2 shows how temperature affects 2,4-D breakdown. A dry year will mean more herbicide carryover into the following year. Light textured soils have less moisture holding capacity and therefore a greater potential to carry over herbicides than heavier soils. 3 shows carryover of Avadex and trifluralins over 8 years. Notice the differences, especially after a drought in 1980.
Many herbicides become more or less tightly bound to soil particles.
Some will never be released while others are slowly released to microbial decomposition. In these processes, soil pH and organic matter play an important role in the rate of disappearance of some herbicides. For specific recommendations, make sure you consult your label or the crop protection guide. Probably the most important time to keep residue restrictions in mind are when making crop planting decisions. Herbicide records with specific locations are very important.