Soil as a natural resource undergoes various processes which lead to its formation. The topic highlights how weathering and erosion lead to soil formation, and further looks into soil profiles by focusing on soil horizons. It lastly looks into how soil erosion is a threat to the environment and proposes ways in which it can be managed.

1. SOIL
(Whitehouse, 2011)

2. INTRODUCTION
“Land is not merely soil, it is a fountain of energy
flowing through a circuit of soils, plants and animals.”
(Ersek, 2018)

3. SOIL DEFINITION
• It is a renewable resource that forms part of
the natural environment and is important for
most existence of life on earth (Farooqi, Rahman &
Cihani, 2015).
• The soil provides most of the nutrients
needed for plant growth and also helps purify
water.
• It is a mixture of rocks, air, minerals, decaying
organic matter, water and tons of
mircoorganisms e.g. bacteria (Farooqi, Rahman &
Cihani, 2015) (Karsen, Vanek & Zimmerer, n.d )

4. FORMATION
OF SOIL
• Soil forms from
processes of weathering
and erosion.
• The factors that
influence soil formation
are
1. Parent material
2. Climate
3. Time
4. Relief/topography
5. Organisms
(O’Sullivan et al, 2018)

5. 1. Parent material
• It is the original soil from bigger rocks, transported everywhere by
wind or water
• When a soil develops from an underlying rock, its supply of minerals
is dependent on that parent rock (Hirst, 1999).
(Hirst, 1999) (Hirst, 1999)

6. 2. Climate
• Moisture, temperature and wind are responsible for turning rocks or
trees into soil.
• They affect how parent material weathers caused by the type of
precipitation that occurs e.g. rain, wind, ice.
• Precipitation influences the type of vegetation which provides the
organic material and humus for the formation of soil. Temperature
affects the length of the growing season and the supply of humus
(Gautam, 2017).

7. 3. Time
• Soil can take a thousand years to
mature into fully mature soil that
allow sufficient depth for farming.
• It further enables the other factors
to gradually interact with each other
(Marchuk, 2009)
(Hirst, 1999)

8. 4. Relief/ Topography
• The direction a slope faces (aspects) influences the amount of
sunlight received.
• And the slope orientation determines the angle at which the sun hits
the surface and also affects run-off of soil (Gautam, 2017).
(NZ Soils, n.d)
(NZ Soils, n.d)

9. 5. Organisms
• Plants, animals and microscopic organisms interact with soil in
different ways.
• The more the vegetation, the greater the amount of organic matter
in that soil because when the plants die, the bacteria returns
nutrients back into the soil (Whitehouse, 2011).
• Earthworms play a major role in converting
organic matter into rich humus, improving soil fertility
(ViaAfrika, 2012)
(Johnson, 2014)

10. SOIL PROFILES
• Soil profiles are made up of a series of soil layers each called a
horizon.
• These extend from the surface to the parent rock material
• Four types of horizons
* The O horizon
* The A horizon
* The B horizon
* The C horizon
(Kretch, 2005)

11. The O and A horizons
• The O horizon is regarded as the humus, because it contains Organic
material such as leaves, pine, twigs and decaying animal tissues
(Krech, 2005)
• The A horizon is the topsoil and is the most fertile part of the soil. It is
dark in colour.
(ViaAfrika, 2012)
(ViaAfrika, 2012)

12. The B and C horizons
• The B horizon, also called subsoil is the less fertile part of the soil
because it is far from the organic matter,
• And the C horizon is where the partially weathered parent rock
material is found and is responsible for providing soil with minerals
(Kretch, 2005).
(ViaAfrika, 2012) (Kretch, 2005)

13. PHYSICAL
PROPERTIES OF
SOIL
• Soil has the
following physical
properties:
1. Soil colour
2. Soil texture
3. The pH index
4. Soil structure
(Fant, 2019)

14. 1. Soil colour
• This is the most visible and obvious trait of soils.
• Soil colours range from shade of black and brown to white and grey.
• The darker the soil, the more fertile it is, and the more nutrients it
contain,
• whereas, the lighter the soil, the less fertile it is and the less
nutrients it contains (Whitehouse, 2011).
(Farooqi, Rahman & Cihani, 2015)

15. 2. Soil texture
• Soil texture is dependent on the size of particles found in it.
• It further determines the porosity of the soil, its water holding
capacity and the type of plants that grow in it (Whitehouse, 2011).
• There are three main soil textures: sand, silt and clay.
• Sandy soil is not sticky, it feels gritty and does not have much
nutrients.
• Silt soil is smaller than sandy soil and it feels powdery like flour.
• And, Clay soil is very sticky when wet and very dry and powdery.

16. Soil texture pictures
(Whitehouse, 2015)
(Fant, 2019)
(Kretch, 2005)

17. 3. Soil pH index
• The acidity or alkalinity of the soil indicates the degree of leaching.
• Different plants require a different pH for best growth but a value
between 5 and 7 is suitable for most plants.
• The pH also influences the soil porosity, soil colour, soil texture and
the type of plants that can be grown on the soil (Amritha, 2016).

