To investigate the effect of nitrogen management practices on root traits, the amount of nitrogen absorption at grain maturity, nitrogen fertilizer use efficiency, and to analysis the main root traits of rice responsible for high nitrogen absorption efficiency, a total of 15 conventional Indica rice varieties with marked differences in nitrogen absorption efficiency were pot-cultured in 2011 and 2012. (1) The amount of nitrogen absorption (ANA) at grain maturity was differed significantly among rice varieties and nitrogen fertilizer treatments. Among varieties, nitrogen absorption efficiency was positively correlated with ANA at grain maturity in all nitrogen treatments. In rice varieties with high nitrogen absorption efficiency ANA was greater than that in rice varieties with intermediate and low nitrogen absorption efficiency. In rice varieties with high nitrogen efficiency ANA was increased by increasing nitrogen fertilizer application rates or by using the base+ promoting-spikelet fertilizer treatment. (2) Rice varieties with high nitrogen absorption efficiency showed higher adventitious root numbers, root dry weight, total adventitious root length, and also had relative higher root activity at conventional and high rates of nitrogen supply. Rice varieties with high nitrogen absorption efficiency had higher adventitious root numbers, total adventitious root length, root dry weight, root total absorption area and active absorption, as well as crown:root ratio. Increasing the nitrogen application rate increased total adventitious root length and root activity. The appropriate rate of nitrogen application increased adventitious root number and root dry weight. Nitrogen application at the early growth stage promoted the occurrence and extension of adventitious roots, while at the late growth stage nitrogen addition enriched adventitious roots and improved root physiological activity. In addition, increased nitrogen supply improved the crown:root ratio of rice varieties with different nitrogen absorption efficiencies. (3) Rice varieties with high nitrogen absorption efficiencies had higher nitrogen absorption and use efficiencies than those with middle and low nitrogen absorption efficiencies at the conventional and high rates of nitrogen supply. (4) Increasing adventitious root number, total adventitious root length, root activity and crown:root ratio at heading stage improved ANA in all rice varieties. Increasing root dry weight also had a significant and positive effect on ANA in all rice. Correlation analysis and path analysis indicated that crown:root ratio at heading stage, adventitious roots number, root activity, total adventitious root length and adventitious root dry weight were the main root traits that affected nitrogen absorption in the rice varieties with high nitrogen absorption efficiencies.