What is healthy soil and how to improve it

Maia Welbel

What is healthy soil?

You might not be able to tell by looking at it, but soil is a living, evolving, generative entity. Like other living things, soil relies on oxygen, water, nutrients, and other ecosystem resources to stay healthy. It also happens to be one of the most critical assets we have to sustain our global population.

Unfortunately, like many of our life-giving systems on earth, healthy soil is under major threat by climate change and industrial exploitation. According to the Food and Agricultural Organization (FAO), at least a third of the world’s soil is moderately to highly degraded. And degraded soils simply cannot yield the volume of crops we need to feed all of our planet’s inhabitants.

There are countless ways humans have interfered with soil health — from land clearing and monoculture to species eradication. But first, let’s talk about what healthy soil looks like and why we need it in the first place.

Broadly speaking, healthy soil is comprised of four layers.

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  1. The O horizon
  2. is the top layer. It is made up of plant litter and other organic matter that decomposes into nutrients that enrich the soil and form the next layer.
  3. The A horizon
  4. is also called the topsoil. This is where plant roots grow best. It is also where bacteria, fungi, and other microorganisms live and help the soil stay fertile and hold water.
  5. The B horizon
  6. is also called subsoil, it is formed from clay minerals and other compounds that seep down from above. Plants and animals cannot easily penetrate this layer.
  7. The C horizon
  8. is created from weathered rock. Below all of the soil horizons is bedrock.

Healthy soil harbors all sorts of living organisms, from insects and earthworms to fungi and bacteria, and even small mammals like burrowing rodents. All of these critters facilitate the nutrient cycling and aeration necessary for soil to support plant growth. For example, common insects called springtails chew up organic matter like dead leaves, breaking them down into pieces small enough for bacteria and fungi to decompose and fortify the soil.

Plant roots also reinforce a healthy soil ecosystem. By snaking through different mineral layers, they allow the air and water that the whole systems depend on to flow more freely. Of course, plants are also integral to the carbon cycle. During photosynthesis, they pull CO2 from the atmosphere and store it in their biomass. Some of that carbon gets exuded through the plant’s roots throughout its lifecycle. When the plant dies, its roots decompose and store the atmospheric carbon they absorbed as soil organic matter.

All of these living and nonliving elements are necessary to maintain a healthy soil ecosystem. But why is healthy soil so important for humans? Well, it is the basis of almost all agriculture and is also earth’s primary mechanism of carbon storage!

We need healthy soil to grow food

The Intergovernmental Panel on Climate Change states with “very high confidence” in a 2019 report, that land degradation represents “one of the biggest and most urgent challenges” that humanity faces.

The process of generating high-quality, fertile topsoils — the stuff we need to grow crops at high volumes — can take centuries. But with about 40% of earth’s land area already being used for farming, and animal agriculture, which is especially land and resource intensive, expanding more and more rapidly, we’re degrading healthy soil much faster than it can replenish.

Ronald Vargas, secretary of the global soil partnership at the FAO in Rome, reported to BBC, “Many types of soil degradation are invisible. You just don’t see the loss of organic carbon from soils or pollution building up in it until you try to plant crops there.” If we want to keep growing healthy food, we need to do a better job keeping our soil alive.

Tilling, which is standard practice on intensive and industrial farms, destroys natural soil structure, killing bacteria and fungi and leaving it vulnerable to erosion. The IPCC reports that conventionally tilled soils erode more than 100 times faster than they form. No-till farming ensures the longevity of an area's soil for long-term crop output by maintaining soil’s structural integrity and ecological community.

Monoculture, the practice of cultivating a single crop on the same land repeatedly, depletes soil of its diversity of nutrients. Planting a variety of different plants species within a field and setting up seasonal crop rotations allows the soil to maintain a healthy balance of minerals and microbes to nourish vibrant crops.

Heavy use of chemical pesticides and fertilizers also disrupt soil ecosystems. Organic alternatives such as composting, which breaks down organic matter into nutrient-rich, carbon-filled material, replenishes and revitalizes soil, rather than stripping it. Regenerative practices like no-till, intercropping, and crop rotation also make synthetic inputs less needed because they act as natural defenses against pests, disease, and nutrient depletion.

Healthy soil keeps carbon out of the atmosphere

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Soil is earth’s most efficient method of storing carbon. In fact, more carbon resides in soil than in the atmosphere and all plant life combined (about 2,500 billion tons). In other words, it’s one of the main things preventing us from burning alive in a greenhouse gas ridden atmosphere.

Tilling causes massive volumes of carbon to be released into the atmosphere, as it literally unearths the layers designed to keep it safely stored away. The IPCC reports cropland soils have lost 20-60% of their original organic carbon content globally. Investing in soil regeneration must be a key strategy for mitigating climate change if we are to expect a habitable planet for future generations.

Organizations to follow

Zumwalt Acres is conducting research with Yale University on silicate rock weathering and biochar to improve soil health and carbon sequestration capacity.

The Savanna Institute is a  nonprofit organization that works with farmers and scientists to lay the groundwork for widespread agroforestry adoption in the Midwest US.

The Land Institute is a nonprofit organization led by a team of plant breeders and ecologists focused on developing perennial plants to be grown in ecologically intensified, diverse crop mixtures known as perennial polycultures. The Land Institute’s goal is to create an agriculture system that mimics natural systems to produce ample food and reduce or eliminate the negative impacts of agriculture.

Project Drawdown's mission is to help the world reach “drawdown”—the point in the future when levels of greenhouse gases in the atmosphere stop climbing and start to steadily decline, thereby stopping catastrophic climate change—as quickly, safely, and equitably as possible.