2. Soil Horizons (layers)
SOIL HORIZONS (LAYERS)
Soil Horizon Presentation
Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support the growth of plant life and other life forms on Earth.
MOMA : TRUE SOIL CONTAINS 4 MAIN PARTS
1. MINERALS:
- Minerals such as calcium, phosphorous and potassium are nutrients found in the soil and are required for plant growth.
- Minerals come from rock material known as parent material and are drawn to surface by capillary action
- Minerals are acquired through the weathering (breaking down) process of rock into smaller elements such as sand,
silt and clay and migrate up or down through the soil profile due to calcification or leeching
2. ORGANIC MATERIAL AND BACTERIA
- The organic material is flowers, grass, trees/branches etc that are dead and on the ground
- When plants and animals die they are decomposed (broken down) by bacteria in the soil (mold on cheese or bread)
- Decaying organic materials form humus, which provides nutrients and moisture for plants.
- Humus the dark in colour and found on the surface or O horizon (layer) where leaves and branches rot and decay.
- The richest layers of humus will always be found in a forest or swampy area.
3. MOISTURE:
- Water dissolves nutrients and is absorbed by the roots of plants.
- Water also necessary dissolve minerals and help in the decay of organic material.
4. AIR:
- Plants need air most around their roots and within 30cm of the surface
- Lots of loose humus near roots allows for lots of air spaces
- Air spaces are also created by worms and ants and other insects and small animals which tunnel through the soil.
SOIL PROFILES: - layers of soil
- Soil is made up of many layers or horizons
- Horizons are composed of different material between
the O horizon and the D (bedrock)
- Each horizon is composed of combinations of different rocks,
minerals, organic material and vegetation.
SOIL LEECHING- downward movement of water
Moisture on the surface (rain) dissolves surface nutrients and chemical fertilizers in the upper organic layer of soil. Some of the surface accumulation of moisture will percolate (drip down) from the surface layer to other soil layers (horizons) below ground. Nutrients are being distributed throughout the soil layer. Plant root systems below the surface can now access and absorb the water and dissolved nutrients to make organic material (the plant). This is how plants get food. Excessive watering can result in a negative result called Leeched Soils.
LEECHED SOILS- negative effect of excessive leeching/watering
Excessive watering can lead to the surface nutrients being washed away too quickly. Soil layers will then lack nutrients and no longer be healthy. You can identify leached soil by its poor, often thin, topsoil layer. Leached soils can be developed into excellent farmland by adding fertilizers, but this too is limited in time.
CAPILLARY ACTION – upward movement of water to the surface from lower layers.
As water on the surface is evaporated by heat from the sun, water from below is drawn upwards to replace it. As the water reaches the surface, it evaporates leaving behind the minerals that were dissolved in it. The result is a thick topsoil layer, rich in minerals, for decades but, too much calcium can poison the soil. Calcium is the main mineral deposited near the surface and can turn large areas into what looks like salt fields.
CALCIFICATION: The negative result of excessive watering of plants in a hot drier climates (deserts) like California. Heavy watering of soil (sprinklers) will destroy the soil over a long period of time.