Effects of Soil Texture on the Rooting Patterns of Thompson Seedless Vines on Own Roots and on Ramsey Rootstock in Irrigated Vineyards

Abstract

The influence of soil texture on the rooting patterns of Thompson Seedless (syn. Sultana) grapevines (Vitis vinifera) on own roots or on Ramsey rootstock (Vitis champim) was studied in irrigated vineyards. Root samples were collected using an auger at 30-, 90-, and 120-cm positions from vine trunks and perpendicular to the vine row. At each position, roots were collected at 20-cm depth intervals down the soil profile and the total length of roots measured in each sample. The root length data was used to calculate the root density (mm/cm³) in each 20-cm depth interval of the soil profile. The soil in the root zone was characterized by measuring the silt + clay content and bulk density. The soil texture in sampled vineyards was either coarse, moderately coarse, or fine. Rooting depths were 220 cm in coarse soil, 100 to 120 cm in moderately coarse soil, and 60 to 120 cm in fine soil. In coarse soil, roots were well spread throughout the soil profile, whereas roots were concentrated in the top 40 to 60 cm in both moderately coarse and fine soil. Maximum root densities measured were 0.4 mm/cm³ in coarse soil, 0.8 to 1 mm/cm³ in moderately coarse soil, and 0.7 to 1.7 mm/cm³ in fine soil. The lateral spread of roots in the traffic row was not dependent on soil texture. Further, in most vineyards sampled, the vines did not show a marked reduction in root growth in the traffic row. Ramsey rootstock vines showed more extensive root growth than own-rooted Thompson Seedless vines, particularly in the deeper layers of the soil.