Abstract
The effects of water management and nitrogen fertilization, on yield, quality, and sensory profile of the red table-grape cultivars Redglobe and Michele Palieri were studied. Two irrigation volumes (1000 and 2000 m3/ha) and two nitrogen levels (120 and 180 kg/ha) were imposed. The effects of these parameters were cultivar-dependent. For Redglobe, irrigation resulted in significant increases in soluble solids and titratable acidity and significant decreases in resistance to compression and resistance to penetration. Increased nitrogen fertilization level exerted a significant effect only on titratable acidity (increased) and resistance to compression (decreased). Significant interactions between the two practices were demonstrated for soluble solids, pH, and resistance to compression. For Michele Palieri, increased irrigation resulted in significant decreases in soluble solids and resistance to penetration and significant increases in resistance to compression. Higher nitrogen caused decreases in berry weight but increases in soluble solid content and resistance to mechanical stress. Significant interactive effects were highlighted on yield, cluster weight, titratable acidity, and resistance to penetration. The lack of a significant correlation between physical/chemical and sensory results indicated that the changes induced by the agricultural practices on composition and mechanical behavior of berries were not perceptible by a trained panel.
Table grapes represent one of the most important crops in the world and particular attention has been paid to the improvement of fruit yield and quality. Quality is the composite of product characteristics that impart value to the consumer. Producers and handlers are interested in increased fruit yield and postharvest life, whereas consumers consider quality fruits and vegetables to have a healthy appearance, good flavor, and high nutritive value (Bruhn et al. 1991).
In table grape, quality is related to characteristics such as seed content, appearance (including berry color, size, and uniformity), firmness, crispness, flesh texture, sweetness (glucose and fructose represent ~99% of the sugar content at the end of grape maturation), acidity level, and flavor. For example, for Spanish consumers, ideal grapes are sweet, thin skinned, seedless, large, and juicy (Piva et al. 2006).
The relationship between consumer preference and fruit chemical composition has been studied in different commodities. Several studies have established that consumer preference is associated with soluble solids concentration, titratable acidity, and their ratio in fruits such as grapes (Wei et al. 2002), kiwifruit (Crisosto and Crisosto 2001), peaches, cherries, and oranges. For table grapes, consumers were more sensitive to the soluble solids concentration–titratable acidity ratio than to soluble solids concentration alone. These parameters are commonly used to evaluate the quality of grapes and to predict the harvest date (Jayasena and Cameron 2008) and are usually expressed as Brix (% by weight of soluble solids) and grams of acid per 100 mL. Traditionally, grape maturity corresponds to sugar–acid ratios of 28 (ideal white table) and 33 (ideal red table). Another approach to combining sugar and acid is to multiply Brix by the square of pH. In this case, the ideal values are 211 and 245 for white and red table grapes, respectively.
The efficacy of new cultivation techniques is determined by a simultaneous increase in vineyard yield without detriment of grape quality. Some studies have reported reduced grape maturity and anthocyanin content in grapes from vineyards with high yields (Petrie and Clingeleffer 2006), whereas others have not reported significant correlation between yield and maturation index (Riu-Aumatell et al. 2002). Treatments based on foliar fertilization with micronutrients, natural growth regulators, and calcium improve yield and quality. Management techniques such as girdling, topping, pinching, cluster thinning, growth regulator spraying, and sprinkler cooling have been evaluated as able to enhance grape quality characteristics.
Deficit irrigation during ripening of Spanish cultivars (Baladí, Airén, Montepila, Muscat Blanc à Petits Grains, and Pedro Ximénez) induced higher titratable acidity, malic acid, and potassium content but had no significant effects on berry sugar accumulation or tartaric acid content (López et al. 2007). For Sultanina grapevines, decreasing irrigation level dramatically reduced all vegetative parameters without affecting fruit quality and yield components (Paranychianakis et al. 2004).
