SOILS, MASS MOVEMENTS, AND SOIL CONSERVATIONFrom 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.

Talus is 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.

Slumps occur 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.