Three Types of Soil Based on Particle Size

Soil can be classified by different characteristics. One of the most important characteristics of soil is the texture. The texture, along with the organic content and pH, determines how well a plant will grow without any interference. The texture of a soil is determined by the minerals, water and air present in the composition of the soil. The minerals present determine the classification of the soil. The soil particles present in a soil vary by size and characteristics.

Facts

Soil is often classified by the following features: color, compaction, moisture content, organic content, pH, profile, structure, temperature and texture. Of these features, the three most important are texture, organic content and pH. Texture is in reference to the size of the individual soil particles. The texture of the soil is determined by relative proportions of clay, sand and silt.

Types

Sand particles can be seen by the naked eye and are the largest of the three size classes of soil particles. Silt particles are smaller than sand particles and can only be seen with a microscope. Clay particles are the smallest of the three size classes of soil particles and can only be seen with an electron microscope.

Size

Clay has a particle size of less than .002 mm and has an affinity to water. Clay distributes itself evenly throughout water, a feature which is exploited by the paint industry to disperse pigment or color evenly throughout paint. Clay can also be mixed with a little bit of water to become mud, which can be shaped and then dried into a relatively rigid solid. This feature is exploited by potters and the ceramics industry. Sand particles range in size from .0625 mm to 2mm. The finer grains of sand will hold more water than the coarser grains of sand. Silt is made mostly from quartz and can range in size from .002 mm to .005 mm.

Features

Since the texture of the soil determines how well a plant will grow, we will discuss the features of the different types of soil texture. Clay soil is made up of approximately 0 zero to 45 percent sand, zero to 45 percent silt, and 50 to 100 percent clay. Clay soil is sticky and feels almost plastic-like when it's wet. It holds water and nutrients well. Silt soil is approximately 25 to 50 percent sand, 30 to 50 percent silt, and 10 to 30 percent clay. Silt soil feels smooth and slippery when it is wet. Sandy soil is approximately 80 to 100 percent sand, zero to 10 percent silt, and zero to 10 percent clay. Sandy soil drains quickly after it rains, is easy to work with and warms up quickly in warm weather. It has a lower moisture and nutrient holding capacity than clay or silt soil and therefore must be watered and fertilized more often.

Considerations

Regardless of the type of soil you have, soils can be greatly improved with the addition of organic matter, such as compost; fertilizer can be added to aid plant growth.

References

• U.S Geological Survey
• University of Saskatchewan Gardenline
• BioFlora Soil Characteristics