Answer:
[tex]\boxed {\tt Use \ more \ subjects \ and \ trials}[/tex]
Explanation:
The scientist is measuring the effectiveness of fertilizers on plants.
In her experiment, she tests multiple fertilizers on one plant. This procedure is not very efficient. She only used one plant, which is not a good practice. She should use many plants and use many trials, to ensure the best results.
To improve her procedure, the scientist should use more trials and test subjects.
