Movement through soil of a biological control agent, Pseudomonas fluorescens

The movement of Pseudomonas fluorescens. 2–79, a biological control agent, was investigated in an unsaturated repacked agricultural soil. The bacterial movement was found to be retarded compared with chloride in both the fine (0–0.5 mm) and coarse (0.5–1.0 mm) fraction of the soil. For the same soil, more retardation was observed in experiments in which bacteria were suspended in CaCl 2; solution than in distilled water. For the same suspending solution, bacteria moved further in the coarse fraction of the soil than in the fine fraction. These results agree with previous experimental studies on sand materials, in which ionic strength and soil particle size were found to be important factors in controlling bacterial movement in soils through their effects on the adsorption of bacteria. It is concluded that adsorption was a key factor in determining the movement of bacteria in this agricultural soil.