Of all the advantages China had for centuries over the rest of the world, the greatest was the superiority of its plows.
Improved iron supplies and casting techniques in China by the third century BC led to the design of iron plowshares called kuan. Greek and Roman shares were usually simply tied on the bottom of the sole with bits of rope, which made them flimsy compared to the Chinese ones. By the first century BC moldboards were available for Chinese plows. Those plows could invert the soil and turn a true furrow.
In Europe, moldboards were unknown until late 10th century, and then they were crude in their design.