Introducing our Grade 12 Agricultural Sciences [Paper 1] Notes - the ultimate study companion for students undertaking paper one of their Agricultural Sciences exam. This comprehensive notebook covers essential topics such as animal feed, reproduction and parasite control, all presented in a colorf...
, GEOLOGY > SOIL SCIENCES
SOIL TEXTURE TYPES OF SOIL PARTICLES :SOIL FRACTIONS
CLAY SAND
→ relative amount of sand, silt & clay in the soil W smallest soil particles [>0.002mm W largest soil particles (coarse) [0.5
→ physical & chemical properties of soil diameter] - 2.0mm diameter]
→ determination of type of crops to plant W large surface area & negative W seen without a microscope or
ONLY inorganic solid fraction of soils charge [ ↑ water & plant magnifying glass
Z proportions of sand, silt and clay = % [soil Labouratory] nutrients] W sandy soils= < 2o% clay, > 5o%
W affects shrinkage & expansion, sand
Z Texture classes = based on the composition of the soil
plasticity, water holding capacity W [sand, loamy sand, sandy loam]
& soil strength W soils are divided according to
SOIL TEXTURE TRIANGLE [∆] W seen only with a microscope particle sizes: coarse, medium and
u classes are classified with increasing proportion of fine particles: W dry particles: smooth and fine
[sand, loamy sand, sandy loam, loam, silty loam, silt, sandy clay loam, clay powdery W contains mineral quartz (SiO₂)
loam, silty clay loam, sandy clay, silty clay, clay] W wet then dried: hard
u Sand, silt and clay soil particles = soil separation → help scientists W wet particles: smooth, tough,
understand soil behaviour [nutrients, water holding capacity] holds shape easily
W clay soil = 3o–35% clay
[sandy clay, silty clay, clay]
Loam → equal amount of sand, clay
& silt particles
, REASONS : KNOW TEXTURE CLASS
u Determine type of crops that can be planted = maximise productivity [seed SOIL PROFILES [MORPHOLOGY]
germination]
u Type of irrigation system to be installed [sprinkler / drip irrigation] BUT
[clay soil = flood irrigation] → water holding capacity
SOIL HORIZONS
u What kind of drainage can be used [sandy = no extra; clay soil = → layer parallel to the soil surface whose physical, chemical and biological
waterlogged easily] → drainage properties properties differ from the layers above and below. Horizons are in many
u root development cases defined by distinct physical features, primarily colour and texture
u pesticide movement
u minimise environmental damage [cover crop in sandy soils = wind erosion ↓ ]
PROFILE HOLE
→ assessment, evaluation and quantification of the type and extent of soil
cover, soil health and cultivation, soil depth, soil type, soil stratification in
INFLUENCE OF SIZE : SOIL BEHAVIOUR upper, middle and lower layers
CLAY SOIL [small particles] SANDY SOIL [large particles] SOIL PROFILE
CHEMICAL Large area Small total area
→ the vertical section of soil from the soil surface down to where the soil
REACTIVITY
DRAINAGE & Poorly / limitedly drained High % macropore space = good meets the underlying rock
AERATION and aerated = waterlogged in aeration & drainage = = easy to
rainy seasons [ ↓ macropore handle in cultivation MASTER HORIZONS
space]
WORKABILITY Heavy soil = difficult to till Easy > ↓ cohesion forces & soil • organic horizon
[hard if dried out] fraction [light soil] O-HORIZON • contains undecomposed organic litter / decomposed
organic matter & humus
EROSION Decomposes faster > large Decomposes more slowly > small
• surface horizon or topsoil
POTENTIAL surface area surface area
A-HORIZON • contains inorganic material [humus & mineral
WATER HOLDING Large surface area = high Low water holding capacity =
particles]
CAPACITY water holding capacity = poor for dryland farming • underground
small micropores = difficult [micropores = drainage] B-HORIZON • illuminated zone [concentration of clay & iron,
to irrigate aluminium & manganese oxides]
GROUND FRUIT High = large surface areas & Absence of colloids = fertility ↓ C-HORIZON • slightly weathered unpaved material [substrates]
ABILITY colloids = plant nutrients [no absorption of plant matter] • solid rock / consolidated material
PH OF SOIL Alkaline Acid R-HORIZON
CROP Not suitable for deep rooted Most vegetables
White • underground horizon
crops > deep clay layers = E-HORIZON
• eluted zone containing little or no organic matter
limited roots Bluish, green / • usually wet and clayey in texture, stains may present
G-HORIZON
greyish again > reduction > anaerobic
, SOIL PROFILES SOIL CLASSIFICATION
INFLUENCE SOIL FORMATION & DEVELOPMENT : SOIL PROFILE
SOIL CLASSIFICATION
→ = grouping of soil with similar properties / characteristics
W Mother Material: unconsolidated material that provides the most soil [morphological, physical, chemical & mineralogical]
horizon character.
W Climate: rainfall and temperature affect the rate of weathering. TAXONOMIC SOIL CLASSIFICATION SYSTEM
W Topography: arrangement of physical features (e.g., slope) that influence
the vegetation and soil type of a location.
W Time: soil formation is extremely slow → younger soil profile more closely LANDFORMS LAND FAMILIES
reflects the parent material. u an upper or general level u a lower and more specific level
W Organisms: type and number of organisms are important → influenced by u defined by a unique vertical u they share characteristics of the
plants sequence of horizons. form
u 73 landforms u they are differentiated within the
u SPECIFIC COMBINATION & form based on other
SOIL HORIZONS > SOIL TYPES
SEQUENCE > diagnostic horizons = characteristics.
Mature / old soil A A inferences about land u There are 404 soil families
u significantly developed soil profile B E u = represents specific combination u Subdivision of landforms
u B-horizon = clay silicate, or oxides C B of soil formation conditions u DIFFERENCE FROM EACH OTHER
[aluminium, manganese and iron]
u yellowish, reddish or dark in colour
R C [features > diagnostic horizon & [soil texture, pH, lime content &
[parent material = high in white successions > soil profile] organic matter + water holding
calcium carbonate] capacity]
u influence = climate, vegetation & Steps involved in binomial soil classification
system:
drainage u delineate master horizons
Young soil A A u identify diagnostic horizons (subdivisions of master horizons)
u minimal horizon C R u name a landform
u A-horizon = directly above R-horizon u identify distinguishing family marks
u parent material = strongest influence u identify soil family
Wet / waterlogged soil A O A u determine texture class of A horizon and add it to the soil family name →
u poorly drained E G G sandy loam, loam
u rubbery consistency G
u shrinks, hardens and cracks into MASTER HORIZONS DIAGNOSTIC HORIZONS
squares when it dries out
→ ground layers = similar → landforms = formation processes
Eroded soil B
→ appearance of soil > soil profile → contains whole / parts of master
u topsoil = wind, water or gravitational C horizons
creep removed
u B-horizon = upper layer
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