Descriptive sensory analysis is a comprehensive and informative tool and is easily applied to the evaluation of table grapes. One method for grape tasting is based on 20 descriptors and the segmentation of the analysis according to the three main tissues: flesh, skin, and seeds (Rousseau and Delteil 2000). Each descriptor is quantified on a four-point notation scale. Another method is based on nine descriptors and a structured scale of three or four points depending on the descriptor (Martinez 2002). Such methods need to consider berry heterogeneity within a cluster, a vine stock, and a parcel. Sensory analysis has also been used for the descriptive profiling of new and commercial British Columbia table grape cultivars (Cliff et al. 1996).
Other researchers investigated the effects of nitrogen fertilization and found that yield was determined primarily by nitrogen availability at flowering and that abundant nitrogen nutrition decreased the weight of grape skins, the skin to berry ratio, pulp sugar, and acid levels by the beginning of the ripening period (Keller et al. 1998). Foliar nitrogen fertilization would seem to reduce sugar content.
The aim of this work was to examine the effects of fertilization and water management on yield, quality, and sensory profile of two red table-grape cultivars, Redglobe and Michele Palieri.
Materials and Methods
Experimental design and plant material.
Trials were conducted from 2005 to 2008 in two vineyards of the same experimental farm of CRA-UTV in the countryside of Turi (Apulia region, southern Italy). Soil and weather conditions were thus the same for all. The site is located in a hilly area ~250 m asl and has a continental climate, characterized by a wide temperature range. January is the coolest month (2 to 10°C) and July is the hottest (16 to 30°C). The temperature rarely falls below 0°C. Rain is scarce (638 mm per year calculated as average of the last 30 years) and concentrated between October and March. Summer is usually droughty and subject to winds mainly directed from north-east and south-west.
The 140 Ruggeri rootstock (Vitis berlandieri x Vitis rupestris du Lot) was planted in 1999 and, one year later Redglobe and Michele Palieri cultivars were grafted on the rootstock. The plant density was 1600 vines/ha, spaced at 2.5 m (within rows) by 2.5 m (between rows). Grapevines were trained to the double-tendone trellis system, which is widely used in southern Italy. The double-tendone, or Apulian, system consists of a stake of ~2.9 m at each vine and two orthogonal stake wires attached 1.8 m aboveground. At the same height, there are two parallel cane wires 0.30 m from the stake. About 0.25 m above the level of the cane wires, there is a grid of wires that supports the shoots originating from the canes. The tendone forms a canopy with free-standing shoots. Vines had a trunk height of 1.4 to 1.6 m, with two arms and two canes per arm fixed on the cane wires. Canes were pruned to 12 to 14 buds. This system improves the canopy management, determines better microclimatic conditions around the clusters, and allows the separation of leaves from fruits, thus preventing cluster damage during wind.
The experimental vineyards were covered by high-density polyethylene nets. These nets cover about 40% of the Tendone table-grape vineyard area in Apulia and 80% in southern Italy in order to protect leaves and grapes from hail and wind, with a secondary effect of a slight delay in maturation and harvest (Rana et al. 2004). The net characteristics (5/4 anti-hail net, Kristal; Retilplast, Salerno, Italy) include: English texture, 30-μm diameter transparent wires, 75% porosity, and 14% shade factor.
The vineyards were irrigated according to two different seasonal irrigation volumes by a localized irrigation system consisting of two 8 L/hr pressure-compensated drip emitters per vine, each placed 0.70 m apart. Rainfall and total seasonal irrigation volume was assumed to counterbalance the evapotranspirated water that, in the considered cultivation area, amounted to 271.6 ± 71.7 mm/ha or 2710.6 ± 717.0 m3/ha for table grapevines trained to the double-tendone system, during the whole productive cycle (an average for the last 20 years). The seasonal irrigation volumes imposed were 1000 m3/ha (100 mm/ha) (V1) and 2000 m3/ha (200 mm/ha) (V2) representing, respectively, 37 and 74% of the seasonal irrigation volume usually applied in the area. Starting 20 days after flowering and until harvest, vineyards were irrigated seven times at a frequency of every two weeks, each consisting of 150 m3/ha (V1) and 300 m3/ha (V2) with the exception of the last irrigation, which consisted of 100 m3/ha (V1) and 200 m3/ha (V2).
