Ch. 18: Soils Flashcards
Define soil, soil science, and pedology. How is soil produced?
-Soil - a complex plant-supporting system that is made of disintegrated rock, organic matter, water, gases, nutrients, Micro-organism
-Soil science - The interdisciplinary study of soil as a natural resource on Earth’s surface
-Pedology - studies origin, classification, distribution, and description of soil
-Soil is produced by mechanical weathering of parent material, and accumulation and decay of organic material
Describe the principal natural soil-formation factors and describe the horizons of a typical soil profile.
Natural factors:
1.) Climate - heat accelerates weathering, decomposition, and decomposition, and biological growth; moisture is needed for biological activity and accelerate weathering
2.) Organisms - they mix and aerate soil by burrowing, and add organic matter. Matter (plants and animals), facilitate decomposition (especially bacteria)
3.) Topography (slope) -affects exposure to the sun, wind, and water; where and how soil and water move
4.) Parent material - physical and chemical properties of parent material (rock, sediment) affect result soil properties
5.) Time - soil formation takes 10s -1000s of yrs; factors above will change overtime
Soil horizons:
-O horizon - 20-30% organic material, including decomposed leaves, branches, mosses, animal waste (humus)
-A horizon (topsoil) - organic and mineral material at or near the soil surface, often characterized by leaching
-B horizon - horizon formed by accumulation of material removed from A horizon or by alteration of parent material
- C horizon - transition zone below B horizon, made of broken up, slightly altered parent material (regolith)
-R horizon - unaltered parent material (rock or sediment)
Describe the common properties used to classify soils: colour, texture, structure, cation-exchange capacity and pH, and relate these concepts to soil fertility
-Color - can suggest composition and chemical makeup
-red soil indicate presence of iron oxide
-black soil indicate high humus content
-Texture - mixture and proportion of different particle sizes (sand, silt, and clay)
-Loam balanced mix of sand, silt, and clay
-Structure - size and shape of the aggregates (compacted clusters) of particles in the soil
-Cation-exchange capacity - refers to the soil’s ability to retain and exchange positively charged ions (cations) like calcium, magnesium, and potassium. Soils w/ higher CEC can hold on to more nutrients, making them fertile
-Soil PH - the acidity and alkalinity of a soil; acidity affects the type of crops that can be grown or treatments that must be done to make a soil support a certain crop
-high soil acidity can accelerate chemical weathering of mineral nutrients and increase their depletion rates
Soil fertility is related to these soil properties in these ways:
-organic matter content affects soil color and provides nutrients as it decomposes, contributing to soil fertility
-texture also influences water retention, drainage and aeration, all necessary for plant growth
-Soil structure affects root development and nutrient accessibility
-CEC determines the soil’s ability to retain and supply essential nutrients to plants
PH influences nutrient availability and microbial activity in the soil
Discuss human impacts on soils. What areas are at the highest risk of erosion and desertification? Explain the differences in the causes and effects of desertification in Central Asia
versus Africa’s Sahel (you may need to consult your textbook for this one)
-Human impacts like overcultivation and excessive tilling, overgrazing, and clearing of forested slopes is causing soil erosion
-the croplands in Canada and USA are at most risk for this
-Desertification is land degradation that occurs in dry regions
-It’s common in areas already affected by poverty; high-risk lands for this are India and countries in Central Asia
Central Asia and Sahel causes and effects:
Causes and effects - Central Asia
Causes:
- Experienced extensive agricultural development during the Soviet era, with large-scale irrigation projects diverting water, but the projects are often poorly planned and managed, leading insufficient water use and soil salinization
-also experiencing aridity and erratic precipitation patterns due to climate change
Effects:
-desertification lead to loss of arable land, threatening food security
-It’s also lead to the degradation of ecosystems, and loss of biodiversity
Causes - Sahel
-deforestation for fuelwood and timber, and agriculture has depleted vegetation cover, making the land more vulnerable to erosion and desertification
-This place also experiences frequent droughts and erratic rainfall pattern, which are worsened by climate change, and lead to increased desertification
Effects:
-Desertification has decreased agriculture activity, leading to food shortages and malnutrition
-It also hampers the economic development, increasing poverty in the nation
