Soil Related Differences in Plant Vigor and Evapotranspiration in Two Merlot Vineyards of the Sacramento-San Joaquin Delta, California.

Vines planted on contrasting soil types within a single vineyard exhibit different growth habits and vigor. Soil properties can modulate water supply despite irrigation, leading to variation in plant water stress. The goals of this study were to evaluate differences in evapotranspiration (ET) of grapevines planted on two contrasting soils using surface renewal methods, and to evaluate site-specific corrective measures. Two Merlot vineyards were studied in the Sacramento-San Joaquin delta. Vineyard 1 contained soils with contrasting morphology. Soil 1.1, with silty loam textures, induced high vine vigor, low grape yield and delayed ripeness. Soil 1.2 had compact clayey subsoil supporting less vigorous growth, lower plant water potential but higher yields and earlier ripening. Vines were 3 years old, had VSP trellising with machine pre-pruning after harvest, and final cordon pruning in March. Vineyard 2 was a 10-year old Merlot vineyard on a nearly level terrace, containing two soils with strong textural differences. Soil 2.1 had loamy topsoil over very clayey, compact subsoil with minimal gravel. Vines were vigorous, plant water potential values were lower and harvest weights were higher than those recorded on Soil 2.2.  Soil 2.2 had sandy loam topsoil over sandy subsoil and contained 35 to 85% gravel and cobbles. Plants displayed lower vigor and had lower yields than those on soil 2.1. Plants had a VSP training system, and were cordon pruned in early January. Measured ET of vines on the four sites showed marked differences, reflecting the contrasting soil properties.