Effect of Soil Depth and In-row Vine Spacing on Yield and Juice Quality in a Mature 'Concord' Vineyard'

A site was prepared with 2 distinctly different soil depths and a vineyard of 'Concord' grapes (Vitis labrusca L.) was established with in-row spacings of 1.52, 1.83, 2.13, 2.44, and 3.05 m. Wider in-row vine spacings resulted in increased vine yields on deeper soils to the point that yields per meter of cordon and per hectare were not reduced; but yield per meter of cordon and per hectare was reduced on the shallow soil when in row vine spacings exceeded 2.44 m. There were few effects on juice quality from either soil depths or in-row vine spacings. Previous research on grapevine spacing has generally indicated that vine yields of some cultivars are inversely related to plant density (2, 4, 7, 8, 9) and that wider spacings can be utilized for economic and cultural advantages with little or no effect on total fruit yield or quality (6, 8, 9). Each cultivar should obviously have a spacing optimum dependent upon inherent vine vigor and the numerous interacting environmental factors which influence vine canopy development and complete utilization of the allocated trellis space. Bioletti and Winkler (1) reported that with a vigorous cultivar and a moderately vigorous cultivar the highest yields were at close vine spacings during the establishment period, but after the vines were established, the vigorous cultivar required fewer vines per hectare than the less vigorous cultivar. Turkington et al. (7) recently reported that with 'Muscat Gordo Blanco' grapevines, the yield was related to cordon and leaf canopy development. Spacing studies on 'Concord' grapevines have indicated that densities of 600 to 700 vines/acre gave maximum production (2, 4). Shaulis et al. (5) showed that spacing between rows had greater effects on 'Concord' yield than in-row vine spacings. The conventional spacing between rows in Arkansas is 3.05 m (10 ft) and an in-row vine spacing of 2.44 m (8 ft). No research has reported the effects of various in-row spacings on yield and quality of 'Concord' grapes grown on different soil depths at a given site, a condition that eliminates environmental factor differences that usually exist between locations. The objective of this study was to determine the yield and quality response of 'Concord' grapes to in-row vine spacing on different soil depths at the same site location. Materials and Methods This study was conducted for 4 years (1975 to 1978) in an own-rooted 'Concord' vineyard at the Arkansas Agricultural Experiment Station, Fayetteville. The soil on this plot was classified as a Captina silt loam. This taxonomic soil class is a fine-silty, mixed, mesic Typic Fragiudults. The Captina series consists of moderately well-drained soils on nearly level to gently sloping uplands and stream terraces of the Ozark Highlands. They formed in loamy residuum weathered from cherty limestone or siltstone. In a typical pedon, the Captina soil has a plow layer about 18 to 23 cm thick of brown silt loam. The upper subsoil is a yellowish-brown silty clay loam to a depth of about 49 cm. The middle subsoil is a firm, brittle, mottled fragipan to a depth of about 120 cm. The lower part is yellowish-red, mottled silty clay loam to a depth of 150 cm or more. Many commercial 'Concord' vineyards in Arkansas are located on this soil type and the major difference between sites is the depth of the plow layer and upper subsoil. Prior to establishing the experimental planting, 2 distinctly different soil depths were created in adjacent blocks to represent the extremes in soil depth found in commercial vineyards. In order to accomplish these 2 extremes the plot was land graded or "leveled." The cut area of the plot has the top and upper subsoil removed to near the fragipan. Twenty-five to 33 cm of soil was stockpiled and respread over the cut area. The adjacent area which was originally lower in elevation had approximately 30 cm of soil filled with the soil from the cut area. The filled area already had a thickened surface layer of soil due to erosional deposition from the higher slopes. This created a soil depth of from 75 to 85 cm to the fragipan layer. The entire plot was then land leveled to a slope of 0.2% to provide for good drainage. At the termination of the study, several holes were angered into each soil to determine root distribution. It was determined that although there was some penetration of grape roots into the fragipan, the soil depth to the fragipan determined the effective rooting zone. Published with the approval of the Director of the Arkansas Agricultural Experiment Station. Professor and Research Assistant. The authors wish to thank the National Grape Cooperative Association, Inc. for financial assistance in this research. The vineyard was established in 1966 by clonal propagation from a single parent vine that had consistently produced good yields of high-quality fruit. All rows were spaced 3.05 m (10 ft) apart and vines were spaced 1.52 m (5 ft), 1.83 m (6 ft), 2.13 m (7 ft), 2.44m (8 ft), and 3.05 m (10 ft) apart within the row, producing 2152, 1793, 1537, 1345, and 1076 vines/ha or 871, 726, 622, 545, and 436 vines/acre, respectively. Plots consisted of 2 to 4 vines and the experiment was designed as a randomized