杏吧原创

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FIND the places where farms give way to the California wilderness and you鈥檙e sure to encounter an endangered species. It is not aggressive, but it is omnivorous, devouring anything that happens to fall dead within its reach. And like most rare beasts, the extinction of would have cascading impacts on the ecosystem around it.

Don鈥檛 be misled by the name. This is neither animal nor plant nor microbe, but a subgroup of soils. Its members nonetheless slot into a classification system every bit as elaborate as that we use to categorise life forms. In the US alone, more than 20,000 soils have been catalogued. Many are facing extinction.

It may seem like madness to speak of soils going extinct, but more than a third of the world鈥檚 top layer is endangered, according to the UN, which declared 2015 the International Year of Soils. This December, it will release a much-anticipated report on the . The news won鈥檛 be good: we are losing soil at a rate of 30 soccer fields a minute. If we don鈥檛 slow the decline, all farmable soil could be gone in 60 years. Given soil grows 95 per cent of our food, and sustains human life in other more surprising ways, that is a huge problem. 鈥淢any would argue soil degradation is the most critical environmental threat to humans,鈥� says , who studies soil microbes at the Cary Institute of Ecosystem Studies in Millbrook, New York. Yet all is not 鈥� quite 鈥� lost.

The degradation of the world鈥檚 dirt has been a disaster in slow motion. 鈥淪oil scientists have been prattling on about this for decades,鈥� says Groffman. All the while, our understanding of just how crucial soil is has only grown. A 100 million bacteria, 10 million viruses, 1000 fungi, and other populations living amid decomposing plants and various rocks and minerals.

That means soils not just grow our food, but have been the source of nearly all of our existing antibiotics, and could be our best hope in the fight against antibiotic-resistant bacteria. Well-conditioned soil certainly seems to have ways to keep out dangerous elements. In 2011, a series of experiments at the University of Groningen in the Netherlands suggested that soil types with more diverse communities of microbes . This strain causes particularly violent diarrhoea and even kidney failure in humans, and the soil鈥檚 action could potentially prevent it entering the food chain. 鈥淭here鈥檚 a clear link between soil microbial diversity, plant health and human health,鈥� says Rick Ostfeld, who works with Groffman at the Cary Institute.

Soil is also a surprising ally against climate change: as nematodes and microorganisms within soil digest dead animals and plants, they lock in their carbon content. Even in their degraded state, it is estimated the world鈥檚 soils hold . Water storage is another talent lost when soils degrade. A UK government report published in 2012 suggested soil degradation costs the country .

Small wonder endangered soil is making ecologists so nervous. It鈥檚 not that the dirt is wiped off the face of the planet. 鈥淲hen folks refer to the soil as endangered, they鈥檙e not thinking of it in the same sense as endangered species,鈥� says Ostfeld. Rather, extinction transforms a fecund soil into a dusty, microbiologically flat shadow of its former self. Once that diversity is gone, it鈥檚 gone for a while. 鈥淪oil takes thousands of years at a minimum to gestate,鈥� says Groffman.

Abruptic durixeralfs鈥檚 problem is that it is of little direct use for farming owing to its 鈥� a dense, compacted layer that repels both roots and water. But it likes to nestle between swathes of prime agricultural land in its habitats in the western US. Frustrated farmers have resorted to using explosives to blow it out of the way: a dramatic method of soil extinction, but only one of many. 鈥淓verything we do causes soil to erode,鈥� says Groffman.

A load of manure

Agriculture is by far and away soil鈥檚 biggest problem. In the wild, nutrients removed by plants are returned to the soil when they die and decay to form rich humus. Humans tend not to return unused parts of harvested crops to replenish those nutrients.

We realised this long ago and developed strategies to get around the problem. We left fields fallow, or rotated crops that required different nutrients, thereby keeping the soil in balance. Growing peas and beans can even add nitrogen, a vital nutrient, to the ground: nodules in their roots host rhizobia bacteria, which grab atmospheric nitrogen and convert it into nitrates.

But these practices became inconvenient as populations grew and agriculture was mechanised. A solution came in the early 20th century with the Haber-Bosch process for manufacturing ammonium nitrate. Farmers have been plying their fields with this synthetic fertiliser ever since.

But over the past few decades, it has become clear this wasn鈥檛 such a bright idea. Chemical fertilisers can release polluting nitrous oxide into the atmosphere and excess is often washed away with the next rain. This leaches nitrogen into rivers, damaging algal blooms. More recently, we have found that indiscriminate fertiliser use hurts the soil itself, . It also suppresses , and can even turn beneficial bacteria against each other.

Long-term use of fertilisers risks turning even fertile soil to desert (Image: Pete Mcbride /National Geographic Creative)

In many ways, fertilisers speed the soil they are supposed to nourish toward extinction. 鈥淭hey really work to grow plants,鈥� says Groffman. 鈥淪o they very effectively hide the nature and extent of soil degradation. As the soil degrades, you just put on more fertiliser.鈥�

What鈥檚 to do? One possible solution is being pursued by of Carleton University in Ottawa, Canada, and his colleagues. Inspired by the way plants coexist with soil bacteria, he is on a mission to make fertilisers smarter.

