Final answer:
In the agricultural research experiment, the chemical fertilizer is the independent variable, as it is the component that is altered to study its effects on the yield of corn. The control in this case is the group of corn plants that do not receive the chemical fertilizer, which serves as a standard for comparison.
Step-by-step explanation:
The fertilizer represents the independent variable in this agricultural research investigation. The independent variable is the one that is manipulated or varied by the researcher to observe the effect on the dependent variable, which in this case is corn yield. In a controlled experiment, other factors must remain constant, such as the amount of sunlight and water, while the independent variable is the one component that is changed. Thus, when comparing different fields with various amounts of fertilizer, the amount of fertilizer is what is being tested.
An experiment must have a control group, which is a group that does not receive the experimental treatment, to serve as a benchmark for the results from groups with the independent variable. In the situation described by the student, the row of corn without fertilizer acts as the control, which is crucial for determining the effects of the fertilizer on plant growth.