Growth and yield responses of sunflower to drainage in waterlogged saline soil are caused by changes in plant-water relations and ion concentrations in leaves

Abstract Purpose While proper drainage systems could improve crop growth and yield by mitigating waterlogging and salinity stresses, field evidence of the responses in plant-water relations and ion concentrations in leaves is scarce. We investigated the changes in solute potential in soil (Ys), plant-water relations and ion concentrations in leaves of sunflower caused by drainage in waterlogged saline soil, and their impacts on growth and yield. Methods Over two growing seasons, we tested four drainage treatments: undrained, surface drains (SD; 0.1 m deep, 1.8 m apart), subsoil drains (SSD; 0.5 m deep, 4.5 m apart) and SSD+SD. All plots were inundated (2–3 cm depth; ECw 1.5–2.5 dS m–1) for 24 h at vegetative emergence and at 8-leaf stage before opening drains. Results Relative to the most drained treatment (SSD+SD), the undrained treatment caused higher waterlogging at 0–30 cm depth, and decreased Ys of soil at 7.5 cm to 52–374 kPa, leaf K+ by 5–20%, stomatal conductance by 5–37% and leaf greenness by 12–25%, but increased leaf Na+ by 25–70%, Na+/K+ ratio by 38–100% and leaf water potential by 90–250 kPa throughout the cropping season; these changes were closely related with reduced growth and yield. Conclusions The improved yield from the combination of shallow surface and sub-surface drains was attributed to an alleviation of salinity-waterlogging stress early in the season and to increased soil water late in the season that increased Ys and decreased Na+/K+ ratio in leaves.