Imagine that you live in a place where the average elevation is more than 4,570 meters above sea level and the oxygen content in the air is just half that in most cities in the world. Moreover, you have been living there and doing the same thing almost every day for more than 20 years.

Now, you have a chance to leave with nearly 3 million yuan ($428,000) and reunite with your family for good. What would you do? For most people, it would not be a hard choice, and it would appear strange if you chose to stay.

Officer Sun Chao (left) and colleagues harvest white radishes in a greenhouse in Tashikurgan Tajik autonomous county, Xinjiang Uygur autonomous region, in August. [Photo by Wang Tao/For China Daily]

Last year, Sun Chao, an immigration officer from the northern province of Hebei, made probably the hardest decision of his life.

"I have spoken with my family many times about my decision to stay at my post, and like everyone else, they were pretty confused initially. On the day I left my home, my wife reminded me that we only meet twice a year at most. I was holding my 7-year-old son tight in my arms when she said that - I had never cried before that moment," the 40-year-old said.

The place that has enchanted Sun is the Khunjerab Pass, China's highest border checkpoint, located in Tashikurgan Tajik autonomous county in the south of the Xinjiang Uygur autonomous region.

The county - about 4,000 kilometers from Gaobeidian, Sun's Hebei hometown - shares a 126-km border with three countries: Tajikistan; Afghanistan; and Pakistan.

Sun (left) feeds chickens at a poultry farm. [Photo by Wang Tao/For China Daily]

Brand-new world

It took Sun some time to become accustomed to life in Khunjerab when he arrived in 1996. It was a brand-new world, especially as most of the locals are members of the Tajik ethnic group, a Persian-speaking people considered the only Caucasians in China.

"At first, my stomach protested because the Tajik diet is different from my hometown food. The staple food was meat and naan, an ovenbaked flat-bread. I could not find enough vegetables," he said.

However, as a 17-year-old rookie who had just been assigned to the People's Armed Police Force at the Khunjerab Pass, Sun had no option but to endure the situation.

In 1968, China established a frontier inspection station in Khunjerab because of its geopolitical significance. The station lies on the Karakoram Highway, aka the China-Pakistan Friendship Highway, which links Xinjiang with the Gilgit-Baltistan territory of Pakistan.

Conditions at the station are improving, thanks to increased government funding since the late 1990s, but as Tashikurgan lies on the edge of the Pamir Plateau, often known as "the roof of the world", the air and temperature have always been obstacles to habitation.

"The oxygen deficit is a problem for people like tourists who only stay a short while. For many recruits, the discomfort caused by the altitude only takes a few weeks to alleviate. However, the lack of vitamins meant we were troubled by a range of ailments, including chapped skin, hair loss and gum ulcers," Sun said.

"In 1997, on my birthday, I ate vegetables for the first time since I arrived. I had some noodles with a little bit of spinach in them, and I realized that all my comrades were staring at the dish. I shared it with them, as I knew it was also the first time for them. On that day, I swore that someday, there would be plates of vegetables on our table."

Normally, the optimal sowing season is spring. However, after Nowruz - the Persian New Year, which marks the beginning of spring - the land in Tashikurgan is as dry as a baguette that has been left out for 10 years.

"The Tajiks are born nomads, and they can only grow potatoes or highland barley. Besides, the frostless season only lasts two months; therefore, there was almost no agriculture in Tashikurgan in the past," Sun said. As the son of a farmer, born and raised in the countryside, Sun learned how to farm by constantly watching and listening to the most experienced farmers. So, in his third year in Khunjerab, he requested a transfer to the station's logistics division to bring his talent into play.

Setback

In his first experiment, based on the plateau's characteristic climate, he used plastic mulch to suppress weeds and maintain temperatures. After a few days, the seedlings he'd planted broke through the soil.

However, an unexpected gale shattered his expectations. As the temperature suddenly plummeted, all the seedlings died.

"I knew that the first step was always the hardest, and once again, I deeply felt the difference between the plains and plateaus. But I knew I was not the first and only person to feel that, and that there must be a way to solve the problem," he said.

For the next few years, he was more like an agronomist than a police officer. He scanned every agricultural book and planting manual he could get his hands on, and when not engaged in daily training or border patrols, he immersed himself in experiments.

"I felt like a graduate student. The farmland was my university, and I found a tutor who was a plateau planting expert at the Academy of Agricultural Sciences in Kashgar. Under his guidance, I easily finished my 'dissertation'," he said.

In 2002, Sun finally made his breakthrough as he worked out the nutrition and temperatures required to grow seeds in the station's feeding block. After the seeds sprouted, he transplanted them to a greenhouse.

Now, more than 30 kinds of vegetables are grown in Tashikurgan - including red peppers, cucumbers, carrots - and gourds, and 90 percent of the vegetables in the station's kitchen come from Sun's greenhouse.

In 2005, after visiting the greenhouse, Zang Aiwu, then Party secretary of Tashikurgan, was so impressed by Sun's achievements that he decided to promote the approach to vegetable cultivation across the county.

Sun became widely known, and was appointed as a planting instructor by a number of establishments.

Moreover, local radio and television stations broadcast programs in which he introduced his techniques to more people.

Tajik herders receive seeds from Sun, who also provides advice on how to sow them. [Photo by Wang Tao/For China Daily]

Sense of achievement

"I got a huge sense of achievement from my efforts. More importantly, it gave me the opportunity to look at Tajik culture from different angles, and I became more open," he said.

Because of the harsh environment, the Tajiks mostly engaged in small-scale animal husbandry for hundreds of years and relied on cultivating the small amount of arable land in the mountainous area.

Sun was happy to help the locals. To introduce and promote his planting techniques to ordinary Tajiks, he traveled from house to house and visited every greenhouse.

"He does not speak Tajik, but the language barrier did not stop me from learning how to plant, because he used all kinds of gestures and illustrations to teach me. Thanks to him, vegetables are now widely used in our cuisine," said Khalip Sadalik, a 49-year-old herdsman who Sun taught to plant seeds 10 years ago.

Now, almost every family has a government-funded greenhouse in their yard, which provides additional income. The development has fundamentally changed people's eating habits.

"When I was young, the only crops available were potatoes and highland barley. I never thought that one day I would eat various vegetables at dinner, and what is even more unbelievable is that I planted them myself," Khalip said.

Sun said: "Tajiks are a traditionally nomadic people, and that shapes their free-and-easy character. It is difficult for them to stick to one place. Sometimes, they forget to water or fertilize the fields on time, but eventually they become accustomed to the schedule.

"Han people have lived in an agrarian society for more than 1,000 years, and that makes us stick to our inherited land, as our livelihoods depend on it. We have to follow the farming program every day, otherwise we may have a poor autumn harvest."

Reforms

Last year, the government made reforms to the law enforcement system, under which the officers of the People's Armed Police Force were transferred from military status to the civil service.

Sun became an immigration officer when his troop was incorporated with the newly established National Immigration Administration.

During his 22 years of service, Sun has had a few chances to leave, but he has turned them all down. The last time (last year), he hesitated, but decided to stay.

"He deserves warm applause and appreciation from everyone at our station for what he did. I told him he could retire with pride, and we offered him a pension of almost 3 million yuan. But, he turned it down," said Wang Xianlei, senior officer at the border inspection station at Khunjerab.

In addition to his memories and love of the Khunjerab Pass, Sun has invested so much time and energy in helping the locals that he is unwilling to leave.

"I only see my family once a year. It is hard to been separated from them, but I dedicated my youth to Tashikurgan and the inspection station; how could I say goodbye to all that?" he said.