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Wine grapes are grown in arid and semi-arid regions of Argentina which have warm climate conditions with high summer temperatures and low rainfall, forcing to use irrigation water which competes with some increasing demand usages. Additionally, the agro-ecological conditions of these regions (soil and climate) define a major vegetative expression of the vineyards. Such features, together with the trellis systems commonly used and a higher leaf area exposed to light, generate water requirement conditions greater than those cited by other authors.

This work was undertaken to determine the water requirement in a vertical shoot position (VSP) trellis system vineyard grown in warm climate conditions, in order to obtain the crop coefficients (Kc). The experiment was conducted between 2003 and 2008 in a vineyard ('Syrah') located at the Instituto Nacional de Tecnologia Agropecuaria (INTA) Experimental Station, San Juan, Argentina. Crop evapotranspiration (ETc) was estimated using the water balance equation. Deep percolation was quantified with three drainage volumetric lysimeters. Reference evapotranspiration (ETo) was estimated with a Type A evaporation pan method. The mean crop cycle water requirement during the 5 year evaluation was of 1297.2 mm. year(-1). The water consumption was 9.5 mm.day(-1) during the month of maximum demand. This value was higher than those mentioned in other world wine grape growing areas. The water consumption was 9.6% of the total amount from budding to flowering; 34.7%, from flowering to ripening, 40.5% from ripening to harvest and 15.2% from harvest to leaf fall. The initial Kc value was 0.40 and then increased until January when it reached its maximum amount (Kc=1.11). It may be inferred then that the crop reached its highest foliar area. Kc diminished in the subsequent months although they remained nearly 1.00.

Taken together, our results suggest that published Kc values underestimate the vineyard water required under local agro-ecological conditions.