Tradition. When Wang Lung in the first chapter goes into the town to claim his wife, he goes to the barber to make himself more presentable for his first meeting with his future wife. Whilst the barber is shaving Wang Lung's upper forehead, he comments:
This would not be a bad-looking farmer if he would cut off his hair. The new fashion is to take off the braid.
However, Wang Lung, horrified, draws back, saying that he could not cut his braid off without asking his father. This is a novel where old ways collide with new habits and fashions, and Wang Lung, as befits a character whose attachment is to hard work and the earth, refuses to cut his braid off because he is a representative of tradition. Symbolically, the braid therefore shows us the kind of character that Wang Lung is and the way that he will not be swayed by the modern fads and fashions that others feel are so important.