It is easy to understate the importance of soil. It seems benign. It seems inert. But the ground beneath our feet is literally teaming with life – most of it too small for us to see or register as important. But all of it IS important and vital to our human life systems. Soil provides the anchor to plant roots. It holds water and nutrients. It is home to micro-organisms and so much more.
When we think of soil, we often think of the physical properties of the soil. How big are the particle sizes? Sand is the biggest, silt is a medium size, and clay is the smallest. We think about the water holding capacity. Clay soils have a lot more surface area of the individual particles and so therefore can hold a lot more water than sandy soils. We think of availability of nutrients and soil structure as indicators of healthy soil. But it is these last two that offer a huge level of complexity that we rarely think about.
Whenever a soil is lacking in available nutrient for the given crop it is easy to consider adding an amendment. If the soil is low in nitrogen, then just add some ammonium nitrate and you are good to go. While this method offers a quick (and needed) solution to the immediate nutrient deficiency, it doesn’t take into consideration the complex biology of bacteria, nematodes, fungi and other microbes in the soil that play a role in nutrient cycling. In theory, with enough organic matter present in the soil and the right microbes in the soil, nutrients like nitrogen should be readily available for whatever crop or plants are currently growing.
Soil structure shows up when soil clumps together and creates peds. These peds allow for cracks and spaces in the soil for water to permeate down and more easily get absorbed. Soil structure can take years and years to form and can easily be destroyed through mechanical cultivation. What causes soils to form these peds? It is largely due to the network of BIOLOGY in the soil. Plant roots send off tiny root hairs that can hold some of the bigger pieces of soil together. Fungi and their mycelium can act as little webs and nets that bind to the plant root hairs and bind to smaller pieces of soil. And proteins excreted from things like protists and other micro-organisms can act like glue that binds individual soil particles together. This inter-connectivity of many different organisms to create soil structure shows the need to pay attention to biology.
Functions of soil
- We consider soil to have six major functions. First and foremost, soil is used for food and biomass production. Eleven percent of the globe’s land surface is used in annual crop production with up to 36% of land suitable for some kind of agriculture (livestock or crop). This land grows our food crops, it raises livestock, and it produces biomass like lumber for houses and paper, cotton for clothes, and biomass for fuel like ethanol. The soil is the anchor for the plant roots.
- Consider that U.S. agriculture produces about 500 million tons of crop residue annually, most of which contributes to maintaining soil organic matter. Plans to use crop residues for bioenergy production could deprive agroecosystems of important inputs for future soil productivity, potentially upsetting existing agroecosystem balances.
- An essential function of soil is the storage, filtering and transformation services that it provides. Soil filters water removing harmful micro-organisms, chemicals, and other pollutants to make for clean and safe drinking water. We have created some artificial processes to clean water for drinking, but soil is still the most important filter for us. Soil can also store our garbage (landfills), it can store excess water (think of heavy rains and the soil absorbing that liquid), it can store carbon (living and nonliving matter in the soil store carbon that would otherwise be released in the air). Removing fossil fuels from the soil and burning them and releasing them into the air has shifted the balance and been a primary cause of global climate change. Soils can also facilitate environmental interactions to transform things. For example, bacteria that live in the soil transform atmospheric nitrogen into plant available nitrogen.
- Wetlands and the soil in the wetlands deliver a wide range of ecosystem services that contribute to human well-being, such as fish and fiber, water supply, water purification, climate regulation, flood regulation, coastal protection, recreational opportunities, and, increasingly, tourism. Despite these important benefits, the degradation and loss of wetlands is more rapid than that of other ecosystems.
- Consider that through natural processes, such as soil adsorption, chemical filtration and nutrient cycling, the Catskill Watershed provides New York City with clean water at a cost of $1-1.5 billion, much less than the $6-8 billion one-time cost of constructing a water filtration plant plus the $300 million estimated annual operations and maintenance cost.
- Covering just 6% of Earth’s land surface, wetlands (including marshes, peat bogs, swamps, river deltas, mangroves, tundra, lagoons and river floodplains) currently store up to 20% (850 billion tons) of terrestrial carbon, a CO2 equivalent comparable to the carbon content of today’s atmosphere.
- Another function of soil is as a biological habitat and gene pool. Soil provides the habitat for seeds to germinate and grow. It provides everything they needs like water, warmth, nutrients, etc. Soil provides habitat for a myriad of animals like worms, moles and insects, but also bacteria, protists, and fungi as well. All of these creatures come into contact with each other and can interact. The insects can mate and produce offspring. The bacteria can divide and reproduce. And sometimes when they do, they evolve and two species can share a little bit of DNA. One success story of this is when a sweet potato absorbed some DNA from a bacteria. This horizontal gene transfer can make the plant resistant to diseases.Consider that there are more living individual organisms in a tablespoon of soil than there are people on the earth.
- Almost all of the antibiotics we take to help us fight infections were obtained from soil microorganisms.
- Functionally, soils are also a source of raw materials. For much of modern human history, ceramic dishes made from clay were the primary tableware. Only in very recent years have we started using more glass, plastic, and one-time-use dishes (styrofoam). Soil can also be the source of countless minerals through mining processes. Soil can also be used for bricks and other materials in building houses.
- Soils can also play a functional role in our physical and cultural heritage. Around the world soils have been shaped for things like effigy mounds potentially for religious ceremonies, burial ceremonies, or other purposes. Soils also protect our cultural past. Artifacts that get covered up by soils can be protected from the elements creating a bookmark and window into our past and heritage.
- Finally, soils can serve as a functional platform for us to build our structures on. Whether it is houses, highways, skyscrapers, or football fields, we need a base of soil to provide the stability to build on. Even things like bridges over water, still go down to the soil at the bottom of the river or lake to rest on.
So, could we live without soil?
Sure, we could produce food through things like hydroponics and aeroponics. But without soil we couldn’t produce the amount of food that we need to sustain human life for all seven-plus billion of us. Sure, we have figured out other ways to filter water and store garbage. But our water filter systems haven’t been scaled up to do what soil does naturally. And garbage management systems like burning garbage has other negative environmental repercussions. Without soil countless organisms like moles, worms, bacteria, and fungi would be without a home. Most of those creatures are uniquely adapted to live in soil. Without soil we wouldn’t have the raw materials we need or the base to build our structures. In short, the answer is no. We couldn’t live without soil.
Soil is easy to overlook and some may even call it dirt. But soils are important for many reasons and as farmers and agriculturalists we can protect and improve soils for the betterment of all.