Objectives The temporal and spatial distribution of roots in soils affects the nitrogen uptake efficiency and yield of crops. Clarifying the response of maize with genotypes of high or low nitrogen efficiency to the nitrogen fertilizer rate is of great importance for exploiting the potential of genotype in nitrogen use efficiency.

Methods High N efficient hybrids (Zhengdan958 and Jinshan27) and low N efficient hybrids ( Mengnong2133 and Neidan314 ) were used as tested materials in a two-years’field experiment. With no nitrogen fertilizer as control (N0), N 300 and 450 kg/hm² were used as treatments of suitable and excessive nitrogen rates ( N300 and N450 ). The root mass and temporal and spatial distribution of root length in soils, and the relationship with nitrogen uptake were investigated.

Results In N450 treatment, there was no difference in root mass before anthesis period between the two genotypes, but the root mass of high N genotype maize was significantly greater than that of low N genotype after anthesis. Root mass of high N genotype was greater than that of low N genotype at N0 and N300. In N0 and N300 treatments, root length at 0-100 cm soil layer of high N efficient genotypes was remarkably greater than that of low N efficient genotypes. From silking to milking stage, root decreasing rate of high N efficient genotypes was clearly lower than that of low N efficient genotypes at 0-20 cm and below 40 cm layer at N0. The situation was quite different when N was applied. There was no difference in root decreasing rate at 0-40 cm layer, but high N efficient genotypes showed significant lower root decreasing rate below 0-40 cm layer compared to low N efficient genotypes. Pre-anthesis nitrogen uptake at zero and moderate nitrogen treatments was primary controlled by unit root N uptake rate, direct path coefficients were 0.590 and 0.649, but when excessive nitrogen was applied, it was mainly controlled by root length, direct path coefficient was 0.536. Post-anthesis nitrogen uptake at zero and moderate nitrogen treatments was primary controlled by root length, direct path coefficients were 1.148 and 0.623, when excessive nitrogen was applied, it was mainly controlled by unit root N uptake rate, direct path coefficient was 0.858.

Conclusions For the response of root distribution and N uptake efficiency of different N use efficiency maize genotypes, there was obvious difference to nitrogen rates. In the low N and suitable N, high N efficiency hybrids had larger root mass, longer root length and lower root senescence rate than low N efficiency hybrids, and at pre-anthesis stage, nitrogen uptake was mainly related to unit root N uptake rate, and related to root length at post-anthesis stage; when excessive nitrogen was applied, nitrogen uptake was mainly affected by root length at pre-anthesis stage, and by unit root N uptake rate at post-anthesis stage.