Monreal wants to exploit the way plants signal to bacteria by releasing chemicals. 鈥淭he plant tells the microbes, 鈥榟ey guys, I need nitrogen!'鈥� he says. The microbes then begin working to free nitrogen from organic matter, and the plant soaks it up. In 2011, after nearly a decade of sifting through hundreds of chemicals in soil samples taken from fields of wheat and canola (oilseed rape), Monreal鈥檚 team identified five compounds that spike just as the plants take in ammonia 鈥� these are the chemical signals plants exude to ask for nitrogen.

Monreal then teamed up with , also at Carleton, to try to build a fertiliser that keeps its payload locked up until it encounters a plant鈥檚 signalling compounds. DeRosa turned to aptamers, short strands of DNA that bind to specific chemicals, much the way antibodies do. After training them to recognise the five compounds, she used the aptamers as scaffolding around a tiny parcel of fertiliser. In the presence of one of the plant signalling compounds, the aptamers would bind to it, .

The pair now have a working product, fertiliser-filled capsules that open up in response to the appetite wheat and canola have for nitrogen. Monreal thinks the same process will work with other crops and soil microbes too 鈥� although the precise details are under wraps while they try to commercialise the technology. First, it must undergo greenhouse trials, scheduled for spring 2016, and pass other tests to make sure it biodegrades after a few years in the soil. are working on similar approaches to reduce the environmental impact of fertilisers and even .

Another school of thought says that any synthetic fertiliser, even in small doses, is bound ultimately to degrade the soil. Such concerns might be addressed by an alternative approach, which replaces synthetic fertilisers and chemical pesticides with the soil鈥檚 own microbiome.

Pius Floris hopes to use soils鈥� own microbes to maintain their fertility (Image: Photographs by Photogenic Agencia Gr谩fica)

This research is in its early days, and Pius Floris is one of the people at its vanguard. Floris, who started out running a tree-care business in the Netherlands, now advises some of the world鈥檚 top soil scientists. He came to realise that the best way to ensure his trees flourished was to take very particular care of the soil, and has developed what he calls a 鈥渦niversal recipe鈥� of beneficial bacteria, mycorrhizal fungi and humus that adheres to plant roots and helps them extract nutrients.

Under the auspices of a , Floris recently teamed up with researchers at the University of Valladolid in Spain to test this cocktail on local soils whose ability to grow plants had been destroyed by years of fertiliser and pesticide overuse. When the team applied Floris鈥檚 mix to the desert-like test plots, they began to sprout oats and leguminous plants called vetches. The few plants that grew in the control plots, dosed with traditional pesticides and fertilisers, were small and stunted; those treated with Floris鈥� cocktail were not just healthy at the surface, but their roots had grown .

Dish the dirt

The promise of these microbial interventions is such that agrochemical companies are taking notice. Microbe-based fertilisers are being developed by chemical giants such as Dupont as well as small . Several countries, including India, have .

Innovative as they are, these measures will at best make a dent in the global soil degradation problem. 鈥淭here are some problems you can鈥檛 invent your way out of,鈥� says soil hydrologist Dara Entekhabi at the Massachusetts Institute of Technology. Soil degradation is a complex issue with tendrils poking into areas like climate change, biodiversity, food security and water (see map). Better fertilisers won鈥檛 stop the drought that is ruining soils in California, or avert bulldozers paving over them in rapidly-urbanising China.

To assess our options on a global scale we first need an accurate picture of what soils are out there, and which are endangered. That鈥檚 not easy. For one thing, it still requires extensive fieldwork; for another, there is no agreed international system for classifying soil (see 鈥�How to organise the earth鈥�).

In an attempt to unify all the different approaches, in 2010 the UN created the Global Soil Map project. Researchers from nine countries are working together to create a real-time, digital repository of the condition of soils worldwide. Right now, the state of the art is a , linked to an online database that can be fed measurements 鈥� field surveys, drone surveys, satellite imagery, lab analyses and so on 鈥� at any resolution. Cross-referenced with existing data, it provides real-time predictions of soil health: its clay, silt and organic carbon levels, together with acidity and overall density. By 2019, researchers aim to have , with the results freely accessible to all.

But sophisticated new ways to classify and map soils is only a first step. Action will require ways of presenting the problem that bring it home to governments and the wider public, says Pamela Chasek at the International Institute for Sustainable Development, a think tank headquartered in Winnipeg, Canada. 鈥淢ost scientists don鈥檛 speak language that policy-makers can understand, and vice versa.鈥� Chasek and her colleagues have proposed a goal of 鈥溾��. Like the idea of carbon neutrality, it is an easily understood target that can help shape expectations and encourage action. It would also offer a banner under which projects like Monreal鈥檚 and Floris鈥� can rally.

鈥淜nowing what soils are where is only a first step to action鈥�

For soils on the brink, that may be too late. Several researchers are agitating for the creation of protected zones for endangered soils, although there has been little official movement on the issue so far. One problem is defining what these areas should conserve: areas where the greatest soil diversity is present? Or areas of pristine soils that could act as a future benchmark of quality?

The US has made an effort to at least recognise the importance of soils, by having every state designate a 鈥渟tate soil鈥�. California鈥檚 is the 鈥� which, ironically, is an informal name for a soil that belongs to the group frequently in local farmers鈥� crosshairs: Abruptic durixeralfs. When law-makers made it the state soil in 1997, they didn鈥檛 accompany the honour with any legal protection. That鈥檚 telling. If we do want to save our soils, we might want to stop treating them like dirt.

This article appeared in print under the headline 鈥淪ave our soils鈥