Abstract

                                Field experiments were carried out in sandy clay loam and clay loam soils from 2007 to 2009 to study the persistence and degradation of common herbicides applied to rice (butachlor, pretilachlor), maize (atrazine, alachlor) and soybean (pendimethalin, metolachlor) crops at two levels of application. Soil samples at depth of 0-15 cm were collected at periodical intervals from 0 day to harvest for residue analysis. Herbicides residue after their extraction was determined using GC-ECD, except atrazine which was determined using GC-FID. Results showed that the initial deposits of herbicides in soil vary with the concentration applied and a gradual continuous dissipation of all herbicides in soil was observed as a function of time irrespective of the crops grown. Dissipation of all the herbicides in soil followed first order kinetics. The correlation coefficient (r 2 ) lies between 0.714 and 0.957 and the best fit was observed for acetanilide group of herbicides. Half life of the herbicides increased with the increased concentration with mean half life of 5.88, 12.44, 31.45, 4.78, 14.63 and 22.42 days for butachlor, pretilachlor, atrazine, alachlor, pendimethalin and metolachlor respectively. Within the period of crop harvest more than 98 per cent of herbicides dissipated from the soil, except metolachlor and atrazine.

Key words : Dissipation, half life, herbicides, sandy clay loam, clay loam