Soil Texture Lab Analysis

Analysis

• Soil laboratories analyze samples by the size and proportion of nonorganic particles in the soil. These particles range in size from microscopic to small, yet visible particles. During testing, particles are mechanically separated into specific groups known as soil separates. The proportionate amount of particles from each group determines which category your soil sample falls under.

Soil Types

• Particles of nonorganic material found in soil are lumped into four categories known as loam, silt, clay and sand. Sandy soils contain the largest particles, measuring between 0.05 and 2.0 millimeters, while clay particles are the smallest with a diameter less than 0.002 millimeters. These four soil types are combined into 12 categories that have specific ratios of each type of soil. Soils that contain a large amount of sand are further broken down by the size of the sand particles in the soil. These categories include very fine sand, fine sand, sand and coarse sand.

Categories

• The 12 categories of soil texture are combined using a variety of models. The USDA textural triangle describes how each of the exact ratios of soil particles make up each category. These categories define mineral soils that do not have a large amount of organic matter. Organic soils are commonly found in swamps, marshes, lakes and other areas with large amounts of decaying organic material. These soils are commonly classified as a combination of muck and peat. Muck consists of highly decomposed material while peat is made of less degraded materials. Mineral soils with a high concentration of organic materials are often classified using one of these terms. Soils with significant quantities of rocks -- enough to affect tilling -- are classified by adding the term gravel. A soil containing sand, clay and gravel is referred to as gravelly sandy clay.

Considerations

• Soil texture tests reveal important soil characteristics including fertility, drainage characteristics and tolerance for changes in pH. However, soil texture analysis does not reveal the effect of human activities or the impact of local water tables. Human activities can compact the soil, changing its drainage characteristics. A high water table will also cause slow drainage while a low water table will increase it.