Chapter 7Chapter 7Weathering and SoilWeathering and Soil

7.2 The nature of soil notes 7.2 The nature of soil notes sheet.sheet.

SoilSoil

► SoilSoil is a mixture of weathered is a mixture of weathered rockrock, decayed , decayed organic material, mineralorganic material, mineral fragments, fragments, waterwater, , and and air.air.

► Soil can take Soil can take thousandsthousands of years to form. of years to form.► There are There are five five characteristics that affect soil characteristics that affect soil

formation.formation.1. Climate1. Climate2. Slope of land2. Slope of land3. Types of rock3. Types of rock4. Types of vegetation4. Types of vegetation5. Amount of time5. Amount of time

SoilSoil

►Different soils can develop in different Different soils can develop in different climatesclimates; tropical soil is different than ; tropical soil is different than polarpolar soil soil

►Soils that develop on Soils that develop on steepsteep slopes are slopes are different than soils that develop on different than soils that develop on flatflat land.land.

Slope will effect soilSlope will effect soil

Erosion will effect soil…Erosion will effect soil…

The composition of soilThe composition of soil

►The rock and mineral fragments found The rock and mineral fragments found in soils come from in soils come from rocksrocks that have been that have been weatheredweathered..

►Organic matter in soil comes from Organic matter in soil comes from plant plant leaves, stems, and roots.leaves, stems, and roots.

►Decayed organic matter turns to Decayed organic matter turns to humushumus, a source of , a source of nutrientsnutrients for plants. for plants.

►Soil has many Soil has many smallsmall spaces between spaces between particles that holds particles that holds waterwater and and airair..

Soil ProfilesSoil Profiles

► Different layers of soil are called Different layers of soil are called horizonshorizons..► All the horizons of a soil form a All the horizons of a soil form a soil profilesoil profile..► There are There are three three main horizons for most soils.main horizons for most soils.

--A A horizon: the horizon: the top top layer of soil.layer of soil.-It is usually covered by -It is usually covered by litterlitter, made up of , made up of

leaves, twigs, and organic matter, which helps leaves, twigs, and organic matter, which helps prevent prevent erosionerosion and and evaporationevaporation of water from the of water from the soil.soil.

-Also known as -Also known as top soiltop soil..-It is -It is darkdark and and fertilefertile..

Soil ProfilesSoil Profiles

B B horizon: the horizon: the middle middle layer of soillayer of soil-Because there is less -Because there is less organicorganic matter in this matter in this horizon, it is horizon, it is lighterlighter in color than the A in color than the A horizon.horizon.

►-Contain materials from A horizon that were -Contain materials from A horizon that were moved down by moved down by leachingleaching: the removal of : the removal of mineralsminerals that have been that have been dissolveddissolved in water. in water. Water reacts with Water reacts with humushumus and carbon and carbon dioxide to form dioxide to form acidacid. The acid dissolves the . The acid dissolves the mineralsminerals in the in the A A horizon and carries them horizon and carries them to to BB horizon. horizon.

Soil ProfilesSoil Profiles

►CC horizon: the horizon: the bottombottom of the soil of the soil profile.profile.-Consists of partially -Consists of partially weatheredweathered rock. rock.-The -The thickestthickest soil horizon. soil horizon.-Does not contain much -Does not contain much organic organic mattermatter and is not affected by and is not affected by leachingleaching..-The soil layer that is the most like the -The soil layer that is the most like the parentparent material. material.

Soil ProfilesSoil Profiles

►At many places of Earth, land is At many places of Earth, land is covered by a thick layer of covered by a thick layer of sedimentsediment that is deposited by that is deposited by glaciersglaciers..-This material is an unsorted mixture -This material is an unsorted mixture

of of clay, silt, sand, and bouldersclay, silt, sand, and boulders that that were left after the glacial ice melted. were left after the glacial ice melted. It is extremely It is extremely fertilefertile..

Soil TypesSoil Types

►Many different Many different types types of soil exist, of soil exist, based on based on climateclimate and and slopeslope..

►Desert soils are Desert soils are drydry and have little and have little organicorganic matter. matter.

►Prairie soils have thick dark Prairie soils have thick dark A A horizons horizons because of the grasses contributing because of the grasses contributing lots of lots of organic matterorganic matter..

Soil TypesSoil Types

►SlopeSlope also affects soils. also affects soils.-Steep slopes have -Steep slopes have poorpoor soils because soils because

material moves downhill before it material moves downhill before it can be weathered.can be weathered.

-Bottomland soils are -Bottomland soils are thick, darkthick, dark, and , and full of organic matter because full of organic matter because sediment and water are plentifulsediment and water are plentiful..

Prairie and Desert SoilPrairie and Desert Soil

Temperate and Forest SoilTemperate and Forest Soil

Soil typesSoil types

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

Size of particlesSize of particles

►The size of the three particles that The size of the three particles that make up soil are broken down by sizemake up soil are broken down by size

►Sand is the largest of soil particlesSand is the largest of soil particles►Silt is the middle size of soil particlesSilt is the middle size of soil particles►Clay the smallest of the soil particlesClay the smallest of the soil particles

Loam Loam

►LoamLoam is is soil composed of composed of sand, , silt, and , and clay in relatively even concentration in relatively even concentration (about 40-40-20% concentration (about 40-40-20% concentration respectively), considered ideal for respectively), considered ideal for gardening and agricultural uses. Loam gardening and agricultural uses. Loam soils generally contain more nutrients soils generally contain more nutrients and and humus than sandy soils, have better than sandy soils, have better infiltration and drainage than silt soils, infiltration and drainage than silt soils, and are easier to and are easier to till than clay soils. than clay soils.

