Soil

What is Soil Made Of? Minerals Bacteria and Organic materials Air A true soil consists of 4 main parts. If one of these parts is missing, the material is not considered a true soil. Minerals Bacteria and Organic materials Air Moisture

Minerals Minerals come from “parent material”. What is parent material?

Minerals An example of parent material is rock. The minerals become a part of the soil when the rock weathers into smaller particles. Plants need minerals such as calcium, phosphorous and potassium to grow.

Bacteria and Organic Materials When plants and animals die (organic material), they are decomposed by bacteria in the soil. This process forms humus, which provides nutrients and moisture to plants. Humus gives soil its dark color.

Air Plants need air around their roots. Air pockets are created by: A high humus level Worms Insects Small animals

Moisture Water is an important part of soil for 2 reasons: Water dissolves nutrients into the soil and is then taken up by plants through their roots. 2. Water is necessary in the weathering process.

Soil Formation Like rock, soil is arranged in layers.

Soil Profiles This is a picture of a typical soil profile. It consists of 3 horizons (sections). A-horizon: topsoil B-horizon: subsoil C-horizon : parent material Draw a diagram of a typical soil profile. Page 161 of text.

Loam The best soil for growing plants is called loam. It is a well balanced mixture of sand, silt, clay and humus. Loam is the best soil for plant growth because it: Encourages root growth Holds moisture Allows water to pass through it at a moderate rate.

Wet Climate Soil In a wet climate where there is an abundance of rain, there is a continued downward movement of water. As the water moves through the soil, it carries away the nutrients that the plants need. This process is called leaching.

Leaching The downward movement of water leads to a process called leaching. Leached soil can be identified by its thin topsoil layer (A-horizon). Draw a diagram of a wet climate soil profile. Page 161 in text.

Dry Climate Soil In dry climates where there is an upward movement of water, minerals such as calcium are brought to the top of the soil from the bottom of the soil profile. This mineral rich soil can be poisonous to many plants. This process is called calcification.

Calcification The upward movement of water leads to a process of calcification. Calcified soils can be identified by their very thick, dark brown to black “A” horizon. Draw a diagram of a dry climate soil profile. Page 161 in text.