AGRICULTURE Session 03: Where does Soil come from?
AGRICULTURE Session 03: Where does Soil come from?
Learning Objectives
- Describe the geologic processes that form the parent material of soil specific to our South Carolina Upstate region.
- Evaluate the contributions of our geologic history to the process of soil formation (pedogenesis).
- Investigate soil composition, soil texture, and the properties of different soil types.
Background
- Pedogenesis can be defined as the process of soil development. Soil is a living part of the ecosystem containing thousands of microbes and organisms. The cycling of nitrogen and carbon in soils is almost completely controlled by the presence of animals and plants. Through litterfall and the process of decomposition, organisms add humus and nutrients to the soil which influences soil structure and fertility. Surface vegetation also protects the upper layers of a soil from erosion by way of binding the soil surface and reducing the speed of moving wind and water across the ground surface.
- Parent Material refers to the rock and mineral materials from which the soils develop. These materials can be derived from residual sediment due to the weathering of bedrock or from sediment transported into an area by way of the erosive forces of wind, water, or ice. Pedogenesis is often faster on transported sediments because the weathering of parent material usually takes a long period of time. The influence of parent material on pedogenesis is usually related to soil texture, soil chemistry, and nutrient cycling.
- Soil is naturally removed by the action of water or wind: such ‘background’ (or ‘geological’) soil erosion has been occurring for some 450 million years, since the first land plants formed the first soil. Even before this, natural processes moved loose rock, or regolith, off the Earth’s surface, just as has happened on the planet Mars.
- In general, background erosion removes soil at roughly the same rate as soil is formed. But ‘accelerated’ soil erosion — loss of soil at a much faster rate than it is formed — is a far more recent problem. It is always a result of mankind’s unwise actions, such as overgrazing or unsuitable cultivation practices. These leave the land unprotected and vulnerable. Then, during times of erosive rainfall or windstorms, soil may be detached, transported, and (possibly travelling a long distance) deposited.
- Accelerated soil erosion by water or wind may affect both agricultural areas and the natural environment, and is one of the most widespread of today’s environmental problems. It has impacts which are both on-site (at the place where the soil is detached) and off-site (wherever the eroded soil ends up).
- More recently still, the use of powerful agricultural implements has, in some parts of the world, led to damaging amounts of soil moving downslope merely under the action of gravity: this is so-called tillage erosion.
- Soil erosion is just one form of soil degradation. Other kinds of soil degradation include salinisation, (salts