Soil - Everything You Ever Wanted to Know (but were afraid to ask)!

By Peggy Case,  Horticulture Chair

Cathy Seamans, a former teacher and currently a research biologist with The Chef’s Garden and Vegetable Culinary Institute in Huron, works each day with seeds, soils, pest management and worm farming. Her talk about soil biology stressed its importance to plants, and ultimately, to all of us.

Good soil - living soil - is composed of 45% minerals (sand, silt and clay), 25% air, 25% water and only 2-5% decaying organic matter plus many minute living organisms. The top six inches of one acre of living topsoil has 900 pounds of earthworms, 2400 pounds of fungi, 1500 pounds of bacteria, 133 pounds of protozoa and 890 pounds of arthropods and algae.

Earthworms burrow down to six feet providing filtration and soil aeration. They eat and break down dead plant material and redistribute organic matter in the topsoil. Their excrement known as castings is high in nitrogen, phosphorus and potassium, the exact elements found in fertilizer. Earthworms thrive best with little or no tillage and produce egg capsules, with 2 to 20 baby worms, every 7 to 10 days which hatch in two to three weeks.

Fungi appear as threadlike colonies or one-celled organisms that feed on decomposing organic matter. They also produce plant hormones, antibiotics and consume parasites. Mycorrhizal fungi attach to plant roots and help them take up nutrients.

There are good forms of bacteria in the soil that release nitrogen, sulfur, phosphorus and trace elements as they break down organic matter. Other bacteria break down minerals releasing phosphorus, magnesium, calcium and iron. Still other bacteria release plant hormones, improve soil structure and fight root diseases.

One-celled protozoa are free living microorganisms that crawl or swim in the moisture between soil particles. These predatory organisms eat other microbes, harmful bacteria and release nitrogen for plants. Their movements also break down soil particles.

Many arthropods in the soil can be seen by the naked eye - sowbugs, millipedes, centipedes, slugs, snails. All these eat and shred larger dead plant particles. Nematodes are abundant in soil, attack parasites and speed the rate of decomposition with only a few nematodes harmful to plants.

Algae live in the upper half-inch of soil and produce their own food through photosynthesis. They improve soil structure by binding soil into aggregates with a slimy glue. Some types fix nitrogen in the soil to be used by plants.

Seamans demonstrated all these soil organisms by using a high powered microscope with the images projected on a large screen.  Local gardeners found it amazing to see organisms like nematodes and protozoa whipping around the screen, things they had read about, but rarely had access to microscopes good enough to examine soil