complete block with 5 replications in each soil depth treatment. Treatments were analyzed by analysis of variance within each soil depth. The vines were trained to a modified double-head spur system until 1972. This training system proved totally unsuccessful and in the fall of 1972 the vineyard trellis was converted to the 1.8-m high Geneva Double Curtain trellis with 1.2-m divided horizontal wires as described by Shaulis et al. (5). Cordons were allowed to establish during the 1973 and 1974 growing seasons. No yields or quality data were collected prior to 1975. Starting in 1974, all vines were balanced pruned on 5 node canes to a 30+ 10 severity (30 nodes retained for the first 454 g of I -year-old dormant prunings and 10 additional nodes retained for each additional 454 g of prunings removed). During this study, all vines were manually shoot-positioned (current season's growth positioned vertically toward the vineyard floor) immediately after bloom and 2 more times at about 3-week intervals each year. Fruit samples consisting of 3 whole basal clusters were collected at harvest from each plot and immediately frozen in polyethylene bags for later juice analysis. Grapes were harvested on Aug. 20, Sept. 3, Sept. 7, and Sept. 6, in 1975 to 1978, respectively. For analysis, samples were thawed and destemmed, and berry weight, number of berries/cluster, and percent green fruit (by count) were determined. Samples were blended for 15 sec in a laboratory blender, percent soluble solids was determined on a Bausch and Lomb refractometer, and samples were heated for 1 hr at 85°C. After pulp was separated from juice using cheesecloth, a 5 ml aliquot was diluted to 100 ml with distilled water, centrifuged and absorbance was read on a Bausch and Lomb spectrophotometer (model 340) at 520 nm. Another 5-ml sample of juice was diluted to 125 ml with distilled water, pH was determined, and the sample was titrated to pH 8.4 with 0.1 N NaOH to determine acidity. Results and Discussion Vines at a given in-row spacing on the deeper soil produced more grapes than vines at that same spacing on the shallow soil, although these values were not compared statistically (Table 1). As the in-row vine spacing increased, the per plant yield tended to increase in all years, except on shallow soils in 1976. This increased vine yield with wider spacings was greater in the deeper soil. The 4-year mean indicated that on the shallow soil an increase in yields per vine did not continue after the 2.13-m (7 ft) spacing and the yield of fruit per meter of cordon was less at the 3.05-m (l0 ft) spacing than for the closer spacings. However, on the deeper soil the increase in yield per plant at the wider in-row spacings prevented any significant reduction in yield per meter of cordon. Row spacing is largely determined by vineyard equipment accessibility requirements, and the spacing between rows for the GDC system in Arkansas has been standardized to 3.05 m (10 ft) by producers. This study indicates that 'Concord' grapes can be spaced within the row at least 3.05 m (10 ft) apart on good soils without experiencing a total yield reduction, provided the cordons and fruiting canes are maintained. However, when vineyards are planted on the shallow soils in this region, the in-row vine spacing should not exceed 2.44 m (8 ft) for maximum yields. The pruning weights per vine responded to the soil depths and in-row vine spacings similar to the vine yield responses with wider spacings and the deeper soil generally producing larger pruning weights (Table 2). However, there were no consistent trends established for pruning weights expressed on a cordon-meter basis. Vines on the deeper soil produced more fruit per retained node than vines on the shallow soil and there was a tendency for the wider vine spacings to produce more fruitful nodes on deep soils. The treatments resulting in increased node fruitfulness produced a larger number of berries per cluster and larger berries (data not shown). There was no significant difference between the percent soluble solids content of the fruit from either of the soils or vine spacings used (Table 3). The yield of soluble solids expressed as MT/ hectare was lowest for the vines on the shallow soil due to the reduced fruit yields. All vine spacings reacted similarly in soluble solids production on deeper soils, but the 3.05-m spacing on shallow soils showed a reduction in soluble solids/hectare due to fruit yield response. Soil depth and vine spacing had little effect on percent tartaric acid, pH, juice color, and percent green fruit. However, there was a tendency for the wider spacing to have slightly lower titratable acidity, higher pH, and a lower percentage of green fruit. In summary, the deeper soils and wider in-row vine spacing increased yield per vine and maintained yields per hectare. Vines on the shallow soil did not increase in mean yields past the 2.13-m in-row spacing. The soil depth or in-row vine spacings had little effect on the juice quality attributes determined. Table 1. Effects of soil depth and in-row vine spacing on yield of 'Concord' grapes per vine and per meter of cordon. Soil depth Yield (kg) . and vine Vines/ 1975 1976 1977 1978 Mean spacing ( m) ha vine cordon-m vine cordon-m vine cordon-m vine cordon-m vine cordon-m