Shiga: Finding creative solutions to plant predicament

The Yomiuri Shimbun
Aquatic plants from Lake Biwa are seen in Nagahama, Shiga Prefecture.

NAGAHAMA, Shiga — A construction company has developed compost by collecting and fermenting aquatic plants that are negatively impacting the ecosystem in Lake Biwa, the largest lake in Japan. The product has worked well on local crops across the country, including olives in Shodoshima and onions on Awaji Island.

Aquatic plants usually help purify the water in lakes and are essential for fish spawning and growth, but in Lake Biwa, they have increased to the point where they emit a foul odor during the summer in recent years.

A drought in 1994 sparked a rise in aquatic plants in Lake Biwa. In 2014, about 45 square kilometers was covered with the plants to the south of the Biwako Ohashi bridge, about 90% of the south part of the lake.

The Yomiuri Shimbun
Hideki Watari surveys an olive grove on Shodoshima island in August where “Ko no megumi” compost has been used.

The plants have many harmful effects, such as depriving native fish and shellfish of their habitat, getting entangled in the screws of fishing boats and emitting a foul odor. It is difficult to predict the year when a large number of the plants will grow, and at present, the only response has been to remove them. The Shiga prefectural government, in cooperation with fishermen, removes 5,000 to 6,000 tons every year, by cutting or uprooting them.

Meiho Construction Inc., based in Nagahama, took notice of the situation after looking for a way to enter into businesses beyond construction. The company decided to start developing the new compost believing that using aquatic plants would help improve Lake Biwa’s environment.

With the support of the Shiga government, the company conducted research for four years and succeeded in commercializing compost in 2019. They call their compost, “Ko no megumi,” meaning “blessings of the lake.”

Courtesy of the Shiga prefectural government
A boat cuts aquatic plants in Lake Biwa.

The aquatic plants were used as fertilizer until before World War II and were so popular that communities fought over the right to collect them. The prefectural government has long used them as compost. They let the plants naturally ferment for two years and distribute them to those who wish to use them, all free of charge.

The fermentation period for Meiho’s compost, however, is a significantly shorter two months. Moreover, the action of various bacteria in the shortened fermenting process has been shown to repel pathogens, which promotes crop growth and improves the soil, the construction company said.

Olive, onion, sweet potato …

Shodoshima island in the Seto Inland Sea is known as an olive producing area in Japan. However, there was a plot of land where anthrax bacteria had infested the ground, wiping out the olives there. Using the new compost on the soil, however, reduced the bacteria, and more than 3 tons of olives can now be harvested annually.

“I was surprised because pesticides had no effect on the bacteria for more than 10 years,” said Hideki Watari, a 47-year-old employee of Toyo Olive Co., which grows and processes olives on the island.

The Yomiuri Shimbun

Awaji Island is a famous onion-producing area in the nation. Takayoshi Horii, the representative of Hatada Vegetable Farm on the island, uses the compost there to grow onions and cabbage.

“The crops grow on their own without the need for delicate care,” he said.

Meiho Construction said the new product has also been used to help grow Naruto Kintoki, a type of sweet potato from Tokushima Prefecture; lettuce in Nagano Prefecture; and mangoes in Okinawa Prefecture.