Self-fertilising crops offer new hope for food security around the world
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By the end of the 20th century, some scientists believed that the planet’s finite food resources would soon cap the world’s population. In his highly controversial 1968 book The Population Bomb, US ecologist Paul Ehrlich went so far as to claim that, unstopped, population growth would lead directly to mass starvation on a dying planet.
Instead, a scientific breakthrough made a few decades earlier revolutionised global food production – as well as the number of people the planet could support. In 1909, two German chemists, Fritz Haber and Carl Bosch, devised a method to pull nitrogen directly from the air and transform it into fertiliser (ammonia).The technique bypassed the much slower natural nitrogen cycle, which relies on nitrogen-fixing bacteria to turn atmospheric nitrogen into a form that plants can use. By the 1960s, it was helping to produce unprecedented crop yields.
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Today, synthetic fertilisers support roughly half of the global population. At the University of California, Davis (UC Davis), researchers are now working on getting crops to produce their own fertiliser – and the results, according to Eduardo Blumwald, a professor of plant sciences at the university, are very promising. To successfully convert nitrogen into ammonia, nitrogen-fixing bacteria rely on an enzyme called nitrogenase, which is highly sensitive to oxygen. Some plants, including legumes such as beans and peas, have evolved root structures called nodules that naturally provide the bacteria with the low-oxygen environment they need.
Still, the vast majority of crops – cereals such as wheat, rice, barley and oats – have not. ‘For decades, scientists have been trying to develop cereal crops that produce active root nodules, or engineer bacteria that can colonise the plants,’ says Blumwald. ‘I thought, “Why don’t we try something else?”’ Using the gene-editing tool CRISPR ,the team at UC Davis has engineered wheat plants to produce more of one of their own naturally occurring chemicals. This chemical triggers soil bacteria to form biofilms – sticky layers that surround them.
‘The biofilm lets the nitrogen in, but is quite impermeable to oxygen.’The team has already demonstrated the same technique’s success with rice plants, but Blumwald explains that wheat is a more genetically complex species to engineer. It’s also the world’s second-largest cereal crop by yield, and uses the largest share of fertilisers.
‘We’re not out in the field just yet,’ says Blumwald, ‘but the greenhouse experiments were a success. I know that there’s a company that wants to buythe technology, and we have another project to develop sorghum and millet for Africa. ’In developing countries, particularly in sub-Saharan Africa, where fertiliser use is low, the breakthrough could be a boon for food security.
‘In Africa, people don’t use fertilisers because they don’t have money, and farms are small,’ says Blumwald. ‘Imagine you are planting crops that stimulate bacteria in the soil to create the fertiliser that the crops need naturally. That’s a big difference! ’While the newly engineered crops won’t remove the need for fertilisers altogether, Blumwald points out that any savings would be beneficial. In the USA alone, the Department of Agriculture estimates that farmers spent nearly US $36billion on fertilisers in 2023. Blumwald calculates that nearly 200 million hectares of US farmland are planted with cereals.
‘Imagine if you could save ten per cent of the amount of fertiliser being used on that land – that should be a saving of more than a billion dollars every year.’ But perhaps the biggest savings could be for the planet itself. While the Green Revolution is estimated to have saved more than a billion people from starvation, it did so at a cost. ‘You have to remember that plants only take up about 30 to 50 per cent of the nitrogen in fertiliser,’ says Blumwald.
‘Much of what they don’t use flows into waterways, where it acts as a fertiliser for tiny aquatic organisms, fuelling algal blooms that result in ‘dead zones’ devoid of oxygen. Excess nitrogen left in the soil is converted by those same bacteria into nitrous oxide, a potent greenhouse gas that also depletes the ozone layer. ‘If you can reduce the amount of nitrous oxide, you’re not only saving money on fertiliser,’ says Blumwald. ‘You’re helping to slow down the heating of our planet.’
