The amount of rent due shall be established by using a schedule to be promulgated by the director, with the approval of the Governor, which shall operate in inverse proportion to the investment made on the lease land, as such investment is certified by the Department of Agriculture. The director, in establishing the schedule, shall attempt to award thereby those lessees who make maximum investment in the leased land and penalized those who make the least. In no event, however, shall the annual rent exceed six percent (6%) of the fair market value of the land at the time of the execution of the lease.