Effect of manure application and rainfall timing on the leaching of labeled bacteria through soil columns

摘要

Pathogens leaching through the soil profile depends on many factors, including how the manure was applied to the soil and the frequency and timing of rainfall following manure application. The effect of various manure application techniques (broadcasting, incorporation, and pre-broadcast tillage) on bacterial leaching following different rainfall events through intact soil cores was examined by using manure inoculated with E.coli strain RS2, that was genetically tagged with Green Fluorescent Protein (GFP). Steady rainfall consisting of 5 cm rainfall was applied at 4, 8, and 16 days after manure application. The level of RS2 (GFP) in the leachate decreased following each rainfall event and manure application technique did not affect leaching. Inoculum recovery averaged 77 percent for the first rainfall event for all manure application techniques. Maximum numbers of RS2 (GFP), irrespective of manure application method, occurred in the top 4 inches of the soil profile followed by a rapid decrease intheir numbers with increasing depth. Columns subjected to manure incorporation had the highest recovery of RS2 (GFP) from the soil samples. Irrespective of the length of time the manure sits on the surface of soil or the manure application technique, the first rainfall event is crucial in pathogens leaching through the soil. However, manure application practices affect survival of pathogens in soil presumably due to differences in bacterial die-off due to exposure to surface environmental conditions.