BEIJING - China saw an "overall improvement" regarding air pollution from burning straw this summer, the Ministry of Environmental Protection reported Friday.

Northern farmers traditionally burn straw after harvest and plough to bury the ashes in the ground, which they believe fertilizes farmland.

Citing satellite data, the ministry observed 1,158 burning sites between May 20 and July 31, a 45.35 percent decrease year on year.

Henan, Hebei and Shandong provinces are the three heaviest burning locations. Hebei, Heilongjiang, Inner Mongolia and Shanxi saw slight increases amid an overall decline.

"While straw burning was effectively kept in check this summer, problems persist," said Wang Dongqing, a senior ministry official.

He said slack government supervision efforts and the absence of burning control policies in some regions are the result of the problem.

Urging local governments to step up controls, Wang warned that straw burning in the autumn period, which normally lasts from late Sept to late Nov, usually results in more air pollution than that in summer.

The ministry vowed to name and shame provincial-level governments whose jurisdictions report more burning activities during autumn compared with last year.