If there’s one thing you find everywhere, its soil! Few things are quite so universal; all over the world soil takes part in our planting, building, cleaning, and playing. Without it, none of the crops we use for food, clothing, or fuel could be grown. Like so many universal things, it is very easy to take our soil for granted; it seems so simple, but soil is really very complex!
What we know as soil is really a mixture of many things: minerals from the rock—or parent material—from which the soil is formed, organic materials from the organisms that live in the soil—such as plants and bacteria, water, and dissolved gasses—nitrogen, oxygen, and carbon dioxide. Soil is formed when time and the elements (wind, weather, and living organisms) break down rock and mix in organic materials in different amounts to create the mixture of fine particles, sand, and stones we know generally as soil.
What we know as soil is really a mixture of many things: minerals from the rock—or parent material—from which the soil is formed, organic materials from the organisms that live in the soil—such as plants and bacteria, water, and dissolved gasses—nitrogen, oxygen, and carbon dioxide. Soil is formed when time and the elements (wind, weather, and living organisms) break down rock and mix in organic materials in different amounts to create the mixture of fine particles, sand, and stones we know generally as soil.
One of the most important characteristics of a particular soil is its texture (that is, how large or small the particles are which make up that soil). The larger the size of the particles that make up the soil, the more coarse the soil will be. Also, the smaller the particles that make up the soil, the finer and smoother the texture of the soil will be. There are essentially three kinds of particles that can make up any soil:
1. Sand: These are very large, coarse mineral particles. Imagine the sand at the beach, or in a sandbox. If you rub it between your hands, it is very rough and scratchy. This is because the grains of sand are very big. Try to squeeze wet sand through your fingers, and it will just crumble. This is how you can test if soil is made up of a lot of sand.
2. Clay: These are the smallest particles you can find in soil. If you have ever played with modeling clay, you know it is very soft, smooth, and silky. This is because the particles of the clay are so small—usually you cannot even see the individual particles! Try to squeeze wet clay through your fingers, and it will form long, smooth ribbons. This is how you can tell if a soil is made up of a lot of clay.
3. Silt: These are particles with a medium size, between sand and clay. Because they have a medium size, silt particles make a soil with a texture that is in between clay and sand. If you squeeze wet silt through your fingers, it will make ribbons, but these ribbons will fall apart shortly after going through your fingers.
1. Sand: These are very large, coarse mineral particles. Imagine the sand at the beach, or in a sandbox. If you rub it between your hands, it is very rough and scratchy. This is because the grains of sand are very big. Try to squeeze wet sand through your fingers, and it will just crumble. This is how you can test if soil is made up of a lot of sand.
2. Clay: These are the smallest particles you can find in soil. If you have ever played with modeling clay, you know it is very soft, smooth, and silky. This is because the particles of the clay are so small—usually you cannot even see the individual particles! Try to squeeze wet clay through your fingers, and it will form long, smooth ribbons. This is how you can tell if a soil is made up of a lot of clay.
3. Silt: These are particles with a medium size, between sand and clay. Because they have a medium size, silt particles make a soil with a texture that is in between clay and sand. If you squeeze wet silt through your fingers, it will make ribbons, but these ribbons will fall apart shortly after going through your fingers.
The reason soil texture is so important is because different soil textures hold water differently. Water is very important for the plants that grow in the soil, so how well the soil holds the water will affect how well that soil is able to grow crops (and if the crops don’t grow well, there will be less food to go around!).
Soil that is very coarse will let water in, but also lets the water run out very quickly. This means the water will travel too deep for the plant roots, and will travel too fast for the plant to soak it up. Very fine soil, like clay, does not let the water in very fast. In fact the water will often sit on top of the soil, and just evaporate or run off without soaking in! Plants growing in clay may not get the water they need from this soil either, because the water will not be able to get to the roots.
Soil that is very coarse will let water in, but also lets the water run out very quickly. This means the water will travel too deep for the plant roots, and will travel too fast for the plant to soak it up. Very fine soil, like clay, does not let the water in very fast. In fact the water will often sit on top of the soil, and just evaporate or run off without soaking in! Plants growing in clay may not get the water they need from this soil either, because the water will not be able to get to the roots.
Very good soil for growing plants should be a mixture of these soil textures: enough sand to let water in, but enough clay to hold onto that water, and not let it flow away too quickly. Soils with equal amounts of sand, silt and clay are called loam, and these are considered the best for growing plants.
EXPERIMENT WITH DIFFERENT SOIL TYPES!!
Here’s what you’ll need:
1. 2-3 cups each of sandy and clay soil. You can usually buy these at home improvement stores, or on the internet. You could also find these soil types in the environment! Just ask a local county extension agent or Natural Resource Conservation Service soil scientist where to look!
2. 2-3 cups of water
3. A ½ cup measuring cup
4. Clear plastic cups
5. A nail or a pin
6. A kitchen scale
7. A sink that can be easily rinsed
HERE’S WHAT TO DO!
