The Soil Texture Triangle

Creates classes which break the distribution of particle sizes (soil textures) into 12 categories: clay, sandy clay, silty clay, sandy clay loam, clay loam, silty clay loam, sand, loamy sand, sandy loam, loam, silt loam, silt.

To Use:1. Place the edge of a ruler at the point along

the base of the triangle that represents the percent of sand in your sample. Position the ruler on the line that slants in the direction that the numbers are facing for percent sand.

2. Place the edge of a second ruler at the point along the right side of the triangle. Position the ruler on the line which slants in the direction that the numbers are facing for percent silt.

To Use:3. Place the point of a pencil at the point where

the two rulers meet. Place the top edge of one of the rulers on the mark, and hold the ruler parallel to the horizontal lines. The number on the left should be the percent of clay in the sample.Note: The sum of the percent of sand, silt, and clay should add up to 100.

3. The descriptive name of the soil sample (textural class) is written in the shaded area where the mark is located. If the mark should fall directly on a line between two descriptions, record both names.

An additional Soil Texture Triangle Practice Worksheet is available online.

Soil DegradationThe breakdown of our most

important resource.

Wednesday, November 18th, 2015

Soil: The Final Frontier• Soil is a vital part of the natural

environment. – Habitat

• It controls the flow of water and chemical substances between the atmosphere and the earth

• Acts as both a source and store for gases (like O and CO2) in the atmosphere.

• Soils not only reflect natural processes but also record human activities both at present and in the past. – They are therefore part of our cultural

heritage.

– The modification of soils for agriculture and the burial of archaeological remains are good examples of this.

What would we do without it?!

• Soil helps to provide much of the food that humans consume. – Only 25% of the Earth’s surface is

made up of soil and only 10% of that soil can be used to grow food.

• Without it, we cannot support primary producers.

World Soil ConditionsSoils are becoming degraded in many regions.

Major Causes of Soil Degradation

• Overgrazing34%

• Deforestation30%

• Cropland Agriculture28%

• Other Causes

8%

Erosion and Deposition• Erosion = removal of material

from one place and its transport elsewhere (by wind/water)

• Deposition = arrival of eroded material at a new location

– These processes are natural, and can build up fertile soil.

– But where artificially sped up, they are a big problem for farming.

Erosion is commonly caused by:

• Overcultivating, too much plowing, poor planning

• Overgrazing rangeland with livestock

• Deforestation, especially on slopes

• Deforestation is the removal of trees.– Without trees to stabilize the

soil, it erodes.

Erosion from flooding

• Floodplains and tropical rain forests are areas where there is a lot of erosion.– Most concerns about erosion are

related to accelerated erosion, where the natural rate has been significantly increased mostly by human activity

Soil Exhaustion

• Agricultural systems disrupt natural mineral cycling.– The soil may become mineral

deficient and lose fertility.– Plants need minerals to grow

and thrive such as nitrates, phosphates and sulfates.

Desertification• Desertification is the expansion of

dry lands due to poor agricultural practices, improper soil moisture management, salinization and erosion, forest removal, and climate change. – Overuse of agricultural lands is the cause.– 10% of the world’s land has been

desertified.– 25% is at risk.– In Mali, the Sahara desert has expanded

more than 650 km in less than 20 years.

DesertificationA loss of more than 10%

productivity due to:• Erosion• Soil compaction• Forest removal• Overgrazing• Drought• Salinization• Climate change• Depletion of water resources• etc.

Soil degradation on drylands is caused mostly by erosion

Chemical Problems

• Chemical emissions: Industrial processes and vehicles release toxic substances which are heavier than air and settle on the soil.

• Toxic Seepage & Chemical contamination: improperly disposed chemicals seep into soil

•Pesticides that are applied to fields can also destroy beneficial organisms in the soil.– Bacteria that fix nitrogen,

organisms that break down soil (worms)

– Bioaccumulation causes the concentrations of these pesticides to increase up the food chain.

Salinization• Salinization is a gradual

increase in salt (ionic compounds) in soil.– Irrigation in areas where the

bedrock contains high salt levels will cause these aqueous salts to be brought to the surface

– Irrigation water contains dissolved salts• when evaporates, leave behind in soil• Leaching

Desalination• Desalination is used to

remove ions from water.– The Middle East has the least

amount of freshwater than any other area on the planet and desalination is used to provide freshwater for agricultural and household purposes. This prevents salinization of the soil through agriculture.

Soil Conservation

Techniques that can be applied before a parcel of

land is prepared for agricultural land use.

Starts with the identification of areas that should not be planted. Considerations to be included are slope, soil type, existing waterways, critical endemic plant and

animal habitat.

Prevention Methods

• Conservation tillage– Residues from previous year’s

crops are left in place to prevent soil erosion

• Crop rotation– Planting a series of different

crops in the same field over a period of years

• Contour plowing– Plowing around hill instead of

up/down

• Strip cropping– Alternating strips of different crops

along natural contours

• Terracing– Creating terraces on steep slopes to

prevent erosion

Preserving Soil Fertility• Organic fertilizers

– Animal manure, crop residue, bone meal & compost

– Nutrient available to plants only as material decomposes

• Inorganic fertilizers– Manufactured from chemical compounds– Soluble

• Fast acting, short lasting• Mobile: Easily leach and pollute groundwater

Soil Reclamation

• Two steps1. Stabilize land to prevent further

erosion2. Restoring soil to former fertility

• Best way to do this is shelterbelts– Row of trees planted to reduce

wind erosion

• Soil Conservation Act 1935– Authorized formation of Soil Conservation Service,

now called Natural Resources Conservation Service (NRCS)

– Assess soil damage and develop policies to improve soil

• Food Security Act (Farm Bill) 1985– Farmers with highly erodible soil had to change their

farming practices– Instituted Conservation Reserve Program

• Pays farmers to stop farming highly erodible land

Soil Conservation Policies