soil…..not, just dirt! “the soil is the great connector of our lives, the source and destination...

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