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Transcript
Soil and Natural Vegetation SOIL • SOIL: surface layer of the earth, composed of mineral and organic materials, air , and water SOIL • True soil consists of 4 main parts: – – – – 1. Minerals, 2. Bacteria and Organic Material 3. Air 4. Moisture • If one of these parts is missing, the material cannot be considered soil COMPONENTS OF SOIL Minerals • The minerals in soil come from rock, known as the parent material. • Rock is broken down by weathering into smaller particles of sand, silt, and clay. • Many minerals are nutrients needed by plants for growth. e.g. calcium, potassium, etc. Bacteria & Organic Materials • When plants & animals die, they are decomposed by bacteria in the soil. • As bacteria break down the organic matter, nutrients are released. Bacteria & Organic Materials • Decaying organic materials form humus which provides nutrients and moisture for plants • HUMUS: Dark, upper layer of soil made up of partially decayed plant material • The process of decay is nature’s way of recycling nutrients • Humus gives the soil its dark colour Air • Air is found in all soils usually in between soil particles • Plants need air around their roots • Air spaces also created by insects / worms and small animals that tunnel through the soil Moisture (Water) • Water dissolves nutrients in the soil and is then taken up by plants through their roots • Helps weather rock and decay organic materials ANIMALS • Not an essential component of true soil but few soils exist w/o them (worms, mice, insects, etc.) • Helps distribute soil particles and nutrients & provide pathways / openings for water and air • Add organic material to the soil after they have died. Soil Profile • O/A - TOPSOIL -this top layer contains humus. It is rich in organic material. It is dark brown/black in colour • B-SUBSOIL- combines minerals and organic layers • C- PARENT MATERIAL mineral materials from which soil is made. Usually bedrock or glacial deposits Soil Formation Two processes contribute to soil formation: • LEACHING • CALCIFICATION Leaching • Is a continual downward movement of water through the soil • As the water moves down, it dissolves the chemical nutrients and carries them away • This downward movement removes nutrients that plants need • You can identify leached soil by its poor, often thin, topsoil layer • Leached soils can be developed into excellent farmland by adding fertilizers Calcification • Occurs in dryer climates • As water in the topsoil evaporates, water from below is drawn up to replace it - CAPILLARY ACTION • As the water reaches the surface, it evaporates leaving behind the minerals that were dissolved in it • The result is a thick topsoil layer, rich in minerals • Calcium is the main mineral deposited near the surface • In very dry climates the amount of mineral deposits can be poisonous to plants