Sample Soil Profile

Below is a sample soil profile from Washington State.

You can use soil horizon properties to identify the master and subordinate horizon designations. Using the pictures and characteristics, can you identify the horizons in this profile? Can you identify the soil order?

By the way, if you don't understand a term use the glossary to obtain a definition. For help classifying the soil, see Soil Basics or the Keys to Soil Taxonomy.

This soil is found in low elevation areas of southwestern Washington on glacial outwash covered with volcanic ash deposits. Slopes are 0 to 15 percent. Soils are well-drained. Average annual precipitation is 125 cm and mean annual temperature is 11 degrees centigrade.

 

Depth/Description

1. 2.5-0 cm; black (10YR2/1); well decomposed organic matter, mostly from grass roots and moss
2. 0-35 cm; black (10YR2/1); gravelly sandy loam; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many fine roots; very high organic matter content; sooty feel; 35% pebbles; pH=5.4; clear smooth boundary
3. 35-46 cm; dark grayish brown (10YR4/2); very gravelly sandy loam; weak fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common fine roots; 50% pebbles, 10% cobbles; pH=5.8; clear smooth boundary
4. 46-150+ cm; light brownish gray (10YR6/2); extremely gravelly sand; single-grained; loose; few fine roots; 60% pebbles, 10% cobbles; pH=6.1

In the Spanaway Soil, there are 4 horizons delineated. The master horizons with subordinate designations are:

Oa

A

Bw

C

You can tell the Oa horizon by the fact that it consists of well-decomposed organic matter.

The A horizon is apparent from the black color (the sooty feel is from charcoal) but the horizon is predominantly mineral in composition (from texture) therefore an A not an O horizon.

A Bw horizon is next because this horizon has developed color and structure, but there is not gleyed, brightly colored or have any unique features.

You can tell the last horizon is a C horizon because it is poorly developed (no structure), and it has little color other than from the minerals of the glacial outwash minerals.

Can you figure out which Soil Order this belongs to?

The Spanaway is an Andisol because it has volcanic ash as a parent material and it doesn't have features of a Spodosol. In addition, the A horizon is deep, dark, acidic, does not have a high base saturation, and has developed andic properties such as low extractable phosphorus.

To try and describe a profile yourself, go to the Soil Quiz.