Einfluss von Pflanzenschutzmitteln einer Zuckerrüben-Spritzfolge auf biologische Aktivitäben und auf den Abbau von Chloridazon im Boden. I. Freilandversuche

Effects of rarious pesticides of a sugar-beet spray programme on boilogical activities and chloriduzon degradation in soil. I. Feied experiments In a long-term field experiment at three different sites with similar soil and climatic conditions. The effect on chloridzon (Pyramin)-applied alone and in combination with other persticides of a sugar-beet spray programme-on b iological soil activites (dehydrogenase, straw decomposition) and aslo on degradation and plant availability of chloridazon in the soil were investigated. After an initial lag-period, chloridazon was degraded rapidly and 50% of the initial concentration disappeared in 18–53 days, in different years. The amount of chloridazon available to plants expressed as percent of the total amount of herbicide in the soil was 30% at the day of application and about 2% on day 36. Chloridazon persistence in the soil was unaffected by the other pesticides of the spray programme. Dehydrogenase activity was not significantly inhibited by Pyramin alone. However, with the spray programme an inhibitory effect was noticed, especially om the 0–5 cm soil layer in some plots, which lasted until harvest. There was no correlation between biological soil activities and the total and water-extractable chloridazon residues respectively.