Concentration of Picloram in the Soil Profile

Abstract

Soil residue levels were studied to a depth of 2.4 m for a period of 2 years after application of 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). Thirty days after application 93 ppb were recovered in the top 15 cm of soil. Residues were less than 5 ppb at depths of 46 to 122 cm. Six months after application, residues were between 5 and 10 ppb down to 183 cm and less than 5 ppb between 198 and 244 cm. Residues to depths of 244 cm were less than 5 ppb 1 year after treatment. Residue levels to similar depths were studied in two soil types for a period of 1 year after application of conventional and polymerized picloram sprays and granules (3.4 kg/ha of picloram). Conventional sprays resulted in significantly higher soil residues for the sampling period than polymerized sprays. Residues from polymer granules were likewise significantly greater than from polymer sprays. Conventional and polymer formulations were identical with respect to movement through the soil.