The 60kg (132lb) of Koshihikari rice reaped yesterday may fill only a single regulation-sized sack, but its significance is huge: the rice has grown to maturity without natural light or a paddy field.

If the same process were done on a commercial scale, its creators say, Japanese farmers could reap four harvests every year rather than one, and not be affected by seasonal weather patterns that have become more and more extreme.

The company that owns the bank vault, Pasona, converted it in 2004 and has been using it for biological experiments. The former Nomura vault was designed to isolate its precious contents from attack or accident — a level of environmental control that made it perfect for hydroponics.

Yesterday’s crop is the result of several years of trial and error. When the farm was opened, its lettuces, basil and tomatoes thrived under the ultraviolet and infra-red lights. Junichiro Koizumi, the Prime Minister, even visited to give his blessing to the first artificial field of rice — which withered and died a few weeks later.

The repeated failure of hydroponic rice baffled and infuriated the farmers. Yasuyuki Nambu, Pasona’s president, brought in a panel of experts on hydroponics and biotechnology. Yet another crop failed. Mr Nambu then called on an elderly farmer who has worked the fields outside Kyoto for 40 years.

Within moments of arriving at the bank vault farm, Yoshihiko Morita identified the problem. “I saw it immediately,” he told The Times. “There was no wind and no rain.”

Technicians installed large fans above the artificial paddy and significantly raised the oxygen content of the water to simulate rain. The strategy worked instantly, and even Mr Morita was yesterday able to declare that the rice tasted as good as its outdoor-grown counterpart.

Pasona’s business is temporary staffing, and the thinking behind the farm is to train Tokyo urbanites who might be cajoled into a career in farming as an ageing population becomes increasingly reliant on high-tech farming. The company has already recruited hundreds of young city dwellers.

The honour of scything the first bushel went to Heizo Takenaka, the Minister for Economic and Financial Affairs, and the architect of Mr Koizumi’s most controversial reforms.

“It may have failed in the past, but here we have a rich harvest,” he said. “It is somewhat similar to the postal privatisation Bill that failed last year before the election. When you start something new, you need courage. And there are always people who criticise you for it.”

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