China's available labor force of those 35 years old and under has dried up, and one economist says low salaries are to blame.

Zhang Zheng, an expert in rural economy at Peking University's Guanghua School of Management, told China Business News that his survey showed the labor force of this "golden age group", which cities need becasue of its higher work efficiency, has been exhausted in rural areas.

He cited figures saying that among the country's total rural workforce - which stood at 550 million in 2009 - only 200 million were at or below 35. At the same time, industries employed some 230 million farmers-turned workers.

"Judging from these figures, I believe the rural workforce at and below age 35 has been used up," he said.

But he also added that there is a surplus of middle-aged laborers in the countryside.

The current labor structure in China, which is characterized by a scarcity of young migrant workers along with a surplus of middle-aged workforce in the countryside, is caused by the low salaries paid to migrant workers, he said.

The migrant workers are paid according to their work load. The middle-aged migrant workers in labor-intensive manufacturing industries cannot earn enough to survive in cities under the current payment mechanism set up by enterprises that try to compete by low labor cost.

So many middle-aged migrant workers would rather return home and cultivate farmland, he said.