In the middle of removing weeds from his vegetable plot, Mr Bai Ning stops and gazes into the distance.

He casts a rueful look at the soil under his feet which, for generations, had provided a living for his family in Xiaodiantou village.

But a few years ago, the oranges started dying, then the grapes, then the bamboo shoots.

"They could never grow again," he tells The Straits Times.

To survive, Mr Bai, 28, switched to planting hardier vegetables such as coriander. He says he is, like many Chinese farmers in this southern region of Yunnan province, a victim of soil pollution, an area that environmental authorities are now pledging to combat after focusing their earlier efforts on the more visible air and water pollution.

Soil pollution in China is usually caused by industrial activity, fertiliser and pesticide contamination, and improper toxic waste disposal.

Rapid development and unregulated industrialisation had made one-fifth of China's arable land unsafe for farming, according to the country's first nationwide survey on soil quality released in 2014.

Describing the situation as "severe", the government announced a national action plan in May to make 90 per cent of contaminated farmland safe by 2020, then increase it to 95 per cent by 2030.

That works out to some 260,000 sq km of land, an area bigger than the United Kingdom.

Among the affected places are those rich in resources such as south-western Yunnan province, where mining activities can release harmful chemicals into the ground.

"Yunnan also has one of the fastest-growing smelting industries in China, which is a major source of soil pollution," Greenpeace East Asia's toxic campaign manager Ada Kong tells The Straits Times.

Mining has similarly hurt the livelihoods of farmers in Shiliuba village in southern Yunnan, about half an hour's drive from Xiaodiantou.

Mr Li Jianchuan, 25, says crops planted here, which include corn, rice and grapes, no longer grow as well as they did a decade ago.

"We used to drink the water from the nearby river, while using it to irrigate our fields. The water was clear," he tells The Straits Times in between ploughing his field. "But now it's brown and dirty, and leaves a layer of muck on our crops."

In 2008, local authorities did a test for heavy metals on the water flowing through Shiliuba, after villagers complained that their crops were dying. The test found the water contained more than five times the standard level of arsenic and 35 times the standard level of lead.

This was blamed on mining and refinery activities nearby. Both Shiliuba and Xiaodiantou are located near Gejiu city, known as China's "tin capital". After numerous complaints to the authorities, local villagers say pollution is better managed now, but farmlands have still not recovered.

Gejiu locals like Mr Wang Zhiyou, 52, say pollution forced him and other fish farmers in his village to stop their trade about 10 years ago, after thousands of their fish died. He later went to work in a factory.

"I was so angry. Nobody compensated me," he says.

But the people's main concern about soil pollution is its effect on food safety.

Memories are still fresh in the rice-loving nation of a 2013 official report that found 44 per cent of rice samples in coastal Guangdong province had excessive levels of cadmium, which can damage internal organs and cause cancer.

The rice came from neighbouring Hunan province, China's top rice producer and a major producer of metals such as copper and lead, which underscored the dangers of having mining and industry close to agricultural areas.

Mr Bai's wife Zhang Yunjiao, 24, admits that pollution has called into question the safety of the food they grow. "There's no way we can guarantee 100 per cent that what is grown here is safe," she says. "It's not realistic."

The government is hoping that its proposed action plan, as well as the country's first soil pollution law - set to be passed next year - will be able to arrest the situation.

But while many experts see these as good first steps, there have been calls for more transparency.

China had been criticised for being vague about soil pollution data, at one point calling details of its 2014 nationwide survey a "state secret", and raising questions about whether the situation is more serious than the authorities have let on.

Ms Kong says the government needs to be clearer about what it means by "safe soil".

"What is 'safe'? They don't define it clearly," she says.

She suggests that the authorities allow local governments to make their own laws, rather than have national legislation, as "different regions have different causes of pollution, severity and urgency".

There are also concerns about the feasibility of the deadlines, with the first target less than four years away.

"We think these targets are ambitious because soil pollution is caused by so many different industries... and also because soil remediation takes time and is expensive, indicating that much more will need to be invested into the appropriate pollution control equipment," HSBC climate change strategist Chan Wai-Shi wrote in a research note last month.

Mr Bai is not optimistic that years of damage to his home town's soil can be fixed so easily.

The farming yield has dropped so much that he leaves his wife to tend to the fields on weekdays, so that he can find other work to supplement their family income.

"Years ago, a farmer could survive and feed his family. Now it's impossible," says Ms Zhang, who will look for a job once their four-year-old daughter is older.