The Soil Food Web & Your Garden

Learn How to Relate the Soil Food Web to Your Gardening Practices

Have you ever wondered what really goes on in your garden? Have you ever sat down in your garden and marveled at the interconnections amongst living things? Have you ever held a handful of soil and looked at the diversity within or lack thereof? You do not need a degree or even a course to figure it all out. All you need is a love for gardening and an interest in learning and observing. Once you go down the proverbial rabbit hole of soil ecology, you will never see things the same again. What you learn about your garden, in many ways, can be applied to anything in your life. Correlate the functioning of your living garden soil to how you manage your time, how you maintain relationships, and even to how your gut and mind works! Nature is amazing and it provides no end to learning and opportunities for application. This article will provide you with a basic understanding of food webs, specifically soil food webs, and ecosystems. Apply this knowledge to your garden spaces and you'll be well on your way to becoming an advanced gardener.

What is a food web?

A food web consists of interconnected food chains that show the relationships between organisms living in an ecosystem. All life needs energy whether organisms make energy themselves or derive it from other organisms they hunt. Energy allows organisms to maintain and repair their bodies. They need energy for reproduction, excretion, circulation, digestion, growth, cell division, hunting and metabolism. The sun is the ultimate source of energy for life on this planet. Without the sun’s energy, nothing would survive. Therefore, organisms have figured out or evolved ways to harness the sun’s energy and use it for their own well being. Organisms have also evolved to develop special relationships and interactions that transfer energy. Energy is captured and passed around from organism to organism. This transfer of energy between organism defines the food web. Food webs consist of food chains which are direct energy connections between organisms. For example, a fly might eat some sticky mushroom rot and then a frog eats that fly but then a snake comes along and eats the frog. Later, a red-tailed hawk might eat the frog. With each step, some of the sun’s energy is trapped within each organism and gets passed along like a baton. The photo to the left shows two simple food webs. The one on the left starts at the bottom with plants as the producer. Every consecutive organism eats the ones below.

Food chains do not accurately represent the transfer of energy in an ecosystem because there are often multiple organisms that can be eaten and many that do the eating. For example, the fly might also eat some flower nectar and some jam stuck on a picnic table. That fly might then be eaten by a lizard, a beetle, or a bird. Each of these critters might eat a variety of other organisms. So, you can see how complex a food web can become! Therefore, a food web, especially in picture or schematic form, is far more realistic.
To make things easier to understand, food webs are divided into groups of organisms:

• Producers

• Primary, secondary, tertiary, and quaternary consumers

• Decomposers

Producers make up the bottom of the food chain. Producers like green plants, lichens, moss, algae, diatoms, and some bacteria make their own food (energy) by using sunlight, carbon dioxide and water to make glucose, a basic sugar and oxygen, in a process called photosynthesis. The producers store this sugar for use later. Most producers live in the oceans which of course cover about 72% of the planet! That means that most of the oxygen on earth comes from oceans. Rainforests are another ecosystem that contain many producers – mostly plants. In fact, though rainforests only cover about 6% of earth’s surface, they account for 40% of earth’s oxygen.

Primary Consumers like deer, chipmunks, elephants, mice, many birds, horses, and cattle are also called herbivores. These creatures consume producers (plants) but are also prey to other animals higher up in the food web. Marine primary consumers include fish, zooplankton, snails, krill, and sea urchins. As primary consumers digest plants, they break down and release the plant energy, but they do not get a 100% transference of the sun’s energy – just 10% of it.

Secondary Consumers like bears, cats, raptors and even humans are called carnivores (eat only meat) or omnivores (eat both plants and animals). Secondary consumers are hunters. Energy transferred at this level uses only 1% of the original energy of the sun. This means that secondary consumers must eat more food or eat more often to meet all their energy demands. Omnivores are a special group - they can take advantage of both animals and plants. When one form of food is scarce, they can switch to another food source. Examples of omnivores include bears, pigs, and humans. If an omnivore is eating only plants, it is getting 10% of the sun’s energy. If the omnivore is eating only meat, it is getting a meager 1% of the sun’s initial energy.

Tertiary Consumers eat secondary consumers and can be either carnivorous or omnivorous.

Quaternary Consumers usually have no natural predators meaning nothing will eat them. That places them at the pinnacle of the food chain.

Decomposers include living things like fungi and bacteria which thrive on dead and decaying organic matter. Without decomposers in the mix, nutrients would never get recycled to be used by plants.

What is an ecosystem?

