Soils, Mass movements, and soil conservation From a half-sick Mr. Lewis
Soils • Soils are a result of weathering • Without soil there could be no life on land • Soil is made of loose, weathered rock, and organic material with which plants can grow • The rock material in soil contains three noticeable parts: SAND, CLAY, and SILT
Soil • The material from which a soil is formed is called Parent Material • Often this is the bedrock beneath the soil • Soil that has bedrock as its parent material is called Residual Soil • Soils formed from materials left by wind, rivers, and glaciers are called transported soils
Soil • Soil Profile – the cross section of earth exposed by digging through layers of soil. • In most mature soils there are three zones (horizons): • A-horizon is topsoil, it’s gray to black and has organic material (humus) from decayed plant and animal tissue
Soil • B-horizon begins with subsoil. Much of the clay in the topsoil has washed into the subsoil. It’s usually red or brown from iron oxides • C-horizon is made of slightly weathered parent material such as rock fragments. Near the bottom they sit on unweathered bedrock
Soil Types and Climates • The most important factor affecting soil is climate • A tropical soil forms in the areas that have constant high temperature and heavy rainfall • Warm, wet conditions speed up the chemical weathering and soil forms quickly • The soil profile may be more than three metres thick • Frequent heavy rains wash nutrients out of the soil, making tropical soils relatively infertile
Soil Types and Climates • Grassland soils form in areas that receive enough rainfall for heavy grass, but not enough for trees. • The soil profile is usually less than a metre thick • The A-horizon is black or deep-brown • Grassland soils are very rich in organic matter and are very fertile soils
Soil Types and Climates • Forest soils form in humid regions that have cool seasons and forests of hardwood and evergreen trees. • They have well developed A, B, and C-horizons. • The soil profile is usually less than a metre in total thickness. • Not very fertile.
Soil Types and Climates • Desert soils form in very dry climates. • Profiles are seldom more than a few centimetres from top to bottom. • Nutrients are not washed away from the soil, and can be very fertile when watered
Soil Types and Climates • Arctic soils form at high elevations and high latitudes. • The surface is poorly drained and boggy. • The bottom layers are constantly frozen (permafrost). • Soil profile is often only a few centimetres thick.
Mass Movement • Wherever the ground slopes, gravity causes soil and rock fragments to fall, slide, or move at very slow speeds to lowerlevels. • These movements are called mass movements; there are several important types: • Creep is a slow, imperceptible downslope movement of the soil. • Talusis a pile of rock fragments at the base of a cliff, and is the result of mass movements near steep slopes
Mass Movement • A landslide is the sudden movement of a mass of bedrock or loose rock down the slope of a hill, mountain, or cliff. • An avalanche is a landslide made from masses of snow, ice, soil, or rock, or mixtures of these materials. • Landslides are likely to occur on steep slopes, especially those caused by erosion or by mining. • Slumpsoccur when small blocks of land tilt and move downhill [this happens commonly to roads which have been cut into mountains (hwy1)]
Mass Movements • A mudflow is the rapid movement of a water-saturated mass of clay and silt. • A mud avalanche is an especially fast and large mudflow, often caused by volcanic eruptions quickly melting glaciers.
Soil Conservation • Soil erosion is the removal of topsoil by the action of running water or wind, it is a serious environmental and economic problem. • Soil erosion can be reduced by a number of methods. • 1. Planting windbreaks,which are belts of trees along the edges of fields. The trees slow the wind and reduce wind erosion.
Soil Conservation • 2. Contour Farming • Crops are planted in rows parallel to land contours. • This prevents water from flowing rapidly downhill and carrying soil with it. • Flattening hill slopes into terraces also slows stream flow and reduces soil erosion.
Soil Conservation • 3. Strip Cropping • A crop that leaves bare ground between rows is alternated with a crop that completely covers the ground. • The no-till method uses the technique of plowing, planting, fertilizing and weed control being done at the same time. • The soil is not disturbed again until harvest.