Interpretation of the impact of xenobiotics on non-target micro-organisms in soil

Temporal changes in rates of substrate-induced respiration and nitrogen min eralisation were examined in two agricultural soils and differences between successive measurements of up to 50-70% commonly found. Soils sampled on 3 separate occasions were treated with dinoseb acetate. Treatment effects up on ammonification and nitrification differed dramatically between samplings . However, the types of treatment effect seen with substrate-induced respir ation and overall nitrogen mineralisation remained reasonably similar. The results are discussed in relation to the use of cut-off criteria for testin g xenobiotics on free-living micro-organisms in soil.