So far, we've learned a bit about soil particles, about their distribution by wind, and about their ability to retain moisture. Now, we will begin to learn about compaction of
soil. (Compaction of soil relates to how tightly packed it is. Compacting the soil makes the pore spaces smaller, and places the soil particles closer to each other.) Any one of, and/or all of, these characteristics have differing effects on the qualities of soils.

Fill each one of several large juice cans with a different type of soil. Press a sharpened 1/4 inch diameter dowel into each can to see how far it can be inserted. Measure the depth to which the dowel went in, and record it in your notebooks.

Now wet the soil samples in the cans and see how far the dowel can be inserted into them, and record the results.

When the soils dry, insert the dowel into them a third time, and record the results.

Make comparisons among the soils and among the results of the three tests, and determine which types of soil were the most and the least compact.

What do you think would happen if a road were built on regular soil without having compacted the soil?

The machines that are made for the purpose of compacting soil are like great big, heavy hammers. They just pound and pound on the soil, until it is very tightly packed and hard.

We compact soil when we shouldn't, by driving heavy vehicles over the earth repeatedly. Some examples of this are the machines that drive along the rows of fruits and vegetables to harvest the crops, vehicles that are used for planting seeds and seedlings on farms, and tractors that are used to plow and aerate the soil. They actually cause compaction below the surface of the soil, making it difficult for roots of the plants to grow properly.