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You say tomato, we say topsoil: interdependence of soil biodiversity and health

For most of our species’ timeline, humans foraged and hunted/fished for food. The advent of agriculture ultimately led to population growth and complex, specialized societies. Still, not even the exponential development since the Enlightenment has freed us from our dependency on healthy soil to grow most of our food.

Humans depend on agriculture. Big-scale agriculture ultimately relies on the long-term health of the few-inches-thick layer of microbe-rich topsoil that makes our planet unique. If soil conservation is a crucial issue, why do few “innovators” pay soil the attention it deserves?

Instead of considering soil and its microbes an essential part of our planet, supporting us by supporting food and storing water and carbon, events such as a pandemic seem to have created a germophobic public opinion; any microbe is now perceived as a potential threat.

No question about the harm that particular sets of microbes can do to humans, but this reality shouldn’t conflict with our rational ability to understand how crucial microorganisms are to keep everything around us healthy —and, ultimately, alive.

The soil microbiome sustains us

Microbes are essential in ecology, complex organisms’ immunology (including ours), and every environment’s look and feel (from acoustics to color). The lack of abundance and variety of microbes in topsoil is a cry for help from any given ecosystem. Is there time to explain to the public how important it is for mainstream society to understand the basics of topsoil?

So far, pop culture has understood the importance of holistic, small-scale farming and contact with natural environments thanks to theories like E.O. Wilson’s biophilia (the innate human instinct to connect with nature and other living beings like plants) or health studies associating walks in nature to emotional and immune well-being thanks to a higher concentration of phytoncides (airborne essential oils) in such environments.

Even “forest bathing,” an ancient Eastern practice, has become popular in the last decade. But when it comes to topsoil, do we need to appreciate first what we need to preserve? And: are present-day needs such as food production at the scale needed compatible with healthy soils, or will topsoil health relegate to explicitly protected preserves in the future?

From mineral dust to rich ecosystem

There’s no better way to appreciate and reflect on one’s reality than the perspective of distance. When we leave the place we inhabit, the new realities we experience make us reflect on our former location, exposing what makes “home” unique.

When at the end of the Great War, the dollar appreciated against the leading European currencies, young Americans in search of adventure settled in places like Paris with little money, often having side jobs as seasonal workers or press correspondents to entertain artistic ambitions.

American ex-pat Gertrude Stein called a bunch of these cultured youngsters the Lost Generation, a group of writers to could reflect on American culture thanks to the new perspective they gained when living abroad.

We won’t have the chance of doing the same with our planet and, say, abandon Earth for a while to go live somewhere else, then come. Interplanetary travel won’t be a reality in the years, if not decades, to come.

Sci-Fi stories offer the necessary and often credible prospective on interplanetary travel. By imagining that we are going somewhere else in the solar system for a while, we can reflect on our planet’s uniqueness. It’s no coincidence that, after the first color pictures taken from space in the sixties, the expression “blue marble” stuck, and also our planetary self-awareness, represented by the biosphere hypothesis and the idea we live in an interconnected system, dubbed “spaceship Earth” by Buckminster Fuller in 1969.

Life of an earthworm

Most of us aren’t familiarized with the term “regolith,” which describes the loose material covering the surface of other planets with a dry surface. Scientists don’t use “soil” to talk about the loose material and dust accumulating on the moon’s surface, Mars and its moons, and other astral bodies, because they lack organic matter.

Regolith is composed of minerals, small rocks, and inorganic materials. In contrast, soil includes a mixture of both inorganic and organic materials: minerals and decomposed organic matter support plant growth and a complex ecosystem of microorganisms, nematodes, and earthworms acting as decomposing accelerators, as well as insects and other small to medium-sized animals that act as scavengers and detritivores.

The soil on Earth isn’t only “alive,” but it maintains and regenerates life on our planet despite being a layer so thin on the Earth’s crust that, if Earth were a model the size of an onion, the soil would be so thin that it would barely be perceptible when studying its section with the help of a microscope.

And so, by leaving our planet and soon revisiting the moon with human-crewed missions (and probably a manned trip to Mars) as a species, we’ll be able to attest to how precious the soil in our planet is: unlike regolith, a compact layer much thicker than soil that can be several meters deep, the soil is porous and full of life, hence transforming and integrating organic matter, capable of retaining water and nutrients.

But we don’t have to leave our planet to attest to the dramatic difference between depleted and healthy soil. In any healthy patch of soil on our planet, decay propels life: when plants, animals, microorganisms, and other organic residues decompose, they blend with soils and sediments thanks to bioturbation, a constantly ongoing process of soil reworking by organisms by creating burrows, feeding, and constantly ventilating dirt, which helps soil to store water and carbon.

Effects of intensive agriculture and urbanization

The thin layer we call topsoil, with its variable depth but only averaging 5-10 inches (13-25 cm), not only turns “waste” into nutrients to feed terrestrial life (including us) but also stores CO2 and retains water moisture. Thus the health of the planet depends on the health of a layer so thin that we could easily mismanage it, losing its properties to erosion.

