Page 638 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

602 part IV Soils, Ecosystems, and Biomes
3. Briefly describe the contributions of the following factors and their effects on soil formation: parent material, climate, vegetation, landforms, time, and humans.
4. Characterise the principal aspects of each soil hori- zon. Where does the main accumulation of organic material occur? Where does humus form? Which horizons constitute the solum?
5. Explain the difference between the processes of elu- viation and illuviation.
■ Describe the physical properties used to classify soils: colour, texture, structure, consistence, porosity, and soil moisture.
We use several physical properties to assess soil fertility (the ability of soil to sustain plants) and classify soils. Colour suggests composition and chemical makeup. Soil texture refers to the size of individual mineral particles and the ratios of different sizes. For example, loam is a bal- anced mixture of sand, silt, and clay. Soil structure refers to the shape and size of the soil ped, which is the smallest natural cluster of particles in a given soil. The cohesion of soil particles to each other is called soil consistence. Soil porosity refers to the size, alignment, shape, and location of spaces in the soil that are filled with air, gases, or water. Soil moisture refers to water in the soil pores and its avail- ability to plants.
soil fertility (p. 574) loam (p. 576)
soil porosity (p. 578)
6. How can soil colour be an indication of soil quali- ties? Provide two examples.
7. Define a soil separate. What are the various sizes of particles in soil? What is loam? Why is loam regarded so highly by agriculturists?
8. What is a quick, hands-on method for determining soil consistence?
9. Summarize the role of soil moisture in mature soils.
■ Explain basic soil chemistry, including cation-exchange capacity, and relate these concepts to soil fertility.
Particles of clay and organic material form negatively charged soil colloids that attract and retain positively charged mineral ions in the soil. The capacity to exchange ions between colloids and roots is called the cation- exchange capacity (CEC).
soil colloid (p. 578)
cation-exchange capacity (CEC) (p. 578)
10. What are soil colloids? How are they related to cations and anions in the soil? Explain cation- exchange capacity.
11. What is meant by the concept of soil fertility, and how does soil chemistry affect fertility?
■ Discuss human impacts on soils, including desertification.
Essential soils for agriculture and their fertility are threat- ened by human activities and mismanagement. Soil ero- sion is the breakdown and redistribution of soils by wind,
water, and gravity. To slow soil erosion, farmers in the United States and elsewhere use no-till agriculture, a practice in which the land is not ploughed after a harvest. Desertification is the ongoing degradation of drylands caused by human activities and climate change; presently, this process affects some 1.5 billion people.
desertification (p. 581)
12. What is meant by desertification? What world regions are affected by this phenomenon?
13. Explain some of the details that support the concern over loss of our most fertile soils. What cost esti- mates have been placed on soil erosion?
■ Describe the principal pedogenic processes that lead to the formation of soils under different environmental conditions.
The basic sampling unit used in soil surveys is the pedon. Soil classification uses two diagnostic horizons: the epipedon, or soil surface, and the diagnostic subsurface horizon, or the soil layer below the surface (at various depths) having properties specific to the type of soil. Spe- cific soil-forming processes keyed to climatic regions (not a basis for classification) are called pedogenic regimes: laterization (leaching in warm and humid climates, not present in Canada; see Oxisols in Appendix B), salinization (collection of salt residues in surface ho- rizons in hot, dry climates; discussed with Solonetzic soils), calcification (accumulation of carbonates in the B and C horizons in drier continental climates; discussed with Chernozemic soils), podsolization (soil acidification in forest soils in cool climates; discussed with Podzolic soils), and gleysation (humus and clay accumulation in cold, wet climates with poor drainage; discussed with Gleysolic soils).
pedon (p. 582)
epipedon (p. 582)
diagnostic subsurface horizon (p. 582) pedogenic regimes (p. 582) laterization (p. 582)
salinization (p. 582)
calcification (p. 582)
podsolization (p. 582)
gleysation (p. 605)
■ Describe the 10 soil orders of the Canadian System of Soil Classification, and explain the general occurrence of these orders.
The Canadian System of Soil Classification (CSSC) is built around an identification and analysis of physical properties of the soil that can be observed in the field. The system divides soils into five hierarchical categories: order, great group, subgroup, family, and series.
The 10 soil orders are Brunisolic (weakly devel- oped, humid region soils), Chernozemic (grassland soils), Cryosolic (cold soils underlain by permafrost), Gleysolic (saturated, reducing soils), Luvisolic (woodland soils), Organic (peat, muck, bog, and fen soils), Podsolic (northern conifer forest soils), Regosolic (soils without B horizons), Solonetzic (soils with saline parent materials), and Vertisolic (expandable clay soils).