An ecosystem is defined as a community of living (biotic) organisms operating amongst non-living (abiotic) components and interacting with each other. In short, an ecosystem is a chain of interactions between organisms and their environment. Ecosystems can be as tiny as in a droplet of water, on a flower petal or as large as an ocean or desert. There are two kinds of ecosystems: terrestrial and aquatic. Terrestrial ecosystems can be a forest, grassland, tundra, or desert while an aquatic ecosystem can be freshwater or saltwater in nature. Living or biotic components include all living things (all the producers, consumers, and decomposers) while abiotic or non-living components include air, water, soil, minerals, sunlight, temperature, nutrients, wind, fire, altitude, turbidity etc. Ecosystems do many important things; they regulate essential ecological processes, support life systems, and provide balance and stability. They cycle nutrients and minerals between biotic and abiotic components and help in the synthesis of organic components involved in the exchange of energy. Think about it, an ecosystem exists in your gut, in your brain, in your garden, your home, your business, your city. 

What is the soil food web?

Now that you understand what a food web is, let’s apply it to your garden. Take a moment to observe your garden. You might see an earthworm come up and grab a leaf. You might see aphids being eaten by yellow jackets. You might even see a robin grab the worm. Whatever action you see, you are witnessing some part of a larger food web. Let’s go even further – look at your soil. Soil is teaming with life! The soil in your planter is one ecosystem while the soil in your raised vegetable bed is another ecosystem. You may not see much at first glance but if you look hard enough, and your soil is healthy enough, you will see organisms. Grab a hand lens and you will see even more. Pick up a microscope see a whole community of living things. Much of the incredible diversity of life in your soil is tiny to microscopic and they include:

• Bacteria
• Algae
• Fungi
• Protozoa
• Nematodes
• Micro-arthropods

Other organisms you can visibly see:

• Earthworms
• Insects
• Spiders
• Small invertebrates
• Plants

All of these organisms eat, grow, excrete, and relate to one another. In concert, the complex interconnections between these organisms help clean the water, the soil, the air, feed the plants and moderate water flow. They ensure excellent soil health and make gardening easier. Can you imagine a soil without such connections? The result would be dirt – useless material devoid of life. What can grow in that other than sturdy weeds? Soil organisms decompose organic materials in the soil including plant residues, manures, pesticides, and dead critters preventing them from building up and contaminating water sources. These organisms also sequester nitrogen, carbon, and other critical nutrients. Some organisms can also fix nitrogen from the atmosphere making the nitrogen available to plants for uptake. Many organisms enhance the soil structure, increase soil porosity, and water filtration and reduce runoff. Soil organisms help provide plants with a robust immune system and they prey on plant pests. Of course, many soil organisms – especially the ones we can see like earthworms, are food for above ground critters.

The soil food web is an integral part of landscape processes. Soil organisms decompose organic compounds, including manure, plant residue, and pesticides, preventing them from entering water and becoming pollutants. They sequester nitrogen and other nutrients that might otherwise enter groundwater, and they fix nitrogen from the atmosphere, making it available to plants. Many organisms enhance soil aggregation and porosity, thus increasing infiltration and reducing runoff. Soil organisms prey on crop pests and are food for above-ground animals.

Soil organisms live happily within pore spaces and between soil particles. They also live in the rhizosphere, the area around plant roots, in leaf litter, garden debris, on the surface of soil chunks and above ground and, on plants. In these places they eat other organisms, grow, and convert nutrients from one form to another making many of them available for plants and other soil organisms. Each organism excretes by-products which in turn are utilized by other organisms. So, the mantra is to recycle and reuse materials or transfer energy constantly! Of course, the level of activity of microbes and other critters depends on seasonal patterns as well as on daily patterns. For example, in temperate climates like in the Okanagan, the greatest activity happens in late spring when temperature and moisture conditions are optimal for growth. Some organisms are most active in the winter while others are busy during dry or flood periods. That said, even during periods of high activity, only a fraction of soil organisms is focused on eating, breathing, and altering their environment. The others barely active or may even be dormant so conditions and levels of activity are always changing.

Decomposers must have access to organic matter, or the circle of life cannot occur. Therefore, most gardens do well with added compost which contains a multitude of nutrients. Plant roots also excrete materials used by the soil food web. Plant root hairs produce exudates, sugars, proteins and sloughed off root cells. Fungi and bacteria trade nutrients for plant produced foods. It operates like a barter system.

How does understanding the soil food web help me as a gardener?