Field experiments were conducted in 1991, 1992, and 1993 to evaluate the dissipation and carryover potential of atrazine from starch-encapsulated (SE) and commercial formulations (CF). Formulation was not a significant factor in atrazine dissipation at any application rate. The dissipation time required to reach one-half of the original concentration (DT50) was measured for each formulation. The atrazine DT50 combined over all years (1991 to 1993) and rates (1.1 to 3.4 kg ai ha−1) was 7 wk for the CF, 10.3 wk for the SE large particles (0.85 to 1.4 mm), and 8.2 wk for the SE small (0.425 to 0.85 mm). Oat injury in the spring of 1992 from all rates of both SE formulations applied in 1991 was greater than that from the CF formulation. Increased oat injury from SE formulations was attributed to more atrazine present in the top 0 to 8 cm of soil compared to that for the CF. Despite significant oat injury from the 1991 application, no injury was observed on soybeans planted in 1992. Soybeans planted in 1993 and 1994 also showed no injury from the respective applications. These findings suggest that the potential for atrazine carryover from starch-encapsulated formulations was not greater than that from the commercial formulation.

Experiments were conducted in controlled environment chambers to evaluate the effects of temperature and soil water content on the time of dissipation of commercial (CF) and starch encapsulated (SE) atrazine formulations to one-half the original concentration (T50). SE samples were also analyzed for the amount of atrazine remaining within the starch particles (percent encapsulation). The dissipation of CF atrazine was affected by changes in temperature and soil water content. SE atrazine dissipation was most influenced by changes in soil water content rather than temperature. Independent of soil water, there was no atrazine dissipation from any formulation at 15 C. The T50 for CF atrazine at 20% soil water content was 53.4 and 29.9 d for 25 and 35 C, respectively. At 20% soil water content, all SE treatments gave a T50 greater than 60 d. The percent starch encapsulation at 20% soil water content was greater than or equal to 55.8 and 30.4% for SE large and SE small, respectively. This high level of encapsulated atrazine accounts for the reduced SE dissipation observed at 20% soil water content. At 40% soil water content, the dissipation of CF and SE small atrazine were not different for either 25 or 35 C. Compared to the CF, the SE large formulation extended the T50 by 7.4 and 6.7 d at 25 and 35 C, respectively. At 40% soil water content, there was no encapsulated atrazine present in SE formulations 60 DAT.