The Ground Beneath Our Feet

What Makes Up Healthy Soil?

• Mineral fragments, humus, air, water, and living things–Plant roots, Insects, Worms

• Humus–Organic Material–Can support the growth of vegetation

• Parent rock–source of mineral fragments in the soil

Soil Formation

• Soil starts out as rock• The surface rocks break

down into smaller pieces and is mixed with organic matter.

• Over time this creates a thin layer of soil.

• Decaying matter makes the soil thick and rich

Soil Texture

The soil’s quality is based on the proportions of soil particles.

Soil texture affects–Consistency: • soil’s ability to be broken up.

–Infiltration: • ability of water to move through soil.

Sizes of Weathered Rock That Make Up Soil

Different Types of Soil• Every soil type is

a mixture of sand, silt, clay.

• The right mixture is called loam.

• Loam = • 40% sand• 40 % silt• 20 % clay

Review Questions

• Which particle is the biggest one that goes in soil?– A. Clay– B. Silt– C. Quartz– D. Sand

Review Questions

• Which particle is the biggest one that goes in soil?– A. Clay– B. Silt– C. Quartz–D. Sand

Review Questions

• How does soil texture affect soil consistency?– A. It has nothing to do with it.– B. Allows water to pass through it easier.– C. The soil’s ability to allow farmers to

manipulate it.– D. Allows for plants to grow easily.

Review Questions

• How does soil texture affect soil consistency?– A. It has nothing to do with it.– B. Allows water to pass through it easier.– C. The soil’s ability to allow farmers to

manipulate it.– D. Allows for plants to grow easily.

Review Questions

• What is loam?– A. Loam is the perfect combination of

sand, silt, and clay.– B. Loam is the combination of 30% sand,

40% mud, and 30% clay.– C. Loam is located on in horizon B.– D. Loam is the particle quality of any soil.

Review Questions

• What is loam?– A. Loam is the perfect combination of

sand, silt, and clay.– B. Loam is the combination of 30% sand,

40% mud, and 30% clay.– C. Loam is located on in horizon B.–D. Loam is the particle quality of any

soil.

What is a Soil horizon?• OLitter from dead plants and

animals• A– Topsoil

• E– Zone of intense leaching.

• B– Collects dissolved

substances from upper horizons

• C– Weathered bedrock

• R– Bedrock

Soil Profile

• The vertical display of soil horizons.• Each soil profile is different from

another.

• http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf

Soil pH

• Have you ever seen this?

• Why does this happen?

• What creates CO2?

Soil pH• Carbonic acid and Humic

acid changed the pH of the soil to be more acidic.

• Carbonic acid –come from Carbon

Dioxide.

• Humic acid –various organic acids

produced from humus.

Tropical Climate

• Very rich humus.• Very little topsoil–Leeching of

nutrients from topsoil to horizon B and C.–Plants demand a

lot of nutrients.

Desert Climate

• Deserts get less than 25 cm rain a year.

• Slow rate of weathering = Slow rate of soil formation.

• Due to no water, salt gathers in the ground.

• Salt is toxic to plants!

Temperate Climate

• Lots of weathering = lots of fertile soil

• Most productive soil in the world.

• Most of Continental USA has a temperate climate.

Arctic Climate

• Very cold desert = Slow rate of soil formation.

• Low amount of humus due to cold temperatures.

• Cold temperatures slow down decomposition.

Review Questions

• What acids can change the pH of the soil?–A. Humic acid and Hydrochloric

acid–B. Carbonic acid and Humic acid–C. Carbonic acid and water–D. Water and citric acid

Review Questions

• What acids can change the pH of the soil?–A. Humic acid and Hydrochloric

acid–B. Carbonic acid and Humic

acid–C. Carbonic acid and water–D. Water and citric acid

Review Questions

• Which climate is called the “breadbasket of the world”?–A. Tropical–B. Desert–C. Temperate–D. Arctic

Review Questions

• Which climate is called the “breadbasket of the world”?–A. Tropical–B. Desert–C. Temperate–D. Arctic

Review Questions

• Which climate has very little, but fertile topsoil?–A. Tropical–B. Desert–C. Temperate–D. Arctic

Review Questions

• Which climate has very little, but fertile topsoil?–A. Tropical–B. Desert–C. Temperate–D. Arctic