Principles of Soil Health

Exposure to direct sunlight, especially in our warm summer months will increase temperatures in the top soil and on the soil surface that are not optimal for most soil life. Just like humans, soil life flourishes at around 60-80° F. Starting at around 100°F, soil food web species will begin to function less optimally and at temperatures of 140° F, most bacteria, fungi, protozoa, and insects will not be able to live in the soils. You can use compost, straw, and last year’s dead plant material to armor the soil. Residues also feed earthworms, as seen in figure 2. The worms then deposit the plant material in their castings, back into the soil which makes the nutrients available for other soil food web organisms and plants.

We cannot engineer or create a habitat for the soil food web as well as Mother Nature. So it is imperative we leave her to do her work. When we till our soils these habitats get disturbed and the soils are exposed to excess oxygen which over stimulates the soil bacteria putting the soil food web out of balance. When exposed to excess oxygen, bacteria digest available forms of carbon at higher rates depleting the soil of its food source all at once, leaving it less fertile for the remainder of the growing season.

Just like us, the soil food web needs a diverse diet to stay healthy. Plants have unique enzymes that work with different organisms in the food web. Some species form symbiotic relationships with fungi, called mycorrhiza that can even help feed the plant directly into the roots by mining nutrients from minerals and transporting soil water directly into the root. Also, different plants have different ratios of carbon such as cellulose, hemicellulose, and lignin, each providing a source of food that is digestible by different portions of the soil food web. Companion planting, and using grasses, forbs and legumes along with cool and warm season plants will ensure diversity in your garden, landscape or cropping system.

By keeping the plants alive in our soils throughout the growing season, we continue to nurture the soil food web with a food source. Most soil organisms are like humans, in that they need food, water and oxygen to survive. Plants help provide essential food for the soil food web in the form of exudates, such as carbohydrates, water soluble vitamins, organic, nucleic, and amino acids. Excretions from fungal hyphae called glomalin and the other soil exudates help aggregate soil particles together to provide both habitat and a food source for the life in soil. Additionally increase water storage which benefits both the plants and soil life. Using cover crops or biological primers during all times of the growing season is one practice that can be used to keep a living root to feed the soil all year long. To learn more about the soil food web please visit the International Years of Soils website.

Did you know that one or two teaspoons of soils contains more organisms than there are people on planet Earth? It is almost hard to comprehend that the life beneath our feet is made up of a complex interwoven web of carbon based organisms that support and feed the plants, trees, and shrubs we see above ground in our landscapes. But that is exactly what is happening. The soil food web starts with the liquid carbon pathway, which is better known as photosynthesis. The sun’s light is absorbed by plant tissue and CO2 is absorbed through the plant’s stomata, harvesting both the light and gas to produce sugar to feed itself. But that is not the end of the story. Plants also need essential elemental nutrients from the soil. To get these nutrients, plants send the excess sugars out through their roots in the form of exudates, feeding soil organisms such as bacteria, fungi, and protozoa. The microbial organisms in turn provide food for each other and the higher forms of life such as nematodes, micro and macro invertebrates, worms, insects, birds, and mammals (as seen in figure 1). The food web cycles the carbon in these organisms until eventually it is stabilized as hummus, completing the liquid carbon pathway! Every land management decision we make has the potential to either foster or degrade the soil food web. If we think about these basic principles before we make decisions on the land, we will help foster the soil food web which in turn will keep our plants and soils healthy.

“…the Latin name for man, homo, derived from humus, the stuff of life in the soil.”

Dr. Daniel Hillel


“To see a world in a grain of sand and a heaven in a wildflower.”

William Blake, Auguries of Innocence

The Soil Food Web