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 should have used a large sample size.

Johannes wanted his experiment to be improved, this can be done only when the experiment will be conducted with a large sample size.

Any experiment should be conducted based on the fact that the sample size should be large.

Here, in this experiment Johannes used only a single tree for five years. He should have used large sample size for more accurate result.

The effect of soil, water or both can be studied when there is a control and a experimental sample.

He needs to use a larger sample size to improve his experiment.

Explanation: So Johannes wants to determine whether soil, water, or both are needed for plant growth. He selects a willow tree to conduct experiments on for five years. To get the progress in his experimental procedures he can pick a bigger size of the sample and examine its results. As the larger size will be easier for him to measure as compared to the smaller sample and at the same time results will be more reliable. Larger samples will ensure the homogeneity of the test sample, which will produce better and reliable results.