1. SOIL GEO 401: Foundation Geography
Dr. MD. ASIF IQUBAL Department of Geography FNU Lautoka

3. Soil is the mixture of rock debris and organic materials which develop on the earth’s surface.
The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time.
Besides these, human activities also influence it to a large extent.
Components of the soil are mineral particles, humus, water and air.
The actual amount of each of these depend upon the type of soil.

5. Apart from mineral particles, true soils are influenced, modified, supplemented and developed by living organisms through the addition of organic matter.
Fungi and bacteria decompose this organic matter into a semi-soluble chemical substance known as humus.
Humus is the biochemical substance that makes the upper layers of the soil become dark. It is colored dark brown to black. Humus helps in binding the larger mineral and organic particles.

6. Characteristics of Humus
It enhances a soil's ability to hold and store moisture.
It is the primary source of carbon and nitrogen required by plants for their nutrition.
It improves soil structure which is necessary for plant growth.

8. Soil Pedogenesis
The kinds of soils that develop in a particular area are largely determined by five interrelated factors: climate; living organisms; parent material; topography; and time (Figure ).

9. Grass vegetation contributes to soils with thick A horizons because of the profuse growth of fine roots in the upper 30 to 40 centimeters of soil.
In forests, organic matter is added to soils mainly by leaves and wood that fall onto the soil surface.
Small-animal activities contribute to some mixing of organic matter into and within the soil
As a result, organic matter in forest soils tends to be incorporated into only a thin layer of soil, resulting in thin A horizons.

10. The climate contributes to soil formation through its temperature and precipitation components.
If parent materials are permanently frozen or dry, soils do not develop.
Water is needed for plant growth, for weathering, leaching, and translocation of clay, and so on.
A warm, humid climate promotes soil formation, whereas dry and/or cold climates inhibit it.

11. The topography refers to the general nature of the land surface.
On slopes, the loss of water by runoff and the removal of soil by erosion retard soil formation
Areas that receive runoff water may have greater plant growth and organic matter content and more water may percolate through the soil.
The extent to which these factors operate is a function of the amount of time that has been available for their operation.

12. Thus, soil may be defined as:
“unconsolidated material on the surface of the earth that has been subjected to and influenced by the genetic and environmental factors of parent material, climate, organisms, and topography, all acting over a period of time”

13. SOIL FORMATION
Soil layers are approximately parallel to the land surface and several layers may evolve simultaneously over a period of time.
The layers in a soil are genetically related; however, the layers differ from each other in their physical, chemical, and biological properties.
In soil terminology, the layers are called horizons.
Soil formation consists of the evolution of soil horizons
A vertical exposure of a soil consisting of the horizons is a soil profile.

15. Soil-Forming Processes
Horizonation (the formation of soil horizons) results from the differential gains, losses, transformations, and translocations that occur over time within various parts of a vertical section of the parent material.
Examples of the major kinds of changes that occur to produce horizons are:
(1) Addition of organic matter from plant growth, mainly to the topsoil
(2) Transformation represented by the weathering of rocks and minerals and the decomposition of organic matter
(3) Loss of soluble components by water moving downward through soil carrying out soluble salts and
(4) Translocation represented by the movement of suspended mineral and organic particles from the topsoil to the subsoil

16. Translocation
When water moves downward into the soil, it causes both mechanical and chemical translocations of material.
The complete chemical removal of substances from the soil profile is known as leaching.
Eluviation refers to the downward movement of fine mineral particles (like clay) or dissolved substances from the upper layer in a soil profile.

17. Capillary Action- upward movements of dissolved or suspended matter by groundwater.
Melanization- darkening of the color of a section of soil profile through organic matter.
Leucinization (Decoloration)- lightening of the color of section of the soil profile mainly in A horizon.
Induration- hardening of a section of the soil profile such as kankar pan, iron pan (ferricrete), calcrete, alcrete, silcrete etc.
The deposition of fine mineral particles or dissolved substances in a lower soil layer is called illuviation.

18. Soil Profiles
Most soils have a distinct profile or sequence of horizontal layers. Generally, these horizons result from the processes of chemical weathering, eluviation, illuviation, and organic decomposition.

19. A horizon- below the O layer.
The O horizon- the topmost layer of most soils. Composed mainly of plant litter at various levels of decomposition and humus.
A horizon- below the O layer.
Here humus and other organic materials are mixed with mineral particles.
The zone of translocation- eluviation has removed finer particles and soluble substances, both of which may be deposited at a lower layer.
Is dark in color, light in texture and porous.
Commonly differentiated into a darker upper horizon or organic accumulation, and a lower horizon showing loss of material by eluviation.

20. The B horizon, a mineral soil layer which is strongly influenced by illuviation. Consequently, this layer receives material eluviated from the A horizon.
This also has a higher bulk density than the A horizon due to its enrichment of clay particles.
This horizon is colored by oxides of iron and aluminum or by calcium carbonate illuviated from the A horizon.
The C horizon is composed of weathered parent material. The texture of this material can be quite variable with particles ranging in size from clay to boulders.
No significant influence by the pedogenic processes, translocation, and/or organic modification on this horizon.
The final layer in a typical soil profile is called the R horizon. This soil layer simply consists of unweathered bedrock.

