BIOSPHERE Soils: Soil Profiles What is a soil? What does soil contain? What factors affect soil formation? Soil Profiles 1

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SOIL What is soil? INORGANIC MATERIAL ORGANIC MATERIAL AIR WATER MINERALS FROM WEATHERED ROCKS DEAD AND LIVING ORGANISMS INORGANIC MATERIAL ORGANIC MATERIAL SOIL AIR WATER 3

WHAT ARE SOILS? INORGANIC MATERIAL = 45% OF SOIL VOLUME WATER = 25% OF SOIL VOLUME AIR = 25% OF SOIL VOLUME ORGANIC MATERIAL = 5% OF SOIL VOLUME 4

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SOIL FORMATION AND SOIL PROFILES A vertical section through the soil From surface to the bedrock Information comes from boring the soil with an auger Layers are called horizons 8

SOIL FORMATION AND SOIL PROFILES Horizons can be used to work out the type of soil There are usually four horizons in a model profile O horizon – the surface, organic layer of decaying vegetation (where present) LITTER – leaves, pine needles etc. FERMENTATION LAYER – organic material begins to decompose here HUMUS – decomposed remnants of plants and animals along with their waste products 9

SOIL FORMATION AND SOIL PROFILES 2. The A Horizon Main top layer Consists of organic and inorganic materials Usually nutrient rich Often referred to as topsoil 3. The B Horizon Known as the subsoil Coarser in texture: shows importance of weathering Nutrients may be leached into the B horizon from the A Leaching – removal of soluble minerals and humus downwards by rainwater 10

SOIL FORMATION AND SOIL PROFILES 4. The C Horizon Zone of regolith Large particles sit on top of underlying bedrock Soil profiles vary in depth Can be up to 50m Average in the UK is 1.5m 11

SOIL FORMATION AND SOIL PROFILES Depending on the variations within these variations it is possible to group soils into a classification system These zones include soils with certain common characteristics. Closely linked with: CLIMATE VEGETATION 12

SOIL FORMING FACTORS PARENT MATERIAL – the rock underneath, or other source material (e.g. from glacial, alluvial, volcanic deposition) VEGETATION – e.g. Coniferous, Deciduous LIVING ORGANISMS – worms and other creatures help to mix and improve the soil. Plants help stabilise soils and concentrate nutrients at surface of the soil CLIMATE – Temperature and Rainfall RELIEF – steepness of slopes, aspect of slope, height above sea level; TIME – 100,000 YEARS!!! NATURAL EVENTS – e.g. floods, glaciation, volcanic eruptions. HUMAN ACTIVITY – farming, deforestation 13

WHAT ARE SOILS? Soil Formation and Soil Profiles section: ACTIVITIES: It is important to know the main factors which affect soil Formation. Use the Core Textbook to complete the following activities in the: Soil Formation and Soil Profiles section: Questions 1 – 6 on page 174 14

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SOIL FORMATION STAGES IN SOIL FORMATION: Weathering of parent rock over a considerable time period Water, gas, living organisms and decaying organic matter added Rate of weathering of parent rock depends greatly on climate (faster in hotter regions) Where rainfall is heavier minerals are transported downwards in a process called leaching Leached soils tend to be acidic Type of vegetation in an area is linked to precipitation – this provides the humus area – more found in forest areas 16

(Weathered parent material) TOPSOIL SUBSOIL REGOLITH (Weathered parent material) 17

…and in more detail 18

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NEW TERMS Eluviation Downward movement of material where rainfall exceeds evaporation Illuviation Accumulation of material in one layer of soil which have been leached from a layer above Leaching Removal of soluble minerals and humus downwards by rainwater 20

Homework-Biosphere Textbook Questions Homework due next Thursday (20th January) Page 174 ‘Soil Types, Case Studies and Catenas’ Questions 1 and 2 (all of) Qu 2 a) use a whole jotter page for each soil profile.

BROWN EARTHS FOREST SOILS                                                                                                                            BROWN EARTHS FOREST SOILS Brown earth is the soil that develops under deciduous forest. It is found mainly on the west coasts of continents, in the cool temperate zones, 40° to 60° north and south of the equator. These areas include north-western Europe (including the British Isles), the north-west of the United States, southern Chile, Tasmania, and South Island, New Zealand. Brown earths have the second highest primary productivity of all soils, second only to tropical soils, the difference between them resulting from the winter season when deciduous trees are virtually dormant and the colder weather inhibits growth. Brown earths are fertile and can develop to about 2 m (about 6 ft) in depth, because of the action of tree roots breaking up the parent rock. If cleared, this soil can be productive for agriculture. 22

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BROWN EARTH SOILS EXPLANATION: Climate: DESCRIPTION: Horizons less distinct Mildly acidic due to a mull humus A-Horizon is dark brown B-Horizon is light brown A-Horizon has a loamy texture B-Horizon has a light texture Generally free draining soil EXPLANATION: Climate: Precipitation is greater than evaporation only in summer Leads to moderate leaching Warm summers 25

BROWN EARTH SOILS EXPLANATION: Vegetation and Soil Organisms: Mixed broad leaf and much plant litter Broken down easily by active soil biota and warmer climate Greater abundance of earthworms, insects etc. Quicker breakdown of material than podsol soil Dark brown horizon as humus replaces material leached out Leaching is less pronounced because evaporation and precipitation are more equally balanced Colour lightens in the B horizon as humus becomes less abundant Deep roots can penetrate the C horizon and extract minerals to ensure greater recycling 26

PODZOLS Podzol soils are mainly found in the taiga (boreal forest) biome at latitudes greater than 60° in Eurasia and North America, and at higher altitudes in temperate latitudes. They are also found in Britain in many moorland areas. Podzols form under a harsh, cold climate where growth is slow during the winter months and snow accumulates and stays on the ground for long periods. The vegetation consists largely of coniferous trees, which are specially adapted to the climatic conditions, or moor and heathland plants in Britain. Productivity is low due to the climatic conditions. The soils are impoverished and the climate is unsuitable for agriculture, but is suitable for commercial forestry. Leaching is the key process at work in Podzols. 27

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PODSOL (PODZOL) SOILS DESCRIPTION: Horizons well defined Mor humus Thin black layer with decaying litter needles A Horizon very dark, then ash grey B Horizon – red / dark brown Iron pan can develop A Horizon has a sandy texture B Horizon has a denser texture (clayey) Iron pan can impede drainage and cause waterlogging 30

PODSOL (PODZOL) SOILS EXPLANATION: Climate: Vegetation: Colder climate – found at higher latitudes or altitudes Lowers the rate at which litter is decomposed Excess of precipitation over evaporation coupled with; Spring snowmelt and rainfall contribute to leaching Minerals are eluviated from the A horizon This leads to colouring and iron-pan formation in the B horizon Aluminium, iron and clay are re-deposited (illuviated) Vegetation: Coniferous vegetation – needles and cones These are acidic in nature with a waxy coating This leads to slow breakdown of organic matter And an acidic humus layer 31

PODSOL (PODZOL) SOILS EXPLANATION: Biota: Clearly defined horizons show a lack of soil biota Lack of mixing of soil by earthworms Reflects low winter temperatures 32

SOILS PAST PAPER QUESTION For Brown Earth Forest Soil or a Podsol Soil: Draw a soil profile and annotate it to show the main characteristics of the soil. Explain the processes which have created this soil profile. 12 marks Attempt b) 6 marks 33