What is soil?

It is more than just dirt. Soil is a mixture of organic and inorganic paticals that can suport life. Simply put, soil acts as a medium for plants to anchor their roots. It supports an ecosystem of microbes and soil animals ranging from groundhogs to earthworms. While soil is constantly being made at a slow rate, it is also being moved around by people’s activites and nature.

Two Methods of Soil Formation

Soil can be generated from debris on the landscape and from weathering of the parent rock.

What is considered debri varies widely. It can be a natural in appearance as leaves in the fall to lost shoe left behind. Anything that is organic in origin can be broken down in to basic parts weither or not those basic parts are benifical to plant life. It all adds to the upper most layer or the organic layer of soil and is the quickest way to create soil. If you have ever composted, you have made your own soil.

Rock is weathered by chemical reactions with water, by the squeezing pressure of plant roots or even animals such as an earthworm. Water can penetrate as deep as the top of the bedrock, also called parent material. The depth and type of bedrock varies greatly, so it is best to consider the area in which you are dealing with. Are you on a hill or in a valley? What the weather is like and what kinds of animals live in the area? These are important questions you need to be able to answer when you are determining how soil is formed.

Soil Structure

Defined as "arrangement of soil particles into aggregates"

Soil structure can be altered by the addition of organic material such as compost or humus because organic material helps to form aggregates. Aggregates are composed of many soil particles held in a single mass or cluster such as a clod, crumb, block, or prism. These structures distinguishes soil from weathered rock.

The arrangement of aggregates in a soil determines the size and quantity of pore spaces. They can also be created by dead roots, soil animals and mechanical aeration. These spaces are fragile because soil are easily compacted or destroyed.

  1. What can cause compaction?
    • walking across or stand on saturated soil
    • the wheels of a vehicle
    • tilling
    • freeze, thaw

Pore spaces are important because they give room for air and water within the soil. The larger pore spaces tend to be filled with air and the smaller pore spaces hold water. When the ground is considered to be saturated, water is filling all the pore spaces which put plants at risk for drowning. Roots and soil animals need air as much as you do, just in smaller amounts.

Soil Texture

The size of soil particles gives a soil a perticualar texture. It is impossible to change a soil’s texture.

Getting Started
Let’s say you want to learn more about the soil in your yard. First thing you need to do is get a composite sample by taking samples, about from four to six inches deep, from various areas in your yard. If you can, avoid blades of grass or other large organic debris in the sample. Once you break up and mix the samples grab a handful and squeeze the soil in your hand. Is it damp? Does it hold together or fall into smaller clumps when you open your hand?

Feel and Ribbion Test
This section is in progress, waiting on: Pictures, Video, how to description.
  1. We use the feel method / ribbon test to determine particle size
    1. Sand feels gritty
    2. Silt feels smooth
    3. Clay feels sticky

Texture is determined by proportions of sand, silt and clay. Soil settling / bouyoucos hydrometer How do particles settle?