1. Take two of your plastic cups, and poke a few holes in the bottom with your nail or pin.
2. Put ½ of a cup of the sandy soil in one plastic cup, and ½ of a cup of the clay soil in the other cup.
3. Place the cups, one at a time, on the scale, and record their weights.
4. Pour ¼ of a cup of water over each of the cups of soil and place them in the sink. Allow them to drain for 5 minutes.
5. Weigh each of the cups again, and record the weights. How much has each cup gained? All this weight comes from the water.
6. Take a look at each cup. Can you see where the water is? Where did the water go for the sand soil? For the clay soil? Write down what you see!
7. Now take ¼ of a cup of each soil, and mix it in another plastic cup. Be sure to poke some holes in the bottom of this cup too!
8. Weigh the cup with your mixed soil. Record the weight.
9. Pour ¼ cup of water over this soil, and let it drain in the sink 5 minutes.
10. Weigh this cup again, and record the weight. How much extra weight does this soil have?
11. Where is the water in this soil? Is it sitting at the top, or did it move to the bottom? Is the soil holding onto the water any better than the clay or the sand alone?
12. Try mixing the soil in different amounts. Each time you mix the different soils, write down how much of each one you mixed, and then pour ¼ cup of water over it. Let it drain 5 minutes each time. Be sure to weigh the soil before and after to see how much water the soil holds.
What did you find out about how much water the soil will hold? What was the best combination of sand and clay?
Try planting seeds in the soil you have mixed. Choose seeds that do not grow too large. Remember to water the seeds every day, or whenever the soil feels dry. Compare the growth of your seeds to the growth of the same kind of seeds in potting soil you can buy at the home improvement store.
Be sure to WRITE DOWN ALL THE THINGS YOU DO (what types of seeds did you use, how many did you plant, and what type of potting soil did you try), AND ALL YOUR OBSERVATIONS (how many plants grew, how tall did they grow, how much time did it take for the first seedlings to appear)!
References for further reading:
1) Soil. Wikipedia. 2014, Mar 12. Retrieved 3-12-2014. (http://en.wikipedia.org/wiki/Soil)
2) Hausenbuiller, R. L. (1972). Soil Science: Principles and Practices. Dubuqe, IA: Wm. C. Brown Company Publishers. ISBN: 0-697-05851-4.
EXPERIMENT WITH DIFFERENT SOIL TYPES!!
Here’s what you’ll need:
1. 2-3 cups each of sandy and clay soil. You can usually buy these at home improvement stores, or on the internet. You could also find these soil types in the environment! Just ask a local county extension agent or Natural Resource Conservation Service soil scientist where to look!
2. 2-3 cups of water
3. A ½ cup measuring cup
4. Clear plastic cups
5. A nail or a pin
6. A kitchen scale
7. A sink that can be easily rinsed
HERE’S WHAT TO DO!
1. Take two of your plastic cups, and poke a few holes in the bottom with your nail or pin.
2. Put ½ of a cup of the sandy soil in one plastic cup, and ½ of a cup of the clay soil in the other cup.
3. Place the cups, one at a time, on the scale, and record their weights.
4. Pour ¼ of a cup of water over each of the cups of soil and place them in the sink. Allow them to drain for 5 minutes.
5. Weigh each of the cups again, and record the weights. How much has each cup gained? All this weight comes from the water.
6. Take a look at each cup. Can you see where the water is? Where did the water go for the sand soil? For the clay soil? Write down what you see!
7. Now take ¼ of a cup of each soil, and mix it in another plastic cup. Be sure to poke some holes in the bottom of this cup too!
8. Weigh the cup with your mixed soil. Record the weight.
9. Pour ¼ cup of water over this soil, and let it drain in the sink 5 minutes.
10. Weigh this cup again, and record the weight. How much extra weight does this soil have?
11. Where is the water in this soil? Is it sitting at the top, or did it move to the bottom? Is the soil holding onto the water any better than the clay or the sand alone?
12. Try mixing the soil in different amounts. Each time you mix the different soils, write down how much of each one you mixed, and then pour ¼ cup of water over it. Let it drain 5 minutes each time. Be sure to weigh the soil before and after to see how much water the soil holds.
What did you find out about how much water the soil will hold? What was the best combination of sand and clay?
Try planting seeds in the soil you have mixed. Choose seeds that do not grow too large. Remember to water the seeds every day, or whenever the soil feels dry. Compare the growth of your seeds to the growth of the same kind of seeds in potting soil you can buy at the home improvement store.
Be sure to WRITE DOWN ALL THE THINGS YOU DO (what types of seeds did you use, how many did you plant, and what type of potting soil did you try), AND ALL YOUR OBSERVATIONS (how many plants grew, how tall did they grow, how much time did it take for the first seedlings to appear)!
References for further reading:
1) Soil. Wikipedia. 2014, Mar 12. Retrieved 3-12-2014. (http://en.wikipedia.org/wiki/Soil)
2) Hausenbuiller, R. L. (1972). Soil Science: Principles and Practices. Dubuqe, IA: Wm. C. Brown Company Publishers. ISBN: 0-697-05851-4.
