Soils
Components of Soil
Soil is made up of minerals, bacteria, organic materials, air, moisture, and sediments.
Minerals come from a parent material (rock, loose materials). Weathering breaks the parent material down even further into sand, silt and clay which become part of the soil. Minerals such as calcium, phosphorous and nitrogen provide essential nutrients to feed plants. When plants and animals die they begin to decompose as bacteria in the soil "eat" the organic material. The process of decomposition releases nutrients into the soil. This organic rich layer of soil is called humus which provides plants with moisture and nutrients. Humus gives soil its dark colour. Plants need to have air around their roots. The more humus there is in the soil the more air there will be. This is because the organic matter (plants and animals) that are decaying tend to be loose allowing for air pockets to form in the soil. Insects, worms, and small burrowing animals also produce air pockets and help to ventilate the soil. As water percolates through the soil it dissolves nutrients freeing them to be absorbed by plants through their roots. Water is also part of the chemical and physical processes that break down rocks and organic materials. Soil Conservation
Soil erosion, caused by wind and rain, can change land by wearing down mountains, creating valleys, making rivers appear and disappear. It is a slow and gradual process that takes thousands, even millions of years. But erosion may be sped up greatly by human activities such as farming and mining. Soil develops very slowly over a long period of time but can be lost too quickly. The clearing of land for farming, residential, and commercial use can quickly destroy soil. It speeds up the process of erosion by leaving soil exposed and also prevents development of new soil by removing the plants and animals that help build humus. Today's farmers try to farm in a way that reduces the amount of erosion and soil loss. They may plant cover crops or use a no-till method of farming. Soil is an important resource that we all must protect. Without soil there is no life.
Definitions
Active Layer: upper layer of permafrost that thaws only briefly in summertime.
Calcification: process by which, in dry climates, water carrying dissolved minerals moves upward through the soil. At the surface, the water evaporates, leaving the minerals behind. The surface soil is then considered calcified. Capillary Action: movement of water upward through small spaces, as in soil. Carbon Cycle: movement of carbon through plants, animals, water, soil, air and rocks. |
Chapters
14 Canada's Soil & Natural Vegetation Connections (p. 159-171)
Links
Soil Formation
The formation of soil happens over a very long period of time. It can take 1000 years or more. Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. Over time this creates a thin layer of soil. Plants help the development of the soil. How? The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.
Weathering: Weathering is the process of the breaking down rocks. There are two different types of weathering. Physical weathering and chemical weathering. In physical weathering it breaks down the rocks, but what it's made of stays the same. In chemical weathering it still breaks down the rocks, but it may change what it's made of. For instance, a hard material may change to a soft material after chemical weathering. Soil Profiles
Soil Profile refers to the layers of soil; horizon A, B, and C. If you're wondering what horizon A is, here's your answer: horizon A refers to the upper layer of soil, nearest the surface. It is commonly known as topsoil. In the woods or other areas that have not been plowed or tilled, this layer would probably include organic litter, such as fallen leaves and twigs . The litter helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon A provides plants with nutrients they need for a great life.
The layer below horizon A, of course, has to be horizon B. Litter is not present in horizon B and therefore there is much less humus. Horizon B does contain some elements from horizon A because of the process of leaching. Leaching resembles what happens in a coffee pot as the water drips through the coffee grounds. Leaching may also bring some minerals from horizon B down to horizon C. If horizon B is below horizon A, then horizon C must be below horizon B. Horizon C consists mostly of weatherized big rocks. This solid rock gave rise to the horizons above it. Soil profiles look different in different areas of the world. They are affected by climate and other things. |