Influence of soil pH-sorption interactions on imazethapyr carry-over

Soil pH affects imazethapyr sorption-desorption, which in turn can affect p ersistence and bioavailability. Long-term imazethapyr carry-over has been o bserved in soil that is below pH 6.5, resulting in significant sugarbeet da mage. Imazethapyr concentration decreased rapidly in held soil, regardless of pH. Despite similar amounts of imazethapyr remaining in aged soils at di fferent pH levels, there were differences in bioavailability, which can be explained by sorption-desorption. At low pH more imazethapyr was sorbed tha n at high pH, but it readily desorbed. At high pH less imazethapyr was sorb ed initially, but it did not readily desorb. Thus, after 3 months, the rema ining imazethapyr in low-pH soil was desorbable and bioavailable, resulting in injury to canola and sugarbeet. Liming aged, low-pH soil released bound imazethapyr residues, which would then be degraded and result in less carr y-over.