This post has been updated as of 19/05/2021.
Soil is one of the earth’s most important natural resources. It underpins human food production systems, supports the cultivation of vegetation for feed, fibre and fuel, and has the potential to help combat and mitigate climate change. It’s also a rich and complex ecosystem, accommodating a staggering array of biodiversity. Therefore, the importance of soil on life is vast.
Franklin D. Roosevelt once said “The nation that destroys its soil destroys itself.” He wasn’t wrong.
Healthy soil is crucial for human life and wellbeing. However, soils across the globe are being threatened and damaged by human activities. Here, we discuss the importance of soil, the relationship between humans and soil, and the health of our soils is threatened.
Table of Contents
- What is Soil?
- An Evolving Knowledge of Soil
- The Importance of Soil: How Important Is It?
- How Are Humans Impacting Soil?
- The Importance of Soil on Life
- What Can You Do in the Fight to Save Soil?
What is Soil?
Soil. Mud. Compost.
What’s the difference?
Well, mud is a mixture of silt, clay or soil mixed with water. Whereas, compost is a “mix of decaying nutrient-rich soil with medium density that is naturally made using oxygen, bacteria, water, and organic materials“
So what of soil?
Soil has been called the fragile skin of the earth.
This dynamism comes from the interaction of the different components of soil, including minerals, organic materials and living organisms.
Water and air also form a complex network of channels and chambers between the solid components of soil. These components, or solid ‘grains’, are chemically active. They interact with each other continually, so the composition and properties of soil are constantly changing.
Though soil may appear homogenous, it is in fact made up of a diverse range of different components.
Many of the particles that can be seen with the naked eye come from rocks broken down into fine grains. These grains can be classified as sand, clay or silt, depending on their size.
While sand grains are course and feel gritty to the touch, clay is finer and feels sticky. Silt particles, meanwhile, are intermediate in size and have a silky texture.
An Evolving Knowledge of Soil
Until recently, our knowledge of the components of soil was largely limited to these solid, visible grains of rock.
However, 2010 saw the launch of the ‘Earth Microbiome Project’.
The multidisciplinary initiative uses genome sequencing to identify, characterise and analyse microbial communities across the globe.
The project aims to collect samples from all possible environments on the planet. It also aims to sequence the ‘microbiome’ – the combined genetic material of all the microorganisms in a given environment – for each sample.
Before the project’s launch, less than 1% of the total DNA present in a gram of soil had been sequenced. This mean we had little understanding of the living organisms found in soil.
In the years since the project began, the microbial communities it has identified in global soil samples has been nothing short of astounding.
Far from being inert matter, soil is teeming with life. It’s made up of a vibrant, thriving population of bacteria, archaea and fungi.
In fact, there are between hundreds-of-thousands of species in a handful of healthy soil. There is more biodiversity in the bacterial community of a single handful of healthy soil than in all the animals of the Amazon basin.
These microbial communities perform a wide array of ‘ecosystem services’ essential for the health of soil and the organisms it supports. For example, Saprophytic bacteria and fungi decompose the complex substrates of dead plant and animal matter to generate humus. Humus is the dark, organic component of soil from which plants take most of their nutrients. The amount of humus in soil determines both the soil’s capacity for water retention and its fertility.
The Importance of Soil: How Important Is It?
Soils from around the globe are diverse in terms of their structure, depth, texture and fertility.
These differences mean that soils provide a wide range of environmental, economic and social benefits to human societies.
Soil Fertility: Supporting Agriculture and Forestry
We’ve already seen that microorganisms found in soil samples produce humus. It’s the basis for soil’s fertility and for global agriculture and forestry industries.
Therefore, soil fertility is increasingly a factor of vital importance to human health and nutrition.
In addition to improving soil fertility, soil microorganisms often form symbiotic relationships with plants. One cannot survive without the other. An example of this relationship is nitrogen fixation.
Nitrogen is needed by all organisms for the production of amino acids and nucleic acids. However, atmospheric nitrogen is inert and cannot be used by higher organisms such as plants and animals.
Some species of bacteria can ‘fix’ atmospheric nitrogen into biologically useful ammonia, which can be used by plants.
Nitrogen-fixing bacteria such as Rhizobium invade the root hairs of leguminous plants by inducing specific sets of genes in response to compounds secreted by the host root. Once inside the inner root tissue of the plant, the bacteria synthesize the proteins necessary for nitrogen fixation.
The plant is able to use the ammonia produced by bacterial enzymes known as nitrogenases. The bacteria can utilise carbohydrates, proteins and oxygen generated by the plant.
Similar relationships exist between other species of plant and bacteria, and between plants and other microorganisms.
Meanwhile, microorganisms such as nematodes and arthropods also play a role in regulating the levels of nitrogen available to plants. These microbes consume certain species of nitrogen fixing bacteria, excreting excess nitrogen and other minerals in a plant-available form.
Some species are able to consume up to 5,000 bacteria per minute.
They act as effective regulators of the bacterial population of soil and have great potential as biocontrol agents.
Soil as a Building Material
Soil is still used as a primary building material in many regions across the world.
