28 January 2007

Soil at the Center of the Environment: Part 1

Posted by John Freeland

Photo by Thibaut (Tibo) Cheytion
Photo Credit: High Agriculture by Thibaut (Tibo) Cheytion

Soil is an open and dynamic system and supports all terrestrial life, and to a large extent, by providing nutrients in solution, supports aquatic and marine life, as well. This is evident in the high biological productivity found in estuaries, places where rivers meet the sea.

Soil stands at the crossroads of the earth’s vital spheres: the lithosphere (crust of the earth), the atmosphere, the hydrosphere, and the biosphere. All of these “spheres” intersect at the soil.

The soil is derived from the rocks and minerals of the local lithology, or from sediments naturally transported by various means from elsewhere. Lithology leaves a chemical and textural signature on the soil that develops over time, affecting everything that subsequently grows in the soil.

Water moves into the soil from above as precipitation, from below as groundwater, from the sides as seepage from surface water bodies. The soil may release water to all of these places in different ways.

The soil is the “breathing organ” of the earth, cyclicly exchanging gases with the atmosphere.

Soil serves as structural foundation for land plants. Animals, microbes, and fungi living largely unnoticed in the soil carry out complex
processes in plant root zones, making nutrients available to growing plants, and releasing agents of chemical weathering to the soil.

Considering all it does, one might think the “humble soil” of the earth deserves a more sophisticated name, and it does. It is called the pedosphere, the part we touch with our feet.

A note about the photo taken by Tibo, who’s an economist, in Tibet: There are several alpine glacial and periglacial landforms well represented. There are perhaps five aretes, which are straight, sharp ridges between or adjacent four bowl-shaped cirques carved into the sides of the mountains. There is also a U-shaped valley. The relatively young soils supporting crops in the valley look like they are atop ice-wedge poygons derived from glacio-fluvial sediments that are often saturated and undergo frequent freeze-thaw cycles. Polygons are one type of “patterned ground” found near alpine and continental glaciers. Photo used with Tibo’s generous permission.