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

A study was conducted to relate leaching of a herbicide, atrazine l-N' -(1-methylethyl)-1,3,5-triazine-2,4,-diamine], and inorganic water tra cers, Br- and Cl-, to the amount of deep-percolating water produced fr om irrigation. Soil at the site was classified as a Dehli Loamy Sand ( Mixed, Thermic, Tepic Xeropsamment) which was an unstructured sandy so il that was low in organic C content, conditions conducive to solute l eaching. 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 refe rence evapotranspiration, produced corresponding increases in the dept h of percolated water. Atrazine's soil distribution indicated greater downward movement in response to increases in amount of deep-percolati ng water. Magnitude of leaching differed between irrigation methods an d increased in the order: sprinkler < basin < furrow. Simulations usin g the LEACHM model provided a physically based explanation for the dif ferences in water movement between sprinkler and basin methods. The to tal amount of applied water was similar at each level of percolation b ut sprinkler irrigations were more frequent, resulting in more evapora tion and, consequently, less water available for deep percolation. Bot h amount and method of water application are important factors that de termine pesticide movement and that, in irrigated agriculture, must be considered as integral components of pesticide management.