PROCESSES INVOLVED AND HOW TO MAKE A SOIL PROFILE PIT

Pit method of soil profile pit

Dig a soil pit approximately 1 meter deep or until an impenetrable layer is reached and as big around as is necessary to easily observe all of the soil horizons from the bottom to the top of the pit which is approximately 1.5 x 1.5 m wide. In some situations, people may be able to perform the soil characterization measurements at a site where the soil profile has already been exposed through human or natural action such as a road cut or the side of a ravine. In these instances, teachers need to make sure that the site is safe for individuals and there is no objection to them scraping the surface soil away to expose a fresh soil face.

• Digging is much easier when the soil is moist. If possible, plan digging shortly after a rain.
• As soil is removed from the pit, place it carefully in piles representing each of the natural layers as they occur in the profile.
• The removed soil can be put on a tarp or other type of plastic sheet to make cleaning up the site easier.
• Cover piles of removed soil with plastic to prevent them from eroding away.
• Contact a local soil scientist or other professional who may be willing to assist you in digging a pit and help to describe the characteristics of the soil profile.
• When finished with the soil characterization measurements, the horizons need to be replaced into the soil pit in reverse order.

Defining the soil characterization site

• Give the site a name or number. Then record it on the soil characterization sheet.
• Determine and record the location of the pit
• Describe the area including the slope and aspect of the soil pit area.
• Describe and record the cover type of the site, e.g., bare soil, rocks, grass, shrubs, trees, or other.
• Describe and record the type of parent material from which the soil was formed at the site such as soil bedrock, organic material, construction material, marine, lake, stream, wind, glaciers, volcanoes, loose materials on slope moved by gravity, or other.
• Describe and record the land use at the site such as urban, agricultural, recreation, wilderness, or other.

Procedures involved

• Use a trowel to scrape a few centimeters of soil off of the profile to expose a fresh soil face.
• Determine whether the soil profile is moist, wet, or dry. If the soil profile is dry, moisten it with the spray mist bottle.
• Start at the top of the profile and observe the characteristics of the soil moving towards the bottom of the profile. Mark each layer at the top and bottom of each horizon. Be sure there is a consensus regarding the definition of the layer boundaries.
• Look carefully at the soil profile for distinguishing characteristics such as color, texture, shapes, roots, rocks, small dark nodules, worms, small animals, insects, and worm channels. These observations will help to define the horizons.
• Measure the top and bottom depth of each horizon beginning at the top of the profile. Start with the meter stick or tape measure at 0 cm at the top of the profile. Note the depths at which each horizon starts and ends.
• Record the top and bottom depth of each horizon.

Soil structure

This is the shape that soils take based on physical and chemical properties. Each individual lump of soil structure is called a ped. Look at a sample of undisturbed soil from each layer of your pit and examine the soil structure. Structure refers to the natural shape of groups of soil particles or aggregates (peds) in the soil.