Mainland farmers continue to burn stubble in their fields after harvest, creating a major source of air pollution despite tougher penalties, according to official sources.
Burn-offs across the country were up by nearly 7 per cent year-on-year over two weeks last month, the Ministry of Environmental Protection said.
The burning has already created smog in northern and central areas this year.
The increase is in defiance of warnings such as those erected in Henan, where banners in rural areas spell out the dangers of the practice to farmers.
"Burn corn stalks in the morning, you'll be arrested in the afternoon," one banner says.
"Police will throw you in prison if any smoke comes from your field," reads another.
One Henan farmer, Jiang Yuanwang who lives near Zhoukou, was detained for 14 days for burning crop waste, state television reported.
Read more: Stable autumn weather and burning of harvest stalks create blanket of smog across northern and eastern China
As recently as 20 years ago, many farmers chose not to burn stubble left behind after the harvest of crops, such as wheat, corn and sorghum.
Instead, they would cut and store the stubble, reusing it later as fuel for cooking or compost.
Some stubble was also left to break down in the field to add nutrients to the soil.
It was a sustainable way of dealing with agricultural waste but the labour-intensive practice has become increasingly uneconomic as workers have headed to cities, pushing up wages.
Some estimates suggest that it usually took a week to 10 days for farmers, or migrant workers returning home for the harvest, to bring in all the stubble. Burning was by far the cheapest way of dealing with it.
A state television report suggested that harvesting stubble raised the cost of cultivating each hectare by 1,500 yuan (HK$1,827), cutting the farmers' return by a fifth.
Even government-subsidised recycling projects, such as collecting agricultural waste to generate electricity, have not had a big impact on the problem because farmers do not have a big enough incentive to transport the straw to recycling plants that are often some distance away.
Some experts said that banning burn-offs and enforcing punishments were not a solution and unfair to farmers.
Yu Yang, who researches energy economics, said the environmental ministry should consider more than the interests of urban residents when formulating policy.
Hu Xingdou, a professor of economics at Beijing Institute of Technology, said government officials should work out proper incentive schemes to encourage the recycling of crop waste.
Arresting farmers demonstrated a lazy approach to the problem, Hu said.