Living it up under your lawn
That surface of green between your house and the curb may seem quiet and still, but there is an entire community of life in a healthy lawn. It is its own ecosystem, made up of bacteria and insects such as earthworms, mites, ants, millipedes, snails, and grubs.
Some of the members of this ecosystem (like earthworms, insects, and rodents) are large enough to see. Others, the microorganisms, are invisible without a microscope. There may be as many as 100 million to 15 billion microorganisms per spoonful of soil. In a 1000 square foot plot, you could find 70 pounds of microorganisms. By combining the micro with the visible organisms, you could have 200 to 450 pounds of living organisms beneath your feet in this thousand square foot plot.
The organic matter in the soil (remnants of dead grass, leaves and applied compost) gives life to the soil because it serves as food for the microorganisms. As these lawn tenants eat and expel waste, their activities enrich the soil. Their movement through the soil improves the soil structure and helps plant growth.
Fauna (animal species)
Earthworms stir up the soil, improving aeration and the movement of water into the soil. The average well-established lawn has 20,000 worms per 1000 square feet, and these worms will eat undecomposed organic matter, and generate 40 pounds of worm castings a year. The castings are an important source of plant nutrients.
Insects (millipedes, centipedes, ants, grubs, mites, slugs, and snails) also inhabit the soil. These species feed mostly on decaying vegetation (although some will consume living plants) and through the process of their daily activities, help aerate and fertilize the soil.
Nematodes are small eel worms, usually a few millimeters to a centimetre or two in length. The population per 1000 square feet of nematodes could vary from 4000 to 20 million. The most common type live on decaying organic matter.
Microscopic protozoa are the most elementary form of animal life, and are the most plentiful of all fauna found in the soil. There could be from 300 million to one billion per pound of soil. They live on bacteria, and in turn provide food for higher organisms. When the protozoa consume bacteria, they convert the nitrogen in those bacteria into a form that plants can use.
Flora (plant species)
The roots of all larger plants (like grass and trees) occupy the soil along with microscopic forms of plant life. Tiny but mighty, these organisms change and digest the organic matter added to the soil by the higher plants.
There are billions of bacteria per spoonful of soil. Some grow in the absence of organic matter, but the majority of bacteria in the soil derive their energy by decomposing organic matter, and they require oxygen for growth. Some types attach themselves to the roots of plants and fix nitrogen from the air into a solid form that the plant can use. The life span of a single bacterium is only a few hours and the bodies are continuously in the process of decay, releasing fixed ammonium and nitrates for the use of the host plant. Other forms of bacteria live freely in the soil and trap the nitrogen so it becomes available to plants.
Fungi are second only in population numbers to bacteria in the soil, at about 10,000 to 3 million per spoonful of soil. Fungi are useful in the soil because they break down some resistant soil components, as well as sugars, starches, and proteins. Dead fungi add to the soil's organic matter.
Molds and actinomycetes both decompose organic matter -- actinomycetes are also used in the manufacture in many kinds of antibiotics. Algae are present in the water and the soil. They add organic matter to the soil, and some can even fix nitrogen from the atmosphere.
These organisms are born, eat, expel waste, die and decompose, all within the soil. Those that burrow though the soil profile are constantly bringing up useful materials for plant life, and aerating the soil in the process. Others make the soil nutrients more available to the higher plants.
Healthy plants growing on the surface of the lawn are also an important part of the lawn's ecosystem. Applying either organic or manufactured fertilizers, following the directions on the label, will provide the nutrients your lawn needs to grow at a healthy rate and to resist disease. Those plants will return leaves, roots, and clippings as valuable organic matter to the soil's ecosystem
Plants, flora, and fauna all form an intricate part of the soil complex -- the miracle of life that exists quietly beneath your feet.
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