Farmers in China can follow guidelines laid down thousands of years ago when deciding when to plant and harvest their crops. But while some are sticking to the traditions of their ancestors, some see market opportunities in their response to a changing climate.
Li Shihua, a large-scale farmer in Bayan county, Northeast China's Heilongjiang Province, told the Global Times he strictly follows the solar system when it comes to planting his crops.
The Chinese solar system splits the year up into 24 solar terms, each having its role in a farmer's schedule.
"The crops will not grow very well if we fail to follow the date," Li said.
The 667 hectares that Li farms on behalf of over 200 households is used to grow corn and soybeans. When asked when the crops are sown and harvested, Li is able to answer in less than a second, as he has faithfully followed the solar system his whole working life.
Created in Central China around 2,000 years ago, the solar system was how Chinese people organized their lives for centuries, and it is still deeply rooted in the minds of the country's farmers, Chen Lianshan, a professor who studies traditional customs at Peking University, told the Global Times.
"The system was sacred for Chinese people in the past," Chen said.
However, for Zhao Changfeng, who owns 4 square kilometers of farmland in the village of Beitangtuan, North China's Hebei Province, the solar system is not the most effective way of deciding when to do what on his farm.
There is an old Chinese saying - "at the 'Grain Rain,' plant your gourds and beans." The "Grain Rain" is the sixth of China's 24 solar terms, coming at the end of April on the Gregorian calendar.
However this year Zhao planted his cotton two months earlier than usual. The plants are already 50 centimeters high and doing well. "The old saying tells us when to plant seeds, but the specific date changes depending on the temperature," Zhao told the Global Times.
Zhao, a 49-year-old father of two, used to use the solar system as his main guide. But with the advent of global warming and the introduction of modern farming methods, he and the other farmers in his village are planting their crops - and bringing them to market - earlier and earlier in the year.
His cotton crops are covered with thermal screens, which mean they can grow faster and come onto the market before many of his competitor's crops, thereby ensuring a higher price, Zhao said.
"Farmers can gain huge profits from the application of agricultural techniques by growing crops during different seasons, such as watermelons in the winter," Shi Aidong, a professor at the Chinese Academy of Social Sciences, told the Global Times.
"The maturity of farming techniques and precise weather forecasts will, one day, make all farmers abandon the solar system," Shi added.
Although their practical use is fading, the solar system still has an important place in Chinese culture.
"The 24 term solar system is linked to the philosophical concept of yin and yang, and this is key to working out if a day is 'lucky' or not," Chen said.
Yin and yang are the two contrary forces that, according to traditional Chinese thought, make up everything in the universe.
For example, yang is at its peak during the summer solstice, which means the day is not lucky. The vernal equinox and autumnal equinox see a more balanced yin and yang, and are therefore considered auspicious.
Chen said, "These customs are still followed by the public."
The solar terms can also be found in literature, from proverbs to poetry.
An ode to drizzly Chengdu during the term "Rain Water" by Tang Dynasty (618-907) poet Du Fu is included in sixth-grade textbooks in China, and a popular proverb that says a "chill always follows an autumn rain" depicts the changes that apparently take place during the 13th solar term of the year.
The authorities have worked to preserve the solar terms, having them listed as an Intangible Cultural Heritage by UNESCO in November 2016 and ensuring that calendars feature both Gregorian and solar systems.
"China integrated the solar terms into the Gregorian calendar to make people keep the traditional culture. And it's unlikely to be excluded from the Gregorian calendar in the future," Chen explained.
Those two calendars are not alternative but equal, Shi said. "The solar system, which only contains 24 dates, is easier to remember and carries the cultural memories of Chinese people. It is still the first option for many people from villages. The Gregorian calendar is more accurate and well-recognized by Chinese people from the new generation and the rest of the world."
"In the future, the solar terms will represent solely a cultural denotation and that this will be a sort of historical choice," according to Shi.