As progress is made to reduce emissions from cars and trucks, the focus of scientists and regulators is turning to off-road vehicles. Now there may be a new method to capture and sequester greenhouse gas emissions from agricultural equipment – by injecting it straight into the soil. Slashdot unearths a report from the Australian newspaper The Age on a novel home-grown carbon capture technology with unexpected benefits: Ian Linklater, a farmer in the small town of Gol Gol, NSW, is saving the planet and enriching his harvest by directing exhaust from his 400-hp tractor into his fields. By passing the exhaust underground, he captures and stores the greenhouse gas emissions from his equipment. Furth er, he’s finding that the diesel exhaust enriches his wheat crop to the point that he can forego chemical fertilizers. In the past two years, this has saved him almost million dollars US while producing his most abundant yields since 2001.

This emission-capturing, crop-boosting technology is developed and promoted by the Canadian firm N/C Quest Inc. under the label “Bio-Agtive Emissions Technology.” In short, the process works like this: exhaust from agricultural off-road equipment is captured and cooled to ambient temperature, then injected into the soil through on-board pneumatic tubes. The exhaust emissions are reported benefit the soil by increasing the uptake of phosphorus, potassium, and sulfur, while providing fixed nitrogen to the crops. Dr. Loraine Bailey, a scientist and independent consultant, writes, “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.”

There are two claims here which could benefit from some critical thinking: first, the suggestion that this process reduces off-road carbon emissions, and second, the notion that diesel exhaust can nourish crops rather than poison them. The former is demonstrably false, and the latter is dubious at best.

The BAET method diverges from traditional carbon sequestration techniques, in which CO₂ is stored in an underground cavity such as an oil well, or bubbled through and absorbed into the ocean. In contrast, the only way that agriculture stores carbon dioxide is through the growth of biomass. For crops to capture the off-road GHG emissions injected by the BAET process, they would need to grow larger due to the presence of the additional exhaust CO₂. This could be the case if atmospheric CO₂ were a trace gas (which it is not) or if plants flourished in the presence of a higher CO₂ concentration (which they do not). As a result, any GHG emissions injected into the soil merely escape into the atmosphere, same as they would if they came directly out of the diesel smokestack.

In addition, it is unclear how diesel exhaust could replace chemical fertilizer as an agricultural nutrient. Traditional NPK fertilizer is composed of three key ingredients: solid nitrogen compounds to supplement the nitrogen-fixing action of soil microbes, phosphorous to facilitate photosynthesis and energy transfer, and potassium to promote root growth and water transport. Diesel exhaust contains none of these nutrients, and is instead composed of a dirty combination of smog-producing nitrogen dioxide, acid-rain-causing sulfur dioxide, carcinogenic heavy metals, and lung-damaging soot particles. In fact, studies show that diesel exhaust withers plants and delays blooming. It is unlikely that tractor diesel emissions would have any positive effects on agriculture, let alone act as a viable substitution for fertilizer.

Having said this, there could be an argument that the BAET method would reduce GHG emissions. If diesel engine exhaust could in fact replace chemical fertilizers, then the injection technology could shrink the agricultural industry’s carbon footprint, although not in the way that Linklater and N/C Quest suggest. From a life-cycle perspective, chemical fertilizers are very carbon intensive, due to the energy consumed in extracting raw materials, producing the chemicals, and transporting it to farmers. To the extent that traditional fertilizer can be replaced with alternative methods, agricultural greenhouse gas emissions can be significantly reduced. This argument is strongly made by advocates of organic farming, who claim that organic methods can swing the agricultural industry from a net GHG emitter to a net GHG sink, and can be one tool in fighting climate change. Presumably, this putative diesel-exhaust-fertilization method would carry the same benefits.

There is no doubt that agriculture is a large component of the worldwide greenhouse gas inventory, accounting for 10-12% of total anthropogenic GHG emissions. For this reason, it is crucial to investigate new alternatives for reducing the carbon intensity of current agricultural practices. However, it is just as important to critically examine proposed solutions, to see if their benefit claims are credible. Unfortunately, this method does not live up to that standard. However, more established methods, such as improved land-use management, restoration of degraded regions, alternative crop selection, and reduced water consumption, have the potential to mitigate agricultural emissions, and can be implemented immediately.