Ionic thiocyanate (SCN(-)) production, fate, and phytotoxicity in soil amended with Brassicaceae seed meals.

Brassicaceae seed meals produce ionic thiocyanate (SCN (-)), a bioherbicidal compound. This study determined the fate of SCN (-) in a field soil amended with seed meals of Sinapis alba, Brassica juncea, and Brassica napus and quantified crop phytotoxicity by monitoring carrot ( Daucus carota) emergence. Meals were applied at 1 or 2 t ha (-1), and soils were sampled to 35 cm for SCN (-). Maximum SCN (-) (211 micromol kg (-1) of soil) was measured at 5 days in 0-5 cm samples from plots amended with S. alba meal at 2 t ha (-1). Less than 30 micromol of SCN (-) kg (-1) of soil was measured at soil depths below 15 cm. At 44 days, SCN (-) was <15 micromol kg (-1) of soil in all treatments. Emergence inhibition of carrots seeded 15-36 days after meal amendment was found only in S. alba treatments. The rapid decrease of SCN (-) concentrations in Brassicaceae meal-amended soil indicates limited potential for off-site environmental impacts.