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Tillage Effects on Persistence and Distribution of Trifluralin in Soil

Institut für Pflanzenpathologie und Pflanzenschutz der Universität, Grisebachstr. 6, D-37077 Göttingen, Germany.

^* Corresponding author.

ABSTRACT

The aim of this study was to investigate the effects of the substitution of plowing with harrowing—twice in a 3-yr crop rotation—on persistence and distribution of a persistent herbicide such as trifluralin (,,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) to rate these two tillage systems for their environmental impact (e.g., regarding potential ground water contamination with pesticides). Therefore, studies have been performed in Germany at two sites, a clayey silt in Reinshof and a loamy sand in Eickhorst. The herbicide was applied to oilseed rape (Brassica napus L. var. napus), followed in consecutive years by applications to wheat (Triticum aestivum L.) or to wheat followed by rye (Secale cereale L.). The disappearance time of 50% of the initial concentration (DT-50 value) decreased from >300 d after preplant incorporation of trifluralin to <150 d after pre-emergence treatment, losses being greater due to volatilization resulting from the lack of soil incorporation. No influence of different tillage systems on trifluralin persistence could be observed. Distribution of the herbicide in the top 30 cm of the soils, however, was significantly influenced by the soil cultivation systems. Reduced tillage (harrowing) in two consecutive years resulted in trifluralin concentrations in the soil layers 10 to 20 cm and 20 to 30 cm under the limit of determination (0.005 mg kg^–1). In contrast, plowing led to trifluralin residues of up to 0.019 mg kg^–1 in these soil layers. Although no trifluralin residues could be found in the 30- to 45-cm and 45- to 60-cm soil layers under either soil cultivation system, our results imply an increased risk of ground water contamination after plowing.

Sponsoring organization: Forschungs- und Studienzentrum Landwirtschaft und Umwelt, Universität Göttingen.