Imazamox dissipation in two rice management systems

The current study focuses on the dissipation pattern of imazamox (2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methoxymethylnicotinic acid) in a soil-water environment under the two most adopted rice management systems in Europe, conventional water seeding and dry-seeding. Changes in imazamox concentrations were studied over time in topsoil, field water, irrigation water, outlet water and ground water. The study was performed from 2010 to 2011 in one of the most important rice growing areas of Europe (Vercelli, Northwest Italy). Imazamox dissipated rapidly in both the water and soil environments. In soil, imazamox half-life ranged from 22 to 33 days in 2010 and from 22 to 31 days in 2011. In paddy water, imazamox dissipated rapidly and no important differences among the management systems were found. In addition, the study showed that despite the short half-life of imazamox, the herbicide might be transported from treated fields in outlet waters by means of floodgates. The highest concentrations in outlet waters were found in the conventional water-seeded system, at the sampling site close to herbicide spraying. Imazamox residues were even found in inlet waters, suggesting discharge of the herbicide from paddies located upstream or drift during spraying. Imazamox residues in ground waters were always below the quantification limit. Overall, the low imazamox persistence observed during the 2-year study did not allow important differences between the two systems to be revealed. To reduce imazamox discharge from treated fields in the first days after spraying, a useful practice might be to keep water inside the fields for at least a week after spraying.