PREFERENTIAL MOVEMENT OF ATRAZINE AND CYANAZINE UNDER FIELD CONDITIONS

The relative importance of preferential pesticide transport in agricultural soils was determined in a two-phase study conducted on a silt loam soil in Maryland. The first phase (1984) consisted of evaluating persistence and mobility of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and cyanazine [2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-s-triazine]under no-tillage corn management. The second phase (1986) dealt with persistence and mobility of the same herbicides on fallow tilled soil subjected to frequent, large water inputs. Although preferential flow was observed under both treatments and water regimes, the no-till system had the most rapid movement of herbicide relative to water inputs. Additionally, all treatments indicated that the greatest potential movement of surface-applied pesticide occurred with the first water input subsequent to application. Once the pesticide has been preferentially transported, it appears to diffuse into the soil matrix, where it is no longer subject to significant preferential movement. Based on field data and calculated mass balance, persistence of atrazine and cyanazine was unaffected by tillage practice and water regime.