Identification and significance of sources of spatial variation in grapevine water status

Background and Aims:  Water stress in grapevines is directly linked to grape quality. Differential vine water management should therefore be strongly linked to the water stress in the vine. To do this, an understanding of the dominant drivers and indicators of vine water status are needed from a sub‐block to whole vineyard level. This understanding will help generate effective vine water status models for variable rate irrigation systems. Methods and Results:  A vineyard in the south of France was sampled for pre‐dawn leaf water potential (Ψ PD ) at several dates during the growing season for two consecutive years. Sampling was stratified by soil types and relative within‐block vegetative expression. A recursive partitioning analysis identified that cultivar had a dominant effect at low water stress, while vegetative expression and then soil unit effects became dominant as water restriction increased. Variance in Ψ PD was calculated at difference scales (plant, site, block and vineyard) and Smith's heterogeneity law was used to evaluate the scalar nature of Ψ PD variance. Spatial heterogeneity increased as the season and water restriction increased. Conclusion:  Variance in Ψ PD changed temporally through a season and the dominant drivers/indicators also changed. The opportunity to spatially manage water stress (irrigation) increased as water restriction increased. Significance of the Study:  Managing vine water stress helps optimise production and a Ψ PD model would be a useful addition to a viticulture decision support system. This study identified how the variance in Ψ PD evolved during a season and the best ancillary indicators of Ψ PD for spatial and temporal modelling.