Bringing rice back to Hawaiʻi: Japanese cultivars yield high-quality grains in just three months

In a major step toward enhancing food security and exploring the potential to bring rice farming back to Hawaiʻi, an international research team has successfully cultivated premium Japanese rice varieties on Kauaʻi using a water-saving, upland cultivation method. The rice matured approximately one month earlier than it typically does in Japan, yet produced yields comparable to those of the upland rice grown in Japan, with superior grain appearance and quality.

The challenge: Overcoming 100% import reliance

Hawaiʻi relies almost entirely on outside sources for its rice consumption, even though rice is a major staple food across the islands. As an isolated island state, this extreme dependence presents serious risks to food security in the face of climate change or supply chain disruptions. While rice was once widely grown in Hawaiʻi by early immigrants, commercial rice farming completely disappeared by the 1960s due to water competition and shifting economic factors. Today, thousands of hectares of agricultural land remain unused.

To address this, a joint research group from Tokyo University of Agriculture and Technology (TUAT) and the University of Hawaiʻi at Mānoa (UH Mānoa) focused on “upland cultivation” —growing rice in dry fields rather than flooded paddies. This method requires substantially less water, lowers infrastructure costs, and utilizes existing fallow plantation lands. The paper was published in Frontiers in Agronomy on May 4, 2026.

The discovery: Faster growth, solid yields, and superior quality

Beginning in March 2025, the team tested two of Japan’s most famous short-grain rice cultivars, Koshihikari and Hitomebore, on a local farm in Kapaʻa, Kauaʻi, alongside comparative trials at TUAT’s experimental fields in Tokyo.

The results surpassed expectations:

• High yields: The Hawaiʻi-grown upland rice achieved high yields of approximately 4 tons per hectare (around 3,500 pounds per acre), matching standard upland yields in Japan.
• Shorter cycle: Due to the shorter day lengths in Hawaiʻi, which trigger early flowering in rice plants, the total growth period was shortened by about one month.
• Exceptional quality: Despite the accelerated lifecycle, the harvested brown rice grains were larger and more translucent, and showed a significantly lower rate of “chalky grains” (immature, cloudy grains caused by heat stress) than those grown in Japan.

The science behind the success

Environmental monitoring revealed that, while the overall growth period was compressed, the critical period after flowering (the grain-filling stage) experienced abundant, intense solar radiation and moderately warm temperatures.

“In Hawaiʻi’s unique climate, the number of grains per panicle was naturally and moderately limited,” explains Professor Shunsuke Adachi. “This allowed the assimilates produced via photosynthesis to be efficiently packed into individual grains, resulting in larger, beautifully formed, high-quality rice.”

Public taste-testing events held at UH Mānoa also drew significant local interest and high demand, confirming strong regional enthusiasm for locally grown Japanese rice.

Future outlook and global impact

Supported by Japan’s Peak Research Universities (J-PEAKS) program, this initiative aims to establish low-cost, stable production models, build a local brand for Hawaiʻi-grown rice, and eventually introduce it into local school lunches for food education.

Beyond Hawaiʻi, these insights offer a vital blueprint for sustainable agriculture in other island nations facing food insecurity, as well as in regions worldwide adapting to the agricultural challenges posed by water scarcity.

Reference

Title of original paper: Comparative analysis of yield formation and grain quality of Japanese rice cultivars under upland cultivations in Hawai‘i and Japan

Journal: Frontiers in Agronomy

DOI: https://doi.org/10.3389/fagro.2026.1826804

Funding information

This work was supported in part by JSPS Program for Forming Japan’s Peak Research Universities (J-PEAKS) (grant number: JPJS00420230003), by JST (grant number: JPMJPF2104), by JSPS KAKENHI (grant numbers: 24K01740, 24K01741, and 25K23638), and by a USDA NIFA Hatch (project number: HAW01143-H).