Soil

• Use soil from your yard or garden and compare it to a fresh bag of store-bought potting soil. Make sure to use soil from the surface of the ground that looks the most fertile. Fill four containers with your soil and four with potting mix. For each type of soil, leave one as your control with no pollutants added.
  
  

Method

• Add progressive amounts of motor oil or diesel fuel to each container. For example, in the three non-control potting mix containers add a teaspoon of motor oil to one container, two teaspoons to the second and three to the third. Repeat the same procedure for your own soil. Label all of the containers with the type of soil, how much pollutant was added and the date of planting. After planting three bean seeds in each of the eight containers of soil, thin the plants to one for each container. Keep all growing conditions such as amount of water and sunlight constant.
  
  

Growth Rate

• Monitor the growth rate of the bean plants. Measure them every day and plot a graph of the growth of the plants in each container. Also note the size of the leaves and any other differences among the plants growing in the different amounts of pollution such as color and stem thickness.
  
  

Results

• Because soil pollution inhibits nitrogen absorption by plants, they will be small and sickly looking with greater amounts of pollutants. Because your yard or garden soil probably had more clay in it than the potting mix, it will likely show less pollution damage. This is because the clay particles will have helped buffer and trap the polluting particles. The non-potting soil will likely have more nitrogen-fixing bacteria in it than the store-bought mix. The bacteria will be harmed by the pollution but may be able to provide more of the nutrient to the bean plants than those in the potting mix.