Farmers in northwest China are finding new ways to increase their incomes by growing herbs used in traditional Chinese medicine (TCM).

For many years farmers in Weiyuan county, Gansu province, have made their living by growing TCM herbs like astragalus mongholicus and angelica, but profits have always been thin and the living poor.

Everything changed when in 2010 when Li Haidong started adding selenium-rich fertilizer to his astragalus and suddenly his business boomed.

"One mu (0.07 hectares) of ordinary astragalus produces about 450 kg of the herb, and each kg fetches less than 35 yuan (5.40 U.S. dollars)," Li said.

Li had heard that selenium-rich astragalus sold for a much higher price, so began feeding his plants selenium and was soon the talk of the county. Astragalus with the added selenium element has a reputation as a cancer treatment. It is used to treat cardio-cerebrovascular disease and is said to strengthen the immune system and prevent diabetes.

"Production increased to 650 kg per mu and the very best of the crop fetched 200 yuan per kg," Li recalled.

His costs may be higher, but his income has increased several fold and is more stable. Following his 2010 success, he set up a cooperative with 130 local farmers and more than 500 have since joined.

Cheng Yuantai, 53, joined the cooperative in 2014. He used to grow 10 mu of astragalus and angelica, which brought in an unreliable 30,000 yuan, depending on weather and market conditions.

"In 2014, I enriched six mu of astragalus with selenium and my income grew to 40,000 yuan," he said.

Last year, the cooperative processed more than 400 tonnes of the plant and raked in 260,000 yuan, about 100,000 yuan of which came from online sales.

According to county deputy Party chief Zhang Zhenya, Weiyuan produces more than 55,000 tonnes of traditional medicine ingredients annually, worth 1.4 billion yuan. Of the county's 217 villages, TCM accounts for more than half the revenue of 123.

"We plan to plant 2,000 mu of astragalus this year, so even more farmers can join us in raising their incomes," Li Haidong said.