Farmers: What Smoke Test Can Teach About Fields, Yields and Water


UNION CITY, Ohio — Aug. 12’s Manure Science Review will feature a demonstration of smoke testing — a way to show how fast a liquid, including liquid manure, can flow through and out of a farm field.

Frank Gibbs, retired from the U.S. Department of Agriculture’s Natural Resources Conservation Service and now of Rawson, Ohio-based Wetland and Soil Consulting Services, will give the demonstration.

A video showing smoke rising from the soil during one of Gibbs’ tests can be seen at

Manure Science Review, set for Union City in western Ohio, is an annual learning event for farmers and others in the industry. The College of Food, Agricultural, and Environmental Sciences at The Ohio State University is a co-host.

Details about the event and how to register are at Registration is $30 and includes a continental breakfast and lunch.

Earthworm holes and cracks in the soil — called “macropores” — can play big roles in the flow of liquids from a farm field, said Sam Custer, a co-organizer of the event and an educator with Ohio State University Extension. OSU Extension is CFAES’s outreach arm.

Generally, macropores improve a soil by helping water soak in and crop roots go deeper.

But they also can give liquid manure a path to a fast, early exit — a waste of valuable crop nutrients and a possible source of water pollution.

A smoke test provides a visual representation of a soil’s macropores, Custer said. It shows where they are and the flow they can carry.

The test involves pumping smoke into a farm field’s underground plastic drainage pipes, or tiles. The smoke travels laterally through the pipes, which have drainage holes all along them; rises through those holes; then rises through macropores and up through the soil. Eventually, white smoke swirls at the soil surface.

The process goes in reverse for a liquid, which starts at the soil surface, moves downward through the macropores, enters the drainage holes, and collects in and flows through the tiles, which then empty into a waterway.

Understanding that flow can improve both a farm’s bottom line and water quality, Custer said. Steps can be taken to keep liquid-manure nutrients in a field where they’re needed — as fertilizer for crops and a way to boost yields — and out of streams and lakes where they can cause such problems as algal blooms.

Possible ways to stop the outflow of liquid manure from drainage tiles include adding shutoff valves to the tiles and digging catch basins, according to an article by the U.S. Department of Agriculture’s Agricultural Research Service. The article features some of Gibbs’ macropore research with USDA-NRCS.

Custer said both the smoke testing demonstration and Manure Science Review overall have the same aim: to show how “to incorporate manure to get the best economical value and to be environmentally sound in our management practices.”

For more details on the event, contact the college’s Mary Wicks at 330-202-3533 or

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CFAES News Team
For more information, contact: 

Sam Custer

Mary Wicks