In the 1990s, a national standard was established to regulate the quality of plastic mulch. It stipulates that the thickness of mulch should be around 0.008 mm, but a discrepancy either way of 0.003 mm is allowed. In order to save costs, many mulch manufacturers take advantage of the permitted discrepancy and have chosen to produce mulch only 0.005 mm thick. Farmers also prefer thinner mulch due to cost concerns. According to Xiao, he needs 47.5-60 kg of 0.008 mm mulch to cover 1 hectare of farmland, but only 30-37.5 kg of 0.005 mm mulch.

However, due to its lower density, thinner mulch breaks apart much more easily, creating difficulties for recycling.

"Stricter rules are needed to regulate the production and recycling of plastic mulch, or else the problem of plastic pollution in our farmland cannot be solved," said He Wenqing, another researcher with the CAAS' Institute of Environment and Sustainable Development in Agriculture.

A more effective method for alleviating plastic pollution in farmland is to use biodegradable alternatives, say experts.

Biodegradable mulch has been around for some time, but higher prices make it unpopular with farmers. "Generally, the prices for biodegradable mulch are 3-5 times that of non-biodegradable ones," said Chen Xuesi, a researcher with the CAS' Changchun Institute of Applied Chemistry in Jilin Province.

Chen is leading a research project on biodegradable mulch. He said that his team hopes to develop a kind of biodegradable mulch that can be manufactured cheaply in two years. "The price of the new product will be twice that of non-biodegradable mulch. We hope this lower price-point will help open the market for biodegradable mulch," Chen said.

Wang Xinyong, Director of the Institute of Soil and Fertilizer at the Xinjiang Academy of Agricultural Sciences, called for increased input to speed up the development of biodegradable mulch. "The government should also consider giving subsidies to manufacturers and farmers to encourage them to produce and use pollution-free products," Wang said.