California Code, Revenue and Taxation Code - RTC § 24377

(a) A taxpayer engaged in the business of farming may elect to treat as expenses which are not chargeable to capital account expenditures (otherwise chargeable to capital account) which are paid or incurred by it during the taxable year for the purchase or acquisition of fertilizer, lime, ground limestone, marl, or other materials to enrich, neutralize, or condition land used in farming, or for the application of such materials to such land. The expenditures so treated shall be allowed as a deduction.

(b) For purposes of subdivision (a), the term “land used in farming” means land used (before or simultaneously with the expenditures described in subdivision (a)) by the taxpayer or its tenant for the production of crops, fruits, or other agricultural products or for the sustenance of livestock.

(c) The election under subdivision (a) for any taxable year shall be made within the time prescribed by law (including extensions thereof) for filing the return for that taxable year. The election shall be made in the form and manner as the Franchise Tax Board may prescribe. The election may not be revoked except with the consent of the Franchise Tax Board.