1. Soil Texture & Structure
Intro to Agriculture
AAEC – Paradise Valley
Fall 2014

2. Definition of Soil Texture
Soil texture is the fineness or coarseness of a soil. It describes the proportion of three sizes of soil particles. These are:
Sand—large particle
Silt—medium-sized particle
Clay—small particle

3. Importance of Soil Texture
Texture is important because it affects:
Water-holding capacity—the ability of a soil to retain water for use by plants
Permeability—the ease with which air and water may pass through the soil
Soil workability—the ease with which soil may be tilled and the timing of working the soil after a rain
Ability of plants to grow—some root crops like carrots and onions will have difficulty growing in a fine-textured soil
How will various proportions of each component affect these?
-High Clay?
-High Sand?

4. Determining Soil Texture
Soil texture may be determined in one of two ways:
1. The percentages of sand, silt, and clay may be tested in the lab. Once tested, you may determine the textural class of the soil by referring to the textural triangle. There are 12 basic textural classes.
2. The relative amounts of sand, silt, and clay may also be determined in the field using the ribbon method. Five textural classes may be determined using the ribbon method.
We will be doing a lab using the ribbon method

5. Soil Triangle COME BACK TO AT THE END OF THE PERIOD IF TIME
Walk through various examples on Smart Board:
-40% Sand, 22% Clay, 38% Silt (Medium Loam)
-60% Silt, 15% Sand, 25% Clay (Silty Loam)
-45% Clay, 45% Sand, 10% Silt (Sandy Clay)

6. Soil Structure
Granular—aggregates are small, non-porous, and strongly held together.
Crumb—aggregates are small, porous, and weakly held together.
Platy—aggregates are flat or plate-like. Plates overlap, usually causing slow permeability.
Structure is how Sand, Silt and Clay stick together in the soil – dependent on many factors

7. Soil Structure
Prismatic or Columnar—aggregates are prism-like with the vertical axis greater than the horizontal. Prismatic has flat caps while columnar has rounded caps.
Blocky—aggregates are block-like, with six or more sides. All three dimensions are about the same.

8. Soil Structure
Structureless—there is no apparent structure. It may be found in one of two forms:
Single grain—soil particles exist as individuals and do not form aggregates.
Massive—soil particles cling together in large uniform masses.

9. Examples of Soil Structure