Field dissipation of pendimethalin and alachlor in sandy clay loam soil and its terminal residues in sunflower (Helianthus annus L.)

Abstract

Field experiments were conducted with sunflower as a test crop during 2010-11 to study the dissipation kinetics and the persistence of pendimethalin and alachlor in sandy clay loam soil and its terminal residues in sunflower. Herbicides were applied at recommended and double the recommended dose along with control and the treatments were replicated thrice in randomized block design. The soil and plant samples collected at periodical intervals for herbicides residue determination using GC equipped with ECD detector. Results shows that the degradation of both the herbicides in soil was faster at higher dose of application than at the lower dose and the concentration decreased with the advancement in crop growth. While pendimethalin persisted in soil for 60 – 90 days, the alachlor persisted in soil for 30 - 45 days depending on the quantity of application. Degradation of both the herbicides in soil followed first order kinetics with the mean half life of 14.6 and 9.8 days respectively for pendimethalin and alachlor. Residues of these herbicides were below 0.001 mg/kg at the time of harvest in soil, sunflower seeds and stalks showed that these herbicides a can be safely used for the control of weeds in sunflower cultivation.