The morphological and physiological characteristics of root system were studied with the Northeast japonica rice Mudanjiang 27 and Mudanjiang 31 as experimental materials under different nitrogen levels. The results showed that with rising nitrogen level, the number, length, thickness, volume, dry weight and total absorption area of root increased at growth stage. Shoot dry weight increased dramatically with growth stages under three nitrogen application levels, root dry weight of Mudanjiang 27 and Mudanjiang 31 maximized at booting stage and heading stage, respectively. After heading stage, rootshoot ratio reduced, while shoot dry weight increased. Root bleeding intensity per plant increased firstly and then decreased after heading stage under three levels of nitrogen application. The αNA oxidizing ability of two varieties maximized at heading stage and milkripe stage, respectively. The root oxidizing ability for both varieties in the whole growth duration fluctuated within a narrowing band with increasing nitrogen application level. The correlation between rice root number, root length, root diameter, root weight, rootshoot ratio and yield became significant at the booting stage. The total absorption area, ratio of surface area of root system and yield were positively correlated in the whole growth duration with the correlation coefficient reaching a maximum at milkripe stage.
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