SOIL - OUR BREAD BASKET

INDEX What is soil? What is the importance of soil? What are the different layers of soil? How does soil form? What is calcification and salinisation? What factors influence soil formation? What is the human impact on soil?

The ingredients of soil

uppermost layer of loose inorganic, weathered rock … Soil is the … uppermost layer of loose inorganic, weathered rock … mixed with organic matter, air and water. Varies in depth from few cm to 100’s of metres.

Which of these soils are best for agriculture? Explain Loamy Soils Sandy Soils Clay Soils

Soil is essential because it … provides nutrients and water to plants. anchors plants. provides a habitat for animals and micro-organisms. is used to grow crops.

Soil Profile Soil has different layers or horizons: O Horizon

What are the characteristics of each layer ? Humus: Fallen leaves, organic debris + partially decayed organic matter. Topsoil: Rich in humus, porous, partially decomposed organic matter + inorganic minerals. Water trickles through and carries nutrients to layer B. (leaching) O Horizon A or eluvial Horizon Topsoil True soil (solum) B or illuvial Horizon Subsoil: accumulation of nutrients, clay, minerals from A. Subsoil Parent material: Partially broken down bedrock, forms soil. C Horizon Regolith Bedrock: impenetrable layer of parent rock, solid. R Horizon Bedrock

Explain how the following processes lead to soil formation? Soil forming is continuous as a result of processes such as: Weathering Humus formation Leaching/ Uitloging Eluviation/ Eluviasie illuviation/ illuviasie

Weathering weakens and breaks down the parent rock. Soil organism decompose organic material to form humus Eluviation is the movement of fine particles to the B horizon Leaching by water carries dissolved minerals and nutrients downwards through the soil Illuviation is the accumulation of dissolved minerals, particles and nutrients in the B horizon

What is calcification and salination? Dry regions have rapid evaporation rates Irrigation causes certain salts like sodium, magnesium …. and calcium to be deposited in upper layers of soil. This reduces infiltration … and nutrients become inaccessible to plants. Soil gets a hard crust (calcification) White, salty, toxic crust (salination)

Soil Forming Factors Soil formation is influenced by five soil forming factors: Parent material / Moedermateriaal Relief or topography / Reliëf of topografie Time or age of soil Climate / Klimaat Actions of organisms These factors are all interdependent. Passive factors Active factors

How does parent material influence soil formation? Bedrock from which the soil weathers … influences colour, mineral content, texture. Granite: light coloured soil Rocks with iron: reddish soil Sandstone: has lots of silicon due to quartz Sandstone: will have a sandy, well-drained texture.

How does climate affect soil formation? Amount of rain determines the rate of …. chemical and biological processes... and leaching. Rainfall Determines rate of decomposition… and weathering. In warm tropical areas: organic matter is destroyed rapidly. little humus remains… and soil is deep, but infertile In dry, hot/cold regions: decomposition is slower. poor shallow soils result. Temperature Determines rate of evaporation…. and removal of topsoil. Wind

Actions of organisms: Age of Soil: Topography: Bacteria + fungi decompose matter into humus. fast in tropical regions. too slow in cold regions. Humus forms best in temperate grasslands. Earthworms and termites aerate + mix soil. Age of Soil: Soil forms slowly. Mature soils have well-developed horizons e.g. old landscapes Immature soils have fewer horizons + shallower e.g. river + glacial deposits. Topography: Steep slopes have shallow soils i.e. carried downwards Gentle slopes have deep, well-drained soils. Hollows e.g. marshes have poorly-drained, thick, dark soils.

Topography

Human Impact on Soil Quality Soil forms slowly. 1cm in 400 yrs productive soil takes 2-3000 yrs Soil is non-renewable destroyed faster than it’s being replaced Soil Degradation: decline in soil quality to sustain vegetation Soil Erosion: The removal of topsoil at such a fast rate that it can no longer support its natural vegetation.

Rate of soil erosion in South Africa

Click on A and then B for further information Causes of Soil Erosion Overgrazing Deforestation Click on A and then B for further information Parallel ploughing: Leads to more runoff of rainwater that form gullies and later dongas.

Deforestation Deforestation occurs due to population pressure when: Trees are removed for firewood Vegetation is cleared for agriculture and for development of settlements Soil becomes exposed. Wind and water removes fertile topsoil at a faster rate. More runoff occurs and dongas form. Vegetation binds soil and retains water so less surface runoff occurs. Forest cleared for cultivation

Overgrazing When too many cattle graze on land that exceeds carrying capacity of soil. Vegetation is damaged and soil is trampled. Vegetation dies and soil is left barren and exposed to soil erosion. Avoid overgrazing by: Reducing the number of cattle Rotational grazing

Results of Soil Erosion The loss of topsoil. This leads to lower productivity. Run off increases as a result of soil erosion. Dams silt up (silting of dams) . Conservation measures are costly. Can lead to severe desertification

Preventing soil erosion

Proper road and rail construction Consider carrying capacity Rotational grazing Strip cultivation Add humus and fertilizer Proper road and rail construction Consider carrying capacity

DESERTIFICATION What is desertification? process by which once productive farmland is converted to a wasteland or desert. Soil cannot further support any vegetation.

The Process of Desertification Sustainable community Higher demand for food Over-cultivation Overgrazing Deforestation Cultivation = adequate fallow time for soil to recover No population pressure on land = balance with carrying capacity of land Improved medical services = Higher birth rate

The Process of Desertification Dongas form = Water erosion