Why Soil Matters

Soil is a precious mixture of the living, the never-living, and the dead. It’s a vital resource for 98.8% of our food - and it’s not renewable.

What is soil?

Soil is a complex blend of tiny fragments of weathered rock, dead organic matter, living organisms, and an incredible number of microorganisms - namely fungi, bacteria, protozoa.

Within the innocuous dirt beneath your feet, there is a vast, living microbiome. This microbiome is the most important and mysterious part of soil. Just one gram of soil could hold up to 10 billion microorganisms, most of which are unknown species, all living alongside and interacting with each other. In fact there are so many living organisms that within a single acre of soil, the mass of bacterial life would amount to the weight of around two cows.¹ Soil also acts as a major carbon sink - far more carbon is stored in soil than in the combined vegetation and atmosphere of Earth.²

The continuous cycles of life and death in the microbiome keep the soil in a constant flux of moving nutrients, water, and gases. Everything that dies here becomes dead organic matter, which is devoured and broken down into soil nutrients by the decomposer microbes. Other soil microbes take elements from the air, such as nitrogen and carbon, and build them into organic compounds that are useful for them and other organisms in the microbiome. The excess is either released slowly during the life of the microbe, or all at once when it dies. For plants, these soil microbes produce crucial nutrients that can be absorbed through their roots, with some additional minerals coming from the weathered rock fragments around them. Known as the topsoil, this entire region of rich organic matter provides the conditions needed for our plants to grow.

Learn more about the nuances of carbon farming here.

The fertility of soil for growing crops also depends on its structure. As soil microbes produce substances that bind particles into clusters or crumbs, they create crucial space in the soil for water and gases to flow past. Strands of fungi also connect up plant roots and help to share nutrients, or build ‘bridges’ for travelling bacteria across soil particles. While these strands appear miniscule, one single gram of soil can contain several kilometres of fungal filaments. Meanwhile, bacteria-eating organisms called protozoa patrol through the network, devouring disease-causing bacteria and releasing nutrients from every digested bacterium to the surrounding soil.³

The many ways soil can be damaged

Like any living thing, soil and the microbial ecosystems within it can easily be damaged severely under harsh conditions. Here are a few key causes leading to poor soil health.

Overworking the soil

Hard crusts can form naturally on poor soils for a number of reasons. For example, when raindrops compact soil crumbs and pack soil pores with fine silt, when salt crystals are left behind as water evaporates in arid areas, or even by growing layers of algae, moss or lichens in soil with standing water. To break up, aerate and remove weeds from hard-crusted soil, many farmers till or plough the soil using heavy machinery. But while tilling can break up the hard crust, removing the living roots that help to anchor soil together can make matters even worse. Without these living roots, soil becomes drier and is more likely to be blown away by wind and water. The process also throws the established microbe community into disarray, much like logging a rainforest would destroy the multitude of living relationships within.

While tilling is a potential short term solution to improve soil for seasonal crops, the impacts on long term soil health are far less positive. This is largely due to the fact that tilling causes a sudden burst of atmospheric oxygen to decomposers in the soil as the soil is ripped apart. This burst of fresh air leads to a surge of microbial activity, and a rapid release of nutrients for plants to use in the short term. Over the long term however, repeated tilling can have the opposite effect - leading to a decline of local organic matter and nutrients.

Tilling can’t keep providing these short-term benefits with progressively less organic matter to hold water and provide food to microbes. As organic matter and moisture dissipate, soil becomes deader, drier, less fertile, and easier to erode.⁴ Even a one percent decrease in soil organic matter may mean around 75,000 litres less water held within a single acre of soil - reducing the ability of this land to hold crops.⁵ Overtilling in a time of drought is thought to be one of the major causes of the infamous American Dust Bowl of the 1930s.⁶

A lack of crop diversity

The types of plants growing in soil also influence the local soil biome. Studies show that monocropping - growing just one type of crop on a designated piece of land - reduces soil microbial diversity, and lowers levels of soil nutrients over time.⁷ Monoculture also influences the acidity of soil, making it impossible for certain microbes to flourish and support other life in the region.⁸

Fertiliser & pesticide use

An active and biologically diverse soil biome is also essential to break down pesticides and fertilisers. Without decomposers to break them down and keep them retained in the soil, they can quickly end up draining out into nearby waterways. Adding fertilisers can also throw the microbial community out of balance, causing more carbon dioxide to be released and depleting soil organic matter.⁹

Changing climate

The biome is also affected by climate, and by virtue of this, climate change. Warmer temperatures tend to speed the work of decomposers, which reduces organic matter in the soil. Freshwater and saltwater flooding, caused by heavier periods of rainfall or expanding oceans, can also disrupt which microbes can survive in the soil.

It’s critical we look after it

Less fertile, eroded, or polluted soil means lower crop yields and more economic losses for farmers. And not just for crop farmers - it also means less or no pasture for livestock. But degraded soil also threatens the natural world beyond the realms of farming, raising the risks of desertification, flooding, pollution of waterways with chemicals or eroded soil silt, and more.

And what most of us don’t realise is that soil is a non-renewable resource, with new topsoil naturally produced at a meagre rate of 0.25 -1.5 mm each year. And though the rate varies around the world, the UN warns that altogether we are losing as much as 24 billion tons of fertile soil a year.¹⁰ Considering that soil is responsible for producing 98.8% of our food, it’s time we take better care of it.¹¹