Soil Science: How Moist is that Mud?
Have you ever taken a step onto what appeared to be dry ground, only to find yourself ankle-deep in mud? Yuck! When you walk through damp soil, it can be a very messy experience. How can you tell if soil is wet or dry before you step on it? In this science activity, you will investigate whether the color of the soil can help you determine how dry or wet it is.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
The amount of water present in a sample of soil is called the moisture content. Moisture is very important and the amount of moisture needs to be in careful balance, not too dry and not too wet, for organisms to thrive in it. Specifically, the moisture content of the soil needs to match the needs of the plants, animals and other organisms living in the habitat. Some organisms need a lot of moisture, like ferns and salamanders. Others, like cacti and snakes, are adapted to desert habitats and need very little water. Most often, evenly moist soil is a haven for plants and small, soil-dwelling animals.
Moisture conditions affect the soil structure in many ways too. Soil that is too wet or does not drain properly can suffer from erosion. Soil that is too dry can become hard and compacted. Also, different types of soil respond to moisture differently. A sandy soil will drain water quickly, but a clay soil will prevent water drainage and become soggy.
Extra: You could try to quantify the results from this activity by taking a picture of the damp soil in all of your cups, printing the picture out in grayscale, and comparing it to a grayscale color bar (one that has the different amounts of black or white labeled with percentages). When you quantify your results, just how different are the soil samples? Are some much darker or lighter than others?
Extra: In this science activity, you only tested one type of soil. Try sampling different areas of your yard and compare them to each other and the soil in the original series of cups. Can you use your original soil series to estimate the moisture content of soil from different places in your yard?
Extra: Try estimating the moisture of soil that is in the same location but on different days. Does soil moisture change with the weather, such as on hot days compared to cool days, and cloudy days compared to sunny ones? How much does the moisture vary from day to day?
Observations and Results
Did you see that the soil became darker as you added water to it?
The color of soil can vary depending on the type of soil used, but, in general, dry soil becomes darker in color when water is added to it. The color of the dry soil depends on what little particles make up the soil, specifically what minerals and proteins (i.e., organic matter) it contains. When water is added to soil, the water can replace the oxygen that is naturally in the soil, and make the soil darker. This means that wetter soil will have less oxygen compared to drier soil. When enough water is added, the soil can become saturated and the water will start to form a layer on top of the soil. You may have seen this happen in the cups with the most water added to them. As mentioned earlier, different organisms need soils with different moisture contents. If the soil is too dry, plants, animals and microorganisms that need more water will not survive in it, and the soil may also become hard and compacted. However, if soil is too wet, it will not have enough oxygen in it for some organisms to survive in it either.
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Teisha Rowland, PhD, Science Buddies
Science Buddies |
Soil, water, moisture, colors
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