The gas 300 times more potent than CO2

Temme says that company scientists created the inoculant by isolating a strain of the bacterium Kosakonia sacchari that already had nitrogen-fixing capabilities in its genome, although the genes in question were not naturally active under field conditions. Using gene editing technology, the scientists were able to reactivate a set of 18 genes so the bacterium makes the enzyme nitrogenase even in the presence of synthetic fertiliser. "We coax them to start making this enzyme," Temme says.

Steven Hall, a biogeochemist at Iowa State University, is now testing the product in large, dumpster-sized containers with corn growing in them. Researchers apply the inoculant, along with different amounts of synthetic fertiliser, to the soil and measure corn yields, nitrous oxide production and how much nitrate leaches from the base of the containers. Though results of the trial are not yet out, Hall says there's "good initial support" for the hypothesis that the microbes reduce the need for fertiliser, thereby reducing nitrous oxide emissions.

No-till

But some soil scientists and microbiologists are sceptical of a quick microbial fix. "Biofertilisers" like these have had mixed success, depending on the soil and environment in which they are applied, says Tolu Mafa-Attoye, an environmental microbiology graduate student at the University of Guelph in Canada. In one field study of wheat, for example, inoculating the crops with beneficial microbes enhanced growth of the plants but only resulted in slightly greater yields. Unknowns abound, Mafa-Attoye's Guelph colleagues wrote in February in Frontiers in Sustainable Food Systems – such as whether the microbes will negatively affect the soil ecology or be outcompeted by native microbes. 

Instead of adding in a microbe, it may make more sense to encourage the growth of desirable microbes that already exist in the soil, says Caroline Orr, a microbiologist at Teesside University in the UK. She has found that cutting back on pesticide use led to a more diverse microbial community and a greater amount of natural nitrogen fixation. In addition, production of nitrous oxide is influenced by the availability of carbon, oxygen and nitrogen – and all are affected by adjusting fertiliser use, irrigation and ploughing. 

Take tillage, for example. An analysis of more than 200 studies found that nitrous oxide emissions increased in the first 10 years after farmers stopped or cut back on ploughing their land. But after that, emissions fell. Johan Six, a co-author of the analysis and an agroecologist at ETH Zürich in Switzerland, thinks that's because the soils start out in a heavily compacted state after years of equipment driving over them. Over time, though, the undisturbed soil forms a cookie-crumb-like structure that allows more air to flow in. And in high oxygen environments, microbes produce less nitrous oxide. Such no-till systems also result in more carbon storage because less ploughing means reduced conversion of organic carbon to CO2– thereby providing an additional climate benefit.

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