the processes on

  • this planet. I'm discovering pretty fast that you underestimate the power of earthworms

  • at your peril. And there are places on earth where scientists are realising just how true

  • that is.

  • I'm Erin Cameron and I work in the boreal forests in Canada, but it's actually a biome

  • that stretches across the northern part of the world. And they're basically forests that