1. Topic 5.1: Introduction to soil systems
Starter:
What is soil?
Why is soil so important?
Where does soil come from?

2. Soil is a complex ecosystem
Minerals (Rocks)
Organic material (Humus)
Gases (Air)
Liquids (Water)
The exact mix of these four portions give soil its characteristics.
In addition there are also:
Many plants and animals (and micro-organisms)

3. The majority of food we consume depends ultimately upon soil.

4. “Too many people have lost sight of the fact that productive soil is essential to the production of food”
Hugh Hammond Bennett was a pioneer in the field of soil conservation.
He was convinced that soil erosion was a serious problem facing the planet.
It reduces areas in which crops can be grown.

6. Soil systems are dynamic
Many complex systems are interlinked
Water cycle
Nutrient cycles (e.g. Nitrogenous compounds)

7. Soil Horizons
Using the help sheet create your own soil profile diagram and describe each of the horizons.
You do not need to know their names, but you do need to know the letters.

8. Soil Horizons O Horizon:
New deposited organic matter is being broken down (decomposed) by a variety of different organisms.

9. Soil Horizons A Horizon: Build up of humus.
Partially decomposed organic matter and fine mineral particles.
Dark layer or brown or black organic material – humus layer
Water-logged soils have reduced decomposition

10. Soil Horizons
E Horizon:
Less humus and more inorganic minerals.

11. Soil Horizons B Horizon:
Clay and Iron salts deposited in this horizon.
Soluble minerals and organic matter deposited from layer above

12. Soil Horizons
C Horizon:
Mainly weathered rock

13. Soil Horizons
R Horizon:
Parent or bed rock

14. This is known as leaching.
Water carries particles up or down the layers - translocation
In colder, wet climates water flows down into the soil, dissolving minerals and transporting them downwards.
This is known as leaching.
P>E
In hot, dry climates precipitation is less that evaporation (P<E).
This means that water moves up through the layers.
As water evaporates it leaves the minerals behind, this is called salinization.
Can also happen with irrigation.

16. What type of soil? 20% Clay, 40% Silt, 40% Sand

17. Loam soils are best for agriculture
Sand ensures good drainage and good air supply
Clay retains the nutrients
Silt hold the sand and clay together and make the soil easier to work with

18. Porosity – The space between the particles
Permeability – The ease at which gases and liquids can pass through the soil
Clay soils – High porosity (macropores), low permeability, high nutrients but inaccessible.
Sandy soils – High porosity (micropores), high permeability
Loam soils – Best of both

19. Soil sustainability Non-renewable recourse
1 tonne ha-1 yr-1 = mm
NPK – needs to be replaced