1. Soil Texture, Structure, and the Nature of Soil
Soils Rock!!!

2. Enduring Understanding
Plants can grow in a wide variety of media which can be manipulated to produce healthy plants.
Soil is the basic medium of most terrestrial plants on earth.

3. Essential Questions
How do plants interact with the natural and artificial elements in their environment?
How does the geology of the environment effect plant growth?
How do humans impact soil?
What is the difference between a plant’s food and its nutrients?

4. What’s In Soil 50% Pore Space (25% air, 25% H2O)
45% Minerals (Sand, Silt, Clay)
5% Organic Matter (decaying material)
Soil Formation

5. Organic Matter Dead plants and animals Compost
Essential for plant growth
Made of carbon-based material
Replaces nutrients

6. SOIL AIN’T DIRT
“Dirt” should only refer to displaced or dead soil!

7. Why Do Plants Need Soil? Nutrients Water Stability/support
Plants can be grown in artificial soil called growing media (we use this in the greenhouse).

8. Why Do We Need Soil? FOOD! Plant products (ethanol, wood, etc.)
Ecotourism

10. Good Soil No Soil
Valleys Desert Volcanic Regions Beach Mountains

11. Soil Texture Sand-large particles Silt-Medium Particles
Clay-Small Particles
Sand < 2 mm to 0.05 mm
Silt < 0.05 mm to mm
Clay < m

13. Course Fragments (NOT SOIL!)
>2mm in diameter
Gravel
Pebbles
Rocks
Boulders

14. Sand < 2 mm to > 0.05 mm Porous Doesn’t hold water or nutrients
Gives good drainage

15. Silt < 0.05 mm to > 0.002 mm Flower like feeling Medium size
Typically made from the mineral quartz
Not sticky
Erodes easily
Holds nutrients better than sand

16. Clay
< mm
Small
Holds water and nutrients very well (sometimes to well)
Very sticky holds soil together
It is important to have in soil contrary to popular belief.

17. Soil Texture is…
The percentage of sand, silt and clay

18. Texture is important because it affects
Water holding capacity - how well the soil holds available water
Permeability - the ease in which air and water may pass through the soil
Soil workability - the ease with which soil may be tilled and the timing of working soil after a rain
Ability of plants to grow - some crops, like carrots and onions, have difficulty growing in fine textured soils

19. How do we determine texture?
Lab method
The soil is measured in a lab by separating the three major parts (sand, silt, and clay)
Field method
This method involves taking a sample in the field and spraying it with water and forming a ribbon in your hand. This method is more technically known as the ribbon method.

20. Lab Method
When testing in the lab an accurate measurement can be made resulting in 12 different textural classes of soils
Silt
Silt loam
Silty clay loam
Loam
Sandy clay loam
Sand
Sandy loam
Sandy clay
Clay loam
Silty clay
Clay

21. Loam is the Best!!! Perfect blend of soil particles Good drainage
Good moisture holding capacity
Good black dirt

22. The Ribbon (Field) Method
When performing the ribbon method the measurement is not as accurate but 5 classifications gives one a pretty good idea what the soil is like
Fine-textured--ribbon forms easily and is long and flexible
Moderately fine-textured—a ribbon forms but it breaks into pieces ¾ to 1 inch long
Medium-textured—no ribbon forms. The sample breaks into pieces less than ¾ of an inch long
Moderately coursed-textured---no ribbon forms. The sample feels gritty and lacks smoothness.
Coarse-textured—no ribbon forms. It is composed almost entirely of gritty material

23. The Lab Method First put soil in a glass jar
Then fill the jar with water
Add soap
Shake
Let it sit over night and watch it separate.
Sand falls to the bottom, silt settles next, then comes clay and finally organic matter

25. Soil Structure
The arrangement of soil particles into aggregates of various sizes and shapes
Natural aggregates are peds
Clumps caused by tillage are clods

26. There are two steps that form structure
1) A clump of soil particles sticks loosely together through:
Plant roots surrounding the soil and separating clumps
Freezing and thawing of soil
Soil becomes wet and then dries
The soil is tilled
Fungal activity

27. 2) Weak aggregates are cemented to make distinct and strong
2) Weak aggregates are cemented to make distinct and strong. Clay, iron oxides, and organic matter may act as cements. When soil microorganisms break down plant residues, they produce gums that also glue peds together.

28. Soil structure is important for several reasons
It improves soil tilth
It improves permeability
It resists the beating action of raindrops, minimizing the formation of crusts that reduce crop stands.

29. There are eight types of structures
Granular-aggregates are small, non-porous and tightly held together
Crumb-aggregates are small, porous, and strongly held together
Platy-aggregates are flat or plate-like slowing percolation
Prismatic or Columnar-aggregates are prism like that are very tall
Blocky-aggregates are block-like with six or more sides
Structureless- there is no structure
Single grain-no aggregates
Massive-soil particles cling together and form huge masses

31. Soil Profile

32. Definitions Clods Loam Peds Permeability Soil structure Soil Texture
Soil Workability
Texture Triangle
Water Holding Capacity