Irrigation and nitrogen fertilization were arranged as a split-plot design with three replications. Irrigation represented the main plot (two randomized levels) while nitrogen (two randomized levels) represented the subplot. Each of the three replications consisted of 10 rows of 22 vines. The main plot (irrigation levels) included five rows of 22 vines each, whereas the subplot (nitrogen level) was five rows of 11 vines each. Each irrigation level was separately managed by a specific volumetric valve. For each subplot, only the central three rows and, for each of these rows, the central seven vines were used for data collection.
The nitrogen levels imposed were 120 kg/ha (N1) and 180 kg/ha (N2) representing, respectively, 67 and 100% of the seasonal amounts typical for the area. The fertilizer was applied in a soluble form (urea, 46% N) according to the following timing: the first half dose was applied at budbreak (March 11 to 21) and the second half dose was applied from July 1 to 10 by fertigation. The treatments were labeled V1N1, V1N2, V2N1, V2N2.
Sampling.
The two cultivars were separately considered. The same harvest time (from 5 to 15 Sept) was used for both cultivars and all treatments and corresponded to the point at which soluble solids were equal to at least 14 Brix. For each treatment, 27 clusters were picked (9 clusters per replicate, sampled from 9 different vines). Only clusters placed on the basal position of the shoots, in the median part of the fruit cane, were picked. The samples, placed into fruit boxes (4.5–5 kg per box) were immediately delivered to the laboratory and analyzed within 24 hr.
Yield components.
The mean cluster weight was calculated on 27 clusters (9 clusters per replicate, sampled from 9 different vines). Yield (kg/vine) was determined on the basis of the mean number of clusters per vine and the mean cluster weight evaluated at harvesting. The mean berry weight was determined on 150 berries (50 berries per replicate).
Fruit composition and mechanical measurements.
After weighing, berries were hand-crushed and the juice was collected and centrifuged at 1556 g for 5 min at 20°C. Berry juice soluble solids were measured by a portable refractometer (Atago PR32, Norfolk, VA). Titratable acidity (expressed as g tartaric acid/L) was determined by titration with 0.1 N sodium hydroxide with bromothymol blue as indicator according to the EEC Regulation 2676/90 (EEC 1990). Juice pH was also measured. Resistance to compression and penetration was measured by a penetrometer (Digital Fruit Firmness Tester, TR, Forlì, Italy) and expressed as N. Forty berries were withdrawn from the clusters of each sample: 20 were submitted to penetration tests and the other 20 submitted to compression tests. Since it has been demonstrated that the results of a penetration tests depend on cultivar (berry size) and puncture point but are not affected by berry position in the cluster (Letaief et al. 2008), the analyses were consistently performed at the point corresponding to half berry height.
Sensory evaluation of grapes.
Aspirant judges (20 to 50 years old) were recruited among students, technicians, and researchers of the Faculty of Agriculture of Foggia according to their motivation and availability to pursue a 7-month study with one or two sessions per week. Judges were preliminary selected on the basis of dietary habits, grape consumption, information on any food allergy intolerances and repulsions, and use of tobacco, drugs, and medicine that could interfere with sensory perception. Based on these criteria, 30 people (18 female and 12 male) were admitted to the next step and received training in sense physiology and quality characteristics of grape. A new selection was made based on ability to understand questions, answer questionnaires, discriminate stimuli and evaluate their intensity, identify known tastes, odors, and defects, memorize new odors and flavors, and express repeatable judgments. The sensory analysis was performed by a panel of 15 trained people.
