SOIL BASICS

Just what is soil?

This is a cutout of the earth, with the critical layer of soil.

Soil has been a defining component of cultures since the beginning of civilization. Some of the first written words were recorded on clay tablets and water was carried in clay pitchers. It provides the base for all buildings (although some may be able to support a skyscraper and some others may not be able to support your weight), it holds the clues of past cultures (to be revealed by archeologists or erosion), it supports the web of life (connecting all ecosystems), provides materials to build houses, is a source of nutraceuticals (definite in the American Heritage Dictionary as a food or naturally occurring food supplement thought to have a beneficial effect on human health), and of course, provides the base for our food, fiber, feed, and even some biofuels.

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The core curriculum standards (2013) adapted by 26 states has identified physical sciences; life sciences; earth and space sciences; and engineering, technology, and applications of science as the four main curriculum areas critical for scientific development. Soil fits into ALL of these areas (even SPACE). Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. It forms at the surface of land – it is the “skin of the earth.” Soil is capable of supporting plant life and is vital to life on earth.

Soil, as formally defined in the Soil Science Society of America Glossary of Soil Science Terms, is:

1. The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
2. The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time.

So then, what is dirt?

Dirt is what gets on our clothes or under our fingernails. It is soil that is out of place in our world – whether tracked inside by shoes or on our clothes. Dirt is also soil that has lost the characteristics that give it the ability to support life. Soil performs many critical functions in almost any ecosystem (whether a farm, forest, prairie, marsh, or suburban watershed).

How Much Soil is on Earth?

Even though soil is one of the most important resources, there is not actually that much available for making food, fiber, and shelter. Our earth has 58 million square miles (149 million square kilometers). Deserts and ice sheets make up 31% of land, and forests another 31%. 

The remaining 38% is agricultural. Of this agricultural land, only about 12% of the land can be used to produce food and fiber for us. The remaining 26% are in permanent pasture, feeding sheep, cattle, and goats. 

The worst part is, this land is not evenly distributed. On average, there are 0.2 hectares of land per person (0.5 acres).Africa is at average, however, In East Asia and the Pacific there is only 0.1 hectare per person. North America, however, has 0.61 hectares per person (1.5 acres). As the populations of the world grows, (rapidly in places like Africa and East Asia), more pressure is put onto the same areas of land to create more food. This is very difficult to do. Countries may not have money for fertilizer, or to protect the soil they already have.

Why not use unused land?

Why don't we cut down the forests and make more land agricultural?  Well, these lands do not grow food easily. Most of the existing forests are too cold for food crops. Other areas are too steep or have very shallow soils. This can create problems with erosion. The other forests are in the tropical areas, which have soils that involve very careful management, because they are acidic, and require expensive management.

Deserts are very sensitive. Areas that are drier can be watered through irrigation, but can suffer from salinization if not managed well, and fresh water is getting harder to find. Plowing the semi arid areas can result in wind erosion. 

For more information

Check out the Soils Overview for a printable version of basic soils information. Major role of soils page tells about the major roles that soils play in our lives. There are many soil properties that help us describe and manage soils. Some of the important physical properties are described on the Physical Properties of Soils page. Soils can have many different layers. For a description on what soil layers exist, visit the Soil Horizons page.