Visit a local store and purchase three chemical and three organic fertilizers in liquid form. You also require nine polystyrene or plastic cups, a large bag of potting soil (enough to fill each of your cups two-thirds of the way) and 18 pinto bean seeds.
Pierce a square of four holes in the bottom of each of your nine cups before lining them up and filling each one two-thirds of the way with potting soil. Weigh each of the cups using a scale to ensure that the weight of the cups is the same. Label the side of the cups "Chemical," "Organic" and "Control" based on the conditions they will be exposed to. Wet the soil with a controlled amount of tap water, such as one medicine dropper-full, before planting a pair of pinto bean seeds roughly a quarter to half an inch beneath the soil's surface in each cup. Place all of your plants next to one another on the same windowsill, where they will receive natural sunlight and will not be tampered with by anyone.
Provide each pinto bean cup with a controlled amount of its designated type of fertilizer once each day. For example, add a chemical fertilizer to all three of your "chemical" cups once each day. You should also provide both the chemical and organic plants with a controlled amount of water, such as a medicine dropper-full of tap water. Furthermore, provide your control plants with just a medicine dropper-full of regular tap water and no fertilizer. Finish your experiment and dispose of the plants after no less than three weeks of growth.
When watering and adding fertilizers to your plants each day, observe and photograph the growth of the pinto bean plants. Photographs are ideal to display on your science fair stall and will demonstrate the growth of plants in different conditions pictorially for your stall viewers. Once plants have grown to a reasonable size, you can begin to measure them for height, width (span) and number of beans growing. You should also rate your plant's healthiness out of 10 -- for example, based on the color and strength of the leaves and stem. Graph your results for height, width and healthiness to display on your stall. For example, you could plot a line graph for plant width where the width in inches is on the y-axis and the time in days is on the x-axis. To fill this graph, take an average by measuring the width of the three plants in each condition before plotting three lines on the graph.