- Slides: 26
Weathering and Soil Formation
Soil Composition: § Soil is a mixture of four materials: § Weathered rock particles (Main ingredient) § Organic matter (5 Percent) § Water (20 to 30 percent of soil) § Air (20 to 30 percent of soil)
Weathering and Organic Processes from soil § Water and air make up about 20 -30% of a soils volume. § 5% comes from organic matter which is remains and wastes of plants, animals, and other living organisms.
Organic Matter § The word Organic means, “coming from living organisms. ” § It comes from the remains and waste products of plants, animals, and other living organisms. § (example: leaves fall to the forest floor, decay, and become part of the soil. ) § This decayed organic matter is called Humus.
Different Soils: § Different soils are made of different ingredients and different amounts. § (Black soil- which is much darker tends to have more humus, or decayed organic matter. ) § Black soil- also contains more water. § The combination of these two things make darker soil much better for growing things.
Weathering and Organic Processes from soil § § § There are four world soil types 1. Tropical Soils 2. Desert Soils 3. Temperate Soils 4. Arctic Soils
Weathering and Organic Processes from soil § Tropical soils from in warm, rainy regions. Heavy rains wash away minerals, leaving only a thin surface layer of Humus. Tropical soils are not suitable for growing most crops.
Weathering and Organic Processes from soil § Climate will control what types of soil you find in that area. § The shape of the land also affects soil. Mountainous regions can be very different from soils found in valleys. Why?
Weathering and Organic Processes from soil § Desert Soils form in dry regions. These soils are shallow and contain little organic matter. With the low rainfall, chemical weathering and soil formation occur very slowly.
Weathering and Organic Processes from soil § Temperate soils from in regions with moderate rainfall and temperatures. Some temperate soils are dark colored, rich in organic matter and minerals and good for growing crops.
Weathering and Organic Processes from soil § Arctic soils form in cold, dry regions where chemical weathering is slow. They usually don’t have well developed horizons.
Kind of soil depends on many factors § § § The kind of rock in the area The area’s climate or weather pattern The landforms in the area The plant cover in the area The animals and other organisms. Time (how long it has to form. )
Layers Upon Layers § Soil Horizon: is a layer of soil with properties that are different from those of the layer above. § Soil Profile: in any location there can be different horizons that make up a profile.
Basic Soil Profile Old Al Eats Beans Corn and Rhubarb O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus A Horizon - The layer called topsoil; is made up of humus mixed with mineral particles. E Horizon - This layer is light in color; It is made up mostly of sand silt, having lost most of its minerals and clay as water drips through the soil B Horizon - Also called the subsoil - It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate). C Horizon - slightly broken-up bedrock R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.
Soil Horizons § O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus § A Horizon - The layer called topsoil; is made up of humus mixed with mineral particles. (black soil) § E Horizon - This layer is light in color; It is made up mostly of sand silt, having lost most of its minerals and clay as water drips through the soil § B Horizon - Also called the subsoil - It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate). § C Horizon - slightly broken-up bedrock § R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.
Properties of Soil § Texture: § Color: § Pore Space: § Chemistry:
Soil Texture § A soil’s texture Is determined by the size of weathered rock particles. § The particles are classified as either § Sand- the largest particle, gritty feeling, doesn’t hold water well. § Silt – smaller, is smooth and silky when wet, it holds water better than sand. § Clay- The smallest, sticky when wet, absorbs the most water. (dries very hard. )
§ § § Dirt Knowledge Not all dirt is the same. Based on it's components the suitability for planting can be very different. Things like a very high clay content may mean it holds water very well or if there is too much clay then it could actually create a real problem and not allow any water to pass creating ponding. Too high a sand content can cause the opposite effect It will not hold enough water to support the plant in hot weather or high wind. Silt is an in-between situation in that it's particle size is smaller than sand, it is less plastic than clay and often has a higher organic content associated with it.
Weathering and Organic Processes from soil § What are the differences between the two soils, think about how soil is made.
Soil Color § The color of the soil is a clue to it’s other properties. § Black or brown soils usually contain a lot of humus. § Reddish soil usually contains more Iron.
Pore Space § Pore space § is the space between soil particles. § has two things, Air and Water § Plants will grow the best when the pore space has 50% air and 50% water.
Soil Chemistry § The water in soil has a specific PH level. § This term PH is a measurement of acidity. § When water reaches a certain PH level, it is best to help plants grow. § By knowing this about soil, farmers can make soil more acidic or less acidic to help plants grow.
PH scale and Nutrient availability
Test the two soil’s PH § Follow the instructions carefully. § § In the clear tube, pour 3 ml of the p. H indicator solution. Put only a small pinch (1 ml) of soil into the tube. Put the cap on the tube and shake for 30 seconds. Allow the soil to settle and the solution should change colors. § Compare the color of the solution to the Ph color chart. § How would being about to do this be useful? (summary)