[LUM#7] Major scales
Preserving our Earth, our source of sustenance: this is the critical challenge facing agriculture today. To meet this challenge, scientists are turning their attention to the soil, the cradle of all crops. An ecosystem of unimaginable complexity…
“It’s impossible to understand the soil if you take it out of context, ”warns Robin Duponnois, a soil microbiologist and chair of the French Scientific Committee on Desertification. “Only a comprehensive approach can help us understand these highly complex phenomena.”
Vital Symbioses
A brief glimpse into the complexity at play: without the plant cover that provides the raw material for the underground life cycle—dead leaves and other plant debris—and without the countless hidden inhabitants of the soil—insects, microscopic fungi, and other symbiotic bacteria, which alone are capable of transforming this material (see box)—there is no hope for the plant.
Because this plant doesn’t thrive on just sunlight and fresh water. And it is anything but self-sufficient. On its own, it can only access the nutrients closest to its roots. That’s not enough to sustain its growth… Fortunately, mycorrhizal fungi1 work to colonize these same roots using their “hyphae,” fine filaments capable of exploring a large volume of soil—thus providing access to infinitely more nutrients (Mycorrhizal Associations in Soils, for Better Control of Plant Production, in Soils and Underground Life, 2017).
Even more surprising, these same fungi act as nurturers: “The soilcontains complex organic and mineral molecules that cannot be directly absorbed. The fungus ‘digests’ these large molecules, then uses its hyphae to transfer the recycled nutrients to the plant.” In exchange, the fungus receives carbon from the plant, which is far better equipped than the fungus to extract it from the atmosphere. Plants thus form inextricable interconnected networks with their fungal partners. And they can only thrive thanks to this symbiosis… unless the absence of it is compensated for by the artificial addition of mineral fertilizers.
From the “Green Revolution” to agroecology
It’s true that these fertilizers can boost plant growth very easily: basically, you add a soluble mineral to the soil… and things start growing. This is the long-standing idea behind the“Green Revolution ”: growing varieties selected for their optimal yield potential, with heavy use of fertilizers, as well as pesticides, irrigation, and machinery, while prioritizing large-scale monoculture.
What impact does this have on the soil and the environment? Back then, no one asked that question. It was the 1960s, just after the great famines. The goal was crystal clear: to produce, in large quantities. A revolution that was green in name only; costly in terms of water, chemicals, and oil, this industrial agriculture had serious drawbacks, foremost among them a decline in biodiversity, a major pillar of food security.
Imitating nature
Times have changed: scientists are now calling for a form of agriculture that can simultaneously feed people and protect the environment. The first principle of this “agroecology” is:“Intervene as little as possible! And apply natural biological processes—the ones at work in a forest. For example, reintroducing vegetation cover by replanting trees; promoting the activity of soil microflora (mycorrhizal fungi, nitrogen-fixing bacteria, etc.); or harnessing the symbiotic capabilities of plants with one another.” (Restoring Soil Productivity in Tropical and Mediterranean Regions: The Contribution of Agroecology, IRD publication, 2017)
An approach that is as humble as it is pragmatic. “We try to observe traditional practices that are well-suited to local conditions, to help optimize them.” Family farming thus has many positive characteristics: small plots, endemic species and mixed cropping, local know-how, and minimal irrigation… If we want to ensure food security in developing countries, it clearly offers a model for the future,” explains Robin Duponnois.
Underground oases
“In a single teaspoon of soil from your garden, there can be several million living organisms,” reveals Tiphaine Chevallier of the Eco & Sols laboratory. Soils are composed of clay, silt, and sand. But that’s not all: they also contain water, air… life! While minerals predominate, organic matter is also part of the composition of this living cocktail commonly known as soil. Organic matter recycled for plants by countless underground inhabitants (microorganisms, but also microfauna: protozoa, tardigrades, or mites; macrofauna: woodlice, earthworms, and springtails…). Organisms that ensure the soil functions properly and produce vital nutrients for plants: nitrogen, phosphorus, and potassium. These oases of life are now in danger: every year, worldwide, ten million hectares of arable land are lost due to desertification. A threat that directly impacts the lives of 480 million people.
- Mycorrhiza is the result of a symbiotic relationship between fungi and plant roots. ↩︎
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