Option Unit Geo Ecology

1. Option Unit Geo Ecology Soils

2. Learning Objectives • Describe what soil is made of (soil composition) • Explain how soil is formed. • Describe a typical soil profile. • Name and describe the main characteristics of soil. • Name and explain processes that affect soil formation. • Describe the factors affecting soil formation. • Explain how these factors and processes influcence soil characteristics.

3. Soil composition (what soil is made of)

4. Soil Composition MINERAL MATTER (45%): ROCK PARTICLES FOUND ON THE BEDROCK AND WEATHERED ROCK AIR (25%): FOUND IN THE PORE SPACES BETWEEN THE ROCK GRAINS. WATER (25%): ALSO FOUND IN PORE SPACES. IN DRY WEATHER, WATER FORMS A THIN FILM AROUND THE GRAINS. IN WET WEATHER, IT FILLS THE PORES. HUMUS (4%): PRODUCED FROM DECAYING VEGETATION SUCH AS LEAVES AND THE REMAINS OF DEAD ANIMALS. LIVING ORGANISMS (1%): EARTHWORMS, BEETLES, FUNGI, BACTERIA

5. How Is Soil Formed? • STEP ONE Solid rock particles are broken down by mechanical weathering. This forms small soil grains • STEP TWO Chemical weathering releases important nutrients from the rock e.g. calcium, potassium

6. STEP THREE Seeds are blown or carried onto the soil grains and may grow into plants that enrich the soil when they die. Eg mosses and lichens • STEP FOUR Micro- organisms break down the remains of plants and form humus. This helps bind the soil together and improve fertility of soil. • STEP FIVE The cycle continues until the soil reaches max fertility.

7. Soil Profile

9. Soil Profile A HORIZON – Topsoil. Dark Coloured. O – ORGANIC HORIZON. Leaves, dead animals, dead plants. Humus is formed as the dead organic matter begins to decay. B HORIZON – Zone of mineral accumulation where rainwater percolates through the soil. C – HORIZON

10. Soil Characteristics 6 Soil Characteristics • Colour • Structure – how the soil grains are stuck together • Texture – how the soil feels to touch • Humus • Soil PH • Water Content

11. Soil Characteristics • COLOUR: SOILS HAVE A RANGE OF COLOURS. EG: PEAT IS DARK BLACK, OTHER SOIL MAY BE BRIGHT RED OR YELLOW. THE COLOUR OF A SOIL DEPENDS ON ITS PARENT MATERIAL OR ON THE PROCESSES THAT HAVE OCCURRED SUCH AS LEACHING.

12. Soil Characteristcs 2. STRUCTURE: • THIS DESCRIBES THE WAY IN WHICH SOIL GRAINS ARE LUMPED TOGETHER BY HUMUS AND CLAY PARTICLES. • IF YOU PULL A PLANT AWAY FROM THE GROUND, ITS ROOTS WILL HOLD ONTO THE SOIL GRAINS. LOOK CLOSELY AND YOU WILL SEE THAT THE GRAINS ARE IN SMALL LUMPS KNOWN AS PEDS. • THE SHAPE OF THESE PEDS INDICATES THE STRUCTURE OF THE SOIL. • THE SPACES BETWEEN THE PEDS HOLD AIR AND WATER AND ARE IMPORTANT FOR PLANTS TO ACCESS AIR AND WATER IN SOIL. • OVERCROPPING AND OVERGRAZING DAMAGE THE STRUCTURE OF THE SOIL, REDUCING ITS ABILITY TO SUPPORT PLANT GROWTH.

13. Crumb – small rounded clumps similar to breadcrumbs in size. Loam soils have this structure and it is very good for holding air and water. It is well drained and plants grow well. Blocky Structure – peds are closely packed angular blocks. Well drained but can be compacted easily and plants have difficulty growing in it when this occurs. Sandy soils have this structure. Platy Structure – peds are arranged in thin layers. Forms in clay soils and is poorly drained. Plants have difficulty growing in soils with this structure.

14. Soil Characteristics 3. TEXTURE: http://www.youtube.com/watch?v=ob2AMqZMLiw • CONTROLLED BY THE AMOUNT OF SAND, SILT, AND CLAY PARTICLES IN THE SOIL. • DIFFERENT SOILS HAVE DIFFERNET AMOUNTS OF PORE SPACE WHICH AFFECTS HOW MUCH AIR CAN BE HELD BETWEEN PARTICLES AND ALSO THE WATER CONTENT AND DRAINAGE CAPACITY OF THE SOIL.

