Soil Structure & Texture Low quality soil structure and texture result in greater demand for water and fertilizer required to support a profitable crop.

Soil Structure

When organic material combines with clay particles the soil clumps together into aggregates with spaces, or pores, left in between. The resulting matrix of aggregates and pore space forms the soil’s structure, providing pathways for air, water, and organisms, as well as physical support to anchor plant roots. The size, quantity, and connectivity of soil pores determine the relative ease with which oxygen and water move through soil. Moderately sized and highly connected pores facilitate efficient movement of oxygen and nutrient laden water toward plant roots. When soil pores are too large, too small, or not well connected, water and air are unevenly distributed through the soil profile, compromising crop health and reducing yield.

Example of soil structure with pore space.
Source: Line drawing from USDA.

Source: NRCS “Soil Texture Calculator” nrcs.usda.gov

The proportion of sand silt and clay determines how the soil’s texture is classified. The textural triangle defines the classification based on percent sand, silt, and clay. For example, a soil containing 60% sand, 30% clay, and 10% silt is classified as a sandy clay loam.

Soil Texture

The ratio of sand, silt, and clay-sized particles define the soil’s texture, and texture determines many soil qualities affecting healthy crop production. Sand sized particles are relatively large and visible, like grains of sand on a beach. Silt is smaller than sand, but generally still visible to the naked eye, while clays are microscopic particles that can only be seen with a hand lens or microscope.

Mineral particles are the soil’s building blocks, and their size and shape influence how the soil’s structure develops. Fine textured soils, with high proportions of clay, produce small pores and aggregates, while course textured soils, with higher amounts of silt and sand, have larger aggregates and pore spaces. Soils with a balanced ratio of sand, silt, and clay provide optimum structure and water holding capacity, as long as enough organic matter is available to hold mineral particles together.

Soil texture cannot be changed by management practices, since adding sand, silt, or clay is cost prohibitive under almost all circumstances. Instead, Tri-Tech crop advisors can help growers optimize soil properties by maintaining sufficient organic matter content, while using irrigation and nutrient management practices tailored to their soil’s texture.