Answer:
explanatory variable
Step-by-step explanation:
Explanatory variable: In research, the term explanatory research is described as one of the types of independent variable which can be used or utilized interchangeably and therefore if any of the variables are considered as "independent" then it wouldn't get affected by any of the variables. If a variable is not considered as "independent" to a certain level then it would be referred to as explanatory "variable".
In the question above, the amount of fertilizers used is the explanatory variable.