Interestingly, solutions to soil problems tend to be universal. For example, adding compost makes the soil more fertile. If you want to raise soil pH, you add lime. However, have you ever wondered whether the soil is the same everywhere and why they seem to have blanket solutions?
Soils are not the same everywhere. Their color, texture, and profile are influenced by the parent material, climate, topography, organisms, and the time it took to break down. These build the soil profile and show why some places have shallow, rocky soils while others have deep, soft soil.
I will discuss why soil properties vary from place to place and how activities, such as gardening, change the soil profile.
Why Soil Is Different Everywhere
The soil varies, not just from one region to another, but you may also discover differences in soil color and texture within your home. There are several reasons why soils vary.
Some may be human interference, but the primary explanation lies in the soil’s origin:
1. The Parent Material
All soils emerged from rocks. When the rocks are exposed to elements, such as water, extreme temperatures, wind, chemicals, pressure, wind, and living organisms, they start to weather and break down. The minerals in the rocks will determine the type of soil that will emerge.
For example, sandy soil emerges if the parent rock is granite. Granite is coarse, so naturally, its dirt will have the same texture. Likewise, basalt has smooth particles, so when it breaks down in most conditions, it results in clay soils.
Loamy soils usually form when the parent rock is exposed to rich organic material.
2. Climate
When the parent material disintegrates, the climate will speed up or slow down. For example, if the rock is exposed to high temperatures and high precipitation, it will weather more quickly.
Parent rocks in hilly areas continue forming soil at the same spot. Over time, fine soil forms on mountain slopes and the valley, depending on the parent rock’s location.
Sometimes, rain washes the disintegrating parent material down the hill. This interferes with the breakdown process, so the base of the hill has coarse soils.
Rain also interferes with the soil structure. It sometimes holds some particles in suspension while some minerals leach into the ground. The result is less fertile and highly acidic soils in such areas.
Runoff waters also deposit soils in river banks. Fine soil particles are usually suspended, while the rocky, coarse soils sink lower. This is why the soils along river banks have very fine particles.
Wind also plays a crucial role in soil formation. Fine soil particles are carried further away because they are lightweight. This explains why fine volcanic ash soils are found some distance away from places that experienced volcanic eruptions.
3. Topography
The topography of the area also influences the type of soil.
Hilly areas, primarily because of erosion, have poorly developed soils that are also not fertile. The soils are coarse and have little moisture because of exposure to the sun. Human activities aimed at improving soil quality are also lacking in hilly areas.
As you move to flatter areas, you’ll discover the soil is more refined, and since the water drains into the ground, the soil retains moisture. This encourages living organisms to break the soil further, making it richer and suitable for agricultural activity.
If you look at the soils in the Sierra Nevada and Pacific Coast area, California’s agricultural area, the soil is very different from that in the Death Valley Region.
Death Valley has rugged topography, with coarse soil that holds very little moisture, while Pacific Coast, Sierra Nevada, and the Cascades have rich fertile soils.
4. Organisms
The living organisms in the soil influence the soil quality and color. Areas with heavy plant decay, whether it is from the falling leaves or the plant’s roots, have darker soil.
Animals also keep moving soil around, aerating it. They feed on the plants and leave their wastes which eventually enrich the soil.
Microorganisms break down the soils further as they move around the soil. They also help with nitrate fixation. They help release nitrogen gas and ammonia into the ground.
Plants grow, mature, and eventually die, giving way to new plants to grow. The dead plants start to decompose and release the nutrients into the soil. As the cycle continues, the soil becomes richer and darker in color.
5. Time
As soil matures, it takes on more horizons. Soils that have formed recently have few horizons. Those that undergo weathering over a long period undergo soil transformation, resulting in thicker horizons.
Soils with more horizons tend to have fertile soil which has undergone more translocation and transformation. When you dig these soils, you will dig deep before getting to the next horizon.
You’ll discover soils yet to undergo sufficient weathering have fewer horizons. You’ll find that you won’t need to go deep before reaching the next horizon. Such soils do not support healthy plant growth because the plant’s roots grow past topsoil too soon, and this affects the plant.
Soil Horizons
The planet has four main components. Lithosphere (Earth), hydrosphere (water), atmosphere (air), and biosphere (living material). The bedrock in the earth breaks down and weathers down over time.
As this occurs, the different weathering stages create different soil horizons:
| O Horizon | Dying plants and organic matter present |
| A Horizon (Topsoil) | A mix of minerals and organic matter from the O horizon |
| B Horizon (Subsoil) | Contains minerals and nutrients that are pushed down due to leaching |
| C Horizon (Parent rock) | Was pushed down into the ground and the lighter material moved up |
Soil horizons vary from one area to another. For example, some soils have an E horizon (sand and silt) between the A and B horizons.
Illuviation occurs in the E horizon, where the water pulls the minerals for the soil as it moves downwards. The result will be a dry soil layer distinctly different from the topsoil and subsoil.
This video illustrates soil formation and the developments of soil horizons:
How Particle Sizes Affect Soil Type and Soil Porosity
As mentioned earlier, the parent rock will determine if you will have loam, sand, or clay soil. Sometimes, erosion and the weathering of different parent rocks in the same area can cause a place to have clay, sand, and silt in the same area.
- Soils with large particles (0.02-0.08 inches or 0.5-2.0 mm) are classified as sand.
- Silt has medium-sized particles (0.000078-0.002 inches or 0.002-0.05 mm)
- Clay has the smallest particle sizes (0.000078 inches or 0.002 mm)
The soil particle size adds to the soil dynamics, contributing to the differences in the soils everywhere:
- When more than 50% of the soil has tiny particles, the soil is classified as clay soil.
- When you have 20% clay, 20% silt, and 20% sand, you will have perfect loam soil.
The soil particle size influences soil porosity.
Sand, with its large particles, has a higher porosity. Clay, on the other hand, has very tiny particles, so it has a lower porosity. Water sits in clay soil for too long, such that it will suffocate the plant’s roots.
How Human Activities Affect the Soil
Soil structure keeps changing. Unfortunately, human activities can easily make rich soil dry and lifeless. Many countries are becoming food insecure because the soil structure has changed and is no longer helpful for growing food.
- Deforestation triggers the loss of organic carbon. Soil organic carbon improves soil quality. Naturally, when organic carbon is stripped away, the soil quality diminishes.
- The chemicals in pesticides destroy the biodiversity in soils. However, they also destroy some living organisms, such as worms and bacteria. As seen in soil formation, biodiversity is vital for breaking down soil material. Without living organisms, the soil structure will change.
- Soil salinization is a result of intensive irrigation. Salinity inhibits nitrogen uptake, and this affects plant growth. High concentrations of chloride ions are toxic to plants. These plants will die and not undergo the natural decay process necessary for soil enrichment.
Conclusion
Soil formation is a process that has been going on for millions of years. It is even happening presently, deep in the ground. Unfortunately, the weather conditions and human activities are slowly changing the current soil profile. This explains the different soil properties within regions and across continents.
