(a) If any part of the principal consists of a right to receive royalties, overriding or limited royalties, working interests, production payments, net profit interests, or other interests in minerals or other natural resources in, on, or under land, regardless of whether any natural resource was being taken from the land at the time the trust was established, the receipts from taking the natural resources from the land shall be allocated to principal. If any part of the principal consists of property subject to depletion, including leaseholds, patents, copyrights, royalty rights, and rights to receive payments on a contract for deferred compensation, but excluding interests in minerals or other natural resources as described above, and in timber or in land from which merchantable timber may be removed, the trustee shall determine the value and the useful life of the property as of the beginning of each annual accounting period. Receipts shall be allocated to principal to amortize that value; the balance of the receipts shall be allocated to income.

(b) A trustee that, on July 1, 1991, held an item of depletable property of a type specified in this Code section may allocate receipts from the property in the manner used before July 1, 1991, but as to all depletable property acquired after July 1, 1991, by an existing or new trust, the method of allocation provided in this article shall be used.