Advances in Leaf and Canopy Temperature Sensors for Precision Irrigation: A Review

Precision technologies are crucial for sustainable water management, as water scarcity and ineffective irrigation techniques continue to pose significant challenges in agriculture. One of the bases of plant-based irrigation scheduling is plant canopy temperature, which has become a reliable indicator of crop water status. The primary sensor technologies used to measure the temperature of leaves and canopies are discussed in this review, including integrated circuit sensors, thermistors, thermocouples, infrared thermometers, and infrared thermal imaging systems. Thermistors and thermocouples provide precise and affordable point-based measurements, but their scalability and installation are limited. For real-time canopy monitoring, infrared thermometers and thermal imaging provide non-contact options. Despite their higher price, thermal cameras enable the analysis of spatial variability. Low-cost irrigation system automation is made feasible by integrated circuit (IC) sensors, like the LM35, which combine accuracy and affordability. Research confirms that under deficit irrigation strategies, canopy temperature-based indices, notably the Crop Water Stress Index (CWSI), improve water use efficiency and enhance yield responses. However, sensor calibration, environmental variability, and the balance between accuracy and cost continue to be ongoing challenges.