Soil water variability and its influence on transpirable soil water fraction with two grape varieties under different rainfall regimes

This research aims to analyse soil water variability and its influence on the amount of soil water available to rainfed vines under different rainfall patterns. Frequency domain reflectometry (FDR) sensors were used to measure soil volumetric water content on two plots planted with Chardonnay (CH) and Cabernet Sauvignon (CS) during two vegetative cycles. The Soil Water Assessment Tool (SWAT) model was used to simulate soil water during the period 2000–2012. The representativeness of the years analysed was then evaluated using multivariate techniques. The results obtained confirmed the high variability in soil water observed from year to year as a result of the rainfall and soil characteristics. The fraction of transpirable soil water (FTSW) reached almost 0.1 at the end of the growing season, but depended on the climatic and soil characteristics. Its effect on vines depended on variety, with early ripening varieties suffering most. The lack of water forced an advance in the harvest date and produced a significant decrease in yield. Although water deficits during the grape growing season are frequent, in the last decade, the most commonly observed pattern has been one of major water deficits recorded in the bloom-veraison and veraison-harvest periods. This has had a significant effect on yield, with reductions of up to 38% in the last year with respect to the 15-year average.