Soil Notes PDF

SOIL NOTES  Soil Formation Soil is the loose covering of weathered rock particles and decaying organic matter, called humus, overlying the bedrock on Earth’s surface, and serves as a medium for the growth of plants. Soil formation starts when weathering breaks solid bedrock into small...

SOIL NOTES  Soil Formation Soil is the loose covering of weathered rock particles and decaying organic matter, called humus, overlying the bedrock on Earth’s surface, and serves as a medium for the growth of plants. Soil formation starts when weathering breaks solid bedrock into smaller pieces, which continue to weather and break down further. Soil Formation During the process of soil formation, layers develop in the soil. Most of the volume of soil is formed from the weathered products of a source rock, called the parent material. A soil that develops from weathered bedrock is called a residual soil. A soil that develops from weathered rock material that has been transported and deposited elsewhere is called a transported soil.  Soil Profile A soil profile is a vertical sequence of soil layers. New soils that have not yet developed distinct layers are called undeveloped soils. Mature soils have distinct layers that can have taken tens of thousands of years to develop. A distinct layer within a soil profile is called a soil horizon. There are typically four major soil horizons in mature soils. From the surface downward, they are designated: O, A, B, C and R (bedrock). Soil Horizon Description O top layer of organic material composed of humus and leaf litter A a layer of weathered rock combined with a rich concentration of dark brown organic material derived from the O horizon above B a red or brown layer enriched over time by clay and minerals deposited by water flowing from above, or percolating upward from below C nearest the parent material, contains little or no organic matter, and is made of broken-down bedrock Factors of Soil Formation 01 Climate 04 Biological Activity 02 Topography 05 Time 03 Parent Material 1. Climate The most significant factor controlling the development of soils because it also affects the weathering of rocks. Temperature, wind, and the amount of rainfall determine the type of soil that can develop. 2. Topography Topography refers to the slope and orientation of the land. In the northern hemisphere, slopes that face south receive more sunlight than other slopes, allowing more vegetation to grow, which helps determine the type of soil that develops. 3. Parent Material If the soil is residual, it will have the SAME chemical composition as the local bedrock. If the soil is transported, the minerals in the soil are likely to be DIFFERENT from those in the local bedrock. 4. Biological Activity Organisms including fungi and bacteria, as well as plants and animals, interact with soil. Different types of organisms in a soil influenced the type of soil that will form. Vegetation also helps reduce the amount of soil erosion. 5. Time The effects of time alone can determine the characteristics of a soil. Soils take thousands of years to fully develop. During that time, weathering and erosion change the original mineral composition of the soil. Eventually, most of the original minerals in a soil are changed or washed away.  Soil Texture The size of the different materials that make up soil determine a soil’s texture. This affects a soil’s capacity to retain moisture and its ability to support plant growth.  Soil Fertility Soil fertility is the measure of how well a soil can support the growth of plants. It is affected by topography, availability of minerals and nutrients, the number of microorganisms present, the amount of precipitation available, and the level of acidity.  Soil Color The minerals, organic matter, and moisture in each soil horizon determine its color.