In fact, a large amount of buildings globally are constructed using soil.
While only some types of earth are suitable for use as a building material, the UN Food and Agriculture Association (FAO) suggests that some advantages of using soil for construction are its low cost, its ease of use, its fire-resistant qualities and its high thermal capacity.
This isn’t news to us. We’ve worked on projects using Stabilised Soil Blocks (SSB) as a building material.
The Climate Crisis and Soil
We now know that many soils act as highly efficient carbon sinks. The world’s soils are thought to store approximately 15 gigatonnes (15 thousand million tonnes) of carbon, three times as much as all of the earth’s terrestrial vegetation combined. 27% of this soil carbon is accounted for by a single glycoprotein, glomalin, found in humus.
Glomalin, an extremely stable, iron-bound molecule, is produced by the spores and hyphae of a group of fungi that form symbiotic relationships with vascular plants.
Though not yet well characterised, Glomalin presents exciting new possibilities in carbon management and storage technologies.
Indeed, increased carbon levels actually boost glomalin production. In a 3-year study, an increase in CO2 of 300ppm resulted in a five-fold increase in glomalin production by fungal hyphae, which in turn led to increased soil stability and fertility.
This is an important avenue to explore in a time when the issue of the climate crisis is more urgent than ever before.
Soil and Water
Just as it acts as a carbon store, soil can store large amounts of water. As well as being important for vegetation growth, this can be a key factor in preventing flooding under extreme weather conditions.
Soil can also act as a water filtration system. As water drains through soil, soil microorganisms and minerals act upon it to remove pollutants and toxins. This filtration occurs through physical, biological and chemical processes. Bacteria, fungi and other microorganisms found in soil interact with pollutants carried by water. Meanwhile, the physical and chemical composition of soil affects how water and other particles are able to move through it.
Soil and Biodiversity
Soil is an extraordinarily diverse and complex ecosystem. It plays host to some 25% of our planet’s biodiversity.
The soil food web involves many trophic levels, with microorganisms, plants and animals interacting and contributing to water, nutrient and nitrogen cycling.
How Are Humans Impacting Soil?
“Eventually, all life depends upon the soil…there can be no life without soil, and no soil without life; they have evolved together” – USDA Yearbook of Agriculture, 1938
The pressures of population growth, food insecurity and agricultural intensification are leading to widespread soil degradation in many regions. This degradation can take many forms.
Soil and Erosion
Soil erosion is a serious concern in many parts of the globe (these photos from Tanzania are scary!) It refers to the process by which topsoil is worn away by the natural processes of:
- Other weather patterns
Or by human activities such as:
- Land conversion
- Other human activity
Over the last 150 years, 50% of the planet’s topsoil has been lost in this fashion. There are few reliable estimates of the extent to which humans have contributed to this loss, but studies have shown that it varies widely across different regions. For example, 8% in North Africa and 75% in Australia.
Soil erosion has significant impacts on crop production. It also effects the transport of agricultural inputs and pollutants to waterways.
Overall, rates of soil erosion are significantly higher than rates of soil formation. This represents a substantial long-term threat to world’s soils and – by extension – global food security.
The Process of Soil Sealing
Soil sealing is another physical process, most often associated with the spread of urban land, which leads to a loss of soil fertility and agricultural potential.
Sealing occurs when soil is covered by an impenetrable material, effectively causing it to become ‘non-soil’.
Estimates place the current rate of global soil sealing at 250-300km2 day. However, this rate is likely to increase given ongoing trends of rural migration into urban areas.
Compaction and Other Physical Processes
Soil compaction is another form of soil degradation. It occurs when soil is compressed by the use of heavy agricultural equipment. Compaction reduces the amount of water and air present in soil and it can impair crop emergence, root penetration and nutrient and water uptake by crops.
Physical processes such as over-farming, land clearance and deforestation also drastically disrupt the activities and diversity of soil microorganisms.
The indiscriminate clearance of land for cultivation – as well as the use of herbicides to create a monoculture of a single plant – reduces the quantity and diversity of plant residues within soil, and therefore the quantity and diversity of microbial habitats and food sources.
Meanwhile, the intensive tilling of soil breaks down soil aggregates that are held together by fungal hyphae and reduces the number of fungi in the soil. (It’s why there is a no-dig gardening grassroots movement taking off!)
It’s true that these techniques, alongside the use of chemical fertilizers and herbicides, have allowed large increases in crop yields and food production in Europe, Asia and the Americas in recent years. However, it may be that there is a price to pay for this short-term success.
Use of Agricultural Chemicals
Many modern agricultural practices have a deleterious effect on microbial soil communities.
Chemical fertilizers, fungicides, herbicides, pesticides – those substances on which we have staked our food security – have all been shown have devastating effects on indigenous microbial communities within soil.
Global use of agricultural chemicals occurs on an enormous scale. Worldwide, 3×109kg of pesticides are applied to crops each year. It’s similar for for herbicides. Problematically, only 0.1% of the applied chemical will reach the target organism.
The remaining 99.9% will remain in the soil until it’s degraded. A process which can take several weeks or months.
