Suitable radial heat conductance value for study of transpiration rate of mango seedlings by heat balance technique.
Srichan K., Sangkhasila K.
Author Affiliation: Department of Soil Science, Faculty of Agriculture, Kasetsart University, Thailand.
: 105-117
Abstract : Heat balance technique was used to measure sap flow rate parameters of two 3-month-old mango seedlings, grown under field conditions with 3 different patterns of evaporative demand for the first seedling, and high evaporative demand conditions for the second seedling. The daily initial water content of the growing medium for each seedling was highest on the first day of measurement, then declined. Rates of transpiration for each seedling were collected every 3 h period. The computed sap flow rates followed evaporative demand patterns only during the lower demand periods. Values for the daily sap flow rate for the first seedling were respectively 5, 22 and 0% higher than the daily actual transpiration rates for the first, second and third day of measurement. Values of daily sap flow rate for the second seedling were 7% lower for the first 2 days, and 10% lower than transpiration rate for the third day of measurement. The sap flow rates for a certain period during each day for both seedlings were sometimes higher and sometimes lower than actual transpiration rates. If sap flow rates were computed from varying values of Ksh (value of radial heat conductance), using ±10% of Ksh, then the use of lower Ksh value gave the sap flow rates to be higher than transpiration rates for the whole period of measurement, while the use of higher Ksh value gave sap flow rates to be lower than the actual rates of transpiration. Results were consistent for both seedlings.