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Serpentine Geoecology of Western North AmericaGeology, Soils, and Vegetation$
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Earl B. Alexander, Roger G. Coleman, Todd Keeler-Wolfe, and Susan P. Harrison

Print publication date: 2007

Print ISBN-13: 9780195165081

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195165081.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 15 June 2021

Nature of Soils and Soil Development

Nature of Soils and Soil Development

Chapter:
5 Nature of Soils and Soil Development
Source:
Serpentine Geoecology of Western North America
Author(s):

Earl B. Alexander

Roger G. Coleman

Todd Keeler-Wolfe

Susan P. Harrison

Publisher:
Oxford University Press
DOI:10.1093/oso/9780195165081.003.0009

We walk on soils frequently, but we seldom observe them. Soils are massive, even though they are porous. Soil 1m (40 inches) deep over an area of 1 hectare (2.5 acres) might weigh 10,000–15,000 metric tons. It is teeming with life. There are trillions, or quadrillions, of living organisms (mostly microorganisms), representing thousands of species, in each square meter of soil (Metting 1993). In fact, species diversity, or number of species, may be greater below ground than above ground. We seldom see these organisms because we seldom look below ground or dig into it. The many worms and insects one finds digging in a garden are a small fraction of the species in soils because the greatest diversity of soil-dwelling species exists among microscopic insects, mites, roundworms (or nematodes), and fungi. Even though individual organisms in soils are mostly very small or microscopic, the total mass of living organisms in a hectare of soil, excluding plant roots, may be 1–5 or 10 metric tons. More than one-half of that biomass is bacteria and fungi. Living microorganism biomass generally accounts for about 1%–5% of the organic carbon and about 2%–6% of the nitrogen in soils (Lavelle and Spain 2001). The upper limit of soil is the ground surface of the earth. The lower limit is bedrock for engineers, or the depth of root penetration for edaphologists. Unconsolidated material that engineers call soil can be called “regolith” (Merrill 1897, Jackson 1997) to distinguish it from the soil of pedologists and edaphologists. Regolith may consist of disintegrated bedrock, gravel, sand, clay, or other materials that have not been consolidated to form rock. Pedologists investigate the upper part of regolith, where changes are effected by exchanges of gases between soil and aboveground atmosphere and by biological activity. This soil of pedologists may coincide with that of edaphologists or include more regolith. In fact, the lower limit of soil that pedologists investigate is arbitrary, unless this limit is a contact with bedrock that is practically impenetrable with pick and shovel.

Keywords:   algae, bacteria, chromite, fungi, hydration, insects, lichens, magnesite, nematodes, organic detritus

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