The amount of actual value added which is eligible to be exempt from taxation shall be as follows:
(A) For the first year, 75%;
(B) For the second year, 60%;
(C) For the third year, 45%;
(D) For the fourth year, 30%; and
(E) For the fifth year, 15%.
(Iowa Code § 427B.3) (1999 Code, § 8.04)