Soil Profile Linda Giorno Fall 2006

What is the difference between soil and dirt?  Dirt is what you find under your fingernails. Soil is what you find under your feet.

Soil Characteristics  A thin living skin that covers the land.  Even the most fertile topsoil is only a foot or so deep.

Soil Profile  The horizontal layers (horizons) in the soil from the surface to the bedrock.

Ground Level (O)  Plants grow and animals live here. A thick cover of plants can keep the soil cool and keep it from drying out. Decomposers recycle dead plants and animals into humus.  O layer is about 2 inches in depth.

Decomposer  An organism that breaks down dead plant and animal organic matter. Most decomposers are bacteria and other fungi.

Organic matter  All of the matter in the soil that first came from living things—plants, animals, fungi, and protozoa. It may be fresh or decomposed.

Top Soil (A)  Plants grow and animals live on top of the soil.  A thick cover of plants can keep the soil cool and keep it from drying out. Decomposers recycle dead plants and animals into humus.  A layer is about 10 inches in depth

Root Fungus

Round Worms

Earthworm

Humus  The matter left over after all the nutrients and minerals are gone from dead plant and animal matter.

Uses for Humus  Humus can be used as a root stimulant, chemical free fertilizer, plant growth stimulant, or lawn fertilizer.  Humus is vital to the growth of plants because it helps balance the soil and increases the metabolism of a plant’s natural root system.

Sub Soil (B)  This is a mix of mineral particles and some humus near the top.  Subsoil is very low in organic matter compared to the topsoil. This is the layer where most of the soil's nutrients are found.  B layer is about 30 inches in depth.

Weathered parent material  This horizon can be very deep.  There's no organic matter here at all. It's all rock particles, full of minerals.  The entire soil profile used to look like this all the way to the surface.  Physical weathering broke the parent material up into small pieces.

Parent material (C)  The non-living part of all soil comes from the parent material. It may be broken off of bedrock underneath. Or a glacier, wind, or water, can pile up material removed from bedrock somewhere else.  C layer is usually about 48 inches deep.

Bedrock (R)  We finally found solid rock! The bedrock formed before the soil above it.