“A nation which destroys its soil, also destroys itself.” Such were the words of Franklin D. Roosevelt back in 1937 when the United States was in the midst of its dust bowl years. Overplowing and the removal of prairie grasslands, which anchor the topsoil, had transformed once-fertile plains into a barren, parched wasteland that was swept by duststorms.
We still use the word “dirt” to mean soil. But there is a world of difference between the rich, fertile earth that nourishes ecosystems and the desiccated ground that gave the US depression — compounded by crop failures — the nickname the “dirty thirties.”
A microcosm of biodiversity, teeming with life
Soils are the living and breathing surface of our planet. Soils are a mix of organic and mineral material. They are one of the most diverse habitats on the planet, home to countless worms and other insects. A square meter of soil can contain up to 10,000 different species, and a single gram can be home to a billion bacteria.
These organisms break down leaf litter, animals and dead plants, and recycle valuable nutrients back into the soil for new plants.
The soil is further enriched by earthworms, insects, and other creepy crawlies as they burrow. They mix the rich material from the topsoil in the layers below, enriching it. They help to give soil structure and ensure it can absorb and drain water.
Intensive farming drains soils that support life
Only a tiny fraction of the organisms found in our soil has been thoroughly studied. Scientists know that soils are rapidly declining in biodiversity and are in poor condition.
More than half of the world’s arable land has been devoted to wheat, maize and soy. Planting huge expanses of a single crop can boost yield — at least in the short term — and makes mechanized harvesting easier.
But as the same crop draws the nutrients it needs from the soil year after year, that soil becomes depleted. This means farmers must rely heavily on artificial fertilizers that pollute water supplies and disrupt the natural balance in ecosystems. Synthetic pesticides, fertilizers, and other chemicals can also harm soil microbes.
While industrial argriculture can increase yield in the short term but reduce soil nutrients, it is not sustainable.
Plowing can also be costly. It destroys natural networks of fungi and microorganisms while breaking up the resilient structure of soil, leaving it more prone to flooding and drought, and vulnerable to erosion.
In 2015, a study from England’s University of Sheffield found that 33% of the world’s arable land had been lost to pollution and erosion over the previous 40 years. According to the study, it takes around 500 years to create 2.5 cm (1 in) of topsoil.
Brazil, as well as some countries in the Caribbean, Central Africa and Southeast Asia, have lost 70% of their agricultural land to erosion, and around the world an estimated 3.2 billion people — particularly rural communities in the Global South — are already suffering from failing or reduced harvests as a result of land degradation.
Because fertilizers require lots of energy to make, they are also problematic. A loaf of bread can have a carbon footprint that is more than 40% due to the fertilizer it was grown from.
Carbon sinks are at risk
Although artificially enriching soils with fertilizers can result in more greenhouse gas emissions, healthy soils actually trap greenhouse gases and help protect us from climate change.
However, not all human-caused emissions end up in our atmosphere. They are absorbed into the soil, forests, and oceans. Many of the carbon taken from the atmosphere by plants when they die and decay is absorbed into the soil. This process takes time, but cumulatively, it makes soils a major carbon sink — sequestering twice as much CO2 as all the world’s flora and our atmosphere combined.
Scientists believe that it is necessary to conserve and restore the world’s wetlands in order to save our climate.
The most carbon-rich soils of all are found in wetlands, where plant debris sinks into shallow, acidic water. The oxygen-poor environment doesn’t allow plant matter to decompose. Instead, it becomes carbon-storing peat.
Although they make up only 3% of all land on the planet, peatlands account for around a third of all CO2 in soils.
That is all well and good as long as the carbon remains locked in, but it becomes dangerous if we let it out — which is why land-use change is a major contributor to greenhouse gas emissions. Plowing up soils or draining wetlands for agriculture or construction releases the stored carbon into the atmosphere, heating up the planet. Permafrost soils from Canada and Antarctica are also melting with rising temperatures.
A 2019 study was published in the journal by the authors Nature say that without large-scale restoration of these habitats, up to 40% of the greenhouse gas budget still available to meet the Paris climate change targets could be used up by these areas alone.
Traditional farming practices used in subsistence agriculture and some organic farming, could also contribute to recovery of our soils — or at least slow their decline. Soil health can be maintained by rotating crops, sowing without tilling, mixing different species of plants, and allowing crop wastes to decay where it has grown.
These practices are less labor-intensive, and therefore more expensive in the long term. But according to the International Union for Conservation of Nature, increasing soil biodiversity could yield up to 2.3 billion metric tons (25.4 US tons) of additional crop yields per year, worth $1.4 trillion (€1.24 trillion).
Ruby Russell translated it from German