1. Soil

2. Soil Composition
Soils are complex mixtures of minerals, organic materials and organisms that are capable of supporting plant life. Since plants form the base of all food chains which support all animals, soils are indispensable for any terrestrial organism.

3. How Soils Form
Physical and chemical weathering of rocks through the action of air and especially water changes the rock materials into clays and other mineral compounds. Then soil organisms moving through the soil further change it by adding CO2 ,other organic acids and wastes, and humus, black material from the decomposition of remains of dead organisms, their parts and their wastes. This process results in a soil with layers.

4. The Four Components of Soil: Minerals (1)
Minerals in soil come from weathered parent material (solid rock, glacial till, aeolian deposits, or alluvium)

5. The Four Components of Soil: Organic Matter (2)
Organic matter is decomposed plant and animal remains or wastes. It may form a black layer or be mixed with minerals to form yellowish, brownish or reddish layers. When grass is grazed, grass roots die to match the stem level above ground and the dead roots become black humus.
Bison helped produce more soil humus

6. The Four Components of Soil: Air (3)
Spaces between soil particles allow air into soil as do the burrows of organisms like earthworms and gophers.

7. The Four Components of Soil: Water (4)
Water is very important in soils since it is needed by plant roots and animals. Water also transports mineral particles and dissolved minerals from place to place through the soil.

8. Soil Texture
Soil texture refers to the sizes of non-organic materials found in a soil (like sand, silt and clay).

9. Agricultural Soil
Loam refers to a soil type in which the percents of sand, silt and clay are such that they promote good plant growth. As such loam soils are good for growing agricultural crops.

10. Sandy Loam Soils
Sandy loam soils contain more sand. They are well-drained and are prone to faster heating and drying out. Sandy soils are favourable for vegetable crops since they allow earlier ploughing, planting and harvesting. These soils are called “light” soils. They tend to be less fertile and to hold less nutrients which are flushed away (leached) as water seeps through them.

11. Clay Soils
Clay soils hold water well and take longer to heat up, so farmers refer to them as “cold” soils. The smaller size of clay particles and the charges on clay particles cause water to be held more by clay soils. These soils are best for growing pasture crops for grazers like alfalfa or hay.

12. Loamy-Textured Soils
Loamy-textured soils have sand and clay so they retain water but also have better drainage. They hold nutrients better and are easier to till. Loamy-soils will form a crumbly ball when squeezed in the hand.

13. Soil Structure
Undisturbed s oil grains tend to clump together to form large units called peds. The kind of ped structure is referred to as a soil’s structure. Peds improve a soil, providing better drainage, more air spaces for soil organism to move about, protection from erosion and less overland water flow. Organic matter aids the formation of peds. In organic-rich soils, peds in upper soil layers can provide up to 60% air space. Over-tilling a soil breaks down soil structure.

14. Soil Colour: Tropical Rainforest and Temperate Grassland
Soils from particular climates often have specific colours due to the degree of oxygen reaction in the soil and to the kind and amount of organic matter present in the soil. Equatorial rain forests tend to have reddish soils caused by highly oxidized iron (like rust) and negligible organic matter. Temperate grasslands tend to have black soils due to high organic content. Different decomposition rates and water leaching cause these colours.

15. Soil Colour: Coniferous Forest and Arid Regions
Boreal or Taiga coniferous forest soils tend to have an ash-grey or blue-grey colour due to high silica content and poorly-drained conditions which keeps iron reduced (like iron metal, not oxidized). Also, acidic conifer leaves cause leaching of organic materials. Arid regions often have whitish soils due to high levels of calcium carbonate, CaCO3 , limestone.

16. Soil Organic Matter
Organic matter like wastes, dead animals, plants or plant parts that fall onto the surface of soil are decomposed by bacteria and fungi into black humus which releases nutrients like nitrogen, phosphorus and potassium into soil water for plant root hairs to absorb. Warmer temperatures and moist conditions tend to speed up decomposition but soils with much water have few air spaces which reduces decomposition since most decomposers require oxygen.

17. Soil Water and Air are Complementary
If a soil holds much air, it will hold little water (well-drained) and if a soil holds much water (poorly-drained) it will hold little air. Loam soils which have moderate amounts of water and air are best for agriculture.

18. The Role of Clay Materials in Soil
Clay materials have negative charges on their surface which attract and hold positive cations that are plant nutrients like Ca2+ Mg2+ K+ and Na+ . Plant root hairs can absorb these cation nutrients.

