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Summary Band 40

Christine Ina Klein: Effects of vegetative filter strips on the losses of selected herbicides with surface runoff and interflow in cultivated soils of highlands. Bonner Bodenkundl. Abh. 41 (2005), 224 S.

 

The losses of four herbicides in surface runoff were investigated at an arable site (ca. 10 % slope) situated in Velbert-Neviges, North Rhine-Westphalia, Germany. The selected herbicides are used in agricultural practice on a regular base. Additionally, effects of vegetative strips as a filter between field and receiving water course were examined. Furthermore, herbicide losses in interflow were investigated as this pathway may become more important due to the increased infiltration in filter strips. During three growth seasons of corn (1997 to 1999) the herbicides Metolachlor, Terbuthylazin and Pendimethalin were applied in May. Additionally, Chlortoluron was applied in late autumn of 1997 on winter wheat. Field plots (40 * 3 m arable land) were used to examine surface runoff after natural precipitation; variants were: without filter strip, with a filter strip that was cultivated without herbicide application (cultivated strip, 12 m) and two grass filter strips of different width (6 m, 12 m). Additionally, rainfall simulations were carried out. Interflow was investigated in the variants without filter strip and with 12 m grass filter strip. Soil samples from different positions along the hill slope were examined several times.

Transport of the single herbicides was strongly influenced by their solubility and sorption properties with relevant losses occurring either in solution or bound to the transported soil sediments. At the different runoff events, average concentrations in the aqueous phase reached 721 g l-1 (Metolachlor); in the solids up to 4977 g kg-1 (Pendimethalin) were measured. In particular, the extent of herbicide losses was determined by the interval between application and runoff event, by the distribution of precipitation and by the runoff rate. Losses of Chlortoluron in winter wheat were negligible. High amounts of herbicide losses were observed in corn during single, heavy runoff events shortly after herbicide application. Accordingly, between 0.51 and 0.84 % of the applied herbicides were lost after a single rainstorm. Averaged over the study period of three years, losses in corn amounted to 0.22 and 0.38 % of the applied herbicides Metolachlor, Terbuthylazin, and Pendimethalin in the variant without filter strip.

Surface runoff and soil losses were decidedly reduced in all variants with vegetative filter strips. Furthermore, herbicide concentrations in the runoff suspensions were mostly lower for the variants with filter strips than for the variant without filter strip. In all, losses after natural precipitation were reduced between 56 and 58 % in the cultivated strip variant; retention in the grass strip variants amounted to 87 to 94 % (6 m width) and 96 to 98 % (12 m width), respectively. These results were supported by the rainfall simulations. Regarding interflow, the findings did not indicate enhanced losses via this pathway. Furthermore, the herbicides that were transported into the filter strips were mostly degraded or bound there. In conclusion, vegetative filter strips can bring about a strong protection for surface waters even at losses of high amounts of herbicides. Effectiveness increased from the cultivated strips via the 6 m grass strip to the 12 m strip. Accordingly, the installation of vegetative filter strips near surface waters can be recommended.

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