15. Texture • THERE ARE THREE MAIN TEXTURES: CLAY (PARTICLE DIAMETER 0.0002mm – NOT VISIBLE TO NAKED EYE) SILT (PARTICLE DIAMETER BETWEEN 0.0002 AND 0.05mm – BARELY VISIBLE TO NAKED EYE) SAND (PARTICLE DIAMETER 0.05mm TO 2mm – VISIBLE TO NAKED EYE). • WHEN DESCRIBING SOIL TEXTURES, THE TERMS SILT, CLAY AND SAND ARE IMPORTANT BECAUSE THEY INDICATE THE SIZE OF THE GRAINS IN THE SOIL.

16. CLAY SOILS: SMALLEST SIZED PARTICLES. STICKY SOIL WHEN WET. CONTAIN APPROX 0-45% SAND, 0-40% SILT AND 40-100%CLAY. NATUARALLY HIGH IN NUTRIENTS SO PLANTS GROW WELL. OFTEN BAKED DRY IN SUMMER WITH VISIBLE SURFACE CRACKS. OFTEN CONSTANTLY WET AND WATERLOGGED IN WINTER. CAN BE DIFFICULT TO DIG. HOLDS TOGETHER LIKE PLAYDOUGH.

17. SILTY SOILS: CONTAINS PARTICLES SMALLER THAN SAND BUT LARGER THAN CLAY SOILS. FEELS POWDERY. STICKS TOGETHER WHEN WET BUT OFTEN WILL NOT HOLD ITS SHAPE WHEN DRY. CAN BE BADLY DRAINED.

18. SANDY SOILS: CONTAINS PARTICLES VISIBLE TO NAKED EYE. FEEL GRITTY – TEND NOT TO STICK TOGETHER WHEN WET. GENERALLY CONTAIN 85-100%SAND,0-15%SILT-0-10%CLAY. WATERLOGGING RARE AS THEY ARE VERY FREE DRAINING. WATERING AND FEEDING OF PLANTS OFTEN NECESSARY AS NUTRIENTS CAN DRAIN AWAY EASILY. QUICK TO WARM IN SPRING SO PLANTING CAN BE DONE EARLIER IN SANDY SOILS THAN OTHER TYPES.

19. LOAM SOILS: RARELY COMPOSED OF JUST SAND, SILT OR CLAY- USUALLY MIXTURE OF THE THREE. LOAM CONTAIN ROUGHLY EQUAL AMOUNTS OF EACH. MOST PLANTS WILL GROW IN LOAM SOILS. BROWN AND CRUMBLY IN TEXTURE. RARELY WATERLOGGED IN WINTER OR OVERDRY IN SUMMER. LIGHT AND EASY TO DIG. NATURALLY HIGH IN NUTRIENTS.

20. Soil Characteristics 4. HUMUS CONTENT: • IMPORTANT DUE TO ITS ABILITY TO SUPPORT PLANT GROWTH. • SOLS RICH IN HUMUS TEND TO BE DARK IN COLOUR. HUMUS IS A DARK BLACK GEL FORMED BY ROTTING PLANTS AND VEGETABLE MATERIAL IN SOIL. • THIS GEL HELPS TO BIND SOIL GRAINS TOGETHER. AS IT IS WASHED INTO THE GROUND BY RAIN, IT ADDS NUTRIENTS TO THE SOIL. LIVING THINGS ALSO ADD HUMUS TO SOIL BY EXCRETION. • EARTHWORMS, BEETLES AND LARVAE BURROW THROUGH SOIL AND CREATE AIR SPACES FOR PLANT ROOTS. • WHEN THESE CREATURES DIE, THEIR BODIES DECOMPOSE AND FURTHER ENHANCE THE NUTRIENT QUANTITY IN THE HUMUS.

21. Soil Characteristics 5. ACIDITY/ALKALINITY OF THE SOIL: • THE PH OF THE SOIL IS HOW ACIDIC OR ALKALINE IT IS (LITMUS TEST – JC SCIENCE). MOST PLANTS PREFER A SLIGHTLY ACIDIC SOIL WITH A PH OF 6.5 • PEAT SOILS ARE EXTREMELY ACIDIC AND CONTAIN FEW LIVING PLANTS. • NEUTRAL SOILS ARE MOST SUITED TO BACTERIA WHICH HELP IN TURN TO RELEASE NUTRIENTS SUCH AS NITROGEN INTO THE SOIL.