Table-grape professionals were interviewed to collect sensory criteria for a first generation of attributes on the basis of their grape-tasting practices. A classical generation of the attributes was carried out with the panel during two specific sessions where different table-grape types were presented to the judges. Based on the generation sessions, a final list was developed of visual (4), olfactory (2), taste/tactile/mechanical attributes (9), and odor and flavor descriptors (23) (Table 1⇓). Attributes and descriptors were chosen to be discriminating among samples, nonredundant, clear, and unambiguous and to have a relationship with the acceptance/rejection by the consumer and with the chemical, physical, and instrumental measurements. Definitions and descriptions of the attributes were established by consensus with the panel.
A combined profile sheet was submitted to judges for a variation of the quantitative descriptive analysis (QDA). First, judges were asked to perform a visual evaluation of berries, pedicels, and stalks, an olfactory evaluation of the sectioned berries, and a taste/tactile/mechanical evaluation on a 0 (very weak) to 6 (very intense) scale. Judges then described the perceived odors and flavors by choosing among the descriptors generated and listed. In addition to the scores attributed to the QDA descriptors, the trained judges were also requested to express an overall liking score (overall judgment on a 0 to 6 scale) since they were regular consumers of table grapes.
Twelve clusters for each of the three replications were sampled from 12 different vines. For each of the field replications, the sensory analyses were performed in triplicate and, for each, nine berries were submitted to the single judge. Each session was 2 hours whereas the time between sessions was 24 hours. Products were presented on white plastic plates and tasted 1 hour after they were taken out of the 12°C cold room. The sensory sessions were conducted in a sensory room equipped with eight booths according to the ISO standard 8589 (2007). The temperature was kept at 24 ± 2°C. Humidity values were in the 70 to 85% range.
Statistical analysis.
Means and the standard deviations were calculated using Excel software ver. 11.5.1 (Microsoft, Redmond, WA). The analysis of variance (ANOVA) and F-test were made to separate the effects of irrigation and nitrogen fertilization. The least significant difference (LSD) multiple range test was used to compare the means for significant interactive effects. ANOVA, LSD, and the principal component analysis (PCA) were performed using the software Winstat ver. 5.1 (Statsoft, Tulsa, OK). ANOVA of the odor flavor descriptor was calculated as the number of times the descriptor was mentioned over the total number of times it was possible to mention.
Results and Discussion
Yield components, fruit composition, and mechanical behavior of grapes.
The single and interactive effects of irrigation volume and nitrogen fertilization levels on the yield, composition, mechanical behavior, and variability (expressed as standard deviation) of such parameters over four years for Redglobe and Michele Palieri grapes were considered. The coefficients of variation (ratio between standard deviations and mean values) calculated for each parameter were less than 0.22 for Redglobe and generally less than 0.20 for Michele Palieri, except for titratable acidity and resistance to compression, which had values up to 0.40.
Irrigation volume and nitrogen fertilization level exerted different effects on the two grape cultivars. For Redglobe, the two different irrigation levels showed a significant main effect on soluble solids, titratable acidity, and mechanical behavior but not on yield, cluster weight, berry weight, and pH (Table 2⇓). The vines irrigated with the highest volumes had grapes with the highest soluble solid content and titratable acidity but the lowest resistance to penetration (a measure of hardness) and compression.
Although the literature explores these topics, results are often contradictory, depending not only on operative conditions (amount and timing of irrigation and fertilization) but also on weather and soil conditions, location, rootstock, and cultivar. Furthermore, water supply has an additional impact on nutrient uptake by increasing nutrient flow to the roots. In Chardonnay grapes in an Ontario vineyard, increasing irrigation volume resulted in increased sugar content and titratable acidity (Reynolds et al. 2007). According to Freeman and Kliewer (1983), concentration of soluble solids in fruits was reduced by irrigation due to a dilution effect. Another study found that differences in yield and grape quality responses to irrigation were consequences of the different environmental conditions and crop levels. The postveraison water application allowed must sugar level to increase (Intrigliolo and Castel 2010). Goodwin and Jerie (1992) found that vines submitted to deficit irrigation resulted in grapes with lower soluble solid concentration. Peterlunger et al. (2002) did not find significant differences in sugar accumulation on berries of grapevines submitted to different irrigation regimes, thus demonstrating that the success of applying regulated deficit irrigation to achieve higher quality grapes may be related to an accurate evaluation of vine water status.