21. Some Principal Pedogenic Processes
Laterization is a common process in tropical and subtropical environments.
High temperatures and heavy precipitation result in the rapid weathering of rocks and minerals.
Movements of large amounts of water through the soil cause eluviation and leaching to occur.
Iron oxides give tropical soils their unique reddish coloring. Heavy leaching also causes these soils to have an acidic pH because of the net loss of base cations.
Some Principal Pedogenic Processes

22. Podzolization is associated with humid cold mid-latitude climates and coniferous vegetation.
Decomposition of coniferous litter and heavy summer precipitation create a soil solution that is strongly acidic. This acidic soil solution enhances the processes of eluviation and leaching causing the removal of soluble base cations and aluminum and iron compounds from the A horizon. This process creates a sub-layer in the A horizon that is white to gray in color and composed of silica sand.

23. Calcification is common in the prairie grasslandsand in dry areas.
Calcification occurs when evapo-transpiration exceeds precipitation causing the upward movement of dissolved alkaline salts from the groundwater. At the same time, the movement of rain water causes a downward movement of the salts. The net result is the deposition of the translocated cations in the B horizon.
In some cases, these deposits can form a hard layer called Caliche. The most common substance involved in this process is calcium carbonate.
Calcification is common in the prairie grasslandsand in dry areas.

24. Salinization is a process that functions in the similar way to calcification. It differs from calcification in that the salt deposits occur at or very near the soil surface. Salinization also takes place in much drier climates.
Gleization is a pedogenic process associated with poor drainage. This process involves the accumulations of organic matter in the upper layers of the soil. In lower horizons, mineral layers are stained blue-gray because of the chemical reduction of iron.

25. Soil Texture
The texture of a soil refers to the size distribution of the mineral particles found in a representative sample of soil.
Particles are normally grouped into three main classes: sand, silt, and clay.
 Clay is the most important type of mineral particle found in a soil. Clay particles have a very large surface area relative to their volume. This large surface is highly reactive and has the ability to attract and hold nutrient, which helps plants to grow.

26. Sandy Soil

27. Silt & Loam Soil

28. Clay Soil

30. Particle size ranges for sand, silt, and clay.

32. Audification- accumulation of H ions, mainly in surface horizon
Transformations
Audification- accumulation of H ions, mainly in surface horizon
Neutralization- counteraction of H ions.
Oxidation- formation of iron oxides.
Reduction- loss of oxygen ions Neutralization- counteraction of H ions.
Humification- formation of humus from original materials
Mineralization- release of minerals in various forms during the process of decomposition of organic matter.
Hydration- swelling of minerals through the absorption of water resulting into the formation of new compounds.

33. Soil pH
Soils support a number of inorganic and organic chemical reactions. These reactions are dependent on some particular soil chemical properties.
Soil pH is primarily controlled by the concentration of free hydrogen ions in the soil matrix.
Soils with a relatively large concentration of hydrogen ions tend to be acidic.
Alkaline soils have a relatively low concentration of hydrogen ions.

34. A value of 7.0 is considered neutral.
The pH scale.
A value of 7.0 is considered neutral.
Values higher than 7.0 are increasingly alkaline or basic.
Values lower than 7.0 are increasingly acidic.
The illustration above also describes the pH of some common substances.

35. Soil Fertility
Soil fertility is directly influenced by pH through the solubility of many nutrients.
At a pH lower than 5.5, many nutrients become very soluble and are readily leached from the soil profile.
At high pH, nutrients become insoluble and plants cannot readily extract them.
Maximum soil fertility occurs in the range 6.0 to 7.2.

36. Soil Color
Soils tend to have distinct variations in color both horizontally and vertically.
Soils of the humid tropics are generally red or yellow because of the oxidation of iron or aluminum, respectively.
In the temperate grasslands, large additions of humus cause soils to be black. Organic matter colors the soil black.

37. The heavy leaching of iron causes coniferous forest soils to be gray.
High water tables in soils cause the reduction of iron, and these soils tend to have greenish and gray-blue hues.
The combination of iron oxides and organic content gives many soil types a brown color.
Other coloring materials sometimes present include white calcium carbonate, black manganese oxides, and black carbon compounds.

38. Dark Color Indicates Organic Matter

39. Soils of Fiji
Sixty five per cent of soils have developed on steep slopes (over 21o), 20% on gently undulating and hilly land (4-21 o) and 15% on flat land (under4 o) (Leslie 1997). 
Lowland (below 600 m, mean annual temperature over 22o C) soils are formed on beach sands, marine marshes, poorly and well drained alluvia, highly organic parent material, acidic and non-acidic terraces and peneplains.
Soils from lowland rolling and hilly terrain are formed from young and weathered volcanic materials, volcanic ash over reef limestone, calcareous tuffs and marls, and from basic, intermediate and acidic geologies.
Upland soils (over 600 m, mean annual temperature 15-22o C) are formed on recent poorly and well-drained alluvia, raw volcanic materials and basic rocks (Leslie, 1997).

40. Low available soil N, P, sulphur, potassium, copper, molybdenum and are the most likely limiting chemical attributes of grazing land soils.
The most fertile soils are in the floodplains of the Sigatoka, Rewa, Nadi, Ba, Navua and Labasa rivers and are generally derived from basic volcanic parent material. Responses by pasture to N, P and K have been obtained in dairying areas of the Rewa floodplains (Chand, pers. comm; FAO 1996).
Most grazed native grasslands are on "nigrescent - dark top soil" soils and ferruginous latosols or "talasiga" soils. For maximum pasture production the former is usually marginal in available phosphorus (10-14 ppm) and sulphur and the latter is deficient in nitrogen, phosphorus, potassium, sulphur and sometimes molybdenum.

41. Talasiga Soil-Seaqaqa-Dry Climate.

42. Sugarcane field

43. Dalo Farm

44. River Valley Soils

45. The End-Thank You for Listening

48. THE END