22. Soil Characteristics 6. WATER CONTENT/ RETENTION: • THE AMOUNT OF WATER A SOIL CAN HOLD DEPENDS ON THE HUMUS CONTENT, TEXTURE AND STRUCTURE. • SOILS RICH IN HUMUS CAN HOLD MORE MOISTURE THAN THOSE WHICH LACK HUMUS. • SOILS THAT HAVE A SANDY TEXTURE, ARE OFTEN DRY BECAUSE WATER DRAINS BETWEEN THE SAND GRAINS VERY QUICKLY. • A CLAY SOIL TENDS TO HOLD MORE WATER DUE TO THE VERY SMALL GRAINS WHICH HAVE LARGE SURFACE AREAS AND THEREFORE MORE WATER AROUND THEM.

23. Processes affecting soil characteristicsYou know some of these already.. Think!!

24. Processes • Weathering • Humification • Leaching • Podzolisation • Gleying • Laterisation • Salinisation • Calcification The factors of climate, relief, rock type, living things and time all influence which one of these processes take place.

25. Weathering Physical and chemical breakdown of rocks into smaller pieces. Soil grains can be released from rocks by weathering. The soil grains produced by weathering keep the characteristics of the parent rock such as PH, texture and colour. Carbonation and oxidation can release nutrients such as phosphorous, calcium and iron from the mineral grains.

26. Humification • Dead organic matter is converted into humus by fungi and bacteria. Makes the soil fertile as it releases nutrients into the soil. • Rain washes the humus into the soil. • Climate is an important factor affecting the rate of humification. Hot humid climates – humification is very fast. The lack of water in deserts may limit the amount of humus that can be washed into the soil. In Ireland humification occurs more slowly in Winter and in cold artic climates humification may stop.

27. Leaching • The removal of nutrients from the soil by water. • Sometimes minerals build up in a layer lower down in the soil (hardpan) • A certain amount of leaching is needed to wash humus into soil. However excessive leaching makes the soil infertile.

28. Podzolisation • Type of leaching that occurs where rainwater is more acidic. • Podzol soils foirm under coniferous forests as these forests decompose they add to the acidity of the rainwater. • The water seeping through the soil beneath this dead vegetation becomes acidic due to the absorption of humic acids from rotten vegetation. • The top layer of podzolised soils is ash grey in colour. The layer below is enriched with the dissolved mineral from above and is darker in appearance. • Podzols may also contain a layer of reddish iron oxide in the B horizon. This is called a hard pan or iron pan and prevent water from draining through the soil.

29. Gleying • Process when the soil is waterlogged and lacks oxygen. • Water is between the soil peds and prevents living things from surviving. They lack organic matter. • Climate and relief can lead the gleying. Heavy rain can cause the land to become waterlogged. If the land dips and hollows water can collect in the hollows • Gley soils have patches of grey/blue colouration. • Common in Ireland’s drumlin belt (Co. Cavan, Co. Monaghan).

30. Laterisation • Type of severe chemical weathering that occurs in tropical and equatorial regions. • In areas of heavy rainfall such as the tropics and equatorial regions all alkaline material is taken from the soil by carbonation. The PH of the soil is slightly acidic. • The oxidation of iron and alluminium gives the soils a red appearance and they are known as latosols. If the soil dries out it is turned into a hard laterite.

31. Salinisation • Occurs when mineral salts move up through the soil towards the surface. • Can happen in hot desert areas of the world where percipitation is low. The amount of waterevaporating out of the soil is greater than percipitation falling. • Evaporation causes salts in ground water to rise through the soil and collect in the upper layers. Salt is deposited on the surface as a hard white crust. If salt concentration is too high plants are poisoned and die.

32. Calcification • Process by which calcium carbonate is concentrated near the surface of the soil. • Occurs in regions of low rainfall. • The amount of water drawn up through the soil by plants may be greater than the percipitaiton falling on the soil. As a result calcium carbonate builds up in the upper layer of the soil. • Calcium carbonate is a useful substance for plants.

33. Factors Affecting Soil Processes and Soil Characteristics • Climate – most important factor in soil formation • Relief – Can influence the dept and drainage of a soil • Parent Material – The type of rock that a soil develops from can influence PH, colour,water content and texture of soil. • Living Things – Influence soil fertility • Time – The longer the soil forming process the more developed the soil will become.

