Evaluation of Transpiration Rate Based on the Heat Pulse Method in Sugarcane Field in Tanegashima Island in Kagoshima Prefecture

Abstract

Crop transpiration rate is crucial for managing regional water resources and water productivity. In this study, we assessed crop water requirement, transpiration rate, and potential evapotranspiration rate using soil moisture data, sap flow data, and meteorological data, respectively, in a sugarcane field on Tanegashima Island, Japan. The transpiration rate measured using the heat pulse method (with a value of 1.3) was validated as correct by comparison with values obtained using the weighing and potometer methods. The maximum sap flow rate was calculated to be 548 cm³/d; in addition, the maximum transpiration rate was 6.7 mm/d. On the other hand, maximum soil moisture reduction rate was 4.3 mm/d for estimating crop water requirements. It was inferred that the decrease in soil moisture due to transpiration can be accounted for both by capillary supply a soil layer deeper than 50 cm and by water uptake from roots deeper than 50 cm depth. In addition, there was a high correlation between standard crop evapotranspiration and sugarcane transpiration, indicating a linear functional relationship.