In conclusion, maize root growth, especially initiation and development of the shoot-borne roots, as well as the amount of N taken up were coordinated with shoot growth and demand for nutrients. The N-efficient maize 478 had higher shoot growth potential and thus formed larger root system, as presented by longer total root length and better root distribution in the soil than those of the N-inefficient Wu312. Although a larger root system and higher RLD in the soil profile are beneficial for efficient N acquisition, amount of N taken up by the two maize genotypes in the presence of sufficient N supply was determined by the shoot growth potential, and not by the root size.