Sap flow of several olive trees estimated with the heat-pulse technique by continuous monitoring of a single gauge

Abstract

The use of the compensation heat-pulse velocity (CHPV) technique to estimate sap flow in olive trees as a means of irrigation scheduling can be a difficult task because of the naturally heterogeneity of hydraulic functioning of sapwood area in this species. As a result, the monitoring of an unreasonably large number of both trees and CHPV gauges per tree is needed for accurate estimation of orchard transpiration. The approach used in this paper restricts the monitoring of a large number of both trees and gauges to a very short time (a day) and allows the long term estimation of transpiration of several olive trees by the continuous monitoring of a sole CHPV gauge installed in a single tree. In an experimental olive orchard in southern Italy, we monitored six CHPV gauges in three well irrigated trees (treatment T100) and six CHPV gauges in three rain-fed trees (treatment T0) at half hour intervals for 60 days during summer 1999. For each ith gauge at each day, we linearly regressed the sap flow ( Q i , l h −1) against the mean sap flow of the all other n−1 gauges of the same treatment (Qm i ). The regression parameters were used to obtain an estimation of Qm i (EQm i ) throughout the trial using the data of any single ith gauge. In order to test the prediction power of the model of ith gauge, the estimated mean sap flow (EQm i ) values were regressed day by day against the actually measured Qm i . The same procedure was also applied at the time scale of a day, that is to the daily cumulative value of Q i and Qm i . In all cases, we obtained high statistical significance of the models applied to data as confirmed by the high adjusted R 2 estimates. Our analyses show the feasibility of estimating the transpiration rate of many trees by monitoring sap flow in a single tree by the use of a sole CHPV gauge. The results of this work indicate that CHPV can be a useful and powerful method for irrigation scheduling for olive and other tree species.