Soils - Soils:1 Soils Properties Formation Pedogenic...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Soils:1 Soils Properties Formation Pedogenic regimes Soil Classification A soil is the organic and inorganic material located above bedrock and capable of supporting life. (There are many definitions of soil, this is just one.) The inorganic component is the products of chemical weathering we just talked about and it can be residual material , weathered bedrock that stays in place, or transported material that was weathered elsewhere, eroded and deposited at its present location. Combinations of residual and transported material at one location are common. The organic matter in soils is mostly derived from dead plant matter, which is eaten by many types of decomposers, bacteria, fungi, algae, insects, worms, and various other critters and converted to humus . After it has been through the decomposers, the humus is more stable and is better able to release nutrients for plant use. Soil Properties - Soil texture is the combination of particle sizes present in a soil. Soils with mostly clay sized particles are called clay soils , same for sandy soils and silty soils . Soils with significant amounts of all three are called loams . (Clay is a type of mineral, but also a size range. It just so happens that most clay particles are smaller than silt.) Texture is important because it determines the ability of a soil to hold and transmit water. (More on soil moisture in another lecture.). Soil structure involves the clumping of individual soil particles to make larger particles. These aggregates (or dirt clods) change the characteristics of the soil in such factors as erosion and water holding. Clays are sticky and organic matter too can provide cohesion to bind particles together. The structure of a soil can be granular (loose particles), blocky (clumps), platy (layers) or others. The fertility of a soil is determined largely by the clay and humus present. Clay and humus particles tend to be anions , so they attract cations . Fortunetely, the nutrients that plants need are cations. Clay and humus hold onto the nutrients in the soil; otherwise they would be washed away by water. Nutrients, therefore, are available for plants to use. The cation exchange capacity is a measure of the soil's ability to hold cations, and, so, is a measure of the fertility of the soil.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Soils:2 The acidity of a soil also affects the plants growing in it. Acidity is measured with the pH scale , where 7 is neutral (distilled water), less than 7 is acidic, and more than 7 is alkaline. Most crops do best in mildly acidic soils. Our soils here in West Texas tend to be mildly alkaline, which is better for cotton. Soil color is largely determined by the amount of organic matter and the amount and weathering of iron. Organic matter makes soil dark brown or black. Oxidized iron becomes red, yellow and brown. Where oxygen is not present
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 10/27/2011 for the course GEOG 1401 at Texas Tech.

Page1 / 7

Soils - Soils:1 Soils Properties Formation Pedogenic...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online