INFLUENCE OF AMOUNT AND METHOD OF IRRIGATION WATER APPLICATION ON LEACHING OF ATRAZINE

A study was conducted to relate leaching of a herbicide, atrazine 16-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4,-diamine], and inorganic water tracers, Br- and Cl-, to the amount of deep-percolating water produced from irrigation. Soil at the site was classified as a Dehli Loamy Sand (Mixed, Thermic, Tepic Xeropsamment) which was an unstructured sandy soil that was low in organic C content, conditions conducive to solute leaching. The relationship between depth of solute movement and amount of deep-percolating water was measured in sprinkler, basin, and furrow irrigation methods. Soil distribution of inorganic tracers indicated that graded levels of added water treatments, which were based on reference evapotranspiration, produced corresponding increases in the depth of percolated water. Atrazine's soil distribution indicated greater downward movement in response to increases in amount of deep-percolating water. Magnitude of leaching differed between irrigation methods and increased in the order: sprinkler < basin < furrow. Simulations using the LEACHM model provided a physically based explanation for the differences in water movement between sprinkler and basin methods. The total amount of applied water was similar at each level of percolation but sprinkler irrigations were more frequent, resulting in more evaporation and, consequently, less water available for deep percolation. Both amount and method of water application are important factors that determine pesticide movement and that, in irrigated agriculture, must be considered as integral components of pesticide management.