Irrigation interval as a factor in the salt tolerance of eggplant

Summary

The effect of irrigation interval on the relationship between yield and the salt concentration of irrigation water salinity was studied on eggplant (Solanum melongena L.) in 5 × 6 m plots irrigated by a trickle irrigation system. Three levels of irrigation water salinity, having electrical conductivities of 1.5, 4.5 and 10.0 dS · m⁻¹, and five irrigation intervals (2, 5, 8, 12 and 16 days) were applied.

A regression of yield (Y), expressed in units of kg · m⁻², on soil salinity, expressed in dS · m⁻¹ as the saturation extract electrical conductivity (EC _e ) averaged for the 0–0.9 m depth at the end of the experiment was: Y _2–12= 20.8–1.28 (EC _e ); r=0.94 for irrigation intervals of 2 to 12 days. For the 16 day irrigation interval the regression equation was Y ₁₆=17.3-1.13 (EC _e ); r=0.82. Up to 12 days the length of the irrigation intervals had no interactive effect on the relationship between yield and salinity. For the 16 day irrigation interval, relative yield reduction was similar (about 17%) at all levels of salinity. A 50% reduction in yield was obtained at EC _e =8.5 dS · m⁻¹ for both the short and long intervals. Increasing the irrigation frequency from that used under nonsaline conditions did not change the relationship of relative eggplant yield to salinity.

With increasing salinity and increasing irrigation interval, individual fruit weight decreased but the percentage of marketable fruit increased to the extent that the quantity of marketable fruit was not affected by either factor (Table 2). Stomatal diffusion conductance was not affected by either salinity or interval, and was about 0.3 cm s⁻¹. Leaf water potential, on the other hand, decreased with the decrease in soil water potential, due to increase in either soil water suction or solute concentration. The reduction in leaf water potential correlated with yield reduction. CO₂ fixation rate per unit leaf area increased by 35–45% as salinity increased, but decreased by 54–58% as the irrigation interval increased (Table 6).