What variables do you need to consider to prove your hypothesis when you have formed a hypothesis that soybeans will grow larger in clay soil than in sandy soil to test your hypothesis?

Answer 1

The variable that you are testing is the composition of the soil, whether it contains more sand or clay. Many other factors affect the growth of soybeans, including the amount of water that they get, the amount of sunlight that they get, any use of fertilizers, etc. To test your hypothesis you would vary only the soil, and keep all other relevant factors the same.
Well you would need to have the same volume of soil, the same amout of beans, the same size and type of beans also. You would also need to leave them for the same amount of time, and in the same conditions. The only thing that should be changed is the type of soil.