Effects of Soil Water Content on Oxadiazon Dissipation

In a Crowley silt loam, between 30 kPa, continuous flood, and alternate flood laboratory treatments at 25 C, dissipation of incorporated oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] varied little, with an average of 59% remaining after 20 weeks. In the greenhouse, subsurface application of oxadiazon reduced its phytotoxicity but increased its persistence up to four times more than with surface-applied oxadiazon. In the field, 50% of the surface-applied oxadiazon dissipated from the soil within 6 to 11 days when the soil was flush irrigated and then flooded, compared to 15 to 17 days when the soil was irrigated but not flooded in two rice (Oryza sativa L.) management systems. Oxadiazon dissipation in the field was greater during the first 2 or 3 weeks after application than in the laboratory study. This is explained at least partially by the lack of herbicide incorporation in the field.