EVALUATING THE COMPARATIVE THERMAL SENSITIVITY OF MORPHOLOGICAL PARAMETERS IN CUCUMBER (Cucumis sativus l.) UNDER GRADED NITROGEN AND PHOSPHORUS STRESS

Abstract

Thermal infrared (TIR) imaging is a proven non-invasive technique for detecting abiotic stress in crops through canopy temperature variations; however, limited quantitative evidence exists on which morphological parameter exhibits the strongest thermal response. This study addressed this gap by evaluating four traits: leaf area, plant height, stem diameter, and number of leaves, in greenhouse-grown cucumber under graded nitrogen-phosphorus (N-P) stress over 44 days. A Randomized Complete Block Design (RCBD) with four blocks (A, B, C, D) and four treatments was used: T1 (120N/40P mg/kg), T2 (80N/30P), T3 (40N/20P), and T4 (0N/10P), with 12 replicates per treatment. Canopy temperature was measured using a calibrated UTi120s/FLIR thermal camera and processed in MATLAB, alongside periodic morphological measurements. Results showed that leaf area had the highest thermal sensitivity (F = 24.68, p < 0.001, R² = 0.5025), followed by stem diameter (F = 21.76, R² = 0.5890), number of leaves (F = 18.54, R² = 0.6697), and plant height (F = 15.82, R² = 0.6784). Maximum canopy temperature differences reached 7.1°C between T4 and T1. Tukey HSD analysis revealed that leaf area and stem diameter achieved significant discrimination in 5 of 6 treatment comparisons, including adjacent stress levels. These results establish leaf area as the primary determinant of thermal response, supporting its prioritization in precision nutrient monitoring systems.