The ground beneath our feet

Muddy boots

20 September 2013 by Tom Marshall

Fungi are all around. Mostly you don't see them, but under the microscope earth from almost anywhere in the world contains a tangle of branching, interwoven fungal filaments called mycelia. Tom Marshall explains how NERC-funded soil science will help feed our hungry planet over the next century.

Mycelia are the nexus of a world-changing cooperation between fungi and plants. A kilo of soil contains 200km of these superfine threads; worldwide there's an incredible 10,000 light years of them, mostly renewed several times a year. They attach to plants' roots and supply them with essential soil nutrients in exchange for some of the carbon compounds the plants make with photosynthesis. Without them, most plants couldn't survive. The carbon ends up buried underground, some of it for long periods, so soils and the fungi they contain are a vital part of the carbon cycle.

"Everyone takes soil for granted, but it's amazing," says Professor Steve Banwart of the University of Sheffield, leader of a NERC project to investigate how fungi break down rock to help make this deceptively familiar growing medium. Banwart works alongside colleagues at Sheffield and the universities of Bristol and Leeds.

"These fungi form a network of chemical energy that binds the trees to the soil and the rock below. If a tree is a photovoltaic cell, soil fungi are the national grid," Banwart adds. "They take energy and carbon from the roots and pump it underground, sometimes many metres away from the growing tree. So there's this huge amount of biomass out there, pervading the soil beneath our feet. Until recently it got very little attention, but we are now realising it plays an essential part in the Earth's chemical cycles."

Banwart's team estimates around 12 per cent of all the land-based carbon cycle passes through these fungi, known as mycorrhiza. Alongside forests, peat bogs and the ocean, soil fungi provide one of the most important routes by which carbon is transported and transformed.

So soil is critical for carbon cycling. It does a lot more than that, though; it takes care of everything from growing our food to helping filter our water. Recent research even showed some plants can communicate underground to warn of impending aphid attack. But if soil's an underappreciated resource, it's also increasingly under threat. Unsustainable farming techniques, deforestation and changes in weather patterns all help to strip topsoil up to 100 times faster than it's created.

If we're to feed a fast-growing global population by sharply increasing crop yields while also reducing the harm done to the environment - the challenge of 'sustainable intensification' - this can't continue. We don't only need to stem current soil degradation; we also want to reverse losses so that we start to accumulate an ever-increasing stock of this vital natural capital.

All this means soil science is central to a sustainable future for industries from farming and forestry to bioenergy production. If we can somehow boost fungi's natural carbon-absorbing capabilities, it may even help slow climate change.

Science to save soils

All this was on the agenda at a meeting organised by NERC, the Royal Society of Chemistry, the Technology Strategy Board Environmental Knowledge Transfer Network and the University of Sheffield, which brought together attendees from a huge variety of fields including chemists and biologists, engineers, hydrologists, agronomists, business managers, farmers and farm suppliers, as well as officials from Defra, the European Commission and the research councils. Rather than just setting general research priorities, the meeting set out to identify concrete areas that scientists can profitably start investigating now.

Banwart himself gave a presentation on his group's work illuminating exactly how mycelia break down rock into soil and sequester carbon from plants underground. We've known for a while that this happens, but the exact mechanisms have been a mystery until recently. Speakers presented results from other directly applicable research on the next generation of farming techniques and how they could help us manage the land more sustainably.

Tractor ploughing

Tractor ploughing

Major agribusiness firms like Yara and Syngenta talked about their interest in innovations like precision agriculture, which involves using real-time environmental information and GPS-equipped farm machinery to apply seeds, water, fertilisers and pesticides exactly where and when they're needed rather than indiscriminately applying them across whole fields. This is already saving farmers and agribusinesses lots of money on expensive crop inputs. And the environmental impact of the crops drops sharply; we can grow the same amount for less energy and with fewer chemicals to cause problems elsewhere. (See 'The future of farming' to find out more about precision agriculture and other emerging techniques.)

As well as the need for practical research into how farmers can put these new ideas to work, Banwart stresses the importance of 'critical zone observatories' doing long-term monitoring of, and experimentation on, the soil, rock, water and organisms - including crops - in different places.

Named after the thin envelope between the treetops and the bedrock that sustains most of the planet's terrestrial life, these are field research facilities that are covered with instruments and monitored to support experimental design over the long term. They are often at nested scales of observation from a soil profile, to a small stream's catchment, to a whole river basin; Banwart and his collaborators work with data from such sites around the world including ones operated in the UK by the Centre for Ecology & Hydrology.

NERC is committed to supporting soil science over the long term. It recently joined forces with the Biotechnology and Biological Sciences Research Council to offer £4·5m for research into soil ecosystems and their impact on farming and food production through the joint Global Food Security programme. The money will support new work on the complex interactions between plants, microbes, animals, nutrients and water within the soil, as well as how agricultural ecosystems respond to changes in management and the environment.

"There's a vision emerging of how soil science and critical zone research can contribute to truly sustainable agriculture," says Banwart. "Meeting this challenge will drive lots of technological innovation and business development, and at the moment the challenge seems quite daunting. But I've no doubt we can get there. It's what we need if we're going to feed the world while coping with the impacts of still-increasing land degradation, the prospect of climate change and competition for scarce water resources."

The future of farming?

A big field can hold many different kinds of soil. Some places have more nutrients; some are at more risk from pests; some are wet and some are dry. Yet at the moment, most farmers apply similar amounts of fertiliser, pesticide and water across the whole field. What if they could draw on sophisticated environmental data to work out exactly what's needed on every small patch of ground, and then use GPS-equipped precision farm machinery to apply only this much?

That's the idea behind precision agriculture, and it's taking off fast. Farmers save cash on unnecessary spraying; the environment benefits because there are fewer chemicals to run off into waterways and less energy is spent producing chemicals and pumping water in the first place. If we're to move to a truly sustainable food system, techniques like this will be essential.

One possibility is combining data from tiny soil-moisture sensors all over a field with weather forecasts and atmospheric information to control irrigation pumps. Water is applied where it's needed and nowhere else. Satellite imagery is becoming commonplace; drones have attracted such military demand that their prices are plunging. Police are already adopting the technology for things like monitoring traffic or catching wildlife poachers; farmers could soon start using drones to monitor the health of crops and tell them when pesticides or irrigation are needed.

The next step could be using nanotechnology to move from bulk applications of dumb chemicals to tiny amounts of 'smart' ones, engineered to be taken up only by particular crops. A shift from the status quo would have economic benefits for countries like the UK beyond farming itself. Making such chemicals is now dominated by large economies like Brazil and China, but producing more valuable and sophisticated chemicals might be viable in high-wage smaller countries like the UK.

Another approach is no-till farming - growing food without ploughing, which disrupts the soil's structure and fungal networks, and can contribute to soil loss and desertification. Growing crops without turning the land can be challenging, but in many areas it could be a vital step towards sustainably higher yields. This could involve steps like growing two or three crops to a field at the same time, or combining plants and animals in new ways, or combining traditional crops with forestry. None of these are new ideas, but until recently they've received limited interest in mainstream farming.