The literature also suggests a dependency of food texture on water content and water activity. Water acts as a plasticizer in hydrophilic food materials (Karel 1985), facilitating deformation and increasing flowability, extensibility, and softness. In particular, fresh apples characterized by high water content and activity are fairly rigid and have low cohesiveness (Bourne 1986). In raisins, the increase of water activity in the range of 0.6 to 0.7 weakens the skin and increases the probability of its breakage already at stresses lower than 0.3 MPa, since the flow of the diluted sugar solution does not require a high energy input (Lewicki and Wolf 1995).
Nitrogen fertilization showed a significant main effect on titratable acidity and resistance to compression. The vines supplied with the highest nitrogen levels produced grapes with the highest titratable acidity and the lowest resistance to compression. In a study on Concord grapes, titratable acidity was reduced by increasing amounts of nitrogen level (Spayd and Morris 1979), whereas another study highlighted the absence of difference due to rate of nitrogen fertilization applied to Riesling grapes (Spayd et al. 1994). Significant interactions between irrigation and nitrogen fertilization were demonstrated in our study for soluble solids, pH, and resistance to compression. The highest soluble solid content was detected in grapes from vines receiving the highest irrigation volume and the lowest nitrogen, whereas the other samples showed lower values and no differences were detected. The highest pH values were measured on V1N2 samples. Single or combined increases of irrigation volumes and nitrogen levels resulted in significant decreases of resistance to compression.
For Michele Palieri grapes, significant main effects were shown by irrigation volume on soluble solid content and mechanical behavior of berries and by nitrogen level on weight, soluble solid content, and resistance to penetration of berries (Table 3⇓). The increase of irrigation volume caused decreases in soluble solids and resistance to penetration and increases in resistance to compression. The increase of nitrogen level caused decreases in berry weight and increases in soluble solid content, due to photosynthesis stimulation induced by high soil nitrogen level (Keller et al. 2001), and resistance to mechanical stress. Significant interactions between irrigation and nitrogen fertilization were highlighted on yield, cluster weight, titratable acidity, and resistance to penetration. The highest yield was in grapes from vines receiving the highest irrigation volume and nitrogen level, whereas the lowest yield was in the parcels submitted alternatively to low irrigation volume-high fertilization level or high irrigation volume-low fertilization level. The heaviest clusters were obtained from vines supplemented alternatively with the highest or the lowest levels of both water and nitrogen.
Water and nutrients are interactive and in close association in soil. Water flow through the soil-root-shoot pathway is necessary for vine nutrition. Water supplementation stimulates growth and determines an increase in the nitrogen requirements, whereas growth reduction induced by water deficit decreases vine nitrogen requirements (Keller 2005) and makes further nitrogen supplementation unhelpful. Titratable acidity was highest in the parcels submitted alternatively to low irrigation volume-high fertilization level or high irrigation volume-low fertilization level, whereas lower values were measured on V2N2 grapes. Resistance to penetration was the highest in V1N2 grapes, whereas the other grapes showed lower values and no differences were detected.
Sensory profiles and odor/flavor descriptors of grapes.
Analysis of variance was used for a preliminary screening to examine, for each of the sensory attributes, the effects of judges, replications, and treatments. The effect of the judge factor was significant (p < 0.05). The effect of the replication factor was nonsignificant, thus confirming that judges were consistent in their assessments. The effects of treatments were significant for all the descriptors at p < 0.05. The effect of wine x judge interactions was nonsignificant for the sensory profile, demonstrating that judges evaluated grapes in the same way but significant (p < 0.05) for aroma descriptors. Other authors reported similar findings when samples were very similar in their sensory properties and the judges were not able to differentiate easily among them (Tang et al. 1999, Tardaguila et al. 2008).
