The Poop's The Problem

By: Elester Williams

If you aren’t grossed out by manure fertilizing commercial crops, maybe the fact that fecal matter contains intestinal and gut associated microbes will do the trick. Those microbes aren’t a problem if they stay on the field, but rainfall rates can affect how far these microbes get spread from the application site. Researchers in 2015 looked at how rainfall affected rates of removal of enterococci and total coliforms from experimental soil boxes. The researchers discovered that after the initial microbe removal, rainfall intensity did not affect removal rates since bacteria living at deeper depths are less easily removed. But, they also discovered that water run-off occurred sooner in manure treated soils. So yes, these top soil applied microbes can get washed out of the manure, but as long as the water runs off to another side of the field it might not pose a problem. 

From (Blaustein et al 2016). This figure shows the average percentages of various microbes washed out of soil during rainfall in the  experiment.

Original article: Blaustein RA, Hill RL, Micallef SA, Shelton DR, Pachepsky YA (2016). Rainfall intensity effects on removal of fecal indicator bacteria from solid dairy manure applied over grass-covered soil. Science of The Total Environment 539: 583-591.