Healthy Soils Support Life
By Mary Tiedeman
As Urban Farm U patrons, we can all attest that healthy soils are better than their unhealthy counterparts, right? But what is the definition of “soil health”? According to the Natural Resource Conservation Service, soil health (or quality) refers to its’ ability to sustain life while functioning as a vital living ecosystem. In other words, good soils support life while serving as their own unique environments!
Sustaining life is a difficult job.
Anyone with experience producing food knows this firsthand. Organisms that interact with soils directly, such as plants, animals, bacteria, and fungi (to name a few) all require a list of amenities in order to survive and thrive. In many ways, the things that soil-dwelling organisms require for life are not much different than those for people. Protection, temperature control, clean air and water, food, and waste management are all essential.
Just like well-built houses, good soils provide a suite of comforts for their inhabitants. They are stable, have a built-in thermostat, contain clean air and water, and a pantry stocked full of food. They even have their own reliable sewage systems and garbage removal services. In order to serve their tenants, soils must possess a few key features including good structure (the way particles clump together), organic matter, and biological activity.
The foundation of a well-functioning soil is its structure.
Topsoils with the greatest productivity often have a granular structure, meaning they look like cookie crumbles. These relatively small rounded clumps settle together loosely, creating pores, or pockets of space within the soil. Soil pores come in all shapes and sizes, and each plays a role within soil ecosystems. Large pores work as major highways by carrying excess water away from the root zone. They also facilitate proper ventilation. This ensures that life-supporting oxygen makes its way to roots and soil organisms while carbon dioxide and other waste products move out of the system. Smaller pores, on the other hand, operate as water storage containers.
Organic matter, another necessary component of healthy soils, works as a glue that binds mineral particles together. It promotes the formation of granules and prevents aggregates from falling apart easily when disturbed by rain and wind. Organic matter is also a good insulator, and so prevents soil systems from getting too hot or cold. If not for this feature, soil would be too hostile of an environment for most living things. Organic matter also is a food and nutrient source for many living things. By offering these services to the system, organic matter encourages life to inhabit the soil.
The final component of healthy soil is biological activity.
In this way, life begets life. All soil creatures, from the tallest tree to the smallest microbe, contribute to the ecological balance of the soil environment. Though each organism plays a specific role, all are a source of organic matter. In death, plants and animals return to the soil to replenish nutrients that they’d previously taken up. In life, they pump countless compounds into the ecosystem. The presence of these compounds, as well as the physical movement of plant roots and animals, help form the cookie crumble structure that is so important for soil quality.
Soil organisms also serve as nutrient cyclers within a complex food web. Photosynthesizers, like plants and algae, convert carbon from the atmosphere into organic tissue. Decomposers (fungi, fly larvae, ants, bacteria, etc.) on the other hand, release nutrients from dead or dying things – making them available to a suite of other creatures. Microbes in particular contribute greatly to nutrient cycling processes. Some do this by converting nitrogen from the air into plant-available forms while others release phosphorus from minerals and deliver them to plant roots. Many other elements essential to life, such as iron, sulfur, and potassium change forms at the hands of soil organisms.
The size and variety of life forms that influence soil resources are vast, and in many cases, is still being discovered. In fact, scientists estimate that only 5% of soil-dwelling organisms have been identified thus far! What is known is that nearly all soil organisms play a unique role in promoting soil health. In other words, fear not the presence of the various critters living in your soils unless they are doing direct harm to you or your garden!
Soils are the foundation for nearly all terrestrial ecosystems, from rainforests to deserts and everything in between. Even aquatic environments depend on healthy soils, as they purify water that flows from land into surface water and groundwater systems. Like human health, soil health is not static. If we are not careful, mismanagement can reduce soil’s capacity to support life. For farmers, this could mean lost productivity or crop failure in the face of natural disasters. The good news though is that by promoting soil quality, we can insure the health of humans and our planet’s ecosystems for generations to come.
PhD Student, Soil Microbiology