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Bionic leaves create fertiliser

Tanya Blake

Artificial leaves that can make fertiliser directly in the soil around crops could one day help farmers to boost food production in remote locations in the developing world.

The world is facing increasing food shortages, and farmers in remote areas are often unable to get access to the large amounts of fertiliser they need.

To help solve this problem, Daniel Nocera, a chemist at Harvard University in Massachusetts, has invented a ‘bionic’ leaf that uses bacteria, sunlight, water and air to make fertiliser in the very soil where crops are grown.  

Nocera pioneered the use of artificial photosynthesis with the creation of the world’s first bionic leaf in 2008. The idea is to create liquid fuel by using a water-splitting catalyst and bacteria that eat hydrogen and take carbon dioxide out of the air. 

Nocera and his colleague Pamela Silver later developed this concept further, to produce a bionic leaf able to capture one-tenth of the energy in sunlight and turn it into fuel. This outperforms natural photosynthesis, which converts about 1% of solar energy into the carbohydrates used by plants. Nocera says that the fuels were “just the first step” to show you can have a renewable chemical synthesis platform.

“Now we are demonstrating the generality of it by having another type of bacteria take nitrogen out of the atmosphere to make fertiliser,” he adds.

For this application, Nocera’s team designed a system in which Xanthobacter bacteria fix hydrogen captured by the artificial leaf and carbon dioxide from the atmosphere to make a bioplastic that the bacteria store inside themselves as fuel.

The researchers then put the bacteria in the soil where they pull nitrogen from the air. Nocera says that the bacteria use the nitrogen and bioplastic, “which is basically stored hydrogen,” to make ammonia for fertilising crops.

The researchers have used their approach to grow five crop cycles of radish plants. The vegetables receiving the fertiliser derived from the bionic leaf weigh 150% more than the control crops.

The technology could be useful to farmers to solve the “significant amount of wastage and run-off” that happens when using fertiliser, says Min Hao Wong, a graduate student at Massachusetts Institute of Technology. He studies applications of plant nanobionics, and was not involved in Nocera’s research.

“This approach could potentially yield more targeted fertiliser application on to crops,” he adds.

However, farmers are only likely to use the bionic leaf technology, particularly for higher-value crops, if the researchers can address “cost and ease of use,” thinks Wong. He says it is not clear at this stage how much the technology will cost, or how different climates will affect the process.

Nocera agrees that more research is needed, and the team “hadn’t even begun thinking about scale-up or commercialisation”. 

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