Persistence and Movement of Picloram in Two Kansas Soils

Abstract

Persistence and movement of 4-amino-3,5,6-trichloropicolinic acid (picloram) were studied in silty clay loam soils located at Hays and Newton, Kansas. At Hays, picloram was applied to a Harney silty clay loam at rates of 2.24 and 3.36 kg/ha in 1963, 1964, 1965, 1966, and 1968 and at Newton to a Goessel (tentative) silty clay loam at rates of 1.12, 2.24, and 3.36 kg/ha in 1966. Fifteen, 20, or 30-cm increments of soil were taken from as deep at 2.4 m below the soil surface and bio-assayed with soybeans(Glycine max(L.) Merr. ‘Clark 63′) in 1968 and 1969. In both soils the highest concentration of phytotoxic residue remained near the soil surface, but differences between the two sites were evident. In the Goessel soil phytotoxic residues were detected only near the surface. In the Harney soil movement was uneven, but residues were detected as deep as 2.4 m below the surface. Soil cracks probably contributed to penetration of small amounts of the herbicide to as much as 2.4 m below the surface. Total picloram remaining in both soils diminished with time.