Measurement and modelling of the transpiration of a Mediterranean vineyard

This paper presents the results on the spatio-temporal variation in vine transpiration at the scale of a vineyard and derives a simple model relating daily vine transpiration to soil water storage. An experiment was conducted during summers of 1994 and 1995 in a 1 ha vineyard of Southern France in which five monitoring plots had been installed. In each plot, soil moisture was monitored with neutron probes down to 260 cm under the row and between the rows to take into account the heterogeneity of the rooting system. Transpiration was monitored by the stem heat balance method on two vinestocks per plot. The soil water retention characteristics were measured on undisturbed samples with a pressure plate extractor. With decreasing soil water availability, vines react similarly to most crops: in a first stage up to mid-July transpiration remains at a maximum and in a second stage transpiration is reduced due to soil water depletion. Although there is a large variation in the transpiration intensity between vinestocks, the temporal variation of transpiration is predominantly similar over the vineyard. This justifies a uniform modelling approach to simulating vineyard transpiration. Accordingly, we derived a bilinear relationship relating the ratio between the actual transpiration and the potential transpiration of the vineyard to the field average soil water storage. The parameters of the relationship could be related to laboratory determined values of soil moisture content at −0.1 and −1.5 MPa.