Discharge of Escherichia Coli from Agricultural Surface and Subsurface Drainage Water: Tillage Effects

Abstract

Drainage water from agricultural fields with applied manure can degrade the bacterial quality of surface and groundwater. The impact of conventional tillage (CT) and zero tillage (ZT) practices on Escherichia coli (E.coli) discharge through artificially drained soils is not well understood. Consequently, two field trials were conducted during 2002–2004. The first trial involved fall applications of beef manure while the second involved spring applications of dairy manure. Both surface and subsurface drainage water were monitored in the first trial while only subsurface drainage water was monitored in the second. Under fall applied beef manure (trial 1), no differences (p > 0.05) were observed in E.coli concentrations (cfu/100 ml) in combined drainage water under both tillage systems. However, during 2003–2004, subsurface drainage water under ZT had higher E.coli concentrations and loads than drainage water under CT. When the combined (surface + subsurface) annual E.coli loads were considered, CT loads were greater than ZT during 2002–2003 with an opposite situation during 2003–2004. Overall, annual E.coli loads were similar under ZT (4.7 × 1010 cfu/ha) and CT (4.8 × 1010 cfu/ha). Spring dairy manure application (trial 2) produced significant (p > 0.03) tillage effect on E.coli loads in subsurface drainage water only during the second year. During the study period, ZT plots (1.55 × 1010 cfu/ha) discharged 5× more E.coli than CT (0.23 × 1010 cfu/ha). A longer duration of ZT practices resulted in higher subsurface flow volumes and subsequently greater loads of E.coli discharge in both trials.