Soil & Conservation

Soil is a crucial part of Earth's surface layer. Without soil, plants could not flourish. Without plants, most other living things on Earth would eventually perish. Creating soil takes time, which is one reason it is a precious resource.

Soil is composed of weathered sediments and decomposed organic material as well as water and air. The type of sediment and organic material is determined by the available rocks and living things of the area, which creates a variety of soils. So, soil is formed through processes of weathering & erosion as well as decomposition and it can be rocky or fine.

Soil is built up in layers. These layers are called Horizons. Each horizon has a letter label and characteristics, but not all soils will have all horizons. In healthy and well developed soil, there are typically 5 horizon layers (sometimes 6, in very rainy areas). On the surface, a dark/black layer made up of fresh organic matter, like leaf litter, that is decomposing makes up Horizon O and is called Humus. The first layer of soil makes up Horizon A and is called Topsoil. Topsoil contains a mix of mineral sediments and decomposed organics, and it is the layer in which plants grow. The second layer of soil makes up Horizon B and is called Subsoil. Subsoil is rich in mineral sediments with much less decomposed organics; plant roots reach down into this layer. Some soils have a Horizon E between the 1st and 2nd layer called the Eluviation layer because consistent rains cause leeching from the top layer further down into the soil. The third layer of soil makes up Horizon C and is called Regolith or Parent Material. Regolith is mostly pieces of weathered rock debris in varying sizes and contains no organics. It is sometimes called Parent Material because it is the source of most of the minerals in the layers above it. The final layer makes up Horizon R and is called Bedrock. Bedrock is the original, mostly unweathered rock from which the regolith and mineral sediment particles are sourced. When conditions are appropriate, weathering and erosion will break down the bedrock and slowly build up horizons R and C. Once plants can take root, Horizons B and A can slowly form. In areas where plants cannot take root (for various reasons), the soil may have exposed bedrock and regolith. The development of these horizons depend on time and environmental conditions. Human activity such as construction and clear-cutting often disrupts soil and causes increased erosion and degradation.

The quality of the soil greatly depends on resources of the area as well as time allowed to develop and grow in depth. Deserts have very poor soil because they have more sediment than organic material. Forests usually have rich soil because of the variety of plant and animal life, while mountains have to much rock in the soil for fertility. The presence of earthworms is a good sign that soil is healthy because they contribute to the breakdown of organic material and eat soil, ejecting casting that are high in nutrients like fertilizer, and as they move through the soil they open up space for air and water.

Soil particles come in 3 main categories:

• Clay particles come from the break down of rocks mostly containing the mineral feldspar. Clay has the finest, smallest particles - so small they are often individually invisible to the naked eye. Clay is sticky in texture, it retains water and nutrients very well, and it tends to heat slowly. For these reasons, Clay is preferred for constructing items like water containers and bricks for building. Too much Clay in soil is not good for fertility because they soil will become waterlogged.
• Silt particles come from rocks mostly containing the minerals quartz or feldspar, such as sedimentary Siltstone. Silt particles are tiny but larger than Clay. Silt has a smooth, silky-plastic texture often feeling like flour when dry. Silt has moderate ability to retain water and nutrients, allowing some water to drain. Silt can be easily eroded, often by wind, and can form loess hill formations when deposited.
• Sand particles are the largest and clearly visible to the naked eye. These soil particles come from rocks mostly containing the mineral quartz that has not undergone extensive weathering to break it into lattices like silt. Sand heats up quickly and does not hold water or nutrients well. The sand particles rough in texture and are so large that the spaces between allow water to drain right through rather quickly. It is not a fertile soil alone and is easily eroded.
• Loam is the perfect combination of all 3 soil particles and is preferred for farming. Most loam has a 20-40-40% ratio in parts of clay, silt, and sand so that it retains water and nutrients but does not get waterlogged or easily eroded. Loam is a rich and fertile soil, and if containing healthy organic material, is dark in color; though there are variations of loam such as red loam, sandy loam, and clayey loam.

To find out how much of each particle type a soil may have, you can conduct a shake-jar test. Place a sample of soil in a jar (about 1/3 full) and add water to fill the rest of the jar (leave a small space at the top). Shake the jar vigorously then allow it to completely settle (approximately 48 hours). The particles will arrange themselves by size, as finer particles will stay suspended in the water longer than the larger, heavier particles. Clay will make up the first layer, silt the second layer, and the heavy sand will settle to the very bottom. You can measure these proportions and use the soil triangle to calculate the ratio and estimate the type of soil for your sample.

Conservation of soil is very important. Life on land depends on soil because it is the source of plant growth and the beginning of most food chains. When soil is removed, plants cannot survive to support most other forms of life and the location becomes desert-like or barren. Agricultural farmers must also worry about soil erosion because losing the topsoil can harm their crops. Degraded soil that has lost nutrients over time from over use, plowing/tilling, or water/wind erosion is not capable of producing healthy or bountiful crops. Farmers often use techniques such as contour plowing, no-till harvesting that leaves behind plant residue, and crop rotation to help prevent degradation of their topsoil.

Prevention of soil erosion is a major concern.