Montshire Minute: Dirt

Originally aired during the week of July 2, 2000

Monday

Hey, wipe the dirt off your face. Better put that shirt in the laundry. And no tracking dirt through the house! How often have you heard those phrases? In some places, like your mother's dining room floor, dirt is never welcome. But without dirt, well... you, me and just about any other organism you could name wouldn't be alive. Plants depend on nutrients in the soil to grow. Animals feed off the plants, or eat the animals that eat the plants. It's all interconnected - without healthy soil to grow crops, human civilization would collapse. Soils in forests, prairies, and rich cultivated fields were all created by the long process of living, dying and decomposing. In honor of a new exhibit called Dirt that opens at Montshire on Saturday, we'll be exploring some more dirty truths about soil science this week.

Tuesday

We all know we need healthy, nutritious soil to grow productive flowerbeds or vegetable gardens. But what exactly is soil and what is it made of? Soil is a composition made up of mineral particles - basically, little pieces of rock - with water, air, and some organic particles (like decayed leaves) all mixed together. Most soils are called mineral soils because more than 80 per cent of their particles are minerals. The chemistry, texture and color of soils are very different from place to place. In conifer forests, pine needles decay slowly, making acidic soil less suited for growing crops. In the same way that ornithologists identify different species of birds, soil scientists (called pedologists) have identified and named about 150 types of soil. Of course, soil composition changes all the time, due to freezing and thawing, wetting and drying, wind and water flow.

Wednesday

How do you get a cucumber from a rock? As silly as it sounds, solid rock is the starting point for soil and all those garden veggies we grow. Over time, wind, rain and other weathering factors break up rock into little pieces. Lichens also help this process. Usually the first plant to appear on bare rock surfaces, lichens secrete acids which dissolve the rock. Lichens also loosen rock as the plant swells and contracts during wet and dry periods. Scrape off a bit of lichen with a knife and you'll see the gritty rock particles underneath it. These particles are blown or washed into crevices or onto lower ground. Like plants growing between cracks in a sidewalk, mosses, weeds, and tiny organisms move in as the soil collects. Plants and animals die and decompose as growing seasons come and go, adding more organic matter. Sooner or later, we got soil!

Thursday

A pile of dirt seems pretty inert, right? Wrong. Just a tablespoon of rich soil might contain millions of bacteria, not to mention fungi, algae and protozoa. A larger sample of good garden soil might contain thousands of mites, beetles, ants and lots of earthworms, too. All of these creatures play a role in enriching the soil by turning dead plant and animal material into nutrients. Hey it may not sound like a fun job, but someone has to do it. There are many partnerships present in a healthy soil ecosystem. For instance, fungi have special enzymes that break down the cell walls of plants. The fungi spreads with the help of a mite. The mite feeds on the fungi and transports fungal spores with it. As the creature moves about, it expels the spores, allowing the fungus to proliferate.

Friday

A fresh road cut through a forested area is a good way to see how soil has formed since the first glaciers scraped across New England's surface. The dark, thin layer of soil on top is the rich leaf-mold, formed by season after season of wet leaves accumulating. In this layer, insects and microorganisms keep busy breaking down dead material into new soil. Below the leaf mold are older, lighter layers of soil. Tree roots in these lower layers absorb minerals and transport them through trunk, twig, and leaf. In this way, the tree is sort of a natural elevator, bringing up nutrients and redistributing them on the forest floor. Cool huh? Like many things in nature, soil forms slowly and is destroyed easily - it must be conserved so it can continue to support life. A new exhibit called Dirt is opening at Montshire on Saturday, so you can explore some more dirty truths about soil science at the museum!