Johannes wants to know whether soil, water, or both are needed for plant growth. he chooses to conduct experiments on a willow tree for five years to answer his question. how can his experimental methods be changed to improve his experiment?

He could conduct multiple experiments at same time. For example, he can grow one willow tree in just water, one in just soil, and one tree in combination of soil and water. Then after a certain time, say 5 years, he can see their growth and determine what's the best approach for plant growth.

Explanation:

want or the answer