SS105 Soil Formation

What are the 5 soil forming factors?

climate, organisms, parent material, relief (or topography), and time.

How does climate effect soil formation?

Strongly affects the vegetation component of organism factor. total precipitation also influences the rate of weathering of soil minerals as well as the ease of accumulation of stable organic matter.

What is meant by organisms in terms of soil formation?

Usually means dominant vegetation (trees vs. grasses), but sometimes includes earthworms and humans

What is root turnover?

The rate at which plants replace their roots and add organic matter to the soil.

What is the difference in organic matter between forests and grasslands?

Grasses inject far more organic matter through a greater depth than forests do. Tallgrass praires have very thick A horizons.

What taxonomic order are the soils formed under temperate grasslands?

Mollisols (Molli- = "soft")

How does parent material affect soil formation?

Includes both the mineralogy and mode of transport for the raw inorganic material that forms into a soil.

What are the 2 geological generalizations?

1. Rocks have texture based on the size of the internally chemically uniform mineral grains they are composed of. Bigger grains = coarse texture. Coarse-textured rocks weather to produce coarse-textured soils. Fine textured rocks produce fine textured soils.

2. Rocks have overall color: Dark, intermediate, or light. Dark colored rocks weather to produce more fertile, nutrient rich soils than light colored rocks.

How does relief (or topography) affect soil formation?

In topographically low, poorly drained spots on the landscape, flooded conditions can slow humus decomp so much that peat deposits accumulate above the mineral plant material.

What are histosols?

Soil order given to those most effected by relief. (extremely flooded areas that form peat)

How does time effect soil formation?

Soil first forms at the top, accumulating organic matter. Over time, the organic matter accumulates to a greater depth and stuff like clays, Al, and Fe start to loosen up in the top soil and migrate down into B horizons.

Over time what happens to soil?

It penetrates deeper and deeper into the parent material.

What are oxisols?

Ancient tropical soils

What are entisols?

Super young soils

Where do soils form from?

From the top down

What are residual materials?

Parent materials created by weathering-induced disintegration of local bedrock. All other soils form in

What do soils form from if not residual materials?

transported parent materials

What is alluvial (or fluvial) material?

Parent material deposited as sediment in the floodplain of a stream or river.

What is colluvial material?

Originally residual material that has been transported by eroding down a hillside