Root Distribution of Three Grapevine Rootstocks Grafted to Cabernet Sauvignon Grown on a Very Gravelly Clay Loam Soil in Oakville, California

Abstract

Root distributions of the grapevine rootstocks AXR#1,110R, and St. George were examined at the UC Oakville Experimental Vineyard. Four trenches 1.2m deep were excavated 5 cm from the vine trunk for every rootstock and the presence of roots recorded. Root intersections with the trench profile were classified according to size (<2 mm, ≥2 and <5 mm, ≥5 and <12 mm, ≥12 mm). The soil at the site is a Bale (variant) gravelly loam for the top 10 to 30 cm, becoming a very gravelly clay loam to a depth of 100 cm and then an extremely gravelly clay loam to 165 cm. In addition to mapping roots, soil samples along the trench profiles were analyzed for their percent sand, silt and clay contents to determine any trench-specific textural changes. A log transformation of the root count data was used to prevent violation of the homogeneity of variance assumption necessary for analysis of variance. Root frequencies for all size classes were then analyzed for correlation to depth or rootstock using analysis of variance with a repeated measures design. Root numbers from each size class of roots varied significantly with depth. Root frequencies varied significantly with rootstock for the smallest size class and total root number. A test of rootstock-depth interactions was significant for the two intermediate size classes. These interactions and conservative mean separation tests suggest that St. George has a different distribution pattern than either 110R or AXR#1. St. George also had the highest total root number. This is in agreement with six year averages of pruning weights which indicate that St. George had the heaviest one-year-old prunings and the lowest yield/pruning weight ratio.