19. Acids in Soils
Acids are substances that release hydrogen ions, H+ . These hydrogen ions replace other cations, freeing them up to be absorbed or to be leached away. If a soil is highly acidic (natural or acid rain), hydrogen ions displace the nutrients ions, making them all soluble, eventually to be leached away from roots as water percolates down through the soil. Some toxic cations like Al+3 may be released from clays which can kill plants and soil organisms.
Cluster of clay, humus and minerals
hold positive cations by their
negative charges

20. pH and Acidity
pH is a scale (0-14) that measures how acidic a substance is. A pH of 7 is neutral. pH values below 7 are acidic, every number lower being 10x as acidic as the number above it. Distilled water has a pH of 7. It has very few hydrogen ions (one hydrogen ion in 10,000,000 water molecules) and it has an equal number of OH-1 ions as H+ ions (because 1 HOH splits to form 1 H+ and 1 OH- in every 10,000,000 HOH molecules)

21. Acidic Soils and Alkaline Soils
Acidic soils have a pH less than 7 and have more H+ ions and fewer OH- ions. Alkaline soils have a pH higher than 7 and have more OH- ions and fewer H+ ions.

22. Agricultural Products and Soil pH
Different agricultural crops have their own optimum pH requirements. To adjust soils to be more alkaline, lime is added which adds Ca+2, Mg+2 and OH- ions to the soil which is called “sweetening” the soil. To adjust soils to be more acidic, sulfur is added which adds more H+. Rain in the Cowichan Valley and lower mainland usually leaches Ca and Mg from soils which is remedied by adding lime to soils, especially for lawns whose grasses like bluegrass require more alkalinity.

23. Soil Horizons
Soil horizons are distinct horizontal layers in a soil created by water movement downward and upward through a soil over thousands of years. Water transports soluble compounds and fine clay particles up and down from layer to layer and over long time periods this movement forms horizons.

24. Typical Soil Horizons: O and A
Above the soil there is a layer of mostly undecomposed organic debris called the O horizon. The uppermost soil layer is designated the A-horizon, more commonly called the topsoil layer which contains the greatest proportion of decayed organic matter, generally giving this layer a black colour.

25. Typical Soil Horizons: B and C
The B horizon receives material removed from the A horizon. It usually is lighter in colour and lower in organic matter than the A horizon. The C horizon is composed of parent materials (from bedrock or till from glaciers or alluvium) that have not been altered much from the parent materials.

26. Typical Soil Horizons: E
In acidic soils like those under coniferous forests (conifer needles decompose into some acids), a lighter E layer often forms that is lighter in colour due to less organic matter and clay than surrounding layers. Water and acids leach out (elluviate) clay and organic matter leaving sand, silt and resistant minerals.

27. Moisture and Soil Horizons
In general, the moister a climate, the deeper soils become and the wider the horizons become. Elluviation is the removal of soil materials and Illuviation is the deposition, precipitating or dropping of soil materials in a layer.

28. Soil Formation
Soils form due to the action of water, acids from decomposition dissolved in the water, amount of annual precipitation, and the amount of evaporation of water from the soil. In warmer humid environments, leaching (elluviation) occurs throughout the year, removing soluble minerals (nutrients) from the soil. In cooler temperate environments, winter freeze stops leaching. In warm arid regions, high evaporation rates bring dissolved salts to the surface creating a mineral crust, often a hard layer, called caliche in Spanish.

29. Factors Affecting Soil Formation
The soil an area develops depends on the precipitation it receives, the temperatures it experiences, the kinds of plants growing in the soil, the relief of the land (sloped or flat), and the aspect of the land (north-facing slopes are cooler, more prone to have trees while south-facing slopes are warmer, more likely to have tall grasses and scattered trees), the parent rock beneath the soil, and the time the soil has had to form.

30. Soil Classification
Different countries have their own way of classifying soil types. What follows is a general North American soil classification system that has been used since 1938.

31. Latosols
Latosols are tropical red earth soils found in warm moist climates or wet/dry warm climates. Warm temperatures promote very rapid decomposition of organic matter and moisture movement through soils causes leaching of nutrients to lower levels and little horizon formation. Warm, moist conditions increase weathering and oxidation rates for iron compounds causing redness. These deep soils support tropical vegetation, which if cleared, can be productive for a few years until the plant nutrients deplete and then they are unproductive. Tropical Rain Forests and Savannahs have these reddish or yellowish soils which have very little humus.

