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Soil's Chemical Composition & Environmental Effects

Lesson Transcript
Instructor: Nicola McDougal

Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

Soil is one of the most important things for life to exist on earth. Its chemical composition and environmental effects are essential to understand if one truly wants to look at its importance. In this lesson, explore what soil is made of, the different types of soils, and some environmental problems with soil. Updated: 11/10/2021

What Is Soil Made Of?

Hi! Meet Ursula. You may recognize that Ursula is a worm. She is an earthworm, and along with other creatures such as ants, woodlice and centipedes, she lives in the soil. Ursula is here to help us learn all about where she lives, what soil is made of and some of the problems her home can have. So, are you ready for our journey? Off we go!

Let us first ask Ursula what soil is. Ursula tells us that soil is a thin layer of loose materials that covers the surface of the Earth. Soil contains tiny pieces of weathered rock, decomposed plants and dead animals. Things that were once alive, such as decomposing plants and dead animals, are known as organic material.

Soil is not only Ursula's home, but it's also where the roots of plants get nutrients that help them grow. Soil is very important to Ursula, the plants, and all the animals that eat the plants, including us.

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  • 0:02 What Is Soil Made of?
  • 1:07 Different Types
  • 3:12 Environmental Problems
  • 5:48 Lesson Summary
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Different Types of Soils

Hang on, Ursula is trying to tell us something! Okay, Ursula, I haven't forgotten. She also needs to tell us that there are different types of soil. The different types depend on the kind of rock that made it, how much organic material is in it, and its texture. Each type of soil has different properties, and Ursula would like to tell us about different types of soil.

The first soil is called sandy soil. Sand is made of a chemical called silicon dioxide, or more commonly called quartz, and sandy soil is formed from big particles. Sandy soil is light and easy to dig, and many gardeners love it. But the big particle size means that water can pass through easily, and plants need regular watering.

Now we find Ursula in another soil called silty soil. Silty soil is similar to sandy soil, but has smaller particles. This means that water does not pass through quite so easily and does not dry out too much. Silty soil is considered one of the most fertile of soils. Plants grow well in it because it is rich in nutrients.

Clay soil is not a good soil for Ursula or plants. It is made up of very tiny particles, and it does not let the water drain very easily. Clay soil is very heavy after rain and plants rot from too much water at their roots. Gardeners dislike clay soil and often have to dig in sand and other materials to loosen it up.

The final type of soil is the worst of all and that is chalky soil. It is so bad, Ursula won't go near it. Chalky soil is very alkaline and does not hold water. It dries out very easily and is very infertile. Chalky soil requires a lot of fertilizer to make it possible to grow anything.

So now Ursula has told us about the main types of soil, let's find out about some other problems soil can have.

Environmental Problems with Soil

Ursula has already told us that plants grow best in silty soil. This is because silty soil contains a good amount of available chemicals such as nitrogen (N), potassium (K) and phosphorus (P). Plants need these chemicals to grow. These chemicals are essential nutrients for plants. One important chemical property that affects how plants get these nutrients is soil pH. Soils with a pH of less than 7 are acidic; those with a pH of more than 7 are alkaline, or basic; and those with a pH that equals 7 are neutral. The words basic and alkaline mean pretty much the same thing. Soil pH is very important because these nutrients are only available at certain pH values. Nitrogen, for example, is available to plants at a pH greater than 5, and phosphorus is only available between pH 6 and 7.

It is for this reason that most plants do really well in neutral or slightly acidic soils. Hopefully you can see why chalky soils are so infertile. They are highly alkaline, so some of the essential nutrients are no longer available to the plants.

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