Effects of Alachlor and Metolachlor on Microbial Populations in the Soil

A study of the impact of two acetanilide herbicides, viz. alachlor and metolachlor on bacterial and fungal populations and biomass in the Sungai Buluh soil series samples was carried out under laboratory conditions. The effects of the two herbicides were monitored for 70 days under ambient conditions. Metolachlor caused greater reduction in bacterial counts than on fungal populations. There was approximately 75% reduction in bacterial counts 14 days after treatment (DAT) with 2 μg/g metolachlor. Alachlor however was less toxic to bacterial and fungal populations. Alachlor caused a reduction in bacterial counts at 7 and 14 DAT with 2μg/g or above. Fungal population decreased significantly in the presence of 20 μg/g alachlor at 7 DAT but no further effects were observed as the incubation period was prolonged. The study showed that the microbial biomass immediately decreased significantly in the presence of 2 μg/g or more of metolachlor at 0 and 28 DAT. Alachlor, on the other hands, at the lowest experimental dose of 2 μg/g reduced the microbial biomass almost immediately upon incubation, but had no further effects when the incubation period was prolonged.