32. Sierozems
Sierozems are hot desert soils found in mid latitude regions like the southwest US states of Wyoming, Nevada, Utah. These soils have little organic content and their nutrients are found near the surface since any water gets quickly evaporated which pulls nutrients up. These soils have no horizons and typically are rich in CaCO3 (limestone) and other salts which may become a hard caliche layer. The saltiness of the soil may be an issue but often these soils can be very productive if irrigated. Eventually the saltiness of the soil increases with irrigation and the soil needs to be fallow or rested for a period of time to become useful for agriculture again.

33. Chernozems
Chernozem soils form in grasslands, praries, steppes or pampas. These fertile soils are thick with deep black or brown A horizons, lighter perhaps yellowish B horizons and often a C layer that is high in CaCO3 . The brownish chernozems form in drier climates and may require irrigation for agricultural use. Chernozems are the most fertile soils on earth and regions with these soils are called the bread baskets of earth because they produce excellent corn or wheat yields. Because of sub zero temperatures during winter and less precipitation during summers, there is less leaching of nutrients by water and organic matter builds up if it is replenished.

34. Podzols
Podzols are soils found under coniferous forests (Canada) or eucalyptus forests (Australia). These soils have an ash-grey horizon below the surface horizon. These soils develop in cool, moist climates where water and acids from the acidic conifer leaves cause constant leaching of oxides of Fe/Al from the A horizon and deposition of them in the B horizon (giving it a reddish or brown colour) . These soils are infertile due to high sand content (tendency to dry out) and require fertilizers and careful management to be of medium productivity (grazing pastures or agriculture if organic matter is added). Slow decomposition produces some organic matter which is readily leached downward. Coastal BC and high elevations in the BC interior commonly have podzol soils. Gray-brown podzol soil has more organic matter and less leaching, developing from glacial gravels. It is more productive than true podzol soil.

35. Luvisol Soils
These soils form in cool, dry temperate regions with long cold winters and short growing seasons. They have a loam or clay texture. They have an A horizon where clay has been leached from and deposited into a B horizon beneath. These soils are found under coniferous or mixed deciduous forests. In BC, these soils are found in the Central Interior and Peace River regions. Luvisols have medium productivity and can be used for agriculture if organic matter is added. Much of Southern Ontario has luvisol soils (high clay content).

36. Brunisol Soils
Brunisol soils are intermediate between Podzol and Luvisol soils. They have less clay content than luvisols. Mountainous regions in the Okanagan and Kootenay Regions of BC have Brunisol soils as does the Yukon border. Brunisols also develop under coniferous forests.

37. Tundra or Crysolic Soils
Tundra soils form under very cold and dry environments. Plants growing on these soils include moss, lichens, sedges and dwarf shrubs. Tundra regions are too cold for trees to grow. A few cm from the surface is a deep layer of permafrost which stays frozen year round. During the very short summers, the top soil layer thaws and can be very watery from depths of cm. Surface vegetation slowly decomposes into a layer of humus that mixes with water and freezes during the long winters. Alternate freezing and thawing produces a polygon-pattern in many places. Tundra soils have a dark A horizon and a grayish B horizon. They are very poor for agriculture.

38. Bog Soils (Muskeg, Mire, Quagmire)
Bog soils form in cool or cold, moist environments which have many mosses (ex: sphagnum moss) that decomposes into acidic brown or black peat. In some places peat is mined and is burned for heating, cooking or for electrical power generation (heats water to steam which turns turbines that make electricity). Many bogs are depressions which are water-tight and hold rain water below matts of decomposing mosses. Peat soils are very nutrient poor, unproductive soils. Peat moss (partially decomposed sphagnum moss) is added to soil to add humus and to improve water retention of the soil. The acidic nature of bogs pickles and preserves organisms falling into the bog water. The Tolland man fell into a Danish bog 1,500 years old.

39. Alkaline and Saline Soils
Alkaline and salty soils develop in hot arid climates where the rate of evaporation is high and water from lakes evaporates leaving the dissolved salts as salt deposits. These soils can also develop where irrigation is used without having proper drainage of the irrigated water. The elements Na, K, Ca and Mg, commonly found in soil sands cause the soil to become alkaline when they are in abundance as ions. These soils can be managed to be productive if drainage pipes beneath the soil or at the end of a graded field carry away the dissolved ions of Na+ , K+ , Ca+2 and Mg+2 .

40. Alluvial Soils
Alluvial soils are created by the successive deposition of river sediments, often in river deltas. These soils show no layering and are rich in nutrients. Alluvial soils like the Nile Delta and along the edges of the Nile above the Aswan dam can be very productive for agriculture.

41. End of Presentation A