THE APPLICATION OF A RHIZOTRON TO STUDY THE SUBTERRANEAN EFFECTS OF PESTICIDES

We examined the ability of a large, purpose-built rhizotron (undergrou nd observation chamber), to examine the effects of two pesticides on t he interactions between soil invertebrates, root growth and above-grou nd plant production within a grassland ecosystem. The pesticides, Durs ban 5Gn(TM) and Tornado(TM) (Carbaryl), killed most of their target sp ecies (soil arthropods and annelids, respectively), but some taxa thri ved in pesticide-treated plots, probably due to reduced inter-specific competition, decreased predation and/or increased food supply. In art hropod-impoverished (Dursban-treated) plots, the total length of visib le root in a selected portion of the soil profile was reduced by <40% compared to that in control plots and the rate of root turnover was al so reduced. Associated with this was a >30% increase in above-ground f oliar production (by mass). In earthworm-impoverished (Carbaryl-treate d) plots, the total length of visible root was not significantly diffe rent from that in the control plots and the rate of above-ground folia r production was also comparable. The usefulness of rhizotrons in exam ining the effects of pesticides on the interactions between soil inver tebrates and plant roots is discussed.