The provisions of this article shall apply to any substance or mixture of substances intended to be used for promoting or stimulating the growth of plants, increasing the productiveness of plants, improving the quality of crops or producing any chemical or physical change in the soil. Except as provided in section 3-274, this article shall not apply to sales for export outside the state nor to sales of agricultural minerals to any licensed producer, manufacturer, importer, agent or dealer in agricultural minerals, or to sales of fertilizing materials to any licensed producer, manufacturer, importer, agent or dealer in commercial fertilizers, but such exemptions shall not relieve such licensed persons from the tonnage license fee provided for in section 3-268 when purchased fertilizing materials are used upon their own lands within this state.