Effect of Irrigation Amount and Preharvest Irrigation Cutoff Date on Vine Water Status and Productivity of Danlas Grapevines

Abstract

An irrigation study was conducted in a Vitis vinifera L. (cv. Danlas) table-grape vineyard in Morocco with vines receiving no applied water (NI treatment) or one of two applied water amounts with subplots composed of three irrigation cutoff dates: early cutoff (EC) at berry set, late cutoff (LC) at veraison, and no cutoff (traditional irrigation, TI; based on grower practice). Midday leaf water potential (Ψ_l), canopy temperature (T_C), and soil water content were measured in several of the treatments. Midday Ψ_l was significantly correlated with soil water content (r = 0.89), ambient temperature (r = −0.71), and vapor pressure deficit (r = −0.62). The highest yield and berry weights were measured in TI vines followed by LC vines. NI vines had the lowest soluble solids at harvest. No significant differences were observed for fruit pH and titratable acidity among treatments. A comparison of NI and TI treatments indicated that yields increased as T_C - T_A (ambient temperature) and Ψ_l increased. Under the conditions of this study, an average T_C - T_A of −2.5°C or a Ψ_l of −1.0 MPa would be sufficient to maintain yield and fruit quality, while a Ψ_l value of −1.2 MPa would indicate water stress. Estimated vineyard evapotranspiration was much greater than the amount of water normally applied to vines in this region, and values of Ψ_l and temperature differentials indicated such. However, since grapes produced in this region are destined for the early table-grape market, results indicate that vines could be deficit irrigated or water applications could be terminated at veraison without a significant yield loss.