Evaluation of substitutes for paraquat in soil microbial ATP determinations using the trichloroacetic acid based reagent of

The trichloroacetic acid (TCA) based reagent proposed by Jenkinson and Oades (1979) fits all the criteria required to measure soil microbial biomass ATP (biomass ATP). Amongst other components it contains paraquat (0.1 M 1,1′ dimethyl-4,4′ bipyridylium dichloride), usually extracted from the herbicide Gramoxone. Paraquat is added as an analogue of ATP. It is tightly fixed to soil and so decreases ATP fixation. However, Gramoxone is now banned as an agricultural chemical in both Europe and North America. Our aim was to find an effective replacement for paraquat to measure biomass ATP. The best replacement was 0.6 M imidazole in 1.10 M TCA containing 0.25 M P (termed the TIP reagent). Biomass ATP concentrations were not significantly different in five soils extracted by either reagent 10.37 and 11.17 μmol ATP g⁻¹ biomass C, respectively; standard error of differences of means = 0.36; p = 0.091.