Atrazine Dissipation in Conventional‐Till and No‐Till Sorghum

Abstract

Abstract Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropyl amino‐ s ‐triazine) dissipation was compared in conventional‐till and no‐till Holdredge loam soil (fine‐silty, mixed, mesic Typic Argiustolls) during the sorghum phase of a 3‐yr winter wheat ( Triticum aestivum L.)‐sorghum [ Sorghum bicolor (L.) Moench]‐fallow rotation. Dissipation was similar in both tillage treatments and the half‐life of atrazine in the surface 10 cm of soil was estimated by linear regression to be approximately 42 and 50 d in conventional‐till and no‐till plots, respectively. Movement of the herbicide below the upper 10 cm of soil was not significant during the 105‐d sampling period and only traces of atrazine (< 0.05 mg/kg) were found at the 40‐cm depth. Rectangular hyperbola equations were fit to quantitative data and could be used to estimate atrazine levels in the soil profile. Laboratory incubation suggested nonbiological hydrolysis to be the primary means of degradation. Similar atrazine dissipation in conventional‐till and no‐till plots was attributed to the relatively uniform acidity of the soil, which catalyzed atrazine hydrolysis. Long‐term application of NH 4 NO 3 to all plots may have contributed to surface soil acidity and minimized the effect of tillage on atrazine dissipation.