Oxadiazon is a post-emergence herbicide widely used to control several grasses and broad leaved weeds in rice, soybean, sunflower, cotton, orchards and turf. In rice it is mainly used to control Heteranthera spp. The study was carried out over 2007-2009 at Vercelli (45° 17’ 47.99’’ N – 8° 25’ 53.82’’ E), north-west of Italy, in a series of 3 paddy fields of about 2000 m2 each. The aim was to evaluate oxadiazon fate in surface water and top soil in paddy fields under three management systems: A) straw and liquid manure incorporated in autumn and rice seeded in flooded field, B) straw incorporated in autumn and rice seeded in flooded field, C) straw incorporated in autumn and rice seeded in dry field and conventionally flooded starting from rice tillering stage. Oxadiazon was applied in rice pre-seeding at a rate of 380 g ha-1 using a conventional 12-m wide boom sprayer. Water and soil samples were collected at different intervals from herbicide application up to about 3 (water) or 10 months (soil) after the treatment. Water samples were collected both in the flooded fields and from the inlet and outlet floodgates by directly filling 0.5-L flasks. Soil samples were taken using a stainless steel shovel shaped to take the top 1.5 cm layer of soil. Herbicide extraction from water samples was carried out using SPE extraction cartridges. Herbicide extraction from soil was performed by using a cycloexane/ethyl acetate solution (90/10 V/V). Analytical-grade oxadiazon was used as analytical standard. The analysis of the water or soils extracts was performed by using a Perkin Elmer 8500 GC, split injector, equipped with a 30m x0.25µm df SPB 5 column. The injector and detector temperature was set to 250°C and 315 °C, respectively. The trend of oxadiazon presence in flooding water and in outlet water showed remarkable differences between years, even though in paddy water maximum concentration did not exceed 28.0 µg L-1. Over the three years, the concentration in inlet water ranged between 1.24 µg L-1 and 2.25 µg L-1. In all systems, starting from 47 days after treatment, concentration of oxadiazon in flooding water dropped below 3 µg L-1. One year after herbicide application, oxadiazon concentration in soil always exceeded 18 µg kg-1 and system C) showed concentrations two-folds higher than those found in systems A) and B). Oxadiazon seemed to be quite persistent in the soil. The higher presence in system C) could be attributed to the shorter duration of flooding condition that led to a lower occurrence of leaching and dilution phenomena. Among the cultural practices adopted, water management seems to have the strongest effect on oxadiazon dissipation pattern.
Environmental fate of oxadiazon in paddy fields
MILAN, MARCO;VIDOTTO, Francesco;PIANO, Serenella;NEGRE, Michèle;FERRERO, Aldo
2010-01-01
Abstract
Oxadiazon is a post-emergence herbicide widely used to control several grasses and broad leaved weeds in rice, soybean, sunflower, cotton, orchards and turf. In rice it is mainly used to control Heteranthera spp. The study was carried out over 2007-2009 at Vercelli (45° 17’ 47.99’’ N – 8° 25’ 53.82’’ E), north-west of Italy, in a series of 3 paddy fields of about 2000 m2 each. The aim was to evaluate oxadiazon fate in surface water and top soil in paddy fields under three management systems: A) straw and liquid manure incorporated in autumn and rice seeded in flooded field, B) straw incorporated in autumn and rice seeded in flooded field, C) straw incorporated in autumn and rice seeded in dry field and conventionally flooded starting from rice tillering stage. Oxadiazon was applied in rice pre-seeding at a rate of 380 g ha-1 using a conventional 12-m wide boom sprayer. Water and soil samples were collected at different intervals from herbicide application up to about 3 (water) or 10 months (soil) after the treatment. Water samples were collected both in the flooded fields and from the inlet and outlet floodgates by directly filling 0.5-L flasks. Soil samples were taken using a stainless steel shovel shaped to take the top 1.5 cm layer of soil. Herbicide extraction from water samples was carried out using SPE extraction cartridges. Herbicide extraction from soil was performed by using a cycloexane/ethyl acetate solution (90/10 V/V). Analytical-grade oxadiazon was used as analytical standard. The analysis of the water or soils extracts was performed by using a Perkin Elmer 8500 GC, split injector, equipped with a 30m x0.25µm df SPB 5 column. The injector and detector temperature was set to 250°C and 315 °C, respectively. The trend of oxadiazon presence in flooding water and in outlet water showed remarkable differences between years, even though in paddy water maximum concentration did not exceed 28.0 µg L-1. Over the three years, the concentration in inlet water ranged between 1.24 µg L-1 and 2.25 µg L-1. In all systems, starting from 47 days after treatment, concentration of oxadiazon in flooding water dropped below 3 µg L-1. One year after herbicide application, oxadiazon concentration in soil always exceeded 18 µg kg-1 and system C) showed concentrations two-folds higher than those found in systems A) and B). Oxadiazon seemed to be quite persistent in the soil. The higher presence in system C) could be attributed to the shorter duration of flooding condition that led to a lower occurrence of leaching and dilution phenomena. Among the cultural practices adopted, water management seems to have the strongest effect on oxadiazon dissipation pattern.
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