Grasslands and Soil Drainage Project for Kids

Earth Science Unit Study

Week 15: We measured the drainage rates for different types of soil.

Grasslands are found all over the Earth, but are known by several different names. The Savannah in Africa, the Stepps of Asia and the Grasslands of North America are all similar habitats.

BBC's video Wild Africa explores several different plants and animals living on the African Savannah as well as the origins of these grasslands. Much of the food we eat is grown on the grasslands of America, as the soil is rich and the absence of trees facilitates easier planting.

After watching the video, we separated soil into coarse, medium and fine grain samples and then measured the water drainage rate of each type as detailed in Janice VanCleave's A+ Projects in Earth Science: Winning Experiments for Science Fairs and Extra Credit.

One factor which influences the success of growing food is the drainage of the soil. Soil that doesn't drain well is wet and can become very muddy. Conversely, soil that drains too quickly may not hold sufficient moisture required by the plants.

The soil was separated using two different sized strainers. First it was sifted using the holes of a flower pot.

 The grains which passed through the holes in the flower pot were sifted again using a child's strainer toy.

 The double sifting resulted in fine, medium and coarse grain soil.

The quantities of each sample were measured to determine that the soil was comprised mainly of medium size particles.

Next one sample was placed into a yogurt container (flower pot in the picture) containing holes poked through the bottom for the water to drain out and 200 ml of water was poured into the sample. Once the water was added a timer was used to measure the amount of time it took for the water to slow to a drip. The drained water was collected and measured to see how much drained out. Then the drainage rate was calculated by dividing the amount of water collected by the time it took to collect.

* Note that the first time the drainage rate was measured the experiment did not work properly as the flower pot container used (as shown in the picture) had large holes in the bottom. The water and the soil flowed right out.

In addition to calculating the drainage rate of fine, medium and coarse soil, the drainage rate of rocks was also calculated. It was no surprise that rocks drained the quickest, followed by coarse, medium and then fine grain soil. In the future, we plan to repeat the experiment measuring the drainage rate of clay, sand, other types of soil and perhaps oats and lentils.

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