Nitrogen-producing bacteria slash fertiliser use on farms

Nitrogen-fixing microbes can dramatically reduce the fertiliser-related emissions and pollution from farms.

Nitrogen fertiliser plays an essential role in industrial agriculture, but it comes at a steep environmental cost. The production and use of synthetic nitrogen is responsible for around 5 per cent of global greenhouse gas emissions. Excess fertiliser also adds to air pollution and can contaminate water.

In addition to finding greener ways to produce nitrogen fertiliser, researchers and farmers are looking for ways to use fertiliser more efficiently, without sacrificing crop yields. One approach taken by US-based company Pivot Bio is to add bacteria to crops that take nitrogen from the air and fix it in soil as nitrates plants can use.

“Microbes are freeloading couch potatoes when nitrogen is around,” says Karsten Temme, the company’s CEO. If the soil has synthetic fertiliser, bacteria will use that rather than pull nitrogen from the air.

That requires farmers to use more fertiliser to have the same effect on crop yields. It also adds to nitrous oxide emissions from soil as microbes convert excess nutrients from the fertiliser. Nitrous oxide is a potent greenhouse gas and emissions from soil are responsible for the majority of fertiliser-related emissions of the gas.

Using genetic engineering, Pivot Bio developed two bacteria-based treatments that continue to produce nitrogen even when high levels of nitrogen are already present in the soil. Temme says the treatments, which can be applied as a liquid directly to the soil or as a powder to coat seeds, can replace about a quarter of the synthetic nitrogen used without affecting crop yield.

Pivot Bio says its products are now being used on more than 3 million acres (1.2 million hectares) of farmland in the US, mostly on corn crops, but also on wheat, sorghum, barley, millet, oats and sunflower crops.

According to initial estimates, the treatment helped avoid 32,000 tonnes of synthetic fertiliser on farms in 2022. The firm estimates that resulted in a reduction in greenhouse gas emissions equivalent to 220,000 tonnes of CO2, about the same as burning 1200 rail cars full of coal. About a third of those avoided emissions came from not producing the synthetic fertiliser. The other two-thirds come from the avoided nitrous oxide emissions from soil.

Those estimates are based partly on self-reported fertiliser use from farmers and partly on changes in use verified by a third party, and there are large uncertainties associated with linking fertiliser use and emissions, says Jane Franch at Pivot Bio.

A number of other companies have developed similar microbial treatments for plants. Agritech giant Bayer, for instance, has a partnership with synthetic biology company Ginkgo Bioworks to develop more efficient nitrogen-fixing strains of bacteria.

Another is Massachusetts-based Kula Bio, which feeds naturally occurring microbes with a carbon energy source so they live for longer in soil. Bill Brady, the company’s CEO, says the treatment, which is in development, will be able to work on any crop and also reduce nitrogen use by around a quarter.