Dry matter production and physiological responses to a wide range of irrigation levels in two Japanese soybean cultivars

Abstract

Two pot experiments were conducted to compare dry matter production and physiological responses to a wide range of irrigation levels (100% of field capacity (control: iC), 80% (i8), 60% (i6), 40% (i4), and 20% (i2) of irrigation for iC) from the beginning of the bloom stage to the full seed stage of two Japanese determinate soybean cultivars, Hatsusayaka and Sachiyutaka. The phenological stages of both cultivars were delayed correspondingly with the reduction in irrigation levels. Seed yield and total dry matter (TDM) decreased correspondingly with the reduction in irrigation, with some exceptions in which maximum results were achieved with i8 rather than iC for some traits, though the differences between i8 and iC were not significant. The proportional decrease in TDM in line with irrigation levels was due to the decrease in photosynthesis rate (Pn), and the decrease in Pn was closely related to the decrease in stomatal conductance. The response of grain yield to irrigation levels was approximated by a linear-plateau model, which indicated that these traits increased proportionally with the amount of irrigation up to a certain level, and after that, it reached a threshold. Our results showed that Hatsusayaka had higher leaf water potential and TDM than Sachiyutaka in some irrigation levels, but no evidence was found which indicates a significant difference on drought tolerance between Hatsusayaka and Sachiyutaka.