Earthworms increase global grain yield by 128 million tonnes

The unsung underground heroes
31 October 2023

Interview with 

Steven Fonte, Colorado State University


An earthworm


There is so much going on underground that is beneficial to us without us even realising. And one of the groups of animals that encapsulates this the most are the earthworms. Day and night, they labour underneath our feet to make the soil rich for agricultural use. And what thanks do they get? Kids throw them at each other and scream. Now that simply isn’t fair, particularly when you understand just how much earthworms contribute to keeping us fed. Steven Fonte is from Colorado State University...

Steven - Earthworms are really important in terms of recycling the organic matter. The dead plants that fall to the soil contain a lot of nutrients locked up that plants need and earthworms are key for helping to liberate those nutrients and make them available for new plants. They're also changing the soil structure a lot in porosity through their burrows and they make little aggregates or casts as they go through and chew up soil. And that really helps water infiltrate when we have a big rainstorm and also helps avoid erosion.

Will - I did see one estimate that there might be as many as 400 billion, billion individual worms in the top six inches of the Earth’s soil. I don't think they were talking about earthworms specifically, obviously, and there are a lot of other worm groups out there. But even still, if earthworms make up a fraction of that amount, it surely translates to a huge amount of food production that they're involved in.

Steven - So we looked at both two groups of crops. We looked at grains like corn, wheat, rice, and barley. And we found that earthworms contribute just under 7% of the total crop production or total production of grains worldwide. And that adds up to quite a bit. So it's about 128 million metric tonnes according to our estimates. And just to put that in perspective, that 128 million metric tonnes of grain, I was looking up the other day, puts earthworms right on par with Russia and Brazil in terms of global grain producers. So it's fourth and fifth place now at a national scale.

Will - Are these percentages or these amounts constant throughout the world? Is there one unified worm yield or are there places in conditions in which worms contribute more to food production?

Steven - Yeah, so the way our study did this is we looked at the distribution of crops globally and as well as management factors like how much nitrogen is applied and the soil type. And some soil types allow earthworms to have a greater benefit or not. And then we also looked at estimated earthworm populations. And so places where they don't fertilise as much, that's one factor that's allowing earthworms to have potentially a bigger role there. Also, the soil types that we find in a lot of developing places like in Sub-Saharan Africa and in Latin America and the Caribbean are more conducive to that earthworm benefit. And so we're seeing that earthworms are while the global average for grain contribution is about 6.5 or 7%. in Africa, that average bumps up to about 10% and 8% in the Latin American and the Caribbean region. And so it's not completely uniform, at least in terms of the relative increase. At the same time, if we're to look at the absolute increase, production levels are considerably higher, for example, in a lot of Europe and in a lot of Eastern Asia. And those are also places where we've estimated there to be a lot of earthworms. More so than, for example, we see a lot of the great plains in the US. And so in those areas, while the percent increase attributed to earthworms still hovers around seven or 8%, the absolute amount that they're contributing is considerably more. So earthworms are maybe increasing global grain production by 40 million metric tons both in Europe and Eastern and Southeast Asia.

Will - I mean, that brings up an interesting point from a complete layman's perspective here because obviously we are looking at trying to sort of move away from fertilisers, which we know are causing havoc with a runoff and problems in rivers and ecosystems. And we're looking for sort of more renewable 'green alternatives.' It's not as simple, surely, as throwing some more worms into the soil.

Steven - Yeah, and to be clear, we are not advocating that we go and inoculate soils with earthworms. That could be a bit of a contentious issue because a lot of earthworms are considered invasive species in parts of the world, in many parts of the world and can do a lot of damage to natural ecosystems adjacent to our farmlands. Within farms. They're generally positive, but there's management that we can do. If we have the right management practices, you know, like reduced tillage and actually supplying food for earthworms in the form of adding manure or compost or leaving crop residues behind, those practices can really help stimulate earthworm populations and they are there and their populations will increase on their own. We don't have to be adding them.

Will - So if we look after our earthworms, the earthworms look after the soil and hopefully everyone wins.

Steven - Yeah. They all work together so they benefit from any of the same things and hopefully we're able to leverage earthworms and other soil organisms to increase the overall sustainability and resilience of our agricultural systems.


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