importance of sap flow measurements to estimate actual water use of meski olive trees under different irrigation regimes in tunisia

• Published in: Irrigation and drainage Vol. 61; no. 5; pp. 645 - 656
• Main Authors: Vandegehuchte, Maurits W, Mohamed Braham, Raoul Lemeur, Kathy Steppe
• Format: Journal Article
• Language: English
• Published: John Wiley & Sons, Ltd 01.12.2012; Blackwell Publishing Ltd
• Subjects: Dissipation; Drainage; evapotranspiration; Flux; flux de sève; Flux density; Irrigation; irrigation scheduling; Olea; Olea europaea; Olea europaea L. (olive) tree; Olea europaea L. (olivier); Olives; orchards; Penman-Monteith; profil radial; radial profile; sap flow; sonde de dissipation thermique (TDP); surface area; temperature profiles; thermal dissipation probe (TDP); Trees; Water consumption; water stress; Tunisia
• ISSN: 1531-0353; 1531-0361
• DOI: 10.1002/ird.1670

Improvement in irrigation techniques has led to an expansion of the irrigated olive area in Tunisia and consequently a rise in agricultural water consumption. Here, the actual water use of Olea europaea L. ‘Meski’ as estimated by thermal dissipation probe measurements was compared for different irrigation regimes: three plots with irrigation doses based on Penman–Monteith crop evapotranspiration (ETc), 0.33 × ETc and the local grower's experience (about 0.6 × ETc), respectively. The scaling up of sap flux densities proved to be difficult given the azimuthal and radial sap flux density variability and the conductive surface area asymmetry. Moreover, natural thermal gradients may lead to inaccurate use of standard sap flow formulas. Depending on the manner of upscaling, differences in water use of more than 50 l day‐¹ per tree were obtained (up to 0.7 × ETc irrigation dose). Despite these difficulties, sap flow calculations seem crucial to accurately determine the water needs of the orchard under investigation, as they corresponded closely to the lowest irrigation dose which was considered sufficiently high as no significant differences in drought stress variables were detected between the plots. Therefore, irrigation based solely on ETc leads to wasting of water; hence, careful application of both meteorological and sap flow methods is desirable in irrigation scheduling.