Chapter 14 Soil and Its Uses

Geologic Processes The Earth is constantly changing. There are forces that build new land and opposing forces that tear it down. Such events include: earthquakes, volcanic eruptions, floods, and windstorms. Much of the building process involves the shifting of plates (large portions of the Earth’s surface).

Layers of the Earth (p. 306) Crust- An extremely thin, less dense, solid covering around the Earth (the surface). Mantle- The majority of the Earth, surrounds a small core made up primarily of iron and nickel. The outermost portion of the mantle is solid and collectively with the crust is known as the lithosphere. The inner, plastic part of the mantle is know as the asthenosphere. The core has a solid center and a liquid outer region.

Plate Tectonics Large portions (plates) of the Earth’s crust and outer portion of the mantle are slowly moving over the surface of the liquid part of the mantle. The heat from the Earth causes slow movements (like heating liquid on a stove). The movements between the plates and the mantle are independent of each other resulting in some plates pulling apart, while others collide.

Tectonics cont… Where plates pull apart, liquid from the mantle moves up into the gaps then solidifies. When they collide volcanoes, volcanic islands, and mountain ranges can form (like the Himalayan and Appalachian ranges)

Other factors influencing land formation Gravity, moving water and ice (glaciers), and wind work to lower these surfaces. These process that reduce the size of particles are known as weathering processes. There are 2 types of weathering:

Mechanical weathering reduces the size of rock without changing the chemical nature. (Change in temperature, roots of plants, wind and moving water) Chemical weathering involves chemical alteration of the rock –Small fragments may be oxidized (combine with oxygen) –Others may combine with water in the process of hydrolysis –This causes particles to be more readily soluble so may be removed by rain or moving water

Erosion is the loosening and redistributing of particles. The movement is from higher elevations to lower elevations Ex. Waves constantly wear away loose particles and transport them.

Soil and Land Land is the part of the world not covered by ocean Soil is a thin covering over the land consisting of minerals (45 %), organic material (5 %), living organisms, air (25%), and water (25%) These together help plants to grow

Soil Formation Soil is formed from a combination of physical, chemical, and biological events over time 1. Begins with fragmentation of parent material (ancient rock or more recent geologic deposits) – weathering 2. As organisms, such as lichens, become established in communities, their death and decay increases organic matter that incorporates and chemically breaks down small rock fragments

Contd. 3. This material resulting from animal and plant decay is called humus (an important soil component) Contains nutrients for plant use 4. Organisms such as earthworms and fungi improve soil quality by mixing organic and inorganic material, and further breakdown of these materials

Soil properties Include soil texture, structure, atmosphere, moisture, biotic content, and chemical composition

Soil texture Determined by size of mineral particles within the soil 1. Large particles- gravel and sand- –have spaces between to allow air and water through –Water drains very rapidly- –carries nutrients to lower layers (out of reach of plants)

2. Clay particles- small, easily pack together –so reduce movement of water- –do not drain well & poorly aerated 3. Loam- ideal for agriculture- –has drainage properties and aeration of large particles -but water and nutrient holding ability of clay particles

Soil Structure Refers to way various particles clump Sandy soils have granular structure (do not attach ) Clay soils stick to form large aggregates Good soil is friable- crumbles easily (sandy soils)

Organisms In Soil Protazoa, nematodes, earthworms, insects, algae, bacteria, and fungi Help to fragment organic material (insects & arthropods), fix nitrogen (bacteria), decay &recycle materials (nematodes, bacteria, & fungi)

Soil Profile Horizontal layers in soil Differ in chemical composition, physical properties, particle size, & amount of organic matter Each recognizable layer is a horizon

Soil Profile A horizon- topsoil- dark colored since high organic content (may contain a layer of litter- undecomposed/partiall y decomposed organic matter) Leaching-water carries dissolved organic matter and minerals to lower layers E horizon- leaching causes it to contain less nutrients

Horizon cont… B horizon-subsoil- accumulation of nutrients from above leaching/valuable for plants C horizon- weathered parent material R horizon- bedrock

Erosion Wearing away and transportation of soil by water, wind, or ice The Grand Canyon and floodplains of the Nile are a result of water’s ability to move soil Wind erosion is most extensive in Africa and Asia Soil erosion takes place everywhere in the world, especially areas where deforestation or desertification leave land open

Deforested areas erosion

Worldwide, erosion moves about 25.4 billion metric tons of soil each year Badly eroded soil has lost nearly all of its topsoil and some subsoil/ no longer good for farming

Soil Conservation Practices ONLY 20% of U.S. land is suitable for raising crops (only 2% of that does not require some form of conservation) Nearly all land must be managed to reduce erosion Worldwide on 11% of land is suitable 24% permanent pasture

Why is soil conservation important? Whenever soil is lost, the topsoil is the first layer to go This decreases the soil’s fertility More expensive fertilizers are need/ food prices increase Thus, proper soil conservation is needed to minimize topsoil loss

Soil Conservation Methods: Contour farming Strip farming Terracing Waterways Windbreaks Conventional tillage

Contour Farming Tilling at right angles to the slope of the land One of the simplest methods Used on gentle slopes produces small ridges Ridges act as dams to hold water/more water soaks into soil Reduces erosion as much as 50%

Strip Farming For steeper and longer slopes Alternating strips of closely sown crops (Ex. Hay or hay w/crops such as corn or cotton) Closely sown crops retard flow of water and allows more to be absorbed Steepness dictates width of strips

Terracing Used on very steep land Level areas constructed at right angles to the slope Requires use of small machines and considerable hand labor Expensive and requires constant repair and maintenance Used for centuries in areas short of level farm land

Waterways Depressions on sloping land where water collects and flows off land Maintained w/permanent sod covering to reduce erosion

Windbreaks Plantings of trees or other plants to protect bare soil from wind erosion Reduce velocity of wind

Conventional Tillage Require extensive use of farm machinery to prepare soil for planting & to control weeds There are many steps involved/ makes this method quite expensive for farmers Also increase time soil is exposed to wind or water erosion

Conservation Tillage Reduce amount of disturbance Leaves 15-30% of soil surface covered with crop residue Herbicides are used to control unwanted vegetation

Protecting soil on nonfarm land Not all land is suitable for growing crops This land can serve other functions if appropriate conservation practices employed Can be used for grazing, wood production, wildlife production, or scenic or recreational purposes