A farmer dries wheat in the sun in Xinglongdian Village of Zunhua City, north China's Hebei Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Liu Mancang)

Farmers work in a rice field in Sandun Village of Guantan Town in Huai'an City, east China's Jiangsu Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Zhou Haijun)

A farmer works in a field in Nanwangtuan Village of Jiaolai Town in Jiaozhou City, east China's Shandong Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Wang Zhaomai)

Farmers work in a field in Changjia Town of Gaoqing County in Zibo City, east China's Shandong Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Zhang Weitang)

A farmer works in a corn field in Dongrulin Village of Yiyuan County in Zibo City, east China's Shandong Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Zhao Dongshan)

Farmers work in a rice field in Gaoqing County in Zibo City, east China's Shandong Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Zhang Weitang)

A villager works in a rice field in Guankou Village of Longli County, southwest China's Guizhou Province, June 21, 2018. Thursday marked the summer solstice, the northern hemisphere's longest day of the year. (Xinhua/Pan Xilai)