Influence of rootstock and vine spacing on root distribution, vine growth, crop yield, fruit and wine composition, canopy microclimate and wine quality of Cabernet Sauvignon
The effects of seven rootstocks (AxR#l, 110R, 039-16, 5C, 3309, 1616, and 420A) grafted to Cabernet Sauvignon (clone #8) in combination with three between row spacings (2, 3 and 4 m) and two in-row spacings (1 m and 2 m) on root distribution, shoot growth, soil water utilization, leaf and fruit composition and crop yield were evaluated this past season in a replicated field plot established at the Oakville Experimental Vineyard in 1987. Rootstocks 110R, 039-16, 3309, 1616, 5C, 420A, and AxR#l were evaluated at both the UC Oakville Experimental Vineyard and at a rootstock trial on Beringer vineyards Hudson Ranch in Napa. This allowed for investigation of differences in the density and distribution of the rootstock root systems in two different soil environments. A high spring water table and lower soil redox values at the north east end of the Oakville Experimental Vineyard significantly correlated with a lower number of roots indicating that these conditions limit root distribution. Clay subsoils at the Hudson Ranch also limited root penetration. Percent soil gravel at the Oakville Experimental Vineyard correlated with root numbers at deeper depths suggesting that a high percentage of soil gravel allowed for improved root pene¬tration. Roots were counted and categorized into four size classes: small (< 2 mm), medium (2 to 5 mm), large (5 to 12 mm) and very large (> 12 mm). At the Oakville Experimental Vineyard, rootstock 420A had statistically the fewest small, medium and total roots, whereas, rootstock 039-16 had the most large and very large roots. At Beringer, rootstocks 1616 and 420A showed statistically the lowest density of large roots and 039-16 the highest density. Rootstock 039-16 also had a deeper root distribution than 420A at both sites. Vines at closer vine spacings had fewer total roots but higher root densities. Rootstocks 110R, 039-16, 3309, and AxR#l were more aggressive at establishing roots at the widervine spacing. The average crop yield of 2, 3 and 4 m row spacing were 8.1, 6.5 and 6.4 tons/acre, respectively, and for 1 m and 2 m vine spacing were 7.5 and 6.4 tons/acre, respectively. The higher yields were due to greater number of shoots and clusters per acre. Fruits from 1 m vine spacing had higher levels of malic acid than 2 m fruits at harvest. The level of anthocyanin in fruits was greater at 1 m vine spacing than 2 m vine spacing. Decreasing row spacing from 4 m to 2 m reduced pruning weight per vine and per meter of canopy length, whereas decreasing vine spacing from 2 m to 1 m reduced pruning weights per vine, but when compared on a per meter of row length basis, 1 m vine spacing had significantly higher pruning weight than 2 m vine spacing. Closer vine spacing within rows, however, did reduce average weight per cane. The stocks were devided into three groups based on the amount of shoot growth and crop yield; 110R, 039-16 and 1616 had the most shoot growth and highest yield; 5C and 3309 were intermediate, and 420A was lowest. The high¬er yielding stocks had greater number of shoots and clusters per vine and per acre than lower yielding stocks. Shoot length, number of primary leaves, and leaf area of spur shoots of 11 OR and 039-16 were greater than the other four stocks. Pruning weight per vine of the seven rootstocks were in decreasing order of 110R, 039-16, 3309, 5C, 1616, and 420A. At harvest, 039-16 fruits were generally higher in pH, malate, and K than fruits from the other five stocks. The levels of malic acid and titratable acidity in fruits at harvest were directly related to the total amount of shoot growth per vine. 420A, 1616, and 5C fruits were ripened earliest, 110R and 3309 ripened intermediate and 039-16 fruits were generally the last to ripen as measured by °Brix. Mineral petiole analysis at bloom and veraison revealed that 039-16 stock continues to be the highest in K and low¬est in Mg, whereas 420A is lowest in K and highest in Mg, the other stock ranging in between. Wider spacing between vines within rows increased the level of Ca and Mg and decreased K, however, row spacing had little effect on the mineral content of petioles at bloom and veraison.