Producers considering using pit additives to reduce manure odor emissions should proceed cautiously, says Michael Ellis, University of Illinois animal scientist.

Ellis bases his comments on recent research at Purdue University led by Al Heber, who tested 35 pit additives. Heber evaluated each for effectiveness in controlling emissions of ammonia, hydrogen sulfide and odor, measured both chemically and by human panelists using an olfactometer.

The study showed that none of the 35 products could claim a 95 percent or better degree of certainty that any improvements didn't simply occur " by chance." Only four products decreased the odor-dilution threshold at a 75 percent certainty level.

Results of the ammonia and hydrogen sulfide emissions were another story. Seven products did reduce hydrogen sulfide levels and eight products reduced ammonia concentration at 95 percent certainty.

Ellis added that several additives actually increased gaseous emissions, which would make manure odor problems worse.

For a more detailed look at the research results, e-mail