The Nature of soil

Dirt is what you find under your fingernails. Soil is what you find under your feet. Think of soil as a thin living skin that covers the land. It goes down into the ground just a short way. Even the most fertile topsoil is only a foot or so deep. What’s the difference between soil and dirt?

So What exactly is soil? Soil is made up of: Weathered rock Decayed organic material Mineral fragments Water air

Several factors affect soil formation, do you know what they are? Climate Slope of land Types of rock Types of vegetation Time

So, how is soil made? First, rock is weathered. How? Next, plants start to take root, and start to grow. This adds to weathering and now a thin layer of soil forms. What kind of weathering is this? Now bugs and other living things, like plants; so they make a home near them to eat. This adds their waste, and some dead plant material (which is organic matter) to the soil. As organic material grows, and more rock is weathered, soil thickens.

So, what’s with the bugs and dead plants? Bugs, and dead plant material add materials to the soil that decays. This is called organic matter, and as it decays, it turns the soil a dark color and this is called humus. Humus becomes a nutrient in the soil for plants.

Remember us??

Well, these are our friends… We mix the humus with rock fragments, and make richer soil.

Soil Profile…..Horizons

Topsoil : The A Horizon is the top layer of soil. This is the most fertile Horizon. Often there is litter covering the a horizon. Litter is leaves, twigs, and other organic material that is changed to humus by decomposing organisms. Litter prevents erosion and helps retain water. This layer is usually dark and fertile and provides the nutrients for plants Subsoil : This is a mix of mineral particles and some humus near the top. The B horizon is very low in organic matter compared to the topsoil, and contains less humus. It is lighter in color, and gets its minerals and nutrients from the A horizon through leaching. Leaching is the removal of minerals that have been dissolved in water. Water reacts with humus and carbon dioxide to form acid. The acid dissolves the minerals from the A horizon and carries it to the B horizon Weathered parent material : This horizon can be very deep. There's no organic matter here at all. We're out of reach of all living and dead organisms down here. 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. Bedrock : We finally found solid rock! The bedrock formed before the soil above it. It will wait here until erosion or an earthquake exposes it to the surface. Then some of it will be weathered to become the next batch of parent material. The soil-making process will start all over again. “A” Horizon “B” Horizon “C” Horizon

Glacier Deposits Glaciers also contribute to the making of soil They have a mixture of different sands, clay, silt and boulders which were deposited in many areas Because of the moisture, these soils that develop are very fertile, and glaciers are responsible for many of the fertile lands in the Midwest of the United States

Soil Types There are many different types of soils all over the world. They vary by thickness, color, texture, and fertility. Climate, as with other factors of nature, has a major impact on soil. Wet warm areas have more fertile soil, whereas dryer and colder climates do not.

Other factors Rock type- This impacts the type of soil because it affects what plants may grow in its vicinity, as well as the type and speed of weathering that takes place. Vegetation- This affects the type of soil because of the types of insects/animals it attracts, as well as the acidic properties it may give off.

Factors (cont.) Time- this impacts soil because the longer weathering takes place on rocks, the less the soil resembles the parent rock. As it weathers, the minerals continually change with the other factors involved, and the soil develops its distinct properties. Slope- This is a major factor since with slopes, materials tend to travel downward, and the horizons do not develop well. At the bottom of the slope, the soil is richer; at the top, it lacks many nutrients.