Correlation Analysis of Transpiration Rate in Eggplant Canopy: Effects of Solar Radiation and Vapor Pressure Deficit

In greenhouse horticulture, the canopy transpiration rate (Tr) is a dominant factor in water balance and irrigation requirements. This study investigated the relationship between Tr, solar radiation (I), and vapor pressure deficit in air (D) in an eggplant canopy. Tr was measured using open chamber systems for two varieties, ‘Tosataka’ and ‘PC-Oryou’. Simple correlation analysis revealed a strong correlation between Tr and both I and D, with mean correlation coefficients (R) across the two varieties of 0.88 for I and 0.95 for D. However, partial correlation coefficients (Rp) indicated that D had a much stronger direct influence on Tr than I, with mean Rp of 0.84 for D and 0.47 for I. These results suggest that the apparent correlation between Tr and I may be indirectly driven by D. Differences in the relationships between Tr and these variables across the two varieties are likely explained by variations in the leaf area index (LAI). We propose that short-term irrigation management in greenhouse horticulture should consider not only I but also D for greater precision. Additionally, the longterm effects of LAI on Tr should be considered to further optimize irrigation strategies and promote more sustainable water management in greenhouse cultivation.