Loam, Sand & Silt Soil Identification

Characteristics of Silt

• Silt is one of the smallest soil particle sizes ranging from 0.074 mm to 0.002 mm. The only smaller classification of soil particles is clay. While both silt and clay particles are too small to see without a microscope, silt will feel gritty if you rub a sample between your fingers. Clay particles feel smooth to the touch. To identify silt particles, you can pour a sample of soil through a No. 200 sieve. This sieve will allow silt and smaller particles to pass through while retaining larger particles.

Characteristics of Sands

• Sand is a fine to coarse grain size and most particles are easily visible with the naked eye. The particle sizes larger than sands are gravels, cobbles and boulders. Sand particles range in size of 0.074 mm to 4.75 mm. Sands smaller than 0.42 mm are fine sands, while particles larger than 2 mm are coarse sands. Particles in between that range are medium-grained. You can identify sand particles using a No. 200 and No. 4 sieve. The No. 4 sieve has openings that are 4.76 mm and allow sand, silt and clay to pass through while retaining larger particles. After you sift the soil with the No. 4 sieve, you can use the No. 200 to remove silt or clay particles from the sand.

Characteristics of Loam

• Loam is a soil that is a mix of silt, clay, sand and organic matter. This type of soil is desirable for agriculture because the mixture of grain sizes and organics allows water to drain through the system while allowing the necessary degree of water retention and nutrients in the soil. The organic component is the key to the identification of a soil as a loam. A loam that is very high in sand is called a sandy loam, while a mixture with more silt would be a silty loam.

Identification of Soil Mixtures

• Soil identification involves proper naming of soil mixtures as well as the determination of the particle size. A soil rarely has one single particle size and is often a mixture of different amounts of varying grain sizes. Soil scientists use an identification method for soil mixtures that allows anyone to read a soil description and understand the type of soil. During the soil identification process, scientists will separate the silt, sand, clays, organics and gravels and determine which particle sizes are present and how much of each size are part of the mixture. The dominant soil type is listed second in the name. For example, a soil with mostly sand and a little silt would be a silty sand.