Dissipation of Pendimethalin and Fluchloralin in Soil and their Residue in Onion

Degradation of dinitroaniline herbicides viz., pendimethalin and fluchloralin is reported in a sandy loam soil in an onion field during rabi 1989–90 and 1990–91 at Gujarat Agricultural University Farm, Anand, Gujarat. The rate of dissipation of both the compounds showed first-order kinetics. Pendimethalin dissipated with half-life varying from 28,1 to 31.7 d when applied @ 0.75, 1.00, 1.25, 1.50 and 2.00 kg ha⁻¹. Fluchloralin @ 1.0 kg ha⁻¹ showed relatively faster rate of dissipation in a biphasic mode. During phase I (0–10 d), fluchloralin dissipated with half-life of 3.9 d whereas in second phase (10–110 d) the herbicide persisted with half-life valuueof0.5 5ays. Low levels of herbicide residue were detected in onion on the 60th day. The residue were absent at harvest.