Soil, as defined in civil engineering, refers to naturally occurring mineral particles that are loose, un-cemented, weakly cemented, or relatively unconsolidated. These particles can be organic or inorganic in character and are typically found lying over the bedrock. Soil formation occurs through the weathering of rocks, resulting in a mixture of different particles such as gravel, rock, sand, silt, clay, loam, and humus.
Fig 1: Sand Silt and Clay.
The article delves into the properties, characteristics, size, shape, and constituents of the smallest soil types, which include sand, silt, clay, and loam. These soil types are of great importance in understanding soil composition and its impact on various aspects of agriculture, construction, and environmental management.
Sand is a type of soil particle that is characterized by its large size. It is typically gritty in texture and can be easily seen with the naked eye. Sand particles are irregular in shape, ranging from rounded to angular. They are relatively large in size, measuring between 0.05 and 2 millimeters in diameter. Sand particles have low water-holding capacity and are prone to erosion due to their coarse nature.
Silt, on the other hand, is finer in texture compared to sand. Silt particles are smaller, ranging from 0.002 to 0.05 millimeters in diameter. They have a smooth, powdery feel when dry and exhibit a slippery texture when wet. Silt particles are typically more rounded in shape compared to sand, and they have moderate water-holding capacity. Silt soils are susceptible to erosion, especially when they are saturated with water.
Clay is the smallest type of soil particle, with particles that are less than 0.002 millimeters in diameter. Clay particles are extremely fine and have a platy or flaky shape. When dry, clay soils are hard and compact, but when wet, they become sticky and easily moldable. Clay soils have high water-holding capacity due to their small particle size, but they also tend to have poor drainage and aeration properties.
Loam is a type of soil that is a mixture of sand, silt, and clay particles. It is often considered the ideal soil type for plant growth due to its balanced composition. Loam soils have moderate water-holding capacity, good drainage, and aeration properties. They are typically crumbly and easy to work with, making them suitable for agricultural and gardening purposes.
Understanding the properties, characteristics, size, shape, and constituents of these smallest soil types, namely sand, silt, clay, and loam, is crucial in managing and utilizing soils effectively for various applications. Proper knowledge of soil types can help in making informed decisions related to agriculture, construction, and environmental management.
1. Sand
Sand is a widely utilized construction material that is composed of rock and hard mineral particles, predominantly silicon dioxide. These particles are the largest type of soil particles, easily visible to the naked eye. The considerable size of sand particles enhances soil aeration and improves drainage in compacted soils, making it an ideal material for enhancing soil quality. Additionally, the tilting properties of sand contribute to its ability to support plant growth, making it an important component in creating favorable conditions for plants to thrive.
Fig 2 : Sand
Sand particles come in various sizes, with different classifications based on their size ranges. Course sand typically falls within the 2-4.75mm range, while medium sand is between 0.425-2mm, and fine sand ranges from 0.075-0.425mm. The larger particle size of sand gives sandy soil, whether it’s wet or dry, a distinct grainy texture that can be felt when rubbed between fingers. It also contributes to the soil’s lightness and crumbly nature, even when attempting to compact it in the hand. Sand particles can have different shapes, such as angular, sub-angular, rounded, flat, or elongated, and their surfaces can vary in texture from rough to smooth or even polished.
2. Silt
Silt is a type of sediment material that falls between the size of sand and clay particles. It is often carried by water during floods and can settle on valley floors, creating a fertile deposit. The particle size of silt typically ranges from 0.002 to 0.06 mm.
Fig 3: Silt in wet condition
Silt is categorized as a non-plastic or low-plasticity material because of its fine particle size. When silt is wet, it transforms into a smooth mud that can be easily shaped into balls or other forms by hand. Moreover, when silt soil is saturated with water, it seamlessly mixes with water to create fine, runny puddles of mud. The fineness of silt particles contributes to its unique behavior when wet, making it easily moldable and capable of blending with water to form a cohesive and fluid mixture.
3. Clay
Clay particles, measuring less than 0.002 mm in size, are the smallest of all soil particles. They are formed through the chemical decomposition of rocks, resulting in microscopic and sub-microscopic particles. Clay is characterized by its fine-grained and cohesive nature, easily sticking together to form a sticky or gluey texture when wet or dry.
Fig 4: Clay when mixed with water
Clay soils are composed of over 25 percent clay, and their unique structure allows them to hold a significant amount of water due to the spaces between clay particles. When clay comes into contact with water, it expands, and when it dries, it shrinks. In contrast, sand particles are typically round, while clay particles are thin, flat, and covered with tiny plates. Organic clay is known for its high compressibility and strength when dry, making it a common choice in construction for mud mortar applications.
4. Loam
Loam is a type of soil that contains a mixture of clay, sand, and silt. It is characterized by its unique combination of different textures, which confer various beneficial properties. For example, loam soils are known for their ability to retain water, facilitate air circulation, promote drainage, and support fertility. This makes them highly fertile and easy to work with for gardening and farming purposes. The specific characteristics of loam soils can vary depending on their predominant composition, which can range from sandy loam to clay loam. Regardless of the exact composition, loam soils are generally considered ideal for plant growth due to their balanced properties.
Fig 5: Loam
Soil composition can be described by the way different particles combine to form loam. For example, a soil with 30 percent clay, 50 percent sand, and 20 percent silt would be classified as a sandy clay loam, with the soil types listed in order of their dominance in the loam. Similarly, terms such as “clay loam,” “silt loam,” and “sand loam” are used to refer to soils that are predominantly composed of those specific ingredients.