Soil Forming Factors:

Soil Forming Factors: Although many of us don't think about the ground beneath us or the soil that we walk on each day, the truth is soil is a very important resource. Processes take place over thousands of years to create a small amount of soil material. Unfortunately the most valuable soil is often used for building purposes or is unprotected and erodes away. To protect this vital natural resource and to sustain the world's growing housing and food requirements it is important to learn about soil, how soil forms, and natural reactions that occur in soil to sustain healthy plant growth and purify water. Soil is important to the livelihood of plants, animals, and humans. However, soil quality and quantity can be and is adversely affected by human activity and misuse of soil. Certain soils are best used for growing crops that humans and animals consume, and for building airports, cities, and roads. Other types of soil have limitations that prevent them from being built upon and must be left alone. Often these soils provide habitats for living creatures both in the soil and atop the soil. One example of soils that have use limitations are those that hold lakes, rivers, streams, and wetlands. Humans don't normally establish their homes in these places, but fish and waterfowl find homes here, as do the wildlife that live around these bodies of water. Natural processes that occur on the surface of Earth as well as alterations made to earth material over long periods of time form thousands of different soil types. In the United States alone there are over 50,000 different soils! Specific factors are involved in forming soil and these factors vary worldwide, creating varied soil combinations and soil properties worldwide: The Five Soil Forming Factors 1. Parent material: The primary material from which the soil is formed. Soil parent material could be bedrock, organic material, an old soil surface, or a deposit from water, wind, glaciers, volcanoes, or material moving down a slope. 2. climate: Weathering forces such as heat, rain, ice, snow, wind, sunshine, and other environmental forces, break down parent material and affect how fast or slow soil formation processes go. 3. Organisms: All plants and animals living in or on the soil (including micro-organisms and humans!). The amount of water and nutrients, plants need affects the way soil forms. The way humans use soils affects soil formation. Also, animals living in the soil affect decomposition of waste materials and how soil materials will be moved around in the soil profile. On the soil surface remains of dead plants and animals are worked by microorganisms and eventually become organic matter that is incorporated into the soil and enriches the soil. 4. Topography: The location of a soil on a landscape can affect how the climatic processes impact it. Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that directly face the sun will be drier than soils on slopes that do not. Also, mineral accumulations, plant nutrients, type of vegetation, vegetation growth, erosion, and water drainage are dependent on topographic relief. 5. Time: All of the above factors assert themselves over time, often hundreds or thousands of years. Soil profiles continually change from weakly developed to well developed over time. Differences in soil forming factors from one location to another influence the process of soil formation (Image courtesy of the United States Department of Agriculture, Soil Conservation Service) Parent Materials Soil forms from different parent materials; one such parent material is bedrock. As rocks become exposed at Earth's surface they erode and become chemically altered. The type of soil that forms depends on the type of rocks available, the minerals in rocks, and how minerals react to temperature, pressure, and erosive forces. Temperatures inside the Earth are very hot and melt rock (lithosphere) that moves by tectonic forces below Earth's surface. Melted rock flows away from the source of heat and eventually cools and hardens. During the cooling process, minerals crystallize and new rock types are formed. These types of rocks are called igneous rocks, the original parent material rocks formed on Earth. Igneous rocks, under the right environmental conditions, can change into sedimentary and metamorphic rocks. Volcanoes produce igneous rocks such as granite, pumice, and obsidian. Sedimentary rocks are formed when older rocks are broken apart by plant roots, ice wedges, and earth movements and become transported by glaciers, waves, currents, and wind. The transported particles then become bound together (cemented) as secondary minerals grow in the spaces between the loose particles and create a new, solid, sedimentary rock. Sandstone, limestone, and shale are types of sedimentary rocks that contain quartz sand, lime, and clay, respectively. Metamorphic/Crystalline rocks form when pressure and temperature, below Earth's surface, are great enough to change the chemical composition of sedimentary and igneous rocks. Metamorphic rocks, such as quartzite, marble, and slate form under intense temperature and pressure but were originally quartz sandstone, limestone, and shale. Other types of parent material that mineral soils form from are called Recent Cover Deposits and include alluvium, colluvium, eolian deposits, glacial deposits, lacustrine (lake) deposits, loess deposits , marine deposits, and volcanic ash deposits.