Physiological and Productive Responses of Sugarcane to Irrigation Management and Foliar Photoprotection

Calcium carbonate-based photoprotection has been proposed to mitigate thermal and water stress by reducing leaf temperature, but its interaction with irrigation management in sugarcane remains poorly understood. This study evaluated irrigation and photoprotection effects on yield, technological quality, water productivity, leaf gas exchange, and leaf thermal status. The experiment was conducted in Piracicaba, Brazil, in a randomized block design (2 × 3 factorial, four replications), combining two irrigation regimes (full and deficit) with three photoprotection treatments (no product, manufacturer’s recommendation, and concentrated product). Full irrigation increased stalk yield (+98.13%), recoverable sugar (+5.4%), water productivity for stalks (+126.76%) and sugar (+138.37%) compared with deficit irrigation. These gains were accompanied by higher net photosynthesis, stomatal conductance, and transpiration, and by lower leaf temperature and crop water stress index (CWSI), suggesting that improved stomatal regulation and plant water status may have contributed to the yield gains. Photoprotection altered gas exchange and thermal indicators but did not improve yield or technological quality, possibly due to limited product persistence and canopy renewal after application. Principal component analysis connected irrigation, rather than photoprotection, with the main pattern of variation in physiological, thermal, and agronomic responses (86.6% of total variability).