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Abstract
The dissipation of pendimethalin was investigated in soils of cotton fields in Thessaly, central Greece, for a period of two years. The fields were irrigated either with sprinkler or with sprinkler for the first two irrigations plus drip for the rest of the experimental period. Pendimethalin was applied at rates of 1.1, 1.32, and 0.96 kg a.i./ha in a clay loam soil at Rizomylos, a clay soil at Kypseli, and a sandy clay loam soil at Karditsa, respectively. Residues were determined with capillary GC-NPD after ethyl acetate extraction. Recovery of pendimethalin from spiked soils was 82–101% with a repeatability of 2–7%, and the limit of quantification was near 0.04 mg/kg. At 150 days after application (DAA) pendimethalin residues found in the soils were 10–18% of the initial measured concentrations. For the drip-irrigated fields, dissipation of pendimethalin varied within the field between the non-irrigated and the irrigated soil regions, indicating a more rapid loss in the irrigated part of the soil. Residues in the wet region (along the drip irrigation line) at 150 DAA were about 75 and 60% of those measured in the dry region (off the irrigation line) of the soil at the Kypseli field for the 1996 and 1997 season, respectively. At the Rizomylos field the corresponding percentage was about 70%, for the 1997 season. The half-life, calculated from the first-order kinetics dissipation equation, was estimated at between 43 and 62 days. No leaching of pendimethalin was observed below 10 cm during the experimental period of 230 days under cotton growing conditions in Thessalian fields.