The effect of long term 2,4-dichlorophenoxyacetic acid (2,4-D) application on soil nutrient transformation and the microbial community structure

Asuming-Brempong, S., S.J. Flynn, and J.M. Tiedje

Presented at the All Scientist Meeting (1998-07-21 to 1998-07-22 )

2,4-D has been applied to field plots for nine years to investigate the effect of 2,4-D on the microbial community and how changes in the microbial community could effect aspects of the nutrient transformation (C and N mineralization). The application rates were, control which is 0 kg/ha (0x), normal field rate of application 1 kg/ha (1X), 10 kg/ha (10X), 100 kg/ha (100X). During the eight and the ninth year, 2,4-D was applied every other week for five times from the month August and after its application, the microbial community was investigated by Terminal Restriction Fragment Length Polymorphism (TRFLP) of the SSU rDNA genes. The effect of 2,4-D on the microorganisms was assessed by determining the microbial biomass, microbial respiration and the microbial C:N ratio. Carbon mineralization was determined by the static incubation method and similarly for Nitrogen mineralization the ammonium and nitrate concentrations were determined by KCL extraction.Microbial community fingerprint showed the absence of some population profiles in the 100X plots which were present in the other treatments. Differences in the peak profile occurred around the 400-450 bp region for plots with 100X 2,4-D application whilst the profiles of the other treatments were unaffected. An increase in the qCO2 indicated a possible disturbance of high 2,4-D application in the plot where 100X 2,4-D had been applied as compared to the control plots. C mineralization (Fig.2) and Net N mineralization slightly decreased for the 100X plots. Microbial biomass was reduced by 22% (Fig. 1) in treatments where 100X 2,4-D had been applied as compared to the control plots and other treatments. Similarly basal microbial respiration was also reduced as 2,4-D concentration increased. The rate of nitrification increased as the 2,4-D concentration increased indicating that the diamine of the 2,4-D formulation might have been a substrate for the nitrifiers. These results suggest that applying high 2,4-D rates continually for a period of time tends to effect some microbial populations and some ecosystem functionsReturn to Contents           

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