When the smoke from a tractor exhaust goes up, it’s pollution. But get those emissions down into the soil and they become fertiliser, as Canadian farmer Gary Lewis is demonstrating.Mr Lewis has spent the best part of a decade developing and refining a system that pipes tractor exhaust emissions through a condenser and into the pneumatic system of air seeders, which injects the carbon- and nitrogen-rich emissions into the ground with seed.

What is generally considered as pollution is in fact prime soil food, Mr Lewis said, and tractor exhaust has allowed him and other farmers working with his technology to grow excellent crops without conventional fertiliser.

The exhaust gases are claimed to stimulate microbial activity and root growth, allowing the plants to more efficiently extract nutrient and moisture from the soil.

Mr Lewis, an Alberta rancher and former auto mechanic who has specialised in growing timothy hay for export, claims not to have used fertiliser on his 250 hectare irrigation farm since 2001, instead fertilising with his own “BioAgtive” technology.

Mr Lewis said says he has seen no loss of production, his soils have moved from pH 8 (the same as the irrigation water) to a pH of about 7, and his soil organic matter levels are currently about 10 per cent.

In testimonials quoted on the BioAgtive website, former Agriculture Canada scientists turned consultants Dr Jill Clapperton and Dr Loraine Bailey agree that something positive is happening in BioAgtive treated soils,

“…the obvious conclusion is that the exhaust had a positive effect on crop growth, yield, and quality, and may have positively enhanced soil nutrients and nutrient chemistry,” Dr Bailey wrote.

Understanding why BioAgtive is not just “blowing smoke”, as Mr Lewis feels many scientists think he’s doing, requires a different perspective on exhaust emissions.

In excess in the atmosphere, exhaust emissions are undesirable. But a breakdown of the content of diesel exhaust looks like a partial shopping list for plants.