Measurement Accuracy of Pakcoy (Brassica rapa L.) Leaf Area Using Digital Image Processing in a Vertical Hydroponic System with Root Zone Cooling

Abstract

Leaf area is an important indicator in assessing plant growth because it directly affects photosynthetic efficiency and nutrient absorption. Manual measurement methods are considered inefficient, so the use of digital image processing technology is a fast and accurate alternative solution. This study aims to: (1) assess the effect of cold temperatures on the root zone on pakcoy plant growth, (2) analyze the accuracy of digital image processing in measuring leaf area using Easy Leaf Area and ImageJ, and (3) analyze the relationship between leaf area and plant growth. The study was conducted over 30 days using two temperature treatments (cold and control) in a vertical hydroponic system with 48 plants. The observed parameters included environmental parameters (water temperature in the cold temperature treatment, environmental temperature and humidity, light intensity, and nutrient solution concentration) and growth parameters (plant height, number of leaves, root length, and leaf area using Easy Leaf Area and ImageJ). The results showed that the water temperature in the cold treatment was 22°C–24°C, environmental temperature and humidity were 29.47–32.28°C; 72.9–84.3%, light intensity was 2420–3904 lux, and nutrient solution concentration was 926–1338 ppm; for plant height growth of 25.96 cm in the cold treatment, 21.10 cm in the control, number of leaves 15 in the cold treatment, 14 in the control, root length 18–22 cm in the cold treatment, 8–19 cm in the control, and leaf area using Easy Leaf Area 206.87–714.35 cm², ImageJ 288.42–773.23 cm². Cold temperatures significantly affect pakcoy growth parameters, particularly leaf area. The Mean Absolute Percentage Error (MAPE) value of 13.11% indicates high accuracy (10% ≤). Thus, digital image processing has proven to be accurate and can be applied for real-time monitoring of plant growth in vertical hydroponic systems.