4.1 - Introduction

Goal: Understand the processes controlling soil formation and relate the processes of soil formation to the characteristics of a soil profile, through the use of soil horizon designations.

Objectives

1. Describe the four major soil forming processes.
2. Describe how these four processes redistribute soil materials in vertical and horizontal dimensions.
3. Explain which soil processes are dominant in each soil horizon.
4. Develop a profile horizon sequence based on given soil properties and a set of soil forming factors.
5. Describe the general soil forming processes, based on the soil forming factors described in Lesson 3, that led to the development of a given soil profile.

From the surface, soil may seem like an innocuous substance. Soil supports our weight; plants and animals live in it. But long after we’ve come and gone, the soil will remain, baking in the sun, hosting plant and animal life, receiving rain and snow. The soil forming factors – climate, time, organisms, topography, and parent material – affect what is below the surface and, in the long run, how a soil develops: chemically, physically, and biologically.

The vertical dimension of a soil can be variable. What seems homogeneous at the surface can be radically different as you dig in. In conjunction with the soil forming factors, over the lifespan of a soil (which can be tens to tens of thousands of years) the four general soil forming processes – additions, losses, transformations, and translocations – are organizing, reorganizing and altering the soil, creating what are called soil horizons.  These horizons also vary laterally throughout the landscape so that soils are truly three dimensional.