Movement of Bacteria in Unsaturated Soil Columns With Macropores

Rapid movement of bacteria through the soil has been observed after applications of manure to agriculturalfields. Preferential flow through macropores has been suggested as the main reasons for these observations. Experimentswith repacked soil columns were used to study the effect of artificially created macropores, soil type, soil water content,and simulated rain application on movement of a tracer bacterium, nalidixic acid-resistant Escherichia coli. Results formthese experiments showed a significant increase in the number of biotracer cells passing through a soil column whenmacropores were present and the soil was wet. There was no passage of biotracer cells through a dry soil withmacropores. No biotracer cells were eluted from columns without macropores even when the soils were wet. Simulatedrainfall applied on the top of the soil columns caused bacteria to travel deeper into the soil. These results confirm theimportant role that macropores play in the movement of bacteria through heterogenous soils.