34. Activity • Read the handout to discover how the above factors affect the formation of soil. They do by influencing the processes (weathering, leaching etc) and characteristics ( colour, PH, etc)

35. Soil Classification 3 Main Groups

36. ZONAL SOILS • These form where the influence of climate and biological activity have been stable for along time. • These soils often have distinctive profiles and clear horizons. They would include: • Brown Earths:  brown in colour; crumb structure; high natural fertility/ no distinct horizons. Found in many parts of Ireland. • Podzols: Associated with leaching; poorly drained soil; two distinct horizons (ash-grey and reddish brown); need addition of fertilizers. Found in Cork, Kerry, Wicklow, Mayo and Donegal.

37. INTRAZONAL SOILS • These soils form where some local factor such as parent material (e.g. presence of limestone) or drainage conditionspredominate. They would include: Gley and Peat soils.

38. GLEYS • Gleys: These are soils that are often waterlogged due to impermeable underlying rock. The waterlogged condition stopped the breaking down of organic matter. These soils are blue/grey in colour; of poor fertility; mainly suited to pastoral farming. • Found in e.g. north west Munster and in the Drumlin Belt of Cavan/Monaghan.

39. PEAT SOILS • Peat Soils: Black in colour and consist of partially decomposed vegetative matter. Heavily leached and low in fertility. • Blanket peat is found in the uplands, especially on acid underlying rock such as the granite of the Wicklow Mountains. Raised peat found in waterlogged areas of the Central Plain.

40. AZONAL SOILS • Azonal Soils - These are immature soils where the soil farming processes have not had sufficient time to complete their task. These soils do not have a well developed profile. • They would include:Lithosols. Associated with recently weathered bed rock where mass movement and erosion prevent the development of a soil profile. Infertile, used possibly for forestry; some areas of Connemara

41. What to Know…. • Should be aware of the different soil types in each group. • Should describe one Irish soil in detail – Brown Earth soil. • Should describe the aridsols of desert climates (we did this when studying the desert biome!) *Via syllabus you should be able to compare two soil types*

42. Irish Brown Earth Soils Read the handout on brown earth soils. It is broken up into the factors that affect its formation and the characteristics of brown earth soils and the processes affecting the formation of brown earth soils

43. Human Interaction Question

44. Soil Erosion and Conservation Learning Objectives • Name and explain the causes of soil erosion. • Describe in detail how human activities can cause soil erosion. • Name and explain the primary methods of soil conservation.

45. Soil Erosion Most soil erosion is caused by natural processes such as flowing water and by wind. Human activities such as overcropping and overgrazing land and deforestation also cause soil erosion.

46. Natural cause of soil erosion Soil erosion by rain Raindrops on average fall at a speed of 32.19km/hr. The force of impact of raindrops break apart the soil grains. During heavy rain water can no longer seep into the soil and begins to flow over the surface (runoff). The water makes channels called rills and gullies in the soil. Millions of tonnes of soil are removed from farmland by rainwater in this way.

47. Soil erosion by wind Wind is effective at blowing dry exposed soil away. Wind removes soil by • Saltation – fine and medium sand sized particles are lifted a short distance into the air • Suspension – very fine soil particles are lifted from the surface, carried high into the air, it remains suspended in the air for long periods. • Surface Creep – the movement of large soil particles along the surface of the soil.

48. The amount of soil erosion by wind and rain that occurs depends on • The quantity of water moving downhill • The speed of the water • The strength of the wind • The steepness of slope. • The condition of the soil surface and the type of soil.

49. Human causes of soil erosion • Can trigger soil erosion due to poor farming methods and deforestation. • Farming and deforestation can change soil characteristics and damage soil structure. • Human activities such as overgrazing, overcropping and deforestation have led to desertification, soil erosion and famine. • Tourism, outdoor activities such as quad biking damage fragile soil structure. The amount of soil erosion caused by human activities depends on • The type of cultivation – may leave soil exposed to the wind • The amount of vegetation cover removed – deforestation can lead to landslides. • The intensity of land use – heavily used soils are more easily eroded. • The length of time land left rested – overused soils are often dry.

50. Problems caused by soil erosion • Loss of valuable topsoil • Poor soil washed downhill can bury valuable fertile soil on the lowland below. • Damage to fields because gully erosion reduces the field size and takes land out of production. • Erosion causes a steady but slow plant productivity decline. • Desertification