SAP FLOW TRANSPIRATION MEASUREMENTS IN A TABLE GRAPE VINEYARD GROWING IN SOUTHERN ITALY

Abstract

Optimising crop irrigation management is a general concern in semi-arid climates. Actual crop water use in the field has to be determined as a function of microclimate and of soil water availability. The work described here studies stomatal conductance, transpiration and evapotranspiration of an irrigated vineyard to elucidate their relations with microclimate at decreasing soil moisture availability and to assess their usefulness in determining plant water consumption in the field. The experiment was carried out in a vineyard, trained by the overhead system (“Tendone”), in Southern Italy, in July 1998 for six days in the interval between two irrigations. Stem heat balance gauges were installed on six plants and transpiration flow of one shoot per plant was measured; daily course of stomatal conductance was determined by porometry, and actual evapotranspiration was measured by the Bowen Ratio technique. Results can be summarised as follows: i) at decreasing soil water availability stomatal conductance and transpiration rate decreased and modified their daily pattern, shifting their peaks from noon to mid-morning; ii) sap flow transpiration rates per unit leaf area showed considerable variability among shoots; iii) the daily transpiration course measured by sap flow was in good agreement with actual evapotranspiration measured by the Bowen Ratio method.