Page 606 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

18
concepts
kEy LEARNiNG
The Geography of Soils
After reading the chapter, you should be able to:
• Define soil and soil science, and list four components of soil.
• Describe the principal soil-formation factors, and describe the horizons of a
typical soil profile.
• Describe the physical properties used to classify soils: colour, texture, structure, consistence, porosity, and soil moisture.
• Explain basic soil chemistry, including cation-exchange capacity, and relate these concepts to soil fertility.
• Discuss human impacts on soils, including desertification.
• Describe the principal pedogenic processes that lead to the formation of soils
under different environmental conditions.
• Describe the 10 soil orders of the Canadian System of Soil Classification, and explain the general occurrence of these orders.
For over 2000 years, local people have cultivated the Bangaan Rice Terraces rising thousands of metres in elevation on the steep mountain slopes of the island of Luzon, Philippines. The terraces are built using stone and mud walls to create a series of ponded fields called paddies. The pad- dies prevent erosion by holding soil and water obtained from streams originating in the mountains above. Planted, maintained, and harvested by community effort, the terraces exemplify sustainable agriculture
in a country that suffers from soil erosion problems. This terraced region was listed as a UNESCO World Heritage in Danger in 2001 as declining traditional practices led to terrace deterioration. Conservation is ongoing. Worldwide, rice paddy fields are a major source of atmospheric methane, a greenhouse gas. [Dave Stamboulis/Alamy.]