Soil Architecture and Physical Properties PDF

CHAPTER 4 Soil Architecture and Physical Properties  n Success or failure of both agricultural and engineering projects often hinges on the physical properties of the soil used. n Soil scientists use the color, texture, and other physical properties of...

CHAPTER 4 Soil Architecture and Physical Properties  n Success or failure of both agricultural and engineering projects often hinges on the physical properties of the soil used. n Soil scientists use the color, texture, and other physical properties of soil horizons in classifying soil profiles and in making determinations about soil suitability for agricultural and environmental projects. n Color, texture, structure Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 2 Upper Saddle River, NJ 07458. All Rights Reserved.  SOIL COLOR n Although color itself has little effect on the behavior and use of soils, it does provide clues about other soil properties and conditions. n To obtain the precise, repeatable description of colors needed for soil classification and interpretation n Munsell color charts. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 3 Upper Saddle River, NJ 07458. All Rights Reserved.  n The Munsell charts use color chips arranged according to the three components of how people see color: n the hue 色彩 (in soils, usually redness or yellowness) n the value 色值 (lightness or darkness, a value of 0 being black) n the chroma 色度 (intensity or brightness, a chroma of 0 being neutral gray). Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 4 Upper Saddle River, NJ 07458. All Rights Reserved. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 5 Upper Saddle River, NJ 07458. All Rights Reserved.  n https://www.youtube.com/watch?v=sIuphBL_JpA&li st=PLIwM8E408KmC7pRr9brMx7I2h8_awaYj_&ind ex=1 Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 6 Upper Saddle River, NJ 07458. All Rights Reserved.  n Organic matter content Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 7 Upper Saddle River, NJ 07458. All Rights Reserved.  Figure 4.3 Black organic matter coating on peds in the B horizon of a Kansas Mollisol. (Photo courtesy of Ray R. Weil) Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 8 Upper Saddle River, NJ 07458. All Rights Reserved.  n The effect of moisture on soil color. Right side of this Mollisol profile was sprayed with water. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 9 Upper Saddle River, NJ 07458. All Rights Reserved.  n Dark (black) humic accumulation and gray humus depletion spots in the A horizon are indicators of a hydric soil. n Water table is 30 cm below the soil surface. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 10 Upper Saddle River, NJ 07458. All Rights Reserved.  n The presence and oxidation states of iron and manganese oxides. n Well oxidized iron compound: red and brown n Reduced iron compound: gray and bluish n Under prolonged anaerobic conditions, reduced iron (which is far more soluble than oxidized iron) is removed from particle coatings, exposing the light gray colors of the underlying silicate mineralsà gleyed 灰化 Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 11 Upper Saddle River, NJ 07458. All Rights Reserved.  Redox concentrations (red) and depletions (gray) in a Btg horizon from an Aquic Paleudalf. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 12 Upper Saddle River, NJ 07458. All Rights Reserved.  Oxidized (red) root zones in the A and E horizons indicate a hydric soil. They result from oxygen diffusion out from roots of wetland plants having aerenchyma tissues (air passages) 通氣組織. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 13 Upper Saddle River, NJ 07458. All Rights Reserved.  Figure 4.2 Examples of some red, orange, brown, gray, and blue soil colors derived from various iron minerals and influenced by oxidation state. Scale marked in mm. (a) B horizon peds in an Ultisol in Alabama, where the interped cracks often hold stagnant water have turned gray, while the ped interiors have remained oxidized and are red and yellow. (b) B horizon ped in an Alfisol in Maryland showing bluish color where a plant root has used up the oxygen and created localized reducing conditions. (c) A ped from the B horizon of an Alfisol on Chad showing purplish hardened plinthite. (d) A clay inclusion in sandy river bank sediment along the Chesapeake Bay in Maryland showing blue and gray colors where iron has become reduced. (Photos courtesy of Ray R. Weil) Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 14 Upper Saddle River, NJ 07458. All Rights Reserved.  Figure 4.5a Greenish colored clay in a Marlton soil Bss horizon. Slickenside (shiny clay wedges) (Photo courtesy of Ray R. Weil) glauconite Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 15 Upper Saddle River, NJ 07458. All Rights Reserved.  Figure 4.5b Blackish coatings from manganese oxides in a Davidson soil B/C horizon. (Photo courtesy of Ray R. Weil) Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 16 Upper Saddle River, NJ 07458. All Rights Reserved.  https://kknews.cc/zh-tw/photography/x5gpk69.html Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 17 Upper Saddle River, NJ 07458. All Rights Reserved.  SOIL TEXTURE (SIZE DISTRIBUTION OF SOIL PARTICLES) n Knowledge of the proportions of different-sized particles in a soil (i.e., the soil texture) is critical for understanding soil behavior and management. n When investigating soils on a site, the texture of various soil horizons is often the first and most important property to determine, for one can draw many conclusions from this information. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 18 Upper Saddle River, NJ 07458. All Rights Reserved.  n Furthermore, the texture of a soil in the field is not readily subject to change, so it is considered a basic property of a soil. Elements of the Nature and Properties of Soils, 3/e © 2010 Pearson Higher Education, By Nyle C. Brady and Raymond Weil 19 Upper Saddle River, NJ 07458. All Rights Reserved.  SOIL TEXTURE (SIZE DISTRIBUTION OF SOIL PARTICLES) Nature of Soil Separates n Diameters of individual soil particles range over six orders of magnitude, from boulders (1 m) to submicroscopic clays (