Soil Defined as the part of dirt that will support life Found in all places all over the world, but not all soil is the same Oceans and deserts have sandy soil, swamps are muddy soil Soil is divided into four parts Water  Found in pore spaces and supplies the moisture and nutrients for root systems Air  Found in pore spaces and is a source of carbon dioxide and oxygen for plants and animals Mineral Matter All the sediments that make up most of the soil Organic Matter  Humus is the decayed matter from dead animals and plants that supplies nutrients to soils

Soil

Soil Formation Soil is made from the weathering and erosion of rocks Five factors that determine the soil types 1. Climate (most important factor) Warmer and wetter climates that encourage all types of weathering will have some of the thickest soils Drier, cooler climates will have thinner, not good soils 2. Parent Material The sediments in the soil have to come from an original rock that got weathered called a parent rock The harder the parent rock, the less sediments you have in the soil because not many rocks will weather easily

3. Time The longer the time you have to weather the rocks, the thicker the soil that you will have. 4. Organisms Plants are the mains source of organic humus in the soils Microorganisms and fungi will decompose the dead stuff into nutrients that animals and plants can use

5. Slope On steeper slopes, erosion will increase, very little water gets into the soil, and the soil itself is very thin because much of it will be pulled down by gravity Flatter areas will have erosion decrease, lots of water in the soil, and the soil is generally thicker

Soil Profile Soil is not the same all the way down to the crust, it changes as you go further down The layers of soil are called the soil profile There are four layers to the soil profile A-Horizon, B-Horizon, C-Horizon, and the Unweathered Parent Material (UPM) also known as the crust of the Earth

O-Horizon This extremely thin layer is the pure organic layer of the soil profile This layer is made of humus, the dead leaves and organic bodies of the organisms that live there

A-Horizon Top layer of the soil that contains most of the nutrients for the plant’s roots Many roots, bugs, and burrowing animals will be in this layer Mostly made of humus, water and air

B-Horizon Mostly made of clay and water Not much air makes it down here because the pore spaces filled with water that trickled down Deeper roots reach down from older trees to get the water found there Not many bugs or smaller creatures here because the clay is so hard packed that they cannot dig through

C-Horizon Mostly made of weathered parent material (smaller to larger sediments) Only the deepest roots will reach down here for the water that is there Few if any animals or bugs because they cannot dig through the rocks

Unweathered Parent Material (UPM) This should be solid bedrock to some weathering towards the top of the layer. No animals are here because there is no air and very little water

Soil Textures Refers to the proportions of the different particles sizes that are found in all soils Categories are based on the percentages of sand, silt and clay The different textures can be found on a diagram called the soil triangle