Effects of temperature and moisture on the persistence of terbuthylazine in two Malaysian agricultural soils
B.S. Ismail and O. Dan-Lin, School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Malaysia.
The persistence of terbuthylazine in Sungai Buloh and Serdang series soils incubated at different temperature and moisture content was investigated under laboratory conditions using cucumber (Cucumis sativus L.) as the bioassay species. A faster degradation of terbuthylazine was observed in the non-autoclaved soil as compared to the autoclaved soil samples. At higher temperatures the degradation rate in the non-autoclaved soil samples improved with increasing soil moisture content. In non-autoclaved Sungai Buloh and Serdang series soils, the half-life was reduced from 20.3 to 10.7 days and from 38.5 to 16.1 days respectively, when the temperature was increased from 20 to 35°C at 70% field capacity.
In the autoclaved soil, the herbicide residue appeared to have been broken down by non-biological processes. The rate of dissipation was slightly increased after the second application of the herbicide to the non-autoclaved Sungai Buloh and Serdang series soils incubated at 35°C with soil moisture of 30 and 50% field capacity. However the half-life is shorter in non-autoclave soil of the Sungai Buloh and Serdang series soils after the second treatment followed by incubation at 35°C and 70% moisture. The half-life was slightly longer after the second treatment in autoclaved soils of both Sungai Buloh and Serdang series. A shorter half-life of terbuthylazine in non-autoclaved soils as compared to autoclaved soils indicates the importance of microorganisms, besides other non-biological process, that contribute to the dissipation of terbuthylazine.
Plant Protection Quarterly (2003) 18 (2) 48-51.