1. How Much Fertile Soil Does Earth Have?
Soil and Ecosystems – V2
How Much Fertile Soil Does Earth Have?

2. Soil – Essential for Plants
Terrestrial plants need soil to grow. Roots anchor plants in soil. Roots absorb nutrients like nitrates, nitrites, potassium and phosphorus from soil.

3. Soil Profile
The three layers of the soil profile are topsoil, subsoil and bedrock.

4. Three Layers of the Soil Profile
1. Topsoil – mostly made of decaying matter called humus. There are also small inorganic particles and lots of living organisms like worms, bacteria and fungus. Topsoil has the nutrients for plants.

5. Three Layers of the Soil Profile
2. Subsoil – a very compact layer made mostly of inorganic rock, sand and clay particles. 3. Bedrock – this solid rock means water cannot pass through.
Can you see the soil layers?

6. Water table
When water reaches the bedrock ground water forms. A well must be dug so that the tube goes
below the water table which is the top surface of the ground water.

7. Three Types of Topsoil
The types of topsoil are determined by the amount of humus and the amount of inorganic sand, clay and silt particles. 1. Loam Soil – the best soil for crops has lots of humus and inorganic particles of different sizes for air pockets. Loam holds water well and dries out slowly.
2. Clay soil – the tiny clay particles make root growth difficult and clay holds too much water.
3. Sandy soil – Large sand particles let water flow through quickly taking away nutrients and drying out too fast.

8. The Soil Triangle
The soil triangle helps judge the type of soil by the percent of sand to clay to silt.
Use the soil triangle to find percentages of the following particles in medium loam.
Draw lines to the star and read percentages.
Sand? ______
Clay? _____
Silt? ______
40%
20%
40%

9. Loam – The Best Topsoil
Good loam soil surrounds roots with humus, air, water and nutrients in different sized particles of sand and clay.

10. Human Actions Impact Topsoil
The roots of trees and plants prevent soil from eroding with wind or rain water runoff. Deforestation leads to huge losses of topsoil from rainwater runoff. Which country below prevents deforestation?

11. Human Actions Impact Topsoil
Farming also leads to soil degradation from use of pesticides that kill all the microorganisms, or irrigation that adds a little more salt every year.

12. Human Actions Impact Topsoil
If farmers apply excess fertilizer or put fertilizer on the soil before it rains, the fertilizer runs into rivers and lakes causing eutrophication.

13. Human Actions Impact Topsoil
Humans can protect topsoil by protecting forests. Good farming practices like crop rotation and limited applications of pesticides can protect good quality topsoil.