No superphosphate containing less than eighteen percent available phosphate nor any commercial fertilizer in which the sum of the guarantees for the nitrogen, available phosphate, and soluble potash totals less than twenty percent shall be distributed in this state except for fertilizers containing twenty-five percent or more of their nitrogen in water-insoluble form of plant or animal origin, in which case the total nitrogen, available phosphate, and soluble potash shall not total less than eighteen percent. This section shall not apply to specialty fertilizers.