Effects of conventional and mulch tillage on Dicamba transport

Leaching and runoff losses of the postemergence-applied herbicide dicamba w ere evaluated over a 3-yr period (1989 to 1991). Dicamba was applied at the recommended rate (0.56 kg ai/ha) to conventional and mulch tillage planted corn fields on Hagerstown silty clay loam (fine, mixed, mesic Typic Haplud alf). Mulch tillage followed several years of no-tillage corn. Root zone le achates were collected utilizing pan lysimeters placed 1.2 m below the soil surface. Surface runoff was monitored and collected with an HS-flume and a utomated sampling equipment. Leaching was greatest during 1989, and runoff events were recorded only during this season. Leachate samples containing m easurable levels of dicamba were obtained within 21 d of herbicide applicat ion or within slightly more than one soil half-life of this chemical. More dicamba leached under mulch tillage than conventional tillage management. T illage rotation (no tillage to mulch tillage) did not alter the leaching lo ss potential of dicamba beneath the minimally tilled soil surface, as postu lated, compared with the previous untilled surface. The mulch tillage surfa ce reduced runoff water losses compared with conventional tillage, but earl y-season leaching activity, coupled with the minimal persistence of dicamba in soil, negated runoff transport of this herbicide from either tillage sy stem when the first runoff event occurred 12 d after its application.