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

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PurposeWhile well-designed drainage systems could improve crop growth and yield by mitigating waterlogging and salinity stresses, field evidence of the yield responses to changes in plant-water relations and ion concentrations in leaves is scarce. We investigated the changes in ion concentrations in leaves and plant-water relations of sunflower caused by drainage in waterlogged saline soil, and their relationships to growth and yield.MethodsOver 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; water salinity, ECw, 1.5–2.5 dS m–1) for 24 h at vegetative emergence and at the 8-leaf stage before opening drains.ResultsRelative to the most drained treatment (SSD + SD), the undrained treatment caused higher waterlogging at 0–30 cm depth, and decreased solute potential (Ψs) 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 to reduced growth and yield.ConclusionsThe 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 Ψs and decreased Na+/K+ ratio in leaves.