This chapter may not be construed to restrict or avoid sales or exchanges of fertilizers, fertilizer materials, micronutrients, specialty fertilizers, soil amendments, or plant amendments to each other by importers, manufacturers, or manipulators that mix fertilizers, fertilizer materials, micronutrients, specialty fertilizers, soil amendments, or plant amendments for sale or as preventing the free and unrestricted shipments of fertilizer, fertilizer materials, micronutrients, specialty fertilizers, soil amendments, or plant amendments to manufacturers or manipulators that have registered their brands as required by this chapter.