The effect of three vineyard cover types on the microclimate, plant water relations and vineyard evapotranspiration (ET) of an overhead table grape vineyard (cv. "Italia") is characterised in this study. Two covering techniques, thin net (V2) and thin plastic film (V3) were compared with an uncovered vineyard (VI). The trial was carried out in southern Italy. Global (Rg(g)), net (R-n) and photosynthetically active radiations (PAR) were attenuated by the covers. R-g was reduced 8% by the thin net and 14% by the plastic film; PAR was reduced 17% by the thin net and 32% by the plastic. R-n was reduced 20% by the thin net and 25% by the plastic film. The air temperature at the height of the grape clusters was 1 degreesC higher (average diurnal value) in the uncovered vineyard than in the covered ones. Air humidity was 20% lower for the uncovered vineyard. In the uncovered vineyard, predawn leaf water potential (Psi(b)) decreased more rapidly following irrigation than in the other two systems and reached a minimum in a few days. On the day following irrigation uncovered vineyards had higher diurnal stomatal conductance (C-s values than the other two systems. However, at 7 days after irrigation the uncovered vines had lower C-s values than the other treatments. In the uncovered vineyard actual evapotranspiration was high (6.4 turn per day) after irrigation, then it decreased rapidly until reaching its minimum value (about 4 mm per day) after 9 days. In the vineyard covered by plastic, ET was lower (3 mm per day) after irrigation and its decrease was very slow, taking. 24 days to reach its minimum value (1.9 mm, per day). The ET of the vineyard covered by the thin net was intermediate between the other two systems. From these results, it was possible to demonstrate a close relationship between the crop coefficient and the predawn leaf water potential, well-differentiated in the three treatments. Suggestions for the correct management of irrigation water were also proposed and are based on the calculation of the crop coefficient. (C) 2004 Elsevier B.V. All rights reserved.
