Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.
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.
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.
A real problem for Ursula, her friends, and the plants are soils with very low pH values. Here, the soil is very acidic and plants can no longer get any of the essential nutrients they need. Toxic metals such as mercury, cadmium and lead replace the nutrients in the soil. Plants are killed by toxicity in very acidic soils. Now, you may be asking how do soils get so acidic? Well that is a great question and something Ursula wants to finish on. A significant soil polluter is mining, and much of the toxic metal pollution is caused by this. Soils around areas that have previously been mined for zinc, copper or coal are highly acidic and are often contaminated by various toxic metals. Polluted soil contaminates plants, because they take in the pollutants through their roots. Any animal, including humans, that eats the plant will also take in the toxic chemicals. If eaten, these plants can cause a variety of serious illnesses. Ursula is very sad to tell us that soil contamination persists long after the mining activity has stopped.
In this lesson, you have learned that soil is made up of weathered rock and organic materials such as dead animals and decomposing plants. It is essential for plants and animals and forms a thin layer on the Earth. The different types of soil depend on the rocks it is made from, the amount of organic material, and the texture of the soil. One type is sandy soil, which has a large particle size and does not retain water well. Silty soil is similar to sandy soil but with smaller particles and is considered the most fertile of soils, loved by gardeners everywhere. Clay soil is very heavy to work with and does not drain well. And finally, chalky soil is very infertile and does not retain water. Soil pH is an important chemical property that determines the availability of nutrients to plants. Most plants grow best in pH values between about 5.5 and 7.0. A significant polluter of soil is mining. Soils around previously mined areas often are contaminated by toxic metals. For this reason, food grown on contaminated soil should not be eaten.
Soil's Chemical Composition & Environmental Effects Overview
|Soil||a thin layer of loose materials that covers the surface of the Earth|
|Organic material||things that were once alive, such as decomposing plants and dead animals|
|Sandy soil||made of a chemical called silicon dioxide commonly called quartz|
|Silty soil||similar to sandy soil, smaller particles, more fertile|
|Clay soil||is very heavy after rain; made up of very tiny particles; does not let water drain easily|
|Chalky soil||very alkaline and does not hold water; dries out easily and is very infertile|
|Soil pH||soils with a pH of less than 7 are acidic; those with a pH of more than 7 are alkaline, or basic; those that equal 7 are neutral|
Getting to the end of this lesson with understanding of the above topics will enable you to:
- Recognize the components of soil
- List the types of soil
- Determine the importance of pH balance to soil
To unlock this lesson you must be a Study.com Member.
Create your account
Register to view this lesson
Unlock Your Education
See for yourself why 30 million people use Study.com
Become a Study.com member and start learning now.Become a Member
Already a member? Log InBack