Degradation, carryover, and leaching comparison of commercial and starch-encapsulated formulations of atrazine

Gordon Dean Vail, Purdue University

Abstract

Field and laboratory experiments were conducted from 1991 to 1994 to compare the degradation, carryover, and leaching of starch encapsulated (SE) and commercial liquid formulations (CF) of atrazine. In controlled environment growth chambers, SE atrazine degradation was less than that of the CF at 10 and 20% soil water content. At 30 and 40% soil water, there were no differences in atrazine degradation by 60 days after treatment. There was a strong relationship between the amount of atrazine remaining in SE particles (percent encapsulation) and atrazine degradation. High percent encapsulations yielded low degradation rates. As soil water content increased, percent encapsulation decreased with SE large particles (0.85-1.4 mm) degrading more slowly than SE small particles (0.425-0.85 mm). These experiments were performed under constant soil water contents and did not allow for the normal field wetting and drying cycles that contribute to enhanced release and degradation. Atrazine formulation did not effect degradation at any of the rates tested in field studies. SE small particles extended the time for degradation to one-half of the original concentration (T50) by 1.2 wks over the CF while SE large particles extended the T50 by 3.3 wks. Oat injury from SE formulations applied in 1991 was significantly greater than from the CF at all rates. This greater oat injury can be attributed to very low rainfall that prevented adequate atrazine release from SE particles. Atrazine injury to oats from all 1992 and 1993 applications were less than 20%. Soybeans planted in 1992, 1993, and 1994 did not develop atrazine injury symptoms. These data suggest that under normal application timing and use rates, injury will not occur in rotational soybeans. Generally, there were no significant formulation differences detected for any sampling depth below 7.6 cm in field trials from 1991 to 1994. The lack of soil leaching differences may be attributed to the high clay and organic matter content of this silty clay loam soil. Highly variable rainfall conditions contributed to distinctly different field leaching patterns over sample timing for the years 1991 to 1994.

Degree

Ph.D.

Advisors

Schreiber, Purdue University.

Subject Area

Agronomy

COinS