2 Why is soil important?Soil is a natural resource. A natural resource is a material on Earth that is necessary or useful for people. It is not man made.Because it is made from the weathering of rocks, it is considered a “renewable” resource.Without soil, plants could not grow, which means people and animals would have no food!
3 How is soil formed?It is the main product of mechanical and chemical weatheringBacteria breakdown of plants and animals forming HUMUSWorms, ants, moles, burrow through soil allowing water to weather rock and supplying nutrients.
5 What controls soil formation? Parent material/BedrockTime: the more time soil has to develop, the thicker the soil, the less is resembles the parent material.Climate: most influential factorPlants and Animals: fertility depends on amount of organic matterSlope:Steep slopes: poorly developed
7 What makes up a Soil profile? A soil profile is a vertical sequence of soil layersA soil profile is made up of horizons. The number of horizons depends on how “mature” the soil is. “Mature” soils take 1000’s of years to form and contain about 6 horizons. “Immature” soils sometimes only contain 2 horizons.
11 What makes up each of the soil horizons? The “O” Horizon: Topsoil, mostly plant litter at the top and humus at the bottom. Rich in organic material. Brown in color.The “A” Horizon: Topsoil, dark in color, some humus, and biological activityThe “E” Horizon: Light colored mineral materialLeaching: Water percolates down and carries minerals down to lower horizons.
12 What makes up each of the soil horizons continued The “B” horizon: Subsoil, contains clay material. Red-brown color.The “C” horizon: partially altered parent materialRegolith: rock and mineral fragments, NO organic materialResidual soil: soil formed over the original bedrock. Resembles the bedrock/parent rock.The “R” horizon: Solid bedrock/parent rock, unweathered
13 How are soils different? Different soils are found in different places. Some soil is good for growing plants, while other soil is not.Soils differ in color and texture. A soil’s color has to do with what’s in it. For example, red soil may contain a lot of iron. Dark brown or black soil contains a lot of humus.
14 Chemistry and Composition Soil TypesClimate/Soil TypeVegetationTypical Area (s)Common colorsChemistry and CompositionAnnual RainfallFertility
15 What are the different soil textures? Soil texture describes how big the particles, or pieces, of soil are.Most soils are either sand, clay, silt, or loam.
18 What are the different soil textures? Sand: the largest particle in the soil. Water flows through it very easily. Because it doesn’t retain water very well, plants have trouble growing in this type of soil.Clay is the smallest of particles. Clay also can hold a lot of nutrients, but doesn't let air and water through it well. Can result in TOO MUCH WATER for the plant.
19 What are the different soil textures? Silt is a soil particle whose size is between sand and clay. Smaller than sand, larger than clay.Loam: This soil is a mixture of sand, silt, clay and humus.It is considered to be the perfect soil.Holds water well and has many nutrients.
20 What is the difference between porosity and permeability? Porosity is a measure of how much of a rock is open space. This space can be between grains or within cracks or cavities of the rock. Permeability is a measure of the ease with which a fluid (water in this case) can move through a porous rock.
21 The soil texture triangle Soil texture depends on its composition and the relative portions of clay, sand, and silt.
22 How to read the soil triangle Classify a soil sample that is 30% clay, 15% silt, and 55% sand.
25 How is soil eroded?Soil is eroded when it is moved from place to placeIt is more common on steep slopes or where there is little vegetationBalance is maintained when new soil forms at the same rate it is eroded
29 How do humans cause erosion ? Agricultural practices such as plowing and slash and burn removes plant coverClear cutting for lumber, farming, and grazingOvergrazing by sheep and cattleUrban constructionOpen strip mining
30 What can we do to slow the rate of soil erosion? No-till farming is done without plowing leaving topsoil in placeContour and Terracing uses the natural shape and slope of the land to grow cropsRotation system