Estimation of root distribution and water uptake pattern of wheat under shallow water table condition in Damodar Valley irrigation command area

Field experiments were conducted to estimate the water uptake rate of wheat from different soil layers and compare them with root density profile under shallow water table condition (1.20 m) on a sandy loam (Typic Fluvaquent) soil in rabi seasons of 1989–90 and 1990–91. Three irrigation scheduling based on IW/CPE ratios, viz. 1.2 (I₁), 0.9 (I₂) and 0.6 (I₃) were followed. The water uptake data were analyzed using the one dimensional flow equation for water movement in the soil. A remarkable increase in root density between 0–0.30 m depths corresponded well to the location of maximum water uptake zone, which gradually decreased with soil depth. Relatively drier soil moisture regimes induced wheat plant to develop more extensive root system at 0.60–0.90 m depth with 0.05 to × 10⁴ m m⁻³ more root length density values than wetter soil regime. Low root numbers at depth and low hydraulic conductivity in the subsoil limited the water uptake. Linear relationship between wheat root water potentials and soil water potentials for different soil depths showed a similar permeability of old and new roots at around - 0.025 MPa. Interlayer impedance to capillary rise of ground water below 0.75 m depth helped to contribute a larger volume of deep drainage in spite of presence of shallow water table. I₁ regime produced 6.6 and 11.5 per cent more crop water use and 17.5 and 27.5 per cent more water uptake than I₂ and I₃ regimes, respectively. Yields under three water regimes were 3.11, 2.71 and 2.45 Mg ha⁻¹ and the values of water use efficiency were 12.95, 12.09 and 11.53 Mg ha⁻¹ m⁻¹, respectively. Water recovery of wheat in terms of total water uptake and profile moisture change was 93.1 per cent under wetter regime as compared to 80.6 per cent under drier soil water regime.