"I'd be lying if I said I wasn't worried about the effect that global warming might have," said rice farmer Ryoichi Takamura as he inspected his fresh-cropped brown rice fields.

For 17 generations, Takamura's family has grown rice on a plateau between the low mountains that cradle Uonuma, creating a climate of extreme high and low temperatures that are crucial for the production of Koshihikari rice, Japan's premium rice.

But Takamura, 49, who was born and bred in the region, says these unique weather conditions have changed in recent years and the past few summers have been the hottest he can remember.

"I was totally dehydrated as I drove the harvester in the rice fields (this summer)," the slightly built Takamura remarked.

After watching his crop yields fall in recent years, Takamua said he succeeded at sustaining yields and quality this year by using plenty of water to protect rice from the scorching heat.

Japanese rice farmers and experts are growing more concerned about rising temperatures which is leading to poorer yields and the production of immature grains with a poor starch content that fetch a lower price even though they taste almost the same.

Japan's average annual temperature has been higher by 0.2 to 1.0 degrees centigrade for about the past decade, when compared to a base figure which is the average of temperatures taken between 1971-2000, data from the Japan Meteorological Agency shows.

These temperature rises coincide with a period when immature grains of rice, easily identified by their milky white exterior, were becoming conspicuous in freshly harvested crops.

"The 20 or so days after the ear of the rice has appeared is most crucial ... and high temperatures during that period leads to the production of immature grains," said rice expert Ikuo Ueno.

BOWLS OF RICE

Rice is believed to have been cultivated in Japan for the past 2,500 to 3,000 years. Bowls of rice are an integral part of meals, although consumption has dropped as a Western diet has become more prevalent especially among the young generation. Rice is also used to produce sake, an alcoholic beverage.

Per capita consumption of rice in Japan was 61 kg (135 pounds) last year, down 48 percent from its peak in 1962.

Rice is grown in almost every corner of Japan, including areas surrounding Tokyo, but global warming has had the most noticeable impact in the south, particularly on the island of Kyushu.

Ueno, head of the crop research department at the Kumamoto Prefectural Agricultural Research Center in Kyushu, said higher temperatures were to blame in part for poorer quality rice crops in recent years.

The heat, combined with fewer sunlight hours and damage from typhoons had contributed to several years of poor harvest in the prefecture, he said.

Research centres across Japan are studying ways to grow rice grains that can better cope with higher temperatures. They are also developing new grain varieties, although it may take as much as a decade for commercial harvesting of these grains to begin.

Some of these new grain types have started to be planted and have even begun to slowly enter the local markets, although Japanese consumers tend to have conservative palates which means it takes time for new varieties to gain a foothold.

About a decade ago, the National Agricultural Research Center for Kyushu Okinawa Region began to develop "Nikomaru", a rice with a strong tolerance to higher temperatures.

It was discovered by chance, according to Makoto Sakai, head of the centre's Rice Breeding Unit, who said the initial aim of the project was to create a new type of rice that would provide a higher yield and a fine grain appearance.