18. 4. Soil structure
• Soil structure refers to how soil grains are bound together to form a
larger unit (Gautam, 2017).
• The soil can be granular (biscuit crumbs) or columnar with some
vertical columns or blocks.
• Soil structure also gives off the health of the soil, as to whether it is
good, moderate or poor condition.
(Gautam, 2017)

19. SOIL EROSION
• Erosion refers to the wearing away of rocks or soil driven by wind or
water (Amritha, 2016).
• Wind erosion occurs when dust storms blow away more than 6 tons
of soil,
• and water erosion occurs when there are thunderstorms present
where each raindrop dislodges small amount of soil, resulting in run-
off of soil.
(ViaAfrika, 2012)

20. Factors that cause soil erosion
• Poor faring practices such as :
* Overgrazing of animals
* Ploughing against the contour
• Soil pollution caused by natural and manmade factors:
* Natural causes: Hurricanes
* Manmade: Urbanisation, domestic waste, mining.
(Thomlow, 2014) (Sri, 2015)

21. Effects of soil erosion
• Reduction in soil quality which results in food insecurity.
• Food insecurity leads to death of humans (Increase in poverty).
• Pollutes or contaminates water bodies such as rivers, oceans, etc,
resulting in water insecurity (Sri, 2015).
• Destructs and disturbs the interactions that occur in the ecosystem.
• Increases soil acidity
• Results in poor drainage

22. Soil management strategies
• Farmers should crop rotate and contour plough.
• Add humus to bind soil.
• Fencing paddocks and educating the public.
• Planting more trees
• Implementing environmental laws and taking legal action against
environmental offenders (Sri, 2015).
(ViaAfrika, 2012)
(Sri, 2015)

23. REFERENCES
• Amritha, K. T. K. (2016). ‘Soil profile, soil erosion, soil conservation, control on
floods’. [PowerPoint presentation]. Available at:
https://www.slideshare.net/AmrithaKTK/soil-profile-soil-erosion-soil-
conservation-control-on-floods-69527117?qid=a7b04e95-be5f-4eea-8f79-
2a3e4df376a5&v=&b=&from_search=2. Accessed: 17 August 2021.
• Ersek, K. (2018). ‘10 inspirational quotes on soil’. [PowerPoint presentation].
Available at: https://www.slideshare.net/KaitlynErsek/10-inspirational-quotes-on-
soil. Accessed: 20 August 2021.
• Farooqi, S., Rahman, A. & Cihani, J. (2015). ‘Soil profile’. [PowerPoint
presentation]. Available at: https://www.slideshare.net/Saadfarooqi/soil-profile-
54182486?next_slideshow=1. Accessed: 17 August 2021.

24. REFERENCES
• Fant M. O. (2019). ‘Introduction to soil: physical properties (part 1)’. [PowerPoint
presentation]. Available at: https://santacruzpermaculture.com/2019/06/soil-
physical-properties/. Accessed: 23 August 2021
• Gautam, P. (2017). ‘Physical properties of soil’. [PowerPoint presentation].
Available at: https://www.slideshare.net/GautamParghi/physical-properties-of-
soil-74587908. Accessed: 16 August 2021.
• Hirst, M (1999). Weathered olivine basalt. [Image]. Available from:
https://geodil.dperkins.org/h/2458.html. Accessed 21 August 2021.

25. REFERENCES
• Johnson, N. (2014). The secret to richer, carbon-capturing soil? Treat your
microbes well. Available at: https://grist.org/food/the-secret-to-richer-carbon-
capturing-soil-treat-your-microbes-well/. Accessed: 23 August 2021.
• Kretch, M. J. (2005). ‘Soil horizons’. [PowerPoint presentation]. Available from:
https://www.slideshare.net/Teach5ch/soil-horizons?qid=9ffe3b1a-0b18-47a9-
b1e6-8005cfff31d5&v=&b=&from_search=1 . Accessed: 24 August 2021.
• Karsten, H., Vanek S. & Zimmerer, (n.d). Top: pie chart showing the typical
physical composition of most soils used in food production. [Image]. Available at:
https://www.eeducation.psu.edu/geog3/node/1029 . Accessed: 20 August 2021.
• Marchuk, S. (2009). Relationships between soil properties and spatial geophysical
and terrain data in the Angas-Bremer Plains. Geology, 1(5). doi:
10.13140/RG.2.1.1362.9204.

26. REFERENCES
• NZ Soils. (n.d). Soil formation-topography. [Image]. Available
at:http://www.nzsoils.org.nz/Topic-Basics_Of_Soils/Topography/. Accessed: 24
August 2021.
• O’Sullivan L., McConnell B., Scanlon R., Walsh S. & Creamer R. (2018). Soil
formation. World Soils Book Series, 2(1): 11-36. doi: 10.1007/978-3-319-71189-8-
2.
• Sri, K. (2015). ‘Soil pollution’.[PowerPoint presentation]. Available at:
https://www.slideshare.net/kavyasri12/soil-pollution-ppt. Accessed: 17 August
2021.
• Whitehouse, M. (2011). ‘Properties of soil (teach)’. [PowerPoint presentation].
Available at: https://www.slideshare.net/MMoiraWhitehouse/properties-of-soils-
teach-9807299. Accessed: 17 August 2021.
• Via Afrika. (2012). Geography, Grade 11. Cape Town: Via Afrika Publishers.

27. THE END
(Whitehouse, 2011)