A large field at the base of a mountain becomes flooded when heavy rains in the mountains cause a stream to overflow. Each time the flooding occurs, more soil washes away. The owners of the land want to perform an experiment to see if different types of plants could help reduce soil erosion. They choose five areas of ground that are the same size, the same distance from the stream, have the same slope and the same kind of soil, and receive the same amount of sunlight. The type of plant planted in each area is different for each of the five areas. Measurements of soil erosion will be made each time flooding occurs. The results will be compared after six months.

Which hypothesis is being tested in this experiment?