State President Truong Tan Sang started his four-day visit to Japan on Sunday, with an aim to strengthen comprehensive ties between Vietnam and the East Asian country, including cooperation in agriculture.    President Sang and his entourage visited many modern agricultural production units in Ibaraki prefecture, which ranks second in Japan in agricultural production, on the first day of the visit. The president visited glass houses where new seedlings are planted and watched local farmers perform their advanced farming skills.  He also paid a visit to the Ibaraki agricultural machinery center and the Asahi fresh vegetable processing plant. The Vietnamese leader said his visit to Japan aims at boosting the two countries’ all-around cooperation, in which agriculture is one of the fields that interests him the most. “With nearly 70 percent of its population engages in agricultural production, agriculture and rural development are one of the priorities in Vietnam’s development strategy,” President Sang said. On the same day the president had talks with Ibaraki Governor Hasimoto Masaru, during which he announced Japanese Prime Minister Shinzo Abe will have a meeting with him to discuss measures to bring the two countries’ ties to a new height.    After the talks, the Vietnamese leader witnessed the signing of a cooperation agreement between the Vietnamese Ministry of Agriculture and Rural Development and the Ibaraki authorities.