Trial of ten common rootstocks on two different soils in the paso robles AVA of California

Abstract

A total of 704 Cabernet Sauvignon (CS8) vines were grafted on 10 different rootstocks and compared to an own-rooted control as part of new vineyard planting on the terraces above the Estrella River in the Paso Robles AVA. The planting was done on two different sites, each underlain by a different soil type, within the same vineyard block. We hypothesized that rootstock and soil type would independently influence vine growth, nutrient levels, fruit yield, and fruit quality. Soil type 1 was an Alfisol with a sandy loam surface texture over a heavier clay loam subsurface, with higher water and nutrient holding capacities. Soil type 2, an Inceptisol, was a sandy soil with reduced water holding capacity due to coarse texture and high gravel content. Three years after planting, the vines exhibited marked differences in growth rate and canopy development, as measured in two consecutive seasons. Tissue analyses performed in 2009, 2010, 2011, 2012 and 2013 showed differences among rootstocks for all nutrients studied, which included N, P, K, Ca, Mg, Mn, Fe, Cu and Zn. In most cases, the rootstock rank order was similar for vines grown on both soil types, but there were some exceptions to this trend. Juice from the 2011, 2012 and 2013 growing seasons was analyzed for Brix, pH, total acidity (TA), α– amino nitrogen, ammonia, yeast available nitrogen (YAN), malic acid, and potassium. Juice Brix, TA, and malic acid content varied by both rootstock and soil type. Results of these analyses indicated differences in juice properties between vines grown on the two contrasting soil types. Notably, pairwise analyses revealed that grapes grown on the Inceptisol had significantly higher Brix, higher TA, lower pH, and higher malic acid content than their counterparts grown on the Alfisol. Taken together, these results demonstrate that vine growth and fruit characteristics are influenced by both rootstock and soil type.