1. INTRODUCTORY SOILS

2. Subject Outline Introduction What is Soil Functions of Soils
Composition of Soils
Soil Formation

3. Why Soil Science?
Soil is an essential part, and some would argue, the most important component of the terrestrial ecosystem

4. Beyond that, Soil is an environmental interface Lithosphere -rocks
Atmosphere -air
Hydrosphere -water
Biosphere –living organisms

6. What is soil Concepts of soil differ greatly among users of soil
Mining engineer
Civil engineer
Home owner
Farmer

7. Definition
… natural product formed from weathered rock by the action of climate and living organisms modified by topography over a period of time.

8. The Soil Profile
Alabama –Bama Soil

9. How different can they look like?
Tanzania
Quebec
Sri Lanka
Brazil
Virginia
Montana

10. Functions of soils

11. Functions of Soils Medium for plant growth Regulator of water supplies
Recycler of raw materials
Habitat for soil organisms
Engineering medium

12. Soil as Medium for plant growth
Physical support
Air
Water
Temperature moderation
Nutrient elements
Protection

13. Soil as Regulator of Water Supplies
Soil regulates both the quality and quantity of water in rivers, lakes, and underground aquifers
Quantity of water supplies
Some of the water may be stored in the soil and used by trees and other plants
Quality of water supplies
Water is purified and cleansed as it soaks through the upper layers of soil.

14. Soil as Recycler of Raw Materials
Soils play a role in geochemical cycles
Assimilate organic waste
Turn it into beneficial humus
Convert the mineral nutrients into plant and animal usable forms
Returning carbon to the atmosphere to be used for photosynthesis again

15. Soil as Habitat for soil organisms
Handful of soil is home to billions of organisms in thousands of species
How does this happen?
Micro-environment differences
Pore spaces
Moisture
Temperature
Organic matter

16. Soil as Engineering Medium
Soil is firm and solid
Good base to build structures
Soils differ in stability
Designs for structures are different for soils
Physical properties influence engineering uses

17. Composition of Soils
Soil consists of three major phases OR four components:
Solid phase (Soil Minerals)
Liquid phase (Soil Water)
Gas phase (Soil Air)

18. Components of Soil

19. Soil Solid Phase (two components)
Inorganic minerals
Soil minerals are either primary or secondary minerals
Primary minerals were formed in the original igneous rocks.
Secondary minerals formed in soil by weathering of the primary minerals.
Organic matter (humus).
Humus is the product of the decay of organic residues such as wood, leaves, and other biological materials.

20. Soil water (soil solution)
Water is vital to the ecological functioning of the soil.
Soil solution which contains water, dissolved ions, molecules and gases.
Soil water is different from drinking water in 2 ways:
Soil water is held by many types of forces within the pores of the soil.
Soil water is never pure but contains hundreds of dissolved organic and inorganic compounds.

21. Soil Atmosphere
contains similar gases as found in the atmosphere above the soil
But often in very different proportions.
Usually higher in carbon dioxide and lower in oxygen than the atmosphere.

22. Interaction of the Components
The components interact to determine the nature of a soil e.g.,
soil moisture controls air and nutrient supply
mineral particles control water movement
Organic matter controls arrangement of minerals which influence pores that determine water and air relationships

23. Soil Formation

24. Soil Formation Five factors of soil formation
Weathering of rocks and minerals
Processes of soil formation

25. Five factors of soil formation
s = f(cl, o, r, p, t…)
Where:
s = any soil property
cl = climate (rainfall & temperature)
o = organisms (biota)
p = parent material
r = relief (slope aspect and position)
t = time (relative age of soil formation)

26. 1. Parent Material
Nature of parent material influences the characteristics of soils
E.g., texture of sandy soils is determined by parent material
movement of water is controlled by texture of the parent material
Influences the chemistry of the soil
Influences the type of clay minerals present in soil.

27. Weathering of Rocks and Minerals
What is weathering?
.. the modification or breakdown and destruction of the physical and chemical characteristics of rocks and minerals and carrying away the soluble products.
..the nature of the breakdown depends on the type of material

28. Types of Rocks Igneous rocks Sedimentary rocks Metamorphic rocks
Form from molten magma
Granite and diorite
Sedimentary rocks
Compacted or cemented weathering products from preexisting rocks
Sandstone and shale
Metamorphic rocks
Formed by change in the form of other rocks
Gneiss, marble, and slate

29. Two main types of weathering
a) Physical (Mechanical) weathering
.. Causes rocks to disintegrate into smaller pieces without affecting their composition
Factors:
Temperature
Abrasion by water, ice and wind
Plants and animals

30. b) Chemical weathering
.. Degradation of rocks and minerals by the chemical activities of water, oxygen, and microbial action
Factors of Chemical weathering:
Hydration
Hydrolysis
Dissolution
Carbonation
Oxidation-reduction
Complexation

31. Hydration Process of binding of water molecules to a mineral
Hydrolysis
Splitting of water molecules into its components. Split components in turn attack the minerals.
Dissolution
Process of hydrating of ions until they become dissociated

32. Carbonation Oxidation-Reduction Complexation
Carbon dioxide dissolves in water to form carbonic acid which accelerates chemical breakdown of materials
Oxidation-Reduction
Minerals that contain Fe, Mn,or sulfur are susceptible to this reaction when exposed to environments different from the ones in which they formed. This destabilizes the mineral.
Complexation
Biological processes produce organic acids that can form complexes with elements within the structure of a mineral thereby pooling the element from the mineral and destabilizing it.

