Tokachi Kawanishi yam

Tokachi Kawanishi Nagaimo begins in Obihiro's Kawanishi area and nearby Tokachi communities. The wider named growing area includes Obihiro, Memuro, Nakasatsunai, Shimizu, Shintoku, Ikeda Takashima, Ashoro, and Urahoro. In Obihiro, near the center of the Tokachi Plain, large fields rotate wheat, beans, sugar beets, and potatoes; around 1971, growers searching for a vegetable suited to cold swings and well-drained soil brought nagaimo into that rotation.

Tokachi has cool weather, long summer sunlight, and large day-night temperature shifts. Under well-drained black volcanic ash soil, the yam grows slowly, a condition tied to white skin and flesh and lower browning. The short flask-like form gives the root a compact silhouette, while the fine white flesh holds a firm bite before it ever reaches the grater.

The work starts before planting with seed yams. Seed material introduced in 1971 was selected and bred again and again for Tokachi conditions, shape, color, and texture. JA Obihiro Kawanishi manages seed production and sends out only the amount needed for planted area; local propagation takes six years in managed fields, with diseased plants removed so the next crop begins from a carefully maintained seed line.

Nagaimo grows deep enough that soil preparation and harvest decide whether the root leaves the field intact. Fields are opened with trenchers, and harvest uses backhoes followed by hand removal. That combination of heavy machinery and hands-on lifting protects the root from breaks and bruises while keeping the white skin and short flask-shaped outline recognizable.

Each year a start date is set for harvest to reduce browning and acridity. Some fields are dug in autumn, while part of the crop stays in the ground through winter for spring digging. This split eases storage pressure and, together with wide-area cooperative collection across Tokachi's JAs, supports year-round supply rather than a single short season. The cooperative structure widened in 1985, and production had passed 10,000 tons by 1991.

When grated, Tokachi Kawanishi Nagaimo becomes tororo with strong viscosity and elasticity. The white edible flesh has water content of 83.1 percent and starch at 12 grams per 100 grams, figures connected with its dense bite and sticky grated texture. In Taiwan, exports began in 1999 after demand for shanyao in medicinal-food soups; larger 4L yams found a clearer use there, and later overseas use extended to the United States and Singapore.