Abstract: Understanding root water uptake pattern is essential to developing efficient irrigation management practices in water-limited regions. Most models or traditional methods for estimating root water uptake need a detailed knowledge of root morphology, which is difficult to obtain in situ. The Insentek sensor-based approach was used to estimate root water uptake patterns under subsurface drip irrigation. A test-pit experiment under a rain-proof shelter was conducted in 2018-2019 with four subsurface drip irrigation amounts, i.e. 0.4, 0.8, 1.0, and 1.2 of crop evaporation (ETc) respectively, and surface irrigation being the control (CK). There was a complementary effect between the root water uptake in the upper (20-50 cm) and lower (60-100 cm) soil layers. Root water uptake rate in the lower soil layers reduced when the upper soil layer replenished by irrigation water, except for the treatment of 0.4ETc. Root water uptake rate was enhanced in the lower soil layers during late irrigation intervals, but was reduced in the upper soil layers. Compared with CK, 1.0ETc fluctuated small in root water uptake rate, and increased the yield of winter wheat and summer maize by 7.4% and 15.3%, respectively. 0.8ETc mainly reduced cumulative root water uptake in early filling stage of winter wheat and late filling stage of summer maize as compared to 1.0ETc, and increased the yield of winter wheat by 12.7% with no significant decrease in summer maize yield. A significant increase in water use efficiency of wheat and maize was observed in 0.8ETc. It is concluded that appropriate deficit subsurface drip irrigation (0.8ETc) should be considered for water conservation.

Key words: root water uptake rate, irrigation method, cumulative root water uptake, yield, water utilization