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Summary Band 18

Klimsa, Kurt: Sorption, degradation, and leaching of selected pesticides in different soils with and without addition of mulch - laboratory and feld experiments.

 

It was the main aim of this project to study the behaviour of pesticides in different soils with and without addition of mulch. In batch studies Freundlich-sorption isotherms of the pesticides Atrazine, Simazine, Terbuthylazine, Methabenzthiazurone, Isoproturone, and Chlortolurone were established. Also column experiments were carried out to study the leaching behaviour of the pesticides Terbuthylazine, Methabenzthiazurone and Isoproturone. For these purposes three soil samples with different pH-values and different contents of organic carbon were selected. Field experiments with the pesticides Terbuthylazine and Isoproturone were done at the Dikopshof (Cambisol) near Bonn. In the laboratory studies wheat straw and phacelia hay were used as mulch substrata whereas in the field trials wheat straw, paper, and cress were approached as mulch substrata.

The results of the batch studies show increasing sorption of the pesticides in the following sequence:

Isoproturone > Atrazine > Simazine > Chlortolur. > Terbuthylazine > Methabenzthiazurone.

For all six pesticides sorption hysteresis could be recognized. The extent of this hysteresis falls with:

Simazine > Atrazine > Isoproturone > Chlortolurone > Terbuthylazine > Methabenzthiazurone.

The influence of mulch substrata on the sorption of the pesticides depends on the properties of the chemicals, the soil constituents and the properties of the mulch substrata. Only six of 33 examined variants on mulch showed increased pesticide sorption and two showed increased solubility. The reason for the increased solubility was the higher concentration of soluble organic matter in the mulch variants compared to the variants without addition of mulch.

The column experiments confirmed the data of the batch studies, showing an increasing sorption in the order

Isoproturone < Terbuthylazin < Metbabenzthiazurone.

Distribution functions were fitted to describe the leaching behaviour and to calculate linear distribution coefficients. This distribution coefficients were slightly lower than those received from the batch studies. Furthermore, the column studies showed stronger effects when mulch substrata were added to the soils. 50 percent of the variants examined revealed an increased and 14% a slightly decreased pesticide sorption.

Generally, for wheat straw there is a stronger tendency to increase pesticide sorption whereas phacelia hay is stronger to increase the pesticide solubility. But all in all these effects were small.

The field trials show no effect of added mulch substrata on the sorption of pesticides. But there was an increased degradation of Terbuthylazin in the variants with wheat straw and with cress compared to the variant without addition of mulch. Mulch effects on pesticide leaching were not detectable because of the dry weather conditions. Also there was no effect on the behaviour of Isoproturone, which was applied in the following vegetation period. The results of the field trials show, that there were no danger for leaching of Terbuthylazine and Isoproturone into groundwater. 


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