Deficit irrigation management (DIM) of maize needed enough knowledge about plant partitioning reaction to irrigation time and depth. The purpose of this study were considering root and shoot indices, the response factor to water stress (k y ) and irrigation water use efficiency (IWUE) of silage maize at different growth stages under two deficit irrigation managements (DIM). Two DIM methods were fixed irrigation interval-variable irrigation depth (M 1 ) and variable irrigation interval-fixed irrigation depth (M 2 ). Each DIM methods was considered at four irrigation water levels, including: severe, moderate, and mild water stress (referes as W 1 , W 2 and W 3 , respectively), and a full-irrigation level (W 4 ). The experiment was conducted on randomized complete blocks as compound analysis. Irrigation scheduling in both management methods was based on soil moisture depletion (SMD) of W 4 level. Plant samplings were conducted at 8-leaf (V 8 ), 12-leaf (V 12 ), tasseling (V T ), blister (R 2 ), milky (R 3 ) and doughy (R 4 ) stages. Seasonal applied water volume was 7070 m 3 ha -1 for W 4 level for M 1 , and 0.7, 0.81, and 0.9 of seasonal water volume of W 4 were received by W 1 , W 2 , and W 3 , respectively. For M 2 , 0.72, 0.77, and 0.86 of applied seasonal water volume of W 4 were received by W 1 , W 2 , and W 3 , respectively. The effect of irrigation levels was significantly differences (P 0.05) on leaf area index (LAI) and total aboveground biomass (TAB) for both managements. In the doughy stage maximum TAB was observed for W 4 level for both DIM methods, and it was 20.4 and 22.3 T ha -1 for M 1 and M 2 , respectively. The minimum value at the same stage was observed for W 1 level which was 14.1 and 12.3 T ha -1 for M 1 and M 2 , respectively. The IWUE was significantly difference (P 0.05) between all irrigation levels for all stages of both DIM methods. The maximum IWUE for W 4 irrigation level in milky stage was 3.10 and 3.28 kg m -3 for M 1 and M 2 , respectively. Minimum IWUE at the same stage was observed for W 1 irrigation level which were 2.70 kg m -3 for M1 and 2.59 kg m -3 for M 2 . The maximum root biomass (RB) in doughy stages was measured for W 4 level under both DIM methods, which was 18.40 and 20.40 g plant -1 for M 1 and M 2 , respectively. The minimum value of RB at the same stage for M 1 was observed at W 3 irrigation level, 14.2 gr plant -1 , and for M 2 was observed at W 1 irrigation level which was equal to 16.1 gr plant -1 . The maize response factor to water stress (K y ) of LA, total above-ground biomass (TAB) and RB at milky stage were 0.55, 1.14 and 0.80 for M 1 and 1.31, 1.72 and 0.89 for M 2 method, respectively. Key Words : Root of maize, Drip-tape irrigation, Irrigation water use efficiency, Response factor to water stress