Response of wheat to subsoil salinity and temporary water stress at different stages of the reproductive phase

To examine the effects of subsoil NaCl salinity in relation to water stress imposed at different growth stages, wheat was grown in a heavy texture clay soil (vertosol) under glasshouse conditions in polythene lined cylindrical PVC pots (100 cm long with 10.5 cm diameter) with very low salinity level (EC(e) 1.0 dS/m; ESP 1.0 and Cl 30 mg/kg soil) in top 10 cm soil (10-20 cm pot zone) and low salinity level (EC(e) 2.5 dS/m, ESP 5, and Cl 100 mg/kg soil) in top 10-20 cm soil (20-30 cm pot zone). The plants were exposed to three subsoil salinity levels in the 20-90 cm subsoil (30-100 cm pot zone) namely low salinity (EC(e): 2.5 dS/m, ESP: 5, Cl: 100 mg/kg soil), medium salinity (EC(e): 4.0 dS/m, ESP: 10, Cl: 400 mg/kg) and high salinity (EC(e): 11.5 dS/m, ESP: 20, Cl: 1950 mg/kg) in the subsoil (20-90 cm soil layer: 30-100 cm pot zone). Watering of plants was withheld for 20 days commencing at either early booting or anthesis or mid grain filling, and then resumed until maturity, and these treatments were compared with no water stress. Water stress commencing at anthesis stage had the most depressing effect on grain yield and water use efficiency of wheat followed by water stress at grain filling stage and early booting stage. High subsoil salinity reduced grain yield by 39.1, 24.3%, and 13.4% respectively in plants water-stressed around anthesis, early booting, and mid grain filling compared with 36.6% in well-watered plants. There was a significant reduction in root biomass, rooting depth, water uptake and water use efficiency of wheat with increasing subsoil salinity irrespective of water regimes. Plants at high subsoil salinity had 64% of their root biomass in the top 0-30 cm soil and there was a marked reduction in subsoil water uptake. Roots also penetrated below the non-saline surface into salinised subsoil and led to attain high concentration of Na and Cl and reduced Ca/Na and K/Na ratio of flag leaf at anthesis stage. Results suggest that high subsoil salinity affects root growth and water uptake, grain yield and water use efficiency even in well water plants. Water stress at anthesis stage had the most depressing effect on wheat.