1. Linking the Nonliving to the Living
Soil
Linking the Nonliving to the Living

2. Soil is a Mixture
Soil is a mixture of minerals, organic matter, water and air.
There is a relationship between the composition of the soil and the nutritional needs of plants
Decomposers breakdown organic matter and free the nitrates, phosphates, and sulfates that plants require.

3. Introduction to Soils Terrestrial life is supported by soil
Without soil there would not be enough plant growth to feed all of the people and animals on earth
How is soil formed?
Wind, rain, and gravity all act to break up rock (A.K.A Weathering)
Moss and lichens attach to help break down rock
Then grass, then shrubs, and then trees
All of these leave behind organic matter that mixes with the broken down rocks to form soil

4. Soil Profile
Soil is generally found in layers called horizons. These layers make up the soil profile.
A-Horizon – the topsoil
Zone of Leaching – materials from soil dissolve in water and percolate down to the subsoil
Usually gray or black because of the humus
Humus – Decomposed plant and animal residue
Valuable layer – good for growing crops
Thickness – anywhere from 1 inch to 2 feet
B-Horizon – subsoil
Zone of accumulation – Place where all of the dissolved materials from the topsoil accumulate
Poor in organic content
Some organic content has been leached from A-horizon
C- Horizon- parent material
Not a part of the soil but a part of the soil profile
The rock that the soil of the region originated from
No distinct lower limit

5. Soil Texture Soil Texture = %Sand, Silt & Clay in a soil.
Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about:
1) water flow potential,
2) water holding capacity,
3) fertility potential,
4) suitability for many urban uses like bearing capacity

6. Sand < 2 mm to > 0.05 mm Visible without microscope
Rounded or angular in shape
Sand grains usually quartz if sand looks white or many minerals if sand looks brown,
Some sands in soil will be brown, yellow, or red because of Fe and/or Al oxide coatings.

7. Sand
Feels gritty
Considered non-cohesive – does not stick together in a mass unless it is very wet.

8. Sand Low specific surface area
Sand has less nutrients for plants than smaller particles
Voids between sand particles promote free drainage and entry of air
Holds little water and prone to drought

9. Silt < 0.05 mm to > 0.002 mm Not visible without microscope
Quartz often dominant mineral in silt since other minerals have weathered away.

10. Silt Does not feel gritty Floury feel –smooth like silly putty
Wet silt does not exhibit stickiness or plasticity or malleability

11. Silt Smaller size allows rapid weathering of non quartz minerals
Smaller particles – retains more water for plants and have slower drainage than sand.
Easily washed away by flowing water – highly erosive.
Holds more plant nutrients than sand.

12. Clay < 0.002 mm Flat plates or tiny flakes
Small clay particles are colloids
If suspended in water will not settle
Large surface area
spoonful = football field

13. Clay
Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod.
Easily formed into long ribbons
Shrink swell – none to considerable depending on the kind of clay.

14. Clay Pores spaces are very small and convoluted Water holding capacity
Movement of water and air very slow
Water holding capacity
Tremendous capacity to adsorb water- not all available for plants.
Soil strength- shrink/swell affects buildings, roads and walls.
Chemical adsorption is large

15. USDA Textural Classes Sandy soils (coarse) Silty soils (medium)
Do not hold water
Nutrient poor
Hold a lot of air
Silty soils (medium)
Hold a sufficient amount of water
Nutrient rich
Hold a sufficient amount of air
Clayey soils (fine)
Hold a significant amount of water
Nutrient rich/organic material poor
Holds an insufficient amount of air

16. Textural Triangle: 50% clay, 30% silt, 20% sand => Clay Soil