SandSand

►SandSand is a naturally occurring is a naturally occurring granular material composed of finely composed of finely divided divided rock and and mineral particles particles

►Sandy Sandy soils are ideal for crops such as are ideal for crops such as watermelons, , peaches, and , and peanuts and their excellent drainage and their excellent drainage characteristics make them suitable for characteristics make them suitable for intensive intensive dairy farming..

SiltSilt

►SiltSilt is is soil or rock derived granular or rock derived granular material of a grain size between sand material of a grain size between sand and clay. Silt may occur as a soil or as and clay. Silt may occur as a soil or as suspended sediment (also known as suspended sediment (also known as suspended load) in a surface water suspended load) in a surface water body. It may also exist as soil deposited body. It may also exist as soil deposited at the bottom of a water body.at the bottom of a water body.

►Silt is formed by chemical weathering, Silt is formed by chemical weathering, ice wedging, and abrasion. ice wedging, and abrasion.

ClayClay

►Clay minerals are typically formed over Clay minerals are typically formed over long periods of time by the gradual long periods of time by the gradual chemical weathering of rockschemical weathering of rocks

►Clay deposits may be formed in place as Clay deposits may be formed in place as residual deposits in soil, but thick deposits residual deposits in soil, but thick deposits usually are formed as the result of a usually are formed as the result of a secondary sedimentary deposition process secondary sedimentary deposition process after they have been eroded and after they have been eroded and transported from their original location of transported from their original location of formation.formation.

Chapter 7 Sections 3Chapter 7 Sections 3

Soil Erosion Notes SheetSoil Erosion Notes Sheet

Soil ErosionSoil Erosion

►The removal and carrying away of The removal and carrying away of sediment from earth’s surface is called sediment from earth’s surface is called soil erosionsoil erosion

►Soil erosion is harmful because plants Soil erosion is harmful because plants do not grow well where topsoil has do not grow well where topsoil has been removed been removed

Causes of Soil ErosionCauses of Soil Erosion

►Soil erodes when it is moved from the Soil erodes when it is moved from the place where it was formedplace where it was formed

►Water and wind are the 2 main things Water and wind are the 2 main things that erode soilthat erode soil

►Soil erosion is more severe on steep Soil erosion is more severe on steep slopes then on gentle slopes it is also slopes then on gentle slopes it is also more severe in areas with little vegetationmore severe in areas with little vegetation

►Humans cause soil to erode faster then Humans cause soil to erode faster then new soil can be formed new soil can be formed

Causes of Soil ErosionCauses of Soil Erosion

►One way humans do this is by removing One way humans do this is by removing ground coverground cover

►Ground cover is vegetation that covers the Ground cover is vegetation that covers the soil and protects it from erosion. When it is soil and protects it from erosion. When it is cleared erosion increasescleared erosion increases

►When farmers clear and till soil for When farmers clear and till soil for agricultural cultivation soil erosion agricultural cultivation soil erosion increases. If the topsoil erodes then the increases. If the topsoil erodes then the quality of soil becomes reduced, because quality of soil becomes reduced, because topsoil contains many nutrientstopsoil contains many nutrients

Clear Cut ForestClear Cut Forest

Causes for Soil ErosionCauses for Soil Erosion►When forests are removed soil is When forests are removed soil is

exposed and erosion increasesexposed and erosion increases►When areas are overgrazed by cattle, When areas are overgrazed by cattle,

sheep and horses erosion increases sheep and horses erosion increases because there is very little vegetation because there is very little vegetation left to protect the soil. left to protect the soil.

How does this effect soil How does this effect soil erosion?erosion?

Causes for Soil ErosionCauses for Soil Erosion

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

Preventing soil erosionPreventing soil erosion

►Soil must be managed and protectedSoil must be managed and protected►Farmers manage crops to reduce soil Farmers manage crops to reduce soil

erosion. They plant trees and manage erosion. They plant trees and manage grazing.grazing.

►No till farming- is a process where the No till farming- is a process where the seeds for the next crop are planted in seeds for the next crop are planted in the vegetation residue from the former the vegetation residue from the former crop. The left over vegetation protects crop. The left over vegetation protects the soilthe soil

Preventing soil erosionPreventing soil erosion

►Contour farming- is used on gentle Contour farming- is used on gentle slopes. Crops are planted with the slopes. Crops are planted with the natural contours of the land to slow natural contours of the land to slow the flow of water down the slopethe flow of water down the slope

►Terracing is used on steep slopes Terracing is used on steep slopes where level flat steps are built into the where level flat steps are built into the sides of slopes so that crops can be sides of slopes so that crops can be grown. They reduce runoff by creating grown. They reduce runoff by creating flat areas and shorter sections of slopeflat areas and shorter sections of slope

Contour farmingContour farming

TerracingTerracing