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