Farmers use a tractor to plough a field in Linzhou county of Lhasa, Tibet Autonomous Region, in this May 11, 2011 file photo. The world's largest makers of tractors and combines are finding a rare opportunity for growth in China despite a sharp slowdown in the world's No. 2 economy, with big farm machines in demand as the rural labour force shrinks and plot sizes grow. (Photo by Rooney Chen/Reuters)
