“We might say that the earth has the spirit of growth; that its flesh is the soil” ~ Leonardo da Vinci

Soil is complex. It contains many interacting organisms that influence soil health, plant health and water dynamics. There is an entire underground world made up of a diverse ensemble of organisms that contribute to soil function through nutrient cycling, water infiltration and water-holding capacity, disease suppression, degradation of pollutants, and soil structure. The biotic components consist of plants, small animals, and microorganisms.

In science terms, soil biota can be classified into what you might consider large to small types of creatures. First, you have your macro- and megafauna, which are organisms larger than 2 mm.  These are organisms like moles, earthworms and beetles. Second, are mesofauna, or those organisms with body widths between 0.1 mm and 2 mm, like mites and springtails. Third comes microfauna whose body widths are less than 0.1 mm, these are your nematodes and protozoa. Finally, the fourth and most abundant and diverse group are the microorganisms, or microbes, such as bacteria and fungi.

All of these creatures play important roles in the soil ecosystem, but let’s focus on the microbes for a moment. In general, bacteria are important in the system for forming the smaller soil aggregates, breaking down simple sugars, making antibiotics, contributing to the nitrogen cycle, forming humus, and giving soil some of its “healthy” smell. Fungi are composed of saprophytic fungi (decomposers) and mycorrhizae fungi (perform a symbiotic relationship with plant roots). Fungi form the larger soil aggregates, break down complex carbons, play a role in disease suppression, nutrient retention, and produce acids that extract minerals making them available to plants.

It can be difficult to maintain the proper balance of organisms in an underground world, especially in a cold, arid environment with various soil types. Soil tests and assessments can help determine what might be lacking and what types of soil amendments or management techniques to consider. Did you know that soil biological processes are responsible for supplying 75% of the plant available nitrogen and 65% of the available phosphorus in the soil? Yet, just applying fertilizer doesn’t necessarily contribute to biological health in the soil. Below are some principles that can help to maximize diversity and efficiency in the soil to get the most out of your garden or crops:
• Minimize disturbances Fungal mycelia provide the communication network for life underground and breaking up the soil also breaks up that network structure (of course there are times when breaking up the soil might be needed, such as if it is compacted). Similarly, the application of pesticides and soluble fertilizers causes communication breakdown between plants and microbes, interfering with their ability to perform their intended tasks and causing population declines in those communities.
• Keep it covered Bare soil is a sore spot for soil biology. Bare soil contributes to erosion, affects water-holding capacity and increases susceptibility to weed invasions. Think of cover crops as protection from the elements, like your rain jacket or sun hat.
• Diversity Diversity is nature’s system of resilience. A mixed plant crop outperforms mono-crops and they are more resilient to drought, pests and disease. Further, plant diversity can access various parts of the soil and work with different microbial communities to access different minerals and nutrients from the soil.

• Living roots Soil biology is primarily fed from the root exudates (the fluids or substances secreted by the roots) of plants. Plants contribute up to 40% of the sugars they produce to feeding biology in exchange for nutrients and water. Keeping roots in the ground, all year round, are essential for feeding the soil biology.
• Incorporate animals Industrial agriculture changed the game from when people ran a mix of cattle, sheep, goats, chickens and pigs. Different animals produce nutrient-rich composts that are crucial to maintaining soil fertility. By breaking down plant materials through their varied digestive tracts, the resulting excretion stimulates soil biology and enhances the function of the soil-plant system.   

Soil health is once again gaining attraction and soil biology is a key driver in that system. With spring in the air, it’s a good time to consider ways to enhance the soil health of your gardens and fields. While there isn’t a “one size fits all” solution, the above principles provide some guidelines. To support life above ground, the underground world must be nourished. As always, if you want help gathering more information or need technical assistance, contact SCCD at 307-367-2364.