Soil Formation and Composition Biotic living Abioticnonliving 1

Soil Formation and Composition

Biotic (living) Abiotic(nonliving) 1. Make a table and list 5 examples of each

Soil Formation Soil is the loose, weathered material on Earth’s surface in which plants can grow. It is formed wherever bedrock is exposed. Bedrock is the solid layer of rock beneath the soil. It weathers when it is exposed at the surface.

Soil Composition Soil is more than just weathered rock. Soil is a mixture of rock particles, minerals, decayed organic materials, air, and water. All soil is NOT the same - it depends on the bedrock that it was weathered from and the type of weathering. The dead organic material is broken down by decomposers to form humus by decomposition. Humus helps create spaces in soil for air and water.

Soil Formation and Composition 2. Draw the flowchart and fill it in as you go through it. Water Oxygen Acid Carbon dioxide Living organisms Wind Heat Rain Cold Hail ice Mechanical Rock weathering Smaller rock particles Chemical weathering Soil Mix with other materials on the surface Particles with different mineral make up

Soil Texture Soil texture depends on the size of the individual soil particles. Soil particles range in size from gravel to clay particles too small to be seen by the unaided eye. The sand, silt, and clay shown here have been enlarged.

Soil Texture and Plant Growth Soil that is mostly clay is heavy and dense which allows them to hold a lot of water. Is this good? No, plants may “drown” from a lack of air. Sandy soil has a coarse texture and water will drain quickly. Is this good? No, plants may die from a lack of water. Loam - The perfect soil.

“Permeable” is “Porous, ” but “Porous” May Not Be “Permeable” A pore is a space in rock, soil, or sediment that is not occupied by mineral matter and that allows the passage or absorption of fluids. The word comes from Latin porus, Greek poros, where it means “passage. ” A thing that is porous is having pores, and porosity is the condition of being porous.

Porosity is the ratio of the volume of openings (voids) to the total volume of material. Consists of the spaces between the grains Permeability is a measure of the ease with which fluids will flow though a porous rock, sediment, or soil. The larger the pore space or the greater their number, the higher the porosity. Although a rock may be highly porous, if the voids are not interconnected, then fluids within the closed, isolated pores cannot move. The more tightly packed the grains are, the lower the porosity.

Soil Horizons A soil horizon is a layer of soil that differs in color and texture from the layers above or below it. They form over long periods of time. Think centuries not decades. It can take a hundred years for just a few centimeters of soil to form.

Soil Horizons - C The C horizon forms 1 st as bedrock weathers and rock breaks up into soil particles.

Soil Horizons - A - Topsoil The A horizon develops from the C horizon when plant roots weather the rock mechanically and chemically. Plants also add dark, organic material to the soil that is a mixture of humus, clay, and other minerals

Soil Horizons - B - Subsoil The B horizon develops as rainwater washes clay and minerals from the A horizon to the B horizon. Contains little humus.

Rate of Soil Formation Depends on the climate and type of rock. Occurs most rapidly in warm, wet climates. Limestone weathers more quickly than granite in warm, wet climates.

Soil Horizons 3. As the topsoil and subsoil develop, what happens to the bedrock? 4. Make a sketch of the three horizons and label each.

5. Which living things contribute most of the organic materials that form humus? 6. How do decomposers contribute to the formation of soil? Life in Soil The leaves, roots, and stems of plants are a major source of humus. 7. What role do earthworms play in the formation of soil? 8. Which organisms break up hard, compacted soil and mix humus through it?

Fertile soil is rich in nutrients that plants need, such as nitrogen and phosphorus. As plants shed leaves they form a loose layer of litter on the ground. Dead plants add to litter and over time decay to form humus. Life in Soil Main Decomposers Fungi - molds & mushrooms, grow on and digest plant remains Bacteria - microscopic, attack dead organisms and their waste Protists Burrowing animals break up hard, compacted soil and add nitrogen when they excrete waste. Earthworms - mix humus to aerate the soil. They also eat soil and eliminate it as waste that are enriched in nutrients.

Soil Formation and Composition 9. Draw the flowchart in your notebook and fill in the blanks. consists of is made of above the