Shallow Drains and Straw Mulch Alleviate Multiple Constraints to Increase Sunflower Yield on a Clay-Textured Saline Soil Ii. Effects of Favourable Plant-Soil-Water Relations and Lower Na /K Ratio in Leaves

Abstract

Waterlogging under saline conditions restricts plant growth and yield. While shallow drainage can alleviate these stresses, field evidence of the physiological responses of plants and their relationships to growth and yield is scarce. Three field experiments were conducted over two seasons to investigate the effects of drainage and mulch on the plant-soil-water relations and ion relations of sunflower in a waterlogged saline clay-textured soil. Details are described in Part 1 (Islam et al. 2023). Relative to the undrained treatment, drainage treatments reduced the duration of hypoxia by 2–3 days, decreased Na+ and Na+/K+ in leaves by 11–24% and 26–36%, respectively, but increased solute potential (Ys) in soil by 17–276 kPa, K+ in leaves by 9–25%, stomatal conductance by 8–36%, and leaf chlorophyll content by 13–15%. Drainage treatments decreased leaf water potential (Yleaf) by 110–140 kPa throughout the season, which was associated with a larger leaf area. In addition, late in the season once the soil water content had fallen below 20% (w/w), mulch increased Yleaf by 60–70 kPa compared to non-mulch. All such changes were associated with increased growth and yield, but decrease in the Na+/K+ in leaves showed the strongest correlation. A combined subsoil plus surface drainage treatment (SSD+SD) was more efficient than other drainage treatments in bringing about such physiological changes and improving growth and yield. Increased yield of sunflower due to surface drains and to mulch on saline clay soil were attributed to the combination of improved plant-soil-water relations and to reduced Na+/K+ in leaves.

Keywords: Cultivar Hysun-33, Hypoxia, Leaf water potential, Na+ and K+ in leaves, Relative growth rate, Solute potential of soil