25 CFR § 162.229 - How long can the term of an agricultural lease run?
(a) An agricultural lease must provide for a definite lease term, specifying the commencement date. The commencement date of the lease may not be more than one year after the date on which the lease is approved.
(b) The lease term must be reasonable, given the purpose of the lease and the level of investment required. Unless otherwise provided by statute, the maximum term may not exceed ten years, unless a substantial investment in the improvement of the land is required. If such a substantial investment is required, the maximum term may be up to 25 years.
(c) Where all of the trust or restricted interests in a tract are owned by a deceased Indian whose heirs and devisees have not yet been determined, the maximum term may not exceed two years.