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Handbook of Soils for Landscape Architects$
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Robert F. Keefer

Print publication date: 1999

Print ISBN-13: 9780195121025

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195121025.001.0001

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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: 18 September 2021

Physical Properties of Soils

Physical Properties of Soils

(p.27) 4 Physical Properties of Soils
Handbook of Soils for Landscape Architects

Robert F. Keefer

Oxford University Press

Soil texture can be defined as the size and proportion of the soil particles—sand, silt, and clay—that are present in a soil. . . . Sand is the largest—from 0.05 to 2mm—and considered coarse texture; consists of angular spheres or cubes. Silt is intermediate—from 0.002 to 0.05mm—and considered medium texture; consists of properties between sand and clay. Clay is the smallest, being less than 0.002mm, and considered fine texture; appears as plate-like or flakes. . . . Any individual soil can be placed on the soil textural diagram when relative amounts of sand, silt, and clay are specified. As a general rule, the type of soil can be determined by feel when squeezed between the fingers. If the soil feels harsh and gritty it would be classified as a sandy soil. One that feels smooth and not sticky or plastic would be a silt soil, and one that is sticky or plastic would be a clay. Another way to distinguish between soils is their ability to form a ribbon. Soils that will not form a ribbon are sands. Those that form a fragile ribbon are loams; those that easily form a thick ribbon are clay loams; and those that easily form a long, thin, flexible ribbon are clays. . . . To be classified a sand, the soil must have more than 45% sand. To be classified a clay, the soil must have more than 20% clay. Loam is a mixture of sand, silt, and clay in about equal proportions. It is considered “ideal” for growing plants. . . . Weight of the soil solids is called “particle density.” For most common mineral soils (soils in which organic matter is usually less than 20%), particle density is about 2.65 g/cm3. Organic soils (where organic matter is greater than 20%) are usually about half as heavy, with particle density between 1.1 to 1.4 g/cm3. This measurement would be an important factor to consider if much material was to be transported for topsoiling.

Keywords:   bark, capillary movement, diffusion, field capacity, hardpans, infiltration, loam, macropores, organic soils, peat

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