THE STABILITY OF MICROBIC COMMUNITIES IN PESTICIDE-TREATED SOILS

The impact of the fungicide metalaksil (N-2,6-dimethylphenyl-N-methoxy acetyl alanine ether) and the herbicide propachlor (2-chloro-N-isoprop ylacetanylide) on the stability of microbic communities inhabiting red ferrallitic soil in four ecosystems (C-org 0.82-3.76%, pH(water) 6.08 -6.92) within the environs of Athens, Georgia (the United States) was studied. The stability of the soil microbic communities was assessed o n the basis of the microbic respiration quotient (Q(R)), which is the ratio between the rate of basal (V-basal) and substrate-induced (V-SIR ) respiration of soil microorganisms. It is shown that the soils of th e ecosystems under study (pine forest, oak forest, cropland, and pastu re) differed reliably (P = 95%) by the stability of soil microbic comm unities (Q(R) = 0.44, 0.41, 0.37, and 0.29, respectively). Soil incuba tion under laboratory conditions (21 degrees C, 60% PPV, in darkness) was accompanied by a temporal dynamics of Q(R). The application of met alaksil to the soil (10 mg/kg) led to an increase in Q(R) values, whil e the application of propachlor (10 mg/kg) had no impact on the Q(R) v alue whatsoever. The stability of the pine forest soil, the most sensi tive among the ecosystems under study, was considerably affected by pe sticides.