Soil…..not, just dirt!

“The soil is the great connector of our lives, the source and destination of all.”

Wendell Berry The Unsettling of America, 1977

Why is soil important?• Nutrient cycling: soil controls the release and

uptake of nutrients (soil can trap carbon –reducing greenhouse gas)

• Water relations: Soil acts as a filter to protect the quality of water and air

• Biodiversity and habitat: soil supports the growth of a variety of plants, animals and microorganisms

• Physical stability and support: Soil allows plant roots to anchor in the ground and structural support for buildings, roads and parking.

How does soil form?

• Soil erodes from parent material (rock) 1cm in 250 -2,500 years

The soil profile• Soil forms distinct layers

called horizons• The depth of soil varies

from less than a meter to tens of meters thick

• Soil scientists classify soils according to their profiles

• Classification helps to determine how the soil can best be used

Alfisol Andisol

oxisol Vertisol

Iowa - Mollisols• Soils of grassland

ecosystems• Fertile surface

horizon formed from long term addition of plant material

• Most widespread soil order in the U.S.

• Among the most productive agricultural soils of the world

What is soil made of?• 45% minerals• 25% air• 25% water• 5% organic matter• To describe soil we

consider:• Color• Structure• texture

Particle type

Size (mm)

clay 0.002

silt 0.002-0.005

sand 0.05-2.0

Soil texture classification

What lives in the soil?

• Each shovel of soil holds more living things than all the human beings ever born!

• We know more about the movement of celestial bodies than about the soil underfoot.” --- Leonardo daVinci

• Yet, every plant and animal depends on this vast ecosystem

Earthworms

• Up to 1, 750, 000 per acre in good agricultural soil!

• The weight of worms might outweigh the weight of livestock on a farm!

• Worms break down plant material into nutrient rich humus

• Burrowing improves soil structure for plant growth

• Earthworms aerate the soil• Earthworms bring minerals from lower levels to

the plant root zone

What else lives in the soil?

• Insects: 23 million per hectare (2.47 acres)• Bacteria: 2.5 billion per gram