Just last summer, Harvard announced that the artificial leaf they've been working on for years was now 10 times more efficient than real plants at turning sunlight into fuel. The bionic leaf is able to split water molecules into hydrogen and oxygen and then with the help of hydrogen-loving bacteria, produce liquid fuels and potentially many other products.

The potential for other products has now become a reality as the artificial leaf can now make fertilizer too. The leader of this project David Nocera, along his research team, has been improving the artificial leaf technology since 2011, increasing its applications.

"The fuels were just the first step," said Nocera. "Getting to that point showed that 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 fertilizer."

The new bacteria, Xanthobacter, consumes the hydrogen produced by the leaf and when it's exposed to the carbon dioxide in air, it forms a bioplastic. That bioplastic is stored in the bacteria as a fuel which is then used to make ammonia from the nitrogen in the air. The bacteria can be placed in the soil where crops are planted acting as a fertilizer factory.

"I can then put the bug in the soil because it has already used the sunlight to make the bioplastic," said Nocera. "Then the bug pulls nitrogen from the air and uses the bioplastic, which is basically stored hydrogen, to drive the fixation cycle to make ammonia for fertilizing crops."

© Nocera lab, Harvard University

In testing, the bacteria showed impressive results. They compared crops grown with the bacteria to those grown without it over five crop cycles and the crops that received the fertilizer treatment grew 1.5 times larger. The radishes on the right above were grown with the bionic leaf fertilizer.

The benefit to this type of bionic leaf system is that it would work as a cheap, portable source of fertilizer for farmers around the world, particularly in developing countries where the making and distributing of fertilizer is far more difficult and expensive.

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