1. Agricultural Science 1: Soil Science
At the completion of this unit, students will be able to:
Explain the components of soil
Investigate soil texture and structure
Explain soil profile
Explain what soil color indicates
Examine moisture-holding capacity and the characteristics of soil water
Explain soil pH
Describe the meaning and importance of soil fertility
Investigate soil degradation
Describe soil erosion and management practices
Identify careers in soil science and determine educational requirements, working conditions, and earning potential for those careers

2. What is soil?? Is it dirt? Is it mud?
Objective A: Explain the components of soil
What is soil??
Is it dirt?
Is it mud?

3. Objective A: Explain the components of soil
What is soil?
Soil is the top few inches of the earth’s crust and the medium that plant roots grow in.

4. Soil Components There are four major soil ingredients: Minerals Water
Objective A: Explain the components of soil
Soil Components
There are four major soil ingredients:
Minerals
Water
Air
Organic Matter

5. Objective A: Explain the components of soil
Soil Components
Minerals and organic matter are the solid particles in the soil.
Water and air fill the spaces between the particles
Soil also contains living organisms—some small, some large.

6. Mineral Materials
Inorganic elements are compounds that naturally occur.
Minerals in soil comes from rocks and other materials that have weathered

7. Mineral Materials
Sand
Silt
Clay
(and other trace minerals)

8. Mineral Materials: Sand
Sand is the largest-size mineral particle in soil

9. Mineral Materials: Sand
Sand does not hold water well
Soils that are high in sand are not fertile because water moves through it quickly and washes the nutrients away

10. Mineral Materials: Silt
Silt particles are smaller than sand—midsize particle

11. Mineral Materials: Silt
Silt particles fill spaces between sand particles
Sometimes deposited by water when land is flooded or washed into the oceans where streams empty

12. Mineral Materials: Silt
The Mississippi River Delta is an example of a land mass that was developed by silt settling from the flood water of the Mississippi River.
Can you think of another
Famous river delta?

13. Mineral Materials: Clay
Clay is the smallest particle in soil

14. Mineral Materials: Clay
Clay fills the spaces between sand and silt particles
It gives soil the ability to hold water
Soils that are high in clay are slow to dry out after a rainfall

15. Mineral Materials: Clay
Clay holds minerals that plants need for growth

16. The soil texture triangle is a great visual way to examine what soil is made of. To determine what your soil is, follow these instructions:

17. Soil Texture Triangle How To:
To find the type of soil, follow these steps:
1. Find the Clay % on the left side of the triangle, and at that level, draw a straight line going left to right.
2. Find the Silt % on the right side of the triangle and at that % level, draw a line from the top right to the bottom left.
3. Find the Sand % at the bottom and draw a line from the bottom right to the top left.
4. Look for where the lines cross, and that will tell you your soil type!

18. Other Mineral Materials
There are 4 Major Minerals:
Calcium (Ca)
Phosphorus (P)
Nitrogen (N)
Potassium (K)

19. Other Mineral Materials
When reading the label
on a bag of fertilizer,
the 3 numbers on the
bottom stand for
Nitrogen
Phosphorus
Potassium

20. Organic Matter
Organic matter is plant and animal remains in various stages of decay.
The decaying organic matter releases nutrients
These soils are dark brown or black, are high in nutrients, and hold a lot of water

21. Organic Matter Soils with high organic matter are more productive
The soil is more easily tilled and made into a seedbed for planting

22. Air Air fills some of the space between soil particles.
Plant roots need air to live and grow
Some plants need to adapt to different environments in order to get the air they need.

23. Air
For Example:
Cypress trees grow in wet places. For these trees to have hair, the roots grow structures known as “knees”. The knees rise a few feet above the water level.

24. Air Let’s test the amount of air in a soil sample!
1. Collect a clod of soil
2. Spray with polyurethane and let sit for 1-2 minutes.
3. Place the soil clod in a jar of water and watch the bubbles form!
The more bubbles, the more air!

25. Water Water is an important nutrient for plant growth.
It is held between soil particles and sticks to their surfaces
Soil that is too wet or too dry will not support the growth of most crops and ornamental plants

26. Soil Profile A way of looking at a cross section of soil
Soil has layers known as horizons
O Layer: Organic Material
A Layer: Topsoil
B Layer: Subsoil
C Layer: Bedrock

27. Soil Profile
O Horizon: “O” Stands for Organic Matter. Dead plant and animal residues in various stages of decomposition are here.

28. Soil Profile
A Horizon: The topmost mineral horizon, or topsoil. Many soil organisms live here and it is typically fertile. Most plant roots grow here.

29. Soil Profile
B Horizon: This layer is called subsoil and is less weathered and more compact than the A Horizon. Few plant roots penetrate this layer.

30. Soil Profile
C Horizon/Bedrock: This is un-weathered geologic material where soil is formed. It is very dense and typically requires large machinery or blasting to dig through.

31. Soil Color Soil comes from minerals and organic matter.
Color often tells us what quality the soil is. Usually, the darker the soil, the more fertile it is.

32. Soil Color Bright Colored Soils: Brown, Red, or Yellow
These colors mean:
Good Drainage
Oxidized Iron

33. Soil Color Dull Colored Soil: Gray or Olive Gray These colors mean:
Poor Drainage

34. Soil Color Dark Colored Soil: Dark Brown, Black These colors mean:
High levels of organic matter
Very fertile

35. Soil Color Mottled Soil: Clumps of various colors. These colors mean:
Variability of moisture in the soil
Spotted appearance

36. Soil Chemistry-pH Levels
pH=Acidity or Alkalinity
pH is based on a scale from 1 to 14
1=Most acidic
14=Most alkaline
7=Neutral
Most soils are between 4-9
Most plants do well in an acidic soil-6.6 being the best

37. Soil Fertility
The ability of soil to support plant growth and the many beneficial processes that occur in soil.

38. Soil Degradation
Soil Degradation: The decline in soil quality caused by its improper use.
Examples:
Loss of organic matter
Decline in soil fertility an structural condition
Effects of toxic chemicals, pollutants, excessive flooding

39. Soil Erosion What is soil erosion? What causes soil erosion?
The removal of soil by water and wind
What causes soil erosion?
Slope
Water splash, runoff
Wind drying and blowing soil
Accelerated erosion caused by farming and construction

40. Types of Soil Erosion
Sheet Erosion: The gradual and fairly uniform removal of surface soil.
Caused by splash erosion and slow runoff.

41. Types of Soil Erosion
Rill Erosion: Small streamlets that are cut into the soil surface by running water.
Caused by runoff

42. Types of Erosion
Gully erosion is rills that have become extremely large.
Caused by uncontrolled runoff for an extended period of time.

43. Types of Erosion
Sandblows: The result of wind picking up soil particles and carrying them away.
Caused by the removal of vegetative cover, which allows the soil to become dry and loose.

44. Soil Conservation Plant Trees Terraces No/Minimal Till Farming
Contour Plowing
Crop rotation
Soil pH
Water in the Soil
Salinity Management
Soil Organisms
Indigenous Crops