 Vocabulary  Soil: Well weathered rocks and minerals mixed with decaying organic matter which covers much of earth’s land surface.  Humus: Soil containing high levels of decaying organic matter; very rich in nutrients.  Announcements:

 7.EC 25 A. 2  Construct explanations of how soil quality (including composition, texture, particle size, permeability) affects the characteristics of an ecosystem using evidence from soil profiles.   Describe natural processes that change Earth’s surface Interactions among changes in the environment due to natural hazards (including landslides, earthquakes, mountain building, new land being formed, weathering, erosion, sedimentation, soil formation).

 Soil is a mixture of well weathered rocks and minerals with decaying organic matter.  What kind of “organic matter” would naturally be in soil?

 Soil formation occurs over a long period of time.  When mechanical and chemical weathering breaks rocks into very fine pieces, soil is created.  Organisms live and die in the soil, leaving their waste and remains.  Decomposers such as bacteria and fungus also live in the soil, breaking down the remains of organisms and adding the nutrients that composed their bodies to the soil.

 There are several characteristic layers of soil called soil horizons.  The entire collection of horizons is called a soil profile.

 Each layer, or horizon of soil has it’s own characteristics which make it different from other layers of soil.  The depth of each layer depends on the conditions in that particular environment.

 C and R Horizons.  Parent material is solid or slightly weathered or decomposed rock.  Sometimes called bedrock because the rest of the soil lays on it.  The deeper you dig in your back yard, the bigger (less weathered) the rocks get. These rocks are the “parent material” from which the soil above was “born”

 B horizon  Subsoil is more broken down than parent rock, but there are sometimes still fairly large rocks mixed with finely weathered rock, and some organic matter (plant roots, bones).

 A horizon  Finely weathered rock and mineral particles mixed with the highest concentration of organic matter and decomposers.  Usually between 2 and 8 inches in depth.

 Hue-Muss (hummus is food)  O horizon  Usually a part of the A horizon.  Rich with organic matter and nutrients.  Dark brown to black in color due to organic carbon.  Mature compost.

 The speed that soil forms depends not only on the amount of rainfall mainly, but other weathering factors.  U.S. Department of Agriculture estimates that it takes 500 years to form an inch of topsoil.  That’s less than 0.01 mm yr

 Soil is the primary nutrient base for plants.  Thick nutrient rich soil is VITAL for agriculture.  The deeper the topsoil layer, the more sustainable (longer lasting) that land is for agriculture.

 Many people’s lives depend on the quality and quantity of good topsoil.  Topsoil disappears by erosion (mostly due to agriculture) about 1% every year.  Soil can be over- used by people and left useless. This is called desertificaiton.

 1. What are the two main components of soil?  2. How are nutrients added to soil?  3. Why is it important to try to conserve topsoil?