Water productivity in Vitis vinifera L. cv. Alvarinho using dual crop coefficient approach

Water productivity (WP) measurement determines the efficiency of water use by assessing the ratio of the crop yield to the amount of water used in production. The objective of this study was to identify the optimal irrigation treatment for Vitis vinifera L. cv. Alvarinho with ground cover in Northern Portugal, with a focus on water productivity. Two irrigation treatments (full irrigation—FI; deficit irrigation—DI) and a control (rainfed—R) were considered. The FI strategy represented the standard irrigation carried out by the vinegrower, based on the water availability and their experience. The cover crop was a variable factor, evaluated in terms of both height and density, both within the crop row and between the rows. In each of the treatments, the available soil water content (ASW) was measured in eight locations in the field throughout the growing season using a capacitive probe (Diviner 2000) previously calibrated. These measurements were used to calibrate the SIMDualKc model, which employed the dual crop coefficient approach. The successful calibration of the model, carried out with treatment R in 2018, was evidenced by the strong correlation between the ASW measured through the capacitive probe and that simulated by SIMDualKc (b=0.988 and r2=0.995). After the model’s calibration, the separation between the transpiration and evaporation components was determined. The maximum transpiration during the growing season was observed in the full irrigation treatment. In this context, the study proceeded to apply the soil water balance components and transpiration generated by the model in the calculation of the WP. The fruit yield productivity was determined by accounting for the total water use in the growing season. The total water used was calculated by combining the volumes of water applied for irrigation and precipitation and the soil water extracted during the growing season by crops and cover crops. The deficit irrigation strategy showed the best performance in both years, with WP values of 3.31 and 1.81 kg m−3 for the years 2018 and 2019, respectively. Therefore, the study concluded that deficit irrigation proved to be the most effective irrigation strategy in terms of water productivity and crop water use efficiency (WUEc).