The sensory and flavor descriptors characterized the sensory properties of Redglobe grapes obtained through the chosen agricultural practices. Redglobe grapes were characterized by low acidity and astringency; intermediate berry color uniformity, berry abscission, grape fruity flavor, and sweetness; and high pedicel turgidity, hardness, crispness, juiciness, grape fruity taste, and overall liking (Figure 1A⇓). There was an absence of fermented flavor and taste and the presence of only a very few spots/rots. The analysis of variance of the sensory data did not highlight significant differences among treatments, indicating that the changes induced by the applied irrigation and fertilization levels on composition and mechanical behavior of berries were not perceptible by a trained panel. It can be supposed that these differences were below the sensitivity threshold of the human taste. The absence of correlation (number of samples ≥27) between the pairs soluble solids–sweetness (R2 = 0.0007, p = 0.8802), pH–acidity perceived by judges (R2 = 0.0013, p = 0.8369), titratable acidity–acidity perceived by judges (R2 = 0.0010, p = 0.8538), resistance to compression–hardness perceived by judges (R2 = 0.0004, p = 0.9036), and resistance to penetration–crispness perceived by judges (R2 = 0.0845, p = 0.0854) confirmed this result below threshold. Redglobe consumer acceptance has been identified as highly related to the ratio between soluble solid content and titratable acidity (Crisosto and Crisosto 2002).
The most frequent Redglobe aroma attributes were calculated as the number of times a descriptor was mentioned over the total number of times it is possible to mention, expressed as a percentage (Figure 1B⇑). Redglobe grapes were mainly characterized by flavors such as white fruit (apple, pear), red fruit (berries, cherry, strawberry, prunes and plums), citrus, flowers (rose), and green notes (cut grass/leaves). Nine descriptors (39.1%) were attributed to V1N1 samples and three of them (rose, pear, and apple) were identified by >30% of judges. Twelve descriptors (52.2%) were attributed to V1N2 samples, one of which (apple) was recognized by >50% of judges. Twelve descriptors were attributed to V2N1 samples, two of which (blackberry and apple) were identified by >30% of judges. Twelve descriptors were attributed to V2N2 samples, two of which (rose and apple) were identified by >30% of judges. The analysis of variance highlighted significant differences among treatments only for pear flavor that made possible to discriminate V1N1 samples that showed the highest citation frequency from V2N1 and V2N2 samples (intermediate citation frequency) and from V1N2 samples that showed a citation frequency equal to 0.
Literature concerning the effects of irrigation and nitrogen fertilization levels on sensory quality of table grapes is minimal. Analogous research performed on winegrapes showed that changes in grape chemical components did not always correspond to significant qualitative differences in sensory attributes.
Principal component analysis was applied to those quality indices (titratable acidity, soluble solids, resistance to compression and penetration, pH) and attributes (pear flavor) on which significant single and interactive effects were exerted by irrigation and nitrogen fertilization. For Redglobe samples, the first two principal components (PC1 and PC2) accounted for 87.51% of the variance (48.69 and 38.82%, respectively) (Figure 1C⇑). On the basis of the first component, V1N1 samples were clearly distinguishable, for their higher resistance to compression, from V1N2 (characterized by the highest pH) and from the grapes submitted to the highest irrigation volumes independently on nitrogen fertilization level. On the basis of the second component, a good separation was observed between V1N2 (due to higher pH values and citation frequency of the pear flavor) and the samples from the other treatments.
The sensory profile of Michele Palieri grapes was characterized by low acidity and astringency; intermediate pedicel/stalks turgidity, berry color uniformity, berry abscission, grape fruity flavor, juiciness, crispness, and sweetness; and high hardness, grape fruity taste, and overall liking (Figure 2A⇓). Overall, the grapes were healthy, although fermented flavor and taste were perceived (scores less than 1.2) and a certain browning of pedicels/stalks and the presence of some spots on berries were observed.