34. Classification of Parent Materials
Organic Deposits
Weathering of rocks in place
Deposition of weathered rock materials from elsewhere
Parent materials are classified by their mode of placement at their current location.

35. Types of Parent Material
Gravity
colluvium
Ice transport
glacial till, moraine, outwash
Wind transport
Eolian (dune sand, loss, dust)
Water transport
Lakes -lacustrine
Streams –alluvium (floodplain, alluvial fans, delta)
Oceans –marine
Volcanic ash

37. 2. Climate
May be the most influential of the four factors acting on the parent material
Determines the nature and intensity of weathering (precipitation and temperature)
Both affect the physical, chemical and biological processes
Climate also exerts influence indirectly through a second soil forming factor, the living organisms (natural vegetation).
Climate is so important in soil formation that certain evidence of climatic change could be found in the soil

38. Precipitation
Water is essential for all the major chemical weathering reactions.
The deeper water penetrates the parent material, the more effective it is in soil development.
Water percolating through the soil profile transports soluble and suspended material from the upper to the lower layers.
Thus percolating water stimulates weathering reactions and helps differentiate soil horizons.

39. Temperature Every 10 deg C, the rate of chemical reaction doubles
If warm temperatures and abundant water are present in soil at the same time, the processes of weathering, leaching, and plant growth will be maximum and lead to deep soil profiles.
Compare this to very modest soil profile development processes that are obtained in cold areas

40. 3. Organisms (Biota) a) Role of natural vegetation
Soil organisms, both the animals (fauna) and the plants (flora) physically churn the soil and help stabilize the soil structure
a) Role of natural vegetation
Organic matter accumulation
Cation cycling by trees
Heterogeneous rangelands

41. Heterogeneous Rangelands (Plants & soil formation)

42. b) Role of animals
Animals such as gophers, moles, prairie dogs bore into lower soil horizons and bring materials to the surface –tunnels.
Earthworms and termites
Bring about considerable soil mixing
Human influence
destruction of natural vegetation
Soil tillage for crop production
Irrigation
Fertilizer application

43. 4. Topography Relates to the configuration of the land surface
It is described in terms of differences in elevation, slope and landscape position
Steep slopes encourage soil loss by erosion and allow less rainfall to enter the soil
Thus prevents formation of soils from getting ahead of soil destruction
In the depressions where runoff tends to concentrate, the soil is usually more deep

44. Role of Topography in Soil Formation

45. 5. Time
Time that materials have been subjected to weathering is important because soil forming processes take time to show their effects.
Clock of soil formation starts when e.g.
Landslide exposes a new rock
Flooding river deposits sediment on floodplain
Glacier melts and dumps load of debris
Bulldozer cuts and fills landscape, etc.
Rates of weathering and soil development
This is a function of the interaction of time and the other factors of soil formation.

46. Role of Time in Soil Formation

47. Processes of Soil formation
Processes that are involved in soil formation can be placed in four main groups
Additions
Transformations
Transfers or Translocations
Losses

48. Additions
Additions entail the inputs of materials to the developing soil profile from outside sources. E.g.
Addition of organic matter from Plant leaves and sloughed-off roots
Addition of water by precipitation
Addition of dust particles that fall on the soil surface
Addition of salts and silica dissolved in groundwater and deposited near or at soil surface

49. Transformations
Transformations entail disintegration and altering of composition and form of primary minerals
Physical weathering to smaller particles
Decomposition of organic residues
Recombination of decomposition products to form new minerals such as silicate clays and oxides
Synthesis of organic acids, humus and other products
Aggregation of mineral particles

50. Translocations
Translocations involve the movement of organic and inorganic materials laterally within a horizon or vertically from one horizon to the another.
Movement of water
Movement of dispersed fine clay particles
Movement of dissolved organic substances
The most common translocation agents are water and soil organisms.

51. Losses Materials are lost from the soil by the following:
Drainage and leaching to groundwater
Erosion of surface materials
Evaporation
Plant uptake
Microbial decomposition
Animals and humans

52. Combination of Processes
Losses
Translocations
Additions
Transformations

53. Example of the soil forming processes in action
Addition of litter and root residues
Transformation of plant substances into humus
Accumulation of humus enhances water and nutrient capacity (feedback for plant growth)
Microorganisms attracted by humus buildup accelerate transformations and cause translocations

54. Soil Horizon Development
A-Horizon development
Accumulation of organic matter
Clumping of individual soil particles
Distinct from parent material and other layers
B and C horizon development
Carbonic and organic acids are carried by water into soil where dissolve various minerals (transformations)
Soluble materials (ions –Ca2+, CO32-, SO42-, etc) are carried by water and precipitate in the soil from upper to lower horizons (translocation)
Weathering of primary minerals into secondary minerals
Wetting and drying cracks soils and makes structures.

55. Soil Horizon Development

56. Soil-Landscape-Ecosystem Relationships
The above processes of soil genesis, operating under the influence of the five environmental factors discussed previously gives us a framework for understanding the relationships between particular soils and the landscapes and ecosystems in which the soils exist.