Below the earth’s surface life is brimming with activity—moles, insects, worms and billions of microorganisms all live within the soil. To give you a picture a small spoon full of good gardening soil contains a billion invisible bacteria, many meters worth of invisible fungal hyphae, several thousand protozoa and a few dozen nematodes! Just as within all nature, each organism under the ground has an important role to play in relation to his fellow organisms, to plant growth and the maintenance of the whole ecosystem.
We use the Soil Food Web, a diagram that shows the soil’s food chain to further explain the importance of each- and relationship between the different varieties of life found within the soil.
The health, interaction and diversity of life found underneath the ground directly determines’ the fertility and health of your soil and thus your plants. Therefore, learning about the Soil Food Web will help you understand more about your soil, recognize it’s good qualities and how to preserve them in order to produce beautiful gardens and an abundance of delicious crops year after year.
Plants are at the Heart & Center of the Soil Food Web
In the Soil Food Web, plants are at the heart and center; they provide energy and nutrients to the life around them and in return organisms living in harmony offer nutrients, protection from diseases and plagues and help to bring needed air and water to plant roots.
Often when we think about plants we visualize their growth above ground, bustling with leaves, flowers and fruits; however, below the earth’s surface the growth of roots is just as significant and profound. When plants perform photosynthesis a huge amount of energy made is sent underground to the roots of plants, where roots expand searching for nutrients and water, and where the plants themselves get involved in the nutrient creation process. Energy is released directly into an area of soil that immediately surrounds the roots, known as the Rhizosphere in the form of carbohydrates (also known as exudates). Plants secrete these exudates in order to attract those whom enjoy eating them—beneficial bacteria and fungi—and in turn the bacteria and fungi attract those whom like eating them for their carbon nutrients—nematodes and protozoa. Any part of any organism or exudate that is left over after being consumed by the next organism on the food chain is excreted as a waste (i.e. organic matter), thus creating nutrients for the plant. In that way bacteria and fungi are similar to bags of fertilizer, releasing nitrogen necessary for plant growth to plants when eaten by the “fertilizer spreaders”—nematodes and protozoa.
Higher on the food chain, arthropods and other larger critters like earth worms, insect larvae and moles burrow their way through the soil creating extremely important empty spaces and passages for both air and water to reach plant roots. In the process they shred materials in their way, helping to speed the decomposition process that turns waste into nutrients. The soil food web continues in this way, with the smaller forms of life being eaten by the next organism on the food chain, each leaving waste which decomposes and provides nutrients from which plants will grow.
What’s most amazing about this process is that by secreting different levels of exudates plants can control the numbers and the diversity of the fungi and bacteria found living around them in order to influence the amount of nutrients available to them and the population level of others higher on the food chain! Throughout the growing season plants can and will secrete more or less exudates depending on their current needs, and whatever nutrients they don’t currently need are stored within the organisms bodies and organic matter that surround them. In this way nutrients are never wasted or leeched into groundwater, rivers, lakes or oceans, and are readily available to plants whenever they need them.
Beneficial Organisms Protect Soil and Plants
Just as within almost all of nature, life under the ground wishes to operate in harmony together each deriving benefit from the collective whole, but every once and awhile a bad guy comes along that threatens the balance of the whole system. Healthy soils are able to eliminate the threat of these bad guys by sustaining large and diverse populations of organisms. By being diverse and more abundant in numbers beneficial organisms physically block out the stray bad guy from receiving the resources it needs. By outcompeting they eliminate any pathogen or disease that may arrive at the scene. In fact plants attract beneficial fungi to live close to roots because they form a physical barrier to invasion of pathogenic bacteria and fungi. And if the population of one particular species starts to grow too rapidly then another species will prey on it until populations are at a healthy balance. In this way we can see how amazing and delicate the soil food web is; if species are eliminated without care the natural process of life within soil will cease to function and instead create places uninhabitable to plants.
Dangers to the Soil Food Web
Plant life depends on the interplay of microbes, bugs, birds and all animals that share the same habitat. Eliminating or drastically reducing or sometimes even adding species to the mix can put the whole food chain out of whack. If for example a chemical pesticide is used in attempt to control a negative outbreak of nematodes, those chemicals will not only kill the target but billions of other essential organisms that give soil it’s good quality. Excessive use of chemical fertilizers also pose dangers to the soil food web as their synthetic nutrients suck the water out of the microbes that live within the soil. Without microorganisms all life underground begins to die, resulting in weak plants that are reliant on continued chemical fertilizer and pesticide application. Rebuilding the natural food webs in damaged soils may take years or even decades; that is why it’s so important to be very careful about applying products to your soil without understanding the consequences.