Determination of metamifop residues in soil under direct-seeded rice

Metamifop is a herbicide used for the control of annual grass weeds in rice. Agrochemicals leaching into aquatic environments are of concern due to their potential persistence. Thus, this study was undertaken to determine the terminal residue of metamifop in rice crop and soil. Field experiments with rice were conducted at Tamil Nadu Agricultural University, Coimbatore, India. Metamifop was applied during 2-3 and 5-6 leaf stages of the weeds at different doses, namely, 0, 75, 100, and 125 g active ingredient (ai) ha(-1). Paddy grains, straw, and soil samples were collected at harvest and analyzed for metamifop by HPLC. Residues were high in the plots which had received 125 g ai ha(-1) at 2-3 leaf and 5-6 leaf stage. Though the metamifop residues were below 10 mu g kg(-1) in all substrates, N-(2-fluorophenyl)-2-hydroxy-N-methylpropionamide, a metabolite of metamifop, was detected in the soil and grain ranged from 4 to 221 mu g kg(-1). Hence, it is important to study the metamifop residue and its metabolites in soil and its biomagnification potential in crops.