Chapter 7 Section 2&3 Soil PDF

24/11/01 Chapter 7 Section 2 & 3 How do living organisms cause erosion? 1  24/11/01...

24/11/01 Chapter 7 Section 2 & 3 How do living organisms cause erosion? 1  24/11/01 How does soil form? Glacial Erosion Because glaciers can move as dense, enormous rivers of slowly flowing ice, they have the capacity to carry huge rocks and piles of debris over great distances and grind the rocks beneath them into flour-sized particles. Copyright © McGraw-Hill Education Erosion and Deposition 2  24/11/01 Glacial Erosion The features left in the wake of glaciers include steep U-shaped valleys and lakes. The effects of glaciers on the landscape also include deposition. For example, soils in the northern parts of the United States are formed from material that was transported and deposited by glaciers. Copyright © McGraw-Hill Education Erosion and Deposition Wind Erosion Wind can be a major erosional agent, especially in arid and coastal regions, which tend to have little vegetation to hold soil in place. Wind can easily pick up and move fine, dry particles. The abrasive action of windblown particles can damage both natural features and human-made structures. Winds can also easily move fine-grained sediments and sand uphill. Copyright © McGraw-Hill Education Erosion and Deposition 3  24/11/01 Wind Erosion Wind barriers One farming method that can reduce the effects of wind erosion is the planting of wind barriers, also called windbreaks. Windbreaks are trees or other vegetation planted perpendicular to the direction of the wind. Copyright © McGraw-Hill Education Erosion and Deposition Erosion by Living Things As plants and animals carry out their life processes, they often move Earth’s surface materials from one place to another. Copyright © McGraw-Hill Education Erosion and Deposition 4  24/11/01 Soil Formation Soil is the loose covering of weathered rock particles and decaying organic matter, called humus, overlying the bedrock on Earth’s surface, and serves as a medium for the growth of plants. Copyright © McGraw-Hill Education Soil Soil Formation Soil development The soil-development process often begins when weathering breaks solid bedrock into smaller pieces, which continue to weather and break down further. Copyright © McGraw-Hill Education Soil 5  24/11/01 Soil Formation Soil development Worms and other organisms help break down organic matter and add nutrients to the soil as well as create passages for air and water. Copyright © McGraw-Hill Education Soil Soil Layers During the process of soil formation, layers develop in the soil. Most of the volume of soil is formed from the weathered products of a source rock, called the parent material. Copyright © McGraw-Hill Education Soil 6  24/11/01 Soil Layers A soil whose parent material is the local bedrock is called residual soil. Transported soil is soil that develops from parent material that has been moved far from its original location, usually by agents of erosion. Copyright © McGraw-Hill Education Soil Soil Layers Soil profiles A soil profile is a vertical sequence of soil layers. New soils that have not yet developed distinct layers are called undeveloped soils. Mature soils are those that have distinct layers, sometimes after tens of thousands of years. Copyright © McGraw-Hill Education Soil 7  24/11/01 Soil Layers Soil profiles A distinct layer within a soil profile is called a soil horizon. There are typically four major soil horizons in mature soils: O, A, B, and C. Copyright © McGraw-Hill Education Soil Soil Layers Soil profiles The O-horizon is the top layer of organic material and is composed of humus and leaf litter. The A-horizon is a layer of weathered rock combined with a rich concentration of dark brown organic material. The B-horizon, also known as the zone of accumulation, is a red or brown layer enriched over time by clay and minerals deposited by water flowing from above, or percolating upward from below. The C-horizon contains little or no organic matter and is often made of broken-down bedrock. Copyright © McGraw-Hill Education Soil 8  24/11/01 Factors of Soil Formation Five factors influence soil formation: climate, topography, parent material, biological activity, and time. These factors combine to produce different types of soil, called soil orders, that differ by region. The five factors of soil formation result in 12 different soil orders. Copyright © McGraw-Hill Education Soil Factors of Soil Formation Climate Climate is the most significant factor controlling the development of soils because it also affects the weathering of rocks. Temperature, wind, and the amount of rainfall determine the type of soil that can develop. Copyright © McGraw-Hill Education Soil 9  24/11/01 Factors of Soil Formation Topography Topography, which includes the slope and orientation of the land, affects the type of soil that forms. In the northern hemisphere, slopes that face south receive more sunlight than other slopes, allowing more vegetation to grow. Copyright © McGraw-Hill Education Soil Factors of Soil Formation Parent material If the soil is residual, it will have the same chemical composition as the local bedrock. If the soil is transported, the minerals in the soil are likely to be different from those in the local bedrock. Copyright © McGraw-Hill Education Soil 10  24/11/01 Factors of Soil Formation Biological activity Organisms including fungi and bacteria, as well as plants and animals, interact with soil. Different types of organisms in a soil can result in different soil orders. Copyright © McGraw-Hill Education Soil Factors of Soil Formation Time The effects of time alone can determine the characteristics of a soil. After tens of thousands of years of weathering, most of the original minerals in a soil are changed or washed away. Copyright © McGraw-Hill Education Soil 11  24/11/01 Soil Texture The relative proportions of particle sizes determine a soil’s texture, which affects a soil’s capacity to retain moisture and therefore its ability to support plant growth. A soil textural triangle is used to determine a soil’s texture. Copyright © McGraw-Hill Education Soil Soil Fertility Soil fertility is the measure of how well a soil can support the growth of plants. It is affected by topography, availability of minerals and nutrients, the number of microorganisms present, the amount of precipitation available, and the level of acidity. Copyright © McGraw-Hill Education Soil 12  24/11/01 Soil Color The minerals, organic matter, and moisture in each soil horizon determine its color. Scientists use the Munsell System of Color Notation to describe soil color in components of hue (color), value (lightness or darkness), and chroma (intensity). Copyright © McGraw-Hill Education Soil 13