Also in this case, the analysis of variance of the sensory data did not highlight significant differences due to irrigation volume and nitrogen fertilization level applied, and no correlation (number of samples ≥27) was found between the pairs soluble solids–sweetness (R2 = 0.0001, p = 0.9576), pH–acidity perceived by judges (R2 = 0.0007, p = 0.8557), titratable acidity–acidity perceived by judges (R2 = 0.0003, p = 0.9121), resistance to compression–hardness perceived by judges (R2 = 0.0105, p = 0.5296), and resistance to penetration–crispness perceived by judges (R2 = 0.0077, p = 0.5897).
Michele Palieri grapes were mainly characterized by flavors of white fruit (apple, pear), citrus (grapefruit), red fruit (cherry), flowers (rose), and green notes (cut grass/leaves) (Figure 2B⇑). Six descriptors (26.1%) were attributed to V1N1 samples and one of them (cut grass/leaves) was identified by 30% of judges, whereas three of them (grapefruit, cherry, and apple) were identified by 20% of judges. Ten descriptors (43.5%) were attributed to V1N2 samples. Two of them (apple and cut grass/leaves) were recognized by 30% of judges whereas the pear descriptor was perceived by 20% of judges. Five descriptors (21.7%) were attributed to V2N1 samples, two of which (apple and cut grass/leaves) were identified by >30% of judges. Nine descriptors were attributed to V2N2 samples. The apple flavor was perceived by 30% of judges, whereas rose and cut grass/leaves were identified by 20%. The analysis of variance highlighted significant differences among samples for grapefruit and pear flavors. The former made it possible to discriminate V1N1 samples from the other samples that showed citation frequencies equal to 0. The latter made it possible to discriminate V1N2 samples from the others that showed citation frequencies equal to 0.
Principal component analysis was applied to those quality indices (titratable acidity, soluble solids, resistance to compression and penetration, berry and cluster weight) and attributes (pear and grapefruit flavors) that were useful in characterizing differences among Michele Palieri samples (Figure 2C⇑). The first two principal components (PC1 and PC2) accounted for 85.85% of the variance (69.95 and 15.90%, respectively). On the basis of the first component, V1N2 samples were clearly distinguishable from the others for their higher resistance to penetration and frequency of citation of pear flavor. On the basis of the second component, a good separation was observed among V2N1 (with the lowest yield, the highest titratable acidity, and intermediate cluster weight), V1N1 (intermediate titratable acidity), and V2N2 (highest yield and lowest titratable acidity).
Conclusion
With the same weather, soil conditions, location, and rootstock, the single and interactive effects of irrigation and nitrogen fertilization on yield, fruit composition, and mechanical behavior depended on cultivar and their specific requirements. The increases of water volume and nitrogen level supplied to the vineyards did not give consistently desirable results. Water management particularly exerted significant influence on soluble solids and mechanical behavior, whereas the effects of nitrogen fertilization were less specific, involving different parameters in the two cultivars (titratable acidity and resistance to compression in Redglobe; berry weight, soluble solids, and resistance to penetration in Michele Palieri). The interactive effects of irrigation and nitrogen fertilization were also significant on different parameters in the two cultivars (soluble solids, pH, and resistance to compression in Redglobe, yield, cluster weight, titratable acidity, and resistance to compression in Michele Palieri).
This information can be taken into account to manage each agricultural practice and to increase table grape production and quality. For sensory data, the analysis of variance did not highlight significant differences among the treatments, thus indicating that the changes induced by the agricultural practices on composition and mechanical behavior of berries were not perceptible by a trained panel.
Footnotes
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Acknowledgments: This research was a part of the project Prolungamento della Self-Life di Uva da Tavola, supported by the Italian MiPAAF-CIPE.
- Received November 2009.
- Revision received April 2010.
- Revision received July 2010.
- Accepted August 2010.
- Published online December 1969
- Copyright © 2011 by the American Society for Enology and Viticulture