“Commercial fertilizer” means any substance which contains 5 percent or more of nitrogen (N), available phosphoric acid (P2O5), or soluble potash (K2O), singly or collectively, which is distributed in this state for promoting or stimulating plant growth. “Commercial fertilizer” includes both agricultural and specialty fertilizers. “Specialty fertilizers” may contain less than 5 percent nitrogen (N), available phosphoric acid (P2O5), or soluble potash (K2O), singly or collectively.