Question

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 needs to ask scientists what they think. he needs to conduct the experiment for a longer period. he needs to use a larger sample size. he needs to test more factors in the environment.

Explanation:

Johannes is studying plant growth factors over five - years with willow trees. To improve his experiment, a longer - term study can account for more seasonal and environmental variations, leading to more reliable results. Asking scientists' opinions may not directly improve experimental methods. A larger sample size is good but may not be the most crucial here. Testing more environmental factors is not the most pressing improvement when the experiment is already five - years long. Conducting the experiment for a longer period can capture more complex growth patterns and better understand the long - term effects of soil and water on plant growth.

Answer:

He needs to conduct the experiment for a longer period.