Harvard University chemists have invented a new kind of “bionic” leaf that uses bacteria, sunlight, water, and air to make fertilizer right in the soil where crops are grown. It could make possible a future low-cost commercial fertilizer for poorer countries in the emerging world.

The invention deals with the renewed challenge of feeding the world as the population continues to balloon.* “When you have a large centralized process and a massive infrastructure, you can easily make and deliver fertilizer,” Daniel Nocera, Ph.D., says. “But if I said that now you’ve got to do it in a village in India onsite with dirty water — forget it. Poorer countries in the emerging world don’t always have the resources to do this. We should be thinking of a distributed system because that’s where it’s really needed.”

The research was presented at the national meeting of the American Chemical Society (ACS) today (April 3, 2017). The new bionic leaf builds on a previous Nocera-team invention: the “artificial leaf” — a device that mimics photosynthesis: When exposed to sunlight, it mimics a natural leaf by splitting water into hydrogen and oxygen. These two gases would be stored in a fuel cell, which can use those two materials to produce electricity from inexpensive materials.

That was followed by “bionic leaf 2.0,” a water-splitting system that carbon dioxide out of the air and uses solar energy plus hydrogen-eating Ralstonia eutropha bacteria to produce liquid fuel with 10 percent efficiency, compared to the 1 percent seen in the fastest-growing plants. It provided biomass and liquid fuel yields that greatly exceeded those from natural photosynthesis.

Fertilizer created from sunlight + water + carbon dioxide and nitrogen from the air

For the new “bionic leaf,” Nocera’s team has designed a system in which bacteria use hydrogen from the water split by the artificial leaf plus carbon dioxide from the atmosphere to make a bioplastic that the bacteria store inside themselves as fuel. “I can then put the bug [bacteria] in the soil because it has already used the sunlight to make the bioplastic,” Nocera says. “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.”

The researchers have used their approach to grow five crop cycles of radishes. The vegetables receiving the bionic-leaf-derived fertilizer weigh 150 percent more than the control crops. The next step, Nocera says, is to boost throughput so that one day, farmers in India or sub-Saharan Africa can produce their own fertilizer with this method.

Nocera said a paper describing the new system will be submitted for publication in about six weeks.

* The first “green revolution” in the 1960s saw the increased use of fertilizer on new varieties of rice and wheat, which helped double agricultural production. Although the transformation resulted in some serious environmental damage, it potentially saved millions of lives, particularly in Asia, according to the United Nations (U.N.) Food and Agriculture Organization. But the world’s population continues to grow and is expected to swell by more than 2 billion people by 2050, with much of this growth occurring in some of the poorest countries, according to the U.N. Providing food for everyone will require a multi-pronged approach, but experts generally agree that one of the tactics will have to involve boosting crop yields to avoid clearing even more land for farming.



American Chemical Society | A ‘bionic leaf’ could help feed the world