Soil: A Renewable Resource

PA Standards  C: Unifying Themes  B: Technological Devices  C: Ecosystems and their Interactions “Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals.” - Aldo Leopold, A Sand County Almanac, 1949 Evaluate change in natural systems. Analyze how natural changes affect the balance within an ecosystem. Assess and apply recurring patterns in natural systems. Evaluate appropriate instruments and apparatus to accurately measure materials and processes.

Key Questions What are soils and how are they formed? What happens to matter in an ecosystem? What are the soil horizons and how do they indicate the principal soil type? What are the different properties of soil?

What are soils and how are they formed?

Importance of Soil What is Soil?  Soil is a thin covering over most land that is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms (microscopic decomposers) Why is it important?  Base of life on land.  Provides most of the nutrients needed for plant growth and also helps purify percolating water and store water.  Helps decompose and recycle biodegradable wastes.  Stores carbon as carbon compounds.

What happens to matter in an ecosystem?

Soil as a Resource How does it form?  Bedrock broken down into rock fragments and particles by physical, chemical, and biological processes called weathering. Lichens add nutrients and when they die add organic matter Renewable resource  Very slowly – 1 cm (0.4 inch) of soil can take from 15 to hundreds of years to form  Mature soils, or soils that have developed over a long time, are arranged in a series of horizontal layers called soil horizons.

What are the soil horizons and how do they indicate the principal soil type?

Soil Horizons

Soil Profiles of the Principal Terrestrial Soil Types

Layers in Mature Soils Infiltration  The downward movement of water through soil. Leaching  Dissolving of minerals and organic matter in upper layers carrying them to lower layers. The soil type determines the degree of infiltration and leaching.

What are the different properties of soil?

Some Soil Properties Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.

Porosity: the amount of empty pore space in the soil Permeability: the ability of a soil sample to transmit fluid Sand has high porosity and high permeability

© Brooks/Cole Publishing Company / ITP Fig. 5–17 Soil texture is determined by the particular mix of clay, silt, & sand.

Who Am I? 5% clay, 15% silt, 80% sand Loamy sand 40% silt, 35% clay, 25% sand Clay loam 9% sand, 85% silt, 6% clay Silt 16% sand, 55% silt, 29% clay Silty clay loam

Try these… % Sand% Silt% ClayTexture Classification

How did you do? % Sand% Silt% ClayTexture Classification Clay Sandy Clay Loam 40 20Loam Silty Clay Loam Clay Loam Sandy Loam 1045 Silty Clay

Activity Soil Texture Analysis Activity  Texture by Feel  Texture by Sedimentation Soil Texture Triangle

Review Key Questions What are soils and how are they formed? What happens to matter in an ecosystem? What are the soil horizons and how do they indicate the principal soil type? What are the different properties of soil?

Thought Problems What type of soil would produce high crop yields? What type of terrestrial types (biomes) are these found? Why is the humus beneficial? What layers of soil are the roots of most plants and the majority of a soil’s organic matter concentrated? What color soil would be good for growing crops? Which layers have the most amount of inorganic matter? Is a more or less porous soil better for plant growth?

Thought Problems - Answers What type of soil would produce high crop yields? What type of terrestrial types (biomes) are these found?  Fertile soil with thick topsoil layer with lots of humus. They are found in grasslands or deciduous forests. Why is the humus beneficial?  It helps the topsoil hold water and nutrients taken up by plant roots. What layers of soil are the roots of most plants and the majority of a soil’s organic matter concentrated?  The top two layers. What color soil would be good for growing crops?  Dark brown or black – rich in nitrogen and organic matter. Gray, bright yellow, and red topsoil's have low organic matter and nitrogen. Which layers have the most amount of inorganic matter?  The B horizon (subsoil) and C horizon (parent material). Is a more or less porous soil better for plant growth?  More porous – it contains oxygen, necessary for cellular respiration, and nitrogen gas.