1. Soils/ Soil & Water Relationships

2. Soil
The top few inches of the earth’s surface that supports plant growth.
Formed from parent material (rocks and minerals) by a process known as weathering.
Productivity can be lost by soil degradation, such as erosion and pollution.

3. Four Principal Components of Soil
25% water
25% air
40-45% minerals
5-10% organic matter
Organic matter is material made from living or once living material.

4. Soil Formation
Soil is formed from parent material through a process called weathering.
Types of weathering are physical (mechanical) and chemical.
Mechanical/physical:
Plants & animals
Ice wedging
Chemical
water
Acids
oxygen

5. Factors that affect soil formation
Climate
Living organisms
Parent material
Time
How the soil weathered
Topography (the lay of the land)

6. Soil formation factors

7. Soil Particles (separates)
Soil has three particle sizes:
sand – the largest
silt - medium
clay – the smallest

8. Soil Texture
Soil texture is the relative percentage of sand, silt, and clay in a soil sample.
There are 12 soil textures.
Different plants prefer different soil textures.
Different textures have different relationships with water depending on the percentage of particles making up the soil.
Scientists use the soil textural triangle to determine the soil’s texture.

10. Ribboning soil to determine texture

11. Weathering results in particles
Sedentary soils are weathered from large patches of bedrock, so they remain in place and don’t really move.
Transported soils occur when particles are transported.
colluvial- moved by gravity (landslide, mudslide)
alluvial- moved by water (Delta, flood plains)
aeolian- moved by wind
glacial till- particles moved by glaciers

12. Organic matter/humus OM comes from living matter.
Dark colored soils indicate greater amounts of OM.
Benefits of OM in soil:
Makes soil porous.
Adds N and other nutrients to soil.
Helps hold water.
Furnishes food for living organisms.
Minimizes leaching.
Stabilizes soil structure.
Examples of living contributions to soil:
Roots
Algae
Fungi
Small animals
Insects
Slugs
Snails
Worms
Snakes
reptiles
Examples of non-living contributions to soil:
Peat moss
Leaf remnants
Compost
Grass clippings
Saw dust
manure

13. How should your soil smell?

14. Soil Profile

15. How should your soil look?

16. The soil profile has at least 4 horizons or layers.
Name
Colors
Structure
Process Occuring O
Organic
Black, dark brown
Loose, crumbly, well-broken
Decomposition A
Topsoil
Dark brown to yellow
Zone of leaching* B
Subsoil
Brown, red, yellow, gray
Larger chunks, dense, cement-like
Zone of accumulation C
Parent material
Varies by parent material
Dense, rocky
Weathering of parent material
*Leaching: when materials move through the soil profile; often materials like chemicals and pollutants are carried through the soil profile by water.

17. Soil horizons

18. Soil structure: soil particles stick together to make 4 types of aggregates
Granular
Platy
Blocky
Prismatic/columnar
Wedge

20. Soil Structure
Soils with more sand tend not to bind together and therefore do not show much structural arrangement
Clay give soil more structure
Soil structure is important in the absorption of water and the circulation of air
Structure of the A and B horizons should have medium and large particles for a loose structure that is good for water infiltration, root development, and seed germination.

21. Water below the surface
Surface material and soil texture will determine how rapidly water flows through the soil profile.
Water that fills up pore spaces between soil particles accumulate below the earth’s surface to create groundwater.
Porosity is a measure of the amount of open space compared to the total volume of rock/soil.
The ability of material to transmit fluid is permeability.
Sandy soils have a greater porosity and therefore a greater permeability than clay and silt. Clay is the least porous and permeable.

22. Water Relations
The size, shape, and arrangements of soil particles in a given texture will determine the ability of the soil to retain water.
Large pores conduct water more rapidly than small pores.
Water is more easily removed from large pores than small pores.
In sandy soils, water is lost due to gravity faster than plant roots can access it.

23. Plant water
After water is lost due to gravity, the remaining water is stored under tension in the pores of various sizes.
The smaller the pore, the greater the tension, and the more energy is required to the water.
Water cannot be removed by plants from very small pores.
Hygroscopic water, that which is water closely bound to soil particles, is also not available for plant use.

24. Plant water
Field capacity is water available to plants. It’s about 24 hours after soil saturation, after gravity has set in.
This varies depending on the soil, and can be extended by the irrigation method chosen.
The goal is to allow the plant to get as much water as needed, by altering irrigation to overcome the challenges of the soil texture and weather.
Permanent wilting point is when the point at which water is no longer available to the plant.

25. Soil –Water relationships: permeability & drainability
SAND
FAST
SILT
MEDIUM
CLAY
SLOW

26. Soil structure can change over time
Soil structure can change over time. Small and smaller particles make water infiltration more and more difficult.

28. The Water table Just below the surface is the zone of aeration.
Below that is zone of saturation.
Below the zone of saturation is the groundwater.
The upper boundary of the zone of saturation is the water table.
The depth of the groundwater/level of the water table varies with the precipitation and climate as well as what gets pumped out and used.
It is essential that the amount pumped out does not exceed nature’s ability to recharge the water source.

29. The Water Table

30. Aquifers
An aquifer is any underground, water-bearing layer that groundwater can flow through.
Aquitards confine the water.