Soil

An important resource

No Soil…No Life…

WHAT is it???

• Mixture of weathered/eroded rock, nutrients, decaying organic matter, water, air and…

billions of organisms!

Different sizes and types of minerals determine soil texture:

• Clay: very fine and ultrafine particles

• Silt: fine particles

• Sand: medium size particles

• Gravel: course to very course particles

• If soil feels:

– Gritty: lots of sand

– Sticky: lots of clay

– Smooth: lots of silt (like flour)

Loam: a mixture best suited for plant growth

Texture Lab…

• Using a soil triangle to determine texture

• Determining the texture of a soil sample

Texture determines Porosity:

• Porosity: the volume of pore spaces (air spaces)– Porous soil: has many pores so can hold

more air and water.

• Permeability: the rate at which water and air move from upper to lower layers.

Porosity and Permeability Labs…

• Determine the porosity of two soil samples.

• Determine the permeability of two soil samples.

• Clay: high porosity low permeability

• Sand: low porosity high permeability

Soil Nutrients

Basic Chemistry…

The Soil ProfileLayers of soil (horizons) each have their

own distinct textures and composition.

Cross section of horizons = Soil Profile

Notes:

Different Ecosystems have different Profiles:

• Grasslands have a deep/rich layer of topsoil due to yearly decomposition of grasses. PERFECT for farming – nutrient rich. (“breadbasket” of United States)

– However, poor agricultural practices have depleted this resource; plowed soil left to the elements of wind and rain is easily eroded.

–Years of over-plowing + drought = Dust Bowl of the 1930’s

– In some areas of the Great Plains, topsoil has decreased in thickness from 12 inches to less than 4 inches due to human activities!!

• Tropical Rain Forest have thin, very acidic soil due to – rapid cycling of nutrients and – leaching of nutrients due to excessive rainfall

• HORRIBLE for farming – Topsoil is only 1 to 2 inches thick

– However, the world’s rainforests are being deforested or burned to provide room for more farmland (a response to the pressures of overpopulation…)

– These farms are usually abandoned within one to two years after what little nutrients from the soil are used up… and the cycle of burning continues…

Borneo: Deforestation