Enhanced degradation of propyzamide after repeated application in orchards

摘要

The degradation of propyzamide, a benzamide herbicide mainly acting through soil uptake, has been studied with chemical and biological methods in a field experiment on sandy loam soil in a pear orchard at Melle (Province East-Flanders) with long-termrepeated application of propyzamide (1250 g ha~(-1)) on the same plot. With chemical analysis, enhanced degradation of propyzamide was observed in 1998 on plots treated for the 14th time; on these plots, soil half-life time was 10 days only compared to 31 days on plots never treated previously. With greenhouse bioassays, the enhanced degradation of propyzamide could be confirmed at the same time using winter wheat (Triticum aestivum L.) to monitor propyzamide dissipation. Following this detection of enhanced degradation, field experiments were set up in two orchards at Melle and Velm (Province Limburg) respectively, to examine particularly the development of this phenomenon. Therefore, plots were set up receiving 0, 1, 2, 3, or 4 spring applications inconsecutive years with propyzamide (1000 g ha~(-1)). To examine the degradation of propyzamide, soil samples were taken on the different plots prior to a new application, mixed with a range of concentrations of propyzamide, incubated at 15°C and sown with winter wheat. After 15 days, foliage fresh weights were taken. An enhancement of the degradation of propyzamide could be observed already after the second application. Using the above mentioned plots, an other set of bioassay experiments was carriedout with soil samples taken in the field at different intervals after application. These samples were stored frozen until sowing. Based on foliage fresh weights, the fast appearance of the enhanced degradation of propyzamide in the field was confirmed again.