3.4 The Soil System

3.4.1 Outline how soil systems integrate aspects of living systems.

3.4.2 Compare and contrast the structure and properties of sand, clay and loam soils, including their effect on primary productivity.

3.4.3 Outline the processes and consequences of soil degradation.

3.4.4 Outline soil conservation measures3.4.5 Evaluate soil management strategies

in a named commercial farming system and in a named subsistence farming system.

Soils are a major component of the world’s ecosystems. They link the atmosphere, lithosphere (rocks), biosphere (living matter), and hydrosphere (water). Soil itself is comprised of weathered bedrock, organic matter, air, and water.

Soil forming process consists of:

Gains and losses of material to and from the profile

Movement of water between the horizons

Chemical transformation within each horizon

Therefore soils are open systems in a steady-state equilibrium.

Soils are vital to humans, but take a long time to develop, so should be considered a non-renewable resource

• Sand– Mineral Content:

Low– Drainage: High– Water-holding

capacity: Low– Air spaces: High– Biota: Low– Potential to hold

organic matter: Low– Primary

Productivity: Low

• Clay– Mineral Content: High– Drainage: Low– Water-holding

capacity: High– Air spaces: Low– Biota: High to

Medium– Potential to hold

organic matter: High to Medium

– Primary Productivity: Quite Low

• Loam– Mineral Content:

Medium– Drainage: Medium– Water-holding

capacity: Medium– Air spaces: Medium– Biota: Medium to High– Potential to hold

organic matter: Medium to High

– Primary Productivity: High

• Soil Degradation – Decline in quantity and quality of soil

• Issues around it:– Water and Wind

erosion– Acidification (Toxic

metals)– Eutrophication

(Nutrient Enrichment)– Salinization (Too much

salt)– Soil pollution– Desertification

• Factors of erosion:– Erosivity (Rainfall

totals, intensity, and seasonal distribution)

– Erodibility (Suseptibility to erosion)

– Slope length and gradient

– Cover and management (Crop and cultivation practices)

– Erosion control practice (Soil conservation measures)

• Consequences of soil degradation:– Erosion: reduced crop

growth and yields, loss of soil fertility

– Salinization (Too much salt): Stunts crop growth, Lowers crop yields, Destroys fertility and plants, Damage to infrastructure, Reduction of water quality

– Desertification: Economic loses, Lower living standards, Major threat to biodiversity, Prolonged droughts

• Mechanical methods to reduce water flow

• Contour Ploughing – Takes advantage of ridges formed at right angles to the slope to slow water

• Terracing – Slope is broken up into a series of flat steps with raised levees at the edge.

• Land around gullies and ravines can be fenced off and planted with small trees.

• Check dams can be used to slow water in gullies.

• Cropping and soil husbandry methods against wind and water damage

• Maintaining a crop cover as long as possible which is often done through Multi-cropping.

• Keeping in place stubble and root structure of the crop after harvesting

• Planting a grass crop: Maintains action of the roots in binding the soil, and minimizing wind action.

• Management of salt-affected soils

• Flushing the soil with water and leaching the salt away

• Application of chemicals (like gypsum – calcium sulfate – to replace the sodium ions on the clay and colloids with calcium ions.)

• Reduction in evaporation losses to reduce the upward movement of water in the soil

• You will do this with the worksheet you receive. If there is time, we will talk about this as a class.