Soil erosion and degradation aren’t among the main concerns today, unlike issues visibly affecting everyday life (such as access to housing and healthcare, inflation, or violence), according to Pew Research. But most of the Earth’s topsoil will likely be depleted or lost to erosion by 2050 if current trends continue.

When agriculture and urbanization replace local vegetation, topsoil gets exposed to the elements. With less water moisture and reworking by microorganisms, soil fertility decreases, and erosion (soil washing by wind, rain, and big-scale, poorly-planned tilling) can turn former fertile environments into potential wastelands in a few years.

Not all soils used for food production are equally affected by erosion: even in an environment of increasing extreme weather events, topsoil will better withstand hard wind, rain, and flowing water by adopting agriculture procedures that diminish the most damaging farming practices like deep tilling (literally overturning the ground to maximize short-term crop fertility.

From guano wars to chemical fertilizers

Healthy topsoil is full of life, spongy, protected, holds a higher number and variety of organisms, and is more productive in the long term. Healthy soil doesn’t only look different and holds more water, carbon, and food for micro and macro organisms but has different acoustics, according to a recent study from Flinders University (Australia). According to the study’s co-author, Martin Breed:

“Like underwater and above-ground acoustic monitoring, below-ground biodiversity monitoring using eco-acoustics has great potential.”

The abundance of microbes in healthy soils can be measured via underground acoustics. The method also confirms that damaged soil gets restored, and when life microscopic life on it returns to former levels, acoustics confirm the regeneration. The method could hold clues for future tools that could be used in techniques for regenerative agriculture.

One of the most-cited ways to mitigate topsoil loss when farming is embracing no-till practices to grow crops and switching from intensive methods involving fewer high-yield crops to more holistic approaches. But can techniques like no-till methods, polyculture, crop rotation, and systems agriculture (permaculture, traditional aquaculture, etc.) provide affordable food at a similar scale than the fertilizer-dependent intensive agriculture materialized during the Green Revolution?

There’s a reason why— the cynics will say— geopolitics in the late nineteenth century involved a big deal of fighting for the control of the few islands concentrating big amounts of bird excrement or guano, the most concentrated and effective known fertilizer (high in nitrogen, phosphate, and potassium) before the development of industrial fertilizers, and no human procedure focused exclusively on short-term gains will replace current big-scale agricultural methods for the greater good, especially as long-term externalities aren’t accounted for.

When eroded soil turns into dry dust

Several studies suggest that, when exposed to healthy topsoil, humans (including children at a young age) boost their immune system and improve their overall health thanks to early contact with a diverse range of microorganisms in balanced amounts, including bacteria, fungi, and viruses. By being exposed to such organisms, our body reduces the risk of developing allergies and other inflammatory conditions later in life.

But unhealthy soils and ecosystems can bring excessive amounts of pathogenic microorganisms. Drought in the US West and Southwest is helping expand a fungal disease known as Valley fever or Coccidioidomycosis. It turns out erosion isn’t topsoil’s only threat: more extreme temperatures are transforming entire regions.

An even drier and hotter environment in the American West has increased dust near ever-expanding urban concentrations such as the Phoenix area. And a dustier, already damaged, and arid soil is the ideal environment for the dangerous mycelium to expand through rodents and dust storms. Or, as described by Keren Landman in Vox, the way this particular dormant fungus in the region’s soil prospers is like that of “a devil lurking in the dust.”

The expansion of coccidioidomycosis in an area with drier, dustier topsoil that concentrates more and more suburban and exurban population illustrates what extreme climate conditions could cause topsoil across highly populated areas in the world. Strategies to protect topsoil could diminish the risk to human health. We have evolved to benefit from early exposure to beneficial microorganisms living in the soil. With high concentrations of essential nutrients (magnesium, calcium, or zinc, among others), rich soil can have direct effects on us if we are in contact with it; however, exposure to contaminated or unbalanced soil can have negative health effects.

You say “waste,” soil says “nutrient”

There aren’t outright strategies to manage topsoil regeneration at a big, automated scale, yet all techniques that seem to successfully regenerate topsoil’s health combine processes that reduce tilling use and increase crop variety, from Masanobu Fukuoka‘s “natural farming” to Bill Mollison‘s permaculture.

According to such (often small-scale) practices, anybody can protect topsoil locally by minimizing soil disturbance by avoiding tillage or compacting (by foot or vehicle traffic, for example); using cover crops (clover, rye, vetch), which help protect the soil from erosion and add organic matter; rotating crops, which reduce erosion and depletion, helping with pest control; adding organic matter from compost or manure, turning “waste” into nutrients and hence transforming a potential problem into an advantage; managing water to keep moisture levels.

By using responsible farming practices, from contour farming to terrace farming or strip cropping, communities can reduce soil erosion and improve its health over the long term and also add to the beauty and quality of life of any given population.

Often, things that make sense and are most beneficial in the long term are also aesthetically pleasing.