Prior to starting their science fair investigations, the students in Mrs. Hensley's biology class are required to submit a summary of their experimental designs. One student submitted the following: Hypothesis:
Fertilizer X increases fruit production in tomato plants.
Procedure:
Two tomato seeds will be germinated at the same time.
Each germinated seed will be placed in a separate 500 mL container.
Exactly 500 g of soil will be added to each container, and the germinated seeds will be placed 1 cm below the surface.
20 g of Fertilizer X will be added to one plant.
0 g of Fertilizer X will be added to the second plant.
Each plant will receive the same amount of water and light each day.
After 60 days, the total number of tomatoes produced by each plant will be counted

The teacher identified a problem with the procedure and asked the student to revise the method. Which of the following is a problem with the student's procedure?