Sands are shifting around the Minqin oasis as they always do in spring, turning day into night in the northwestern county considered a major source of China's sandstorms.

Sandstorms reduced visibility to less than five meters on Thursday in Minqin, an expanse of arid land surrounded by the Tengger Desert to the east and the Badain Jaran Desert to the west. Experts fear that Minqin, Gansu Province, will eventually be eaten away by encroaching sand dunes.

To survive on the land plagued by a severe water shortage, farmers in Minqin have learned to be shrewd in terms of water use.

Chai Zhumin and his wife picked chili peppers in their greenhouse as sands danced outside the walls of plastic.

Life has become easier since Chai turned to greenhouse farming five years ago, which can cut water consumption by a significant amount compared to traditional farming methods.

The 100-meter long greenhouse, with an area of less than 1 mu (667 square meters), where Chai grows peppers and tomatoes, brings his family at least 17,000 yuan (2,700 U.S. dollars) in annual profits.

Chai, like all farmers in the county, is on a strict water budget.

"Each farmer is only allowed to have 2.5 mu of farmland and the government only allots 400 cubic meters of irrigation water to each mu every year," Chai said.

The government is battling desertification in the catchment of the Shiyang River, a major water source for Minqin, as overdevelopment has accelerated desert encroachment, leaving the basin among the country's worst ecologically-deteriorated regions.

The environmental situation in Minqin, a county with a population of 300,000 that lies in the lower reaches of the Shiyang River, is most critical, as smaller amounts of the river's water reach the area due to increased irrigation at its upstream.

The Minqin oasis, covering an area of 16,000 square kilometers, played an important role in protecting the Hexi Corridor, a major section of the ancient Silk Road, from sandstorms and strong winds.

Extensive farming starting in the 1950s sapped underground water in Minqin and destroyed the local ecology. The 400-square-km, 60-meter-deep Qingtu Lake dried up 30 years after the 1960s, and by the early 1990s, the lake was choked by creeping yellow sands and become part of the Badain Jaran Desert, which spans more than 40,000 square kilometers.

Just a few years ago, farmers had more land, but absolutely no idea as to how much water they used on each mu, Chai said.

China invested 4.79 billion yuan in 2006 for environmental conservation around the Shiyang River basin. Part of the efforts were to cap water use and develop water-saving agriculture techniques.

Today, Chai's 7-person family has a total of 17.5 mu of farmland and is allowed to use 7,000 meters of irrigation water per year.

"The water is far from enough for all the land," Chai said.

Chai had no other choice but to choose his crops carefully. He divided his land into several parcels for different crops.

He chose what to plant based on the plants' economic value and water needs.

Last year, the shrewd farmer grew 10 mu of onions -- the most valuable plant as well as the one that consumes the most water among his crops. He also grew 2 mu of sunflowers, raised some grapes and built greenhouses that covered another 2 mu for vegetables and peppers that, comparatively, consume far less water.

"The water I saved from growing sunflowers and grapes and using the greenhouse can balance out the water cost of the onions," he said.

"Greenhouse farming is among the best choices here in Minqin," said Chai, as it can save water and land and, at the same time, increase farmers' income in the arid but sunlight-rich region.

Over the past few years, Minqin county has cut 441,800 mu of farmland by developing greenhouses covering 66,300 mu, according to a statement from the county government.

Each mu of greenhouse farming produced an average net profit of 12,015 yuan in 2011, said the statement.

Conservation efforts have finally been paid off as ground water consumption in Minqin fell dramatically to 88 million cubic meters in 2011 from 517 million cubic meters in 2006.

The significant drop in irrigation water consumption meant that more water was available for ecological purposes such as taking care of the shelter forest, local authorities said.

Meanwhile, the environment in Minqin has improved in the past few years. The number of strong sand-mixed gale days dropped to three in 2011 compared with the long-time average of 17.5 days.

The Qingtu Lake reappeared in 2010, with a water surface area of 3 square kilometers. The lake continued to expand to cover 10 square kilometers last year.