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Exhaust fumes fuel crop nutrition

The green agenda may not be the most popular topic among the farming community at the moment, as many growers struggle to stay afloat after a horribly tough season.

However, a group in Canada claims to have developed a way of both reducing gas emissions from arable farming and reducing the dependency of grower’s on bagged fertilisers. A desirable combination, to say the least.

By channelling exhaust fumes back into the soil during cultivation and drilling, oxidised earth metals such as carbon dioxide (CO2), nitrogen oxides (NOx) and sulphur oxides (SOx) are re-introduced to the soil. So far, as it is a relatively new concept, there is little scientific data on the topic. However, initial results in Britain have presented a mixed picture highlighting the need for further examination.

Fertilizer reduction

The concept of exhaust fume incorporation into the soil, developed by a Canadian firm called NC-Quest, is being adopted by a growing number of farmers. These are predominantly in North-America, Australia and, more recently, in Britain. One of those Canadian growers using the system, a 2,000ha cereal and oilseed grower in Manitoba, claims to have reduced his nitrogen application rates from 112kg N/ha, down to 8kg N/ha, while maintaining his hard red wheat yield up at 2.7 t/ha - similar yields from both systems.

Such a reduction in nitrogen requirement seems staggering, and one would justifiably question the accuracy of this statement. However, when considered in conjunction with other related research findings on the use of charcoal as a crop nutrient, these claims begin to make sense. One of the examples of human enrichment of soils, using the product of combustion or burning, is the Terra Preta soils found scattered along the Amazon River. These pockets of highly productive carbon rich black soils, which are easily identified as being influenced by man, were caused by spreading charcoal from burnt plants and refuse through the soil, a practice now being implemented, albeit in a different form, by growers injecting exhaust fumes.

Injection system

The exhaust fume injection system is, in principle, quite simple. It involves the initial cooling of the fumes from 500úC to around 65úC, which is the most complex part of the system. The original Canadian designed system used an aluminium cooling frame mounted on the side of the drill (Fig. 1). The fumes are pumped through this, cooling as they pass through each section. The NC-Quest design focuses mainly on exhaust fume injection during drilling in a min-till or no-till system.

This original design has been further adapted by a Leicestershire-based grower, Steve Heard (see Fig. 2). Steve has designed a more compact cooling box system that fits to the front of the tractor. Heard injects exhaust fumes at both the cultivation stage through his Sumo cultivator and the drilling stage through his Vaderstadt drill. Both NC-Quest and Heard market their systems worldwide, with NC-Quest operating a licensing system requiring yearly payments for the use of the system. However, you would expect that there are plenty of growers capable of replicating the system here in Ireland at a much lower cost than that of a purchased system.

Is the return worth the investment?

So far, results indicate that the system has the potential to replace a significant portion of bagged fertilizers. The theory behind the system ties in with other findings. However, an issue that is understandably not broached by NC-Quest or Heard is the potential toxicity of other elements in the fumes such as selenium, zinc and copper, which are toxic when excessive amounts are present in soil.

Initial research on the subject, carried out in Canada by Jill Clapperton, looked at the comparison of crop establishment using exhaust fumes with fertilizer versus standard establishment with fertilizer. The results showed a 10% yield increase in favour of the treatments where the fumes were injected. As well as this finding, those results also showed a 100% increase in the levels of zinc and selenium concentrations in the soil, which can be toxic to crops at excessive levels.

british trials

Following on from these findings, trial data from the 2009 harvest on Heard’s farm in Britain has shown mixed results. During the crop’s growing season, the areas treated with exhaust fumes showed enhanced greening and biomass. This observation was backed up by the use of a Yara N-sensor, which confirmed the perceived colour and biomass variations.

Also, soil samples that were taken post planting and exhaust injection, but prior to any nitrogen applications, were analysed at Reading University. These showed a 300% increase in available ammonia in the treatments that received the exhaust fumes. However, once the combines got rolling, the results were not as significant as had been anticipated.

The trial plots that received no nitrogen fertilizer benefited most from the incorporation of the exhaust gases. The exhaust injected treatment showed a 22% increase in recorded yield. If this observation were to hold across a wide range of trials and locations, the finding could be quite beneficial for organic producers. In the other treatments, where 1/3 rate N, 2/3 rate N and full rate of N were applied, there was no significant yield benefit associated with the incorporation of the exhaust fumes. This is quite different to the Canadian findings.

The initial reaction to the mixed responses following the exhaust fume injection into the soil pointed to our lack of understanding as to how performance may be improved, and how the visible early season promise failed to deliver on its perceived benefits.

Trials will continue in 2010 over a further 5,000 acres and Heard remains hopeful of being able to replicate the results being claimed in North America.

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