The top layers of the planet include topsoil, subsoil, parent material and bedrock. Have the student map the four layers, and explain the content and characteristics of each layer on poster board. Use a tall, clear glass container to display how the layers stack up and how to identify each layer. For example, place a large solid mass at the bottom, a layer of crushed rock, a layer of clay and a top layer of rich topsoil. Use a soil sampling auger to drill into the ground and discover the depth of the soil layers in your area.
Plants need soil nutrients to grow well. Evaluating the soil helps farmers deal with soil deficiencies. Have the student collect various topsoil samples from the surrounding area and send the sample to a local soil lab for mineral content evaluation. For each sample, have the student plant seeds in the untreated soil and similar seeds in soil treated according to the recommendations of the soil lab. Record and compare the growth rates and health of a plant in each soil type.
Adding small rocks to a plant’s environment may help the plant grow better by improving soil drainage and providing valuable nutrients. Place a layer of small pebbles in the bottom of a clay pot and then add topsoil and the plant. Plant a second pot with soil and a plant but no pebbles in the bottom of the pot. Plant a third pot with a layer of clay under the topsoil and plant. Pour identical amounts of water into each pot. Record how long it takes water to seep out of the pot and how much water exits the pot. Check the soil moisture in two days to determine how well each soil mix retains moisture. Water each plant twice weekly for four weeks. Compare the health and growth of the plants on a display board. Include an evaluation of the different soil mixtures and which produces the best crops.
Erosion threatens topsoil when it is exposed. Employ large wash tubs or plastic containers to construct three similar landscape models to demonstrate how important reforesting is in areas damaged by forest fires and landslides. Use bare dirt to construct hills, valleys and a stream in the first landscape. Place small rocks in the hills and valleys, and plant seeds 5 to 6 inches apart in the second landscape. Sow seeds liberally on the soil in the third landscape, as well as burying rocks in the landscape. Allow the seeds to grow for four to six weeks. Use a fan to blow on each of the landscapes to demonstrate wind erosion. Pour water from a watering can on the landscapes to demonstrate water erosion.