Repeated application of agricultural chemicals can therefore cause long-term contamination of the humus and potentially permanent alteration of the soil microbiome.
Agricultural chemicals can alter the physiological, metabolic and biochemical behaviour of microbiota in the soil. This can disrupt the relationships between plants and microbes, decreasing nutrient bioavailability.
Agricultural chemical usage has vastly different effects on different microbes. As such, the effect of pesticide and herbicide usage on microbial communities is extremely difficult to predict.
Certainly, it’s not always negative. Some microbial groups are able to use certain pesticides as a source of energy and nutrients, and therefore thrive upon application. In other instances, a pesticide that is toxic to one group of microorganisms will reduce competition and allow a previously less successful species to become established in the ecosystem.
However, it appears that almost all applications of agricultural chemicals lead to a long-term loss of microbiome biodiversity and soil fertility. In addition, agricultural chemicals significantly reduce microbial infection of plant roots, therefore directly reducing nitrogen fixation and overall growth in many plant species.
Soil acidification occurs at a slow rate as a natural process. However, this process is accelerated dramatically by human inputs.
There are four key mechanisms by which this accelerated acidification takes place:
- Removal of product
- Leaching of nitrogen
- Inappropriate use of certain fertilisers
- Accumulation of organic matter
The removal of crops and vegetation from soil drives acidification because most agricultural products are slightly alkaline. Their removal lowers the pH of the soil, particularly if they are not replaced.
Meanwhile, leaching of nitrogen occurs when soil nitrate levels exceed the quantity that can be used by plants. When this occurs – usually following excessive or inappropriate usage of nitrogenous fertilisers – the nitrate drains below the plant root zone and into the groundwater system. This leaves the soil with a reduced pH.
Increased fertiliser usage can also contribute to build-up of organic matter in soil. This can be beneficial – in terms of impact on soil structure but it also accelerates acidification and reduces soil pH.
Increased soil acidity can limit water and nutrient availability. It can also reduce microbial activity and contribute to aluminium toxicity in soil. This has severe implications for soil fertility and agricultural production.
Recent work indicates that topsoil acidity affects approximately 30% of the ice-free land area of the earth and subsoil acidity is thought to affective up to 75%.
Salinization can have serious negative impacts on soil fertility and crop yields. However, it’s often difficult to directly pinpoint its cause.
Some soils are naturally saline. Although, salinization can also be driven by inappropriate management practices and poorly delivered irrigation programmes.
Salinization occurs most often in arid and semi-arid areas. It is thought to be exacerbated by climate change.
This frequently occurs when insufficient rainfall drives irrigation schemes, which can lead to salinization when executed without proper planning and expertise.
There is little recent data on salinization but studies conducted in the 1990s suggested that up to 77 million ha of land was affected by human-driven salinization.
Contamination of Soil
Soil contamination is driven by a range of factors that frequently introduce excessive amounts of contaminants into the soil:
- Intensive industrial or agricultural activity
- Inadequate waste disposal
- Military activities .
Soil contamination is difficult to trace, measure and assess. However, it’s known that soil contaminants such as heavy metals and organic and inorganic pollutants can reduce soil fertility.
They can also negatively impact biodiversity and – in the case of some organic pollutants – facilitate the spread of infectious disease.
The Importance of Soil on Life
It’s evident that our planets’ soils are facing severe challenges.
Urbanisation, pollution, unsustainable land use and climate change all negatively impact soil.
The UN’s Food and Agriculture Organization (FAO) has highlighted soil as a serious cause for concern. They stated that “the current rate of soil degradation threatens the capacity to meet the needs of future generations”.
They now advocate for the promotion of sustainable soil practices.
This will work towards securing a productive food system. It will improve all livelihoods. It will lead to a healthy environment.
Soil is important. It’s important to microorganisms. Plants rely on it. Animals need it. Humans won’t survive without it.
It’s undeniable. The importance of soil on life is a matter of life or death.
What Can You Do in the Fight to Save Soil?
Currently, the ecological relationship between humans and soil is overlooked.
Both large organizations and grassroots projects are increasingly showing awareness of the issues that surround it.
National and local governments are also placing a growing emphasis on the importance of soil. Similarly, charities and NGOs working at the grassroots level demonstrate that there is hope for healthier soils worldwide.
However, there is still more to be done. For example, individuals can have a huge impact.
Therefore, we’ve put together the following links to explore. They are a range of websites and groups to learn from and join with in the fight for healthier soils.
- Commonwealth Human Ecology Council – we advocate for the environment through projects on topics such as soil health
- Kiss the Ground – a California-based group prioritising education and healthy soils
- The Red Soil Project – eroding poverty through sustainable farming
- Soil Erosion Modelling – a project by the African Conservation Trust
- Living Soil Training – training by the Hummingbird Project in India
- SOIL Haiti – using ecological sanitation to tackle Haiti’s toughest challenges
- The Rodale Institute – an independent agricultural research organization conducting research into soil health and related issues
It is only by concerted action on a range of scales that we can hope to achieve healthier soils worldwide. To do so will by no means be an easy task, but there is little doubt that it’s a crucially important one for the future of our planet and the human life it support.