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Chapter 7 Weathering and Soil

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1 Chapter 7 Weathering and Soil
7.2 The nature of soil notes sheet.

2 Soil Soil is a mixture of weathered rock, decayed organic material, mineral fragments, water, and air. Soil can take thousands of years to form. There are five characteristics that affect soil formation. 1. Climate 2. Slope of land 3. Types of rock 4. Types of vegetation 5. Amount of time

3 Soil Different soils can develop in different climates; tropical soil is different than polar soil Soils that develop on steep slopes are different than soils that develop on flat land.

4 Slope will effect soil

5 Erosion will effect soil…

6 The composition of soil
The rock and mineral fragments found in soils come from rocks that have been weathered. Organic matter in soil comes from plant leaves, stems, and roots. Decayed organic matter turns to humus, a source of nutrients for plants. Soil has many small spaces between particles that holds water and air.

7 Soil Profiles Different layers of soil are called horizons.
All the horizons of a soil form a soil profile. There are three main horizons for most soils. -A horizon: the top layer of soil. -It is usually covered by litter, made up of leaves, twigs, and organic matter, which helps prevent erosion and evaporation of water from the soil. -Also known as top soil. -It is dark and fertile.

8 Soil Profiles B horizon: the middle layer of soil
-Because there is less organic matter in this horizon, it is lighter in color than the A horizon. -Contain materials from A horizon that were moved down by leaching: the removal of minerals that have been dissolved in water. Water reacts with humus and carbon dioxide to form acid. The acid dissolves the minerals in the A horizon and carries them to B horizon.

9 Soil Profiles C horizon: the bottom of the soil profile.
-Consists of partially weathered rock. -The thickest soil horizon. -Does not contain much organic matter and is not affected by leaching. -The soil layer that is the most like the parent material.

10 Soil Profiles At many places of Earth, land is covered by a thick layer of sediment that is deposited by glaciers. -This material is an unsorted mixture of clay, silt, sand, and boulders that were left after the glacial ice melted. It is extremely fertile.


12 Soil Types Many different types of soil exist, based on climate and slope. Desert soils are dry and have little organic matter. Prairie soils have thick dark A horizons because of the grasses contributing lots of organic matter.

13 Soil Types Slope also affects soils.
-Steep slopes have poor soils because material moves downhill before it can be weathered. -Bottomland soils are thick, dark, and full of organic matter because sediment and water are plentiful.

14 Prairie and Desert Soil

15 Temperate and Forest Soil

16 Soil types In terms of soil texture, soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay. Each size plays a significantly different role.

17 Size of particles The size of the three particles that make up soil are broken down by size Sand is the largest of soil particles Silt is the middle size of soil particles Clay the smallest of the soil particles

18 Loam Loam is soil composed of sand, silt, and clay in relatively even concentration (about % concentration respectively), considered ideal for gardening and agricultural uses. Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silt soils, and are easier to till than clay soils.

19 Sand Sand is a naturally occurring granular material composed of finely divided rock and mineral particles Sandy soils are ideal for crops such as watermelons, peaches, and peanuts and their excellent drainage characteristics make them suitable for intensive dairy farming.

20 Silt Silt is soil or rock derived granular material of a grain size between sand and clay. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body. Silt is formed by chemical weathering, ice wedging, and abrasion.

21 Clay Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation.

22 Soil Erosion Notes Sheet
Chapter 7 Sections 3 Soil Erosion Notes Sheet

23 Soil Erosion The removal and carrying away of sediment from earth’s surface is called soil erosion Soil erosion is harmful because plants do not grow well where topsoil has been removed

24 Causes of Soil Erosion Soil erodes when it is moved from the place where it was formed Water and wind are the 2 main things that erode soil Soil erosion is more severe on steep slopes then on gentle slopes it is also more severe in areas with little vegetation Humans cause soil to erode faster then new soil can be formed

25 Causes of Soil Erosion One way humans do this is by removing ground cover Ground cover is vegetation that covers the soil and protects it from erosion. When it is cleared erosion increases When farmers clear and till soil for agricultural cultivation soil erosion increases. If the topsoil erodes then the quality of soil becomes reduced, because topsoil contains many nutrients

26 Clear Cut Forest

27 Causes for Soil Erosion
When forests are removed soil is exposed and erosion increases When areas are overgrazed by cattle, sheep and horses erosion increases because there is very little vegetation left to protect the soil.

28 How does this effect soil erosion?

29 Causes for Soil Erosion
If soil erosion is severe excess sediments can damage the environment. Excess sediment loads degrade the quality of life by damaging wildlife habitats and fill in stream channels

30 Preventing soil erosion
Soil must be managed and protected Farmers manage crops to reduce soil erosion. They plant trees and manage grazing. No till farming- is a process where the seeds for the next crop are planted in the vegetation residue from the former crop. The left over vegetation protects the soil

31 Preventing soil erosion
Contour farming- is used on gentle slopes. Crops are planted with the natural contours of the land to slow the flow of water down the slope Terracing is used on steep slopes where level flat steps are built into the sides of slopes so that crops can be grown. They reduce runoff by creating flat areas and shorter sections of slope

32 Contour farming

33 Terracing

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