Stomatal Conductance and Leaf Temperature Responses of Cucumber (Cucumis sativus L.) to Deficit Drip Irrigation Under Tropical Conditions

Abstract

Water scarcity threatens sustainable vegetable production in tropical regions, which necessitates water-efficient irrigation strategies. This study evaluated physiological responses of cucumber (Cucumis sativus L.) to deficit drip irrigation under tropical field conditions in Ogbomoso, Nigeria. A split-plot randomized complete block design tested three irrigation depths (100%, 85%, and 70% of crop evapotranspiration) as main plots and three irrigation intervals (1, 2, and 3 days) as subplots. Stomatal conductance and leaf temperature were measured weekly from 4 to 8 weeks after planting across vegetative and reproductive stages. Irrigation depth significantly affected both physiological parameters at critical growth stages (p < 0.05), while irrigation interval showed no significant effects. At 5 weeks after planting, deficit irrigation reduced stomatal conductance by 21.6-26.8% compared to full irrigation, indicating water stress during early reproduction. Unexpectedly, moderate deficit irrigation (85% crop evapotranspiration) exhibited 0.9-1.3°C lower leaf temperatures than full irrigation at multiple growth stages, suggesting enhanced thermoregulatory capacity through optimized stomatal regulation. By 6 weeks, moderate deficit showed the highest stomatal conductance among treatments, indicating adaptive physiological responses. Late-stage convergence of physiological parameters demonstrated successful acclimation to water deficit. Results support moderate deficit irrigation (85% crop evapotranspiration) as a viable water-saving strategy for tropical cucumber production, potentially reducing irrigation requirements by 15% while maintaining favourable physiological status. Irrigation scheduling flexibility (1-3day intervals) offers practical advantages for resource-constrained farmers without compromising plant function.