This project three-variable experiment is easy to execute. First, start with two control groups. Take a group of 100 beans and set aside 20 of them. Put 10 of those into soil exposed to sunlight. Water them every day. Take the other 10 and put them in a cool, dark place. These will be your two controls, one with all test variables and one with none. Take the other 80 beans and put them into smaller groups of 10. Take 20 and put them in plastic bags with water, put half in the sun. Take 20 and put them in plastic bags without water and put half in the sun. Of the remaining 40 seeds, plant 20 in soil and keep them in the dark, water half of this group regularly. Take the remaining 20 seeds and plant them in soil in sunlight and water half of them regularly. When you water plants regularly water the same ones each time and label them.
Now you have two control groups and a number of other groups with different variables. If you need to write a report on this project compare the effects of the different variables on the seeds.
Take three different soil samples from your area, one from a field, one from a stream bed and one from your back yard. The project will compare the different soil compositions. Run water through each sample. Take a piece of litmus paper and put it in each sample. Record the color of each strip for each sample. There should be a color chart with the strips, just record the level of pH that corresponds to the color. Now spread out each sample and try to separate each sample into topsoil, clay and plant life. If you need to write a report, compare the type of particulates and acidity to the different locations. Speculate on why each sample is broken up in the manner that it is.
Take soil from three different locations: your backyard, a field and a stream bed. Set aside some of the soil for analysis. Figure out various particle sizes, composition and organic material amounts for each sample. Determine how much clay, dirt and organic material is in each sample. Plant a seed in each type of soil. Water them regularly and place them in the sun. Two weeks later, compare the growth of each seed. If you need to write a report on this project compare the growth rate of the seedlings to the soil composition. For example soil with more clay usually is poorer soil and will lead to a smaller seedling.