It shall be unlawful for any person to manufacture, offer for sale or sell in this state, any commercial fertilizer, or soil conditioner containing any substance used as a filler that is injurious to crop growth or deleterious to the soil, or to use in such commercial fertilizer, or soil conditioner as a filler any substance that contains inert or useless plant food material for the purpose or with the effect of deceiving or defrauding the purchaser.
Iowa Code § 200.11