Edited by: Paolo Inglese, Università degli Studi di Palermo, Italy
Reviewed by: Abraham J. Escobar-Gutiérrez, Institut National de la Recherche Agronomique (INRA), France; Bartolomeo Dichio, University of Basilicata, Italy
This article was submitted to Crop and Product Physiology, a section of the journal Frontiers in Plant Science
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Little information is available about nitrogen (N) content and its concentration in table grape vines. Knowledge of the quantity of N accumulated by the vine organs during the season could support sustainable fertilization programs for table grape vineyards. The aim of the present study was to determine the N content and its concentration in different annual organs, including summer and winter pruning materials, clusters at harvest, and fallen leaves at post-harvest. Specifically, biomass and N were analyzed at six phenological growth stages (flowering, berry-set, berry growth, veraison, ripening, and harvest) from 2012 to 2015. Nitrogen concentration was highest (>40 g/kg d.w.) in the leaves of the secondary shoots at flowering, whereas values >30 g/kg were measured in the leaves of the primary shoots. Nitrogen concentration in the clusters at harvest was 5.3–7.6 g/kg with an accumulation of 18.6–25.4 g/vine in the seasons. The decrease of N content in the primary leaves after flowering indicated a remobilization toward the clusters, which acted as a stronger sink. Later in the season (veraison-ripening), leaves translocated N to permanent organs and primary stems. Pruned wood and fallen leaves accounted for the largest N removal from the vine after clusters, 6.0–7.9 and 9.2–10.2 g/vine, respectively. With regard of the vine annual biomass, the growth followed a sigmoidal model reaching 7300–7500 g of d.w./vine at harvest. Vine leaf area, including both primary and secondary leaves, peaked at veraison (17–21 m2). Vines accumulated ≅35 g/vine of N at harvest, not considering the N removed with the intense summer pruning practices (≅7 g/vine) and the fraction mobilized toward the storage organs (10–15 g/vine). The overall N required by the vine was around 50–55 g/vine, which corresponded to ≅80 kg of N/ha in a vineyard with 1500 vines and a yield of 40 t/ha. Summer and winter pruning practices removed 29–31 g/vine of N which will be partly available (to be considered in the fertilization schedule) for the vine in the successive years if pruned residues were incorporated and mineralized in the soil.
Nitrogen (N) accumulation in grapevines has been investigated in different countries of the world (United States, South Africa, Spain, France, Australia, etc.) and for several varieties (
Nitrogen has several effects on both the vegetative and reproductive development of grapevines (
In both wine and juice grapes, the highest N uptake in grapevines is reported to occur between flowering and veraison, when the greatest vine biomass is achieved (
Leaf surface area depends on several environmental factors including N availability. The leaf area determines in part the potential radiation intercepted by the vine, which thereby affects vegetative growth and yield. The leaf area of mature (15-year-old) Thompson Seedless vines showed a constant increase up to 1000 Growing Degree Days (GDD), approximately corresponding with veraison, in each of 3 years; after 1000 GDD, leaf area declined due to shoot trimming and leaf senescence (
Nitrogen accumulated by grapevines during a growing season needs to be annually restored to the soil by fertilization and mineralization of organic material (leaves, pruning residues, etc.). Organic forms of N from residues and/or cover crops (leguminous species) are less susceptible to leaching, but less readily available, than inorganic forms of N in fertilizers.
Crop yield increases from N fertilization have moderated both in developed and developing countries (
Poor information is available about N concentration or requirements by table grape vines except for Thompson Seedless vines, often grown as raisin grapes (
Table grape cultivation is very important in many countries of the world, particularly in China (9 million tons), India (2 million tons), and Turkey (2 millions of tons), these countries together produce more than half of the world’s production of 26.8 million tons (
Table grape cultivation is very important in Puglia region, Southeastern Italy, since this region is the first producer in Italy with 620,000 tons on an area of 24,160 ha (
The aim of this 4-year research was to study the concentration of N in the following cases: (1) different annual organs of the vine at various phenological stages; (2) grapevine materials removed after both summer and winter pruning, and fallen leaves; (3) clusters at harvest. Moreover, the N content/vine in different organs and the growth of the vine biomass were studied at various phenological stages. These data would help in defining the N demand of table grape vineyards for more sustainable management.
A trial was conducted from 2012 to 2015 in a 1 ha commercial table grape vineyard located in the countryside of Conversano, Puglia region (Southeastern Italy), on 15-year old vines of cv. Italia grafted onto 140 Ru, pruned with four fruiting canes and trained to an overhead trellis system (‘tendone’). Vines were drip irrigated with about 1800–2000 m3/ha during the whole irrigation season (May through September). The values of temperature (°C) and rain (mm) during the growing season for all the 4 years are reported in Table
Mean values of temperature (°C) and rain (mm) during the growing season from March to October (2012–2015).
Month | 2012 |
2013 |
2014 |
2015 |
||||
---|---|---|---|---|---|---|---|---|
T (°C) | Rain (mm) | T (°C) | Rain (mm) | T (°C) | Rain (mm) | T (°C) | Rain (mm) | |
March | 12.32 | 26.60 | 11.70 | 63.80 | 11.06 | 1.14 | 10.75 | 117.62 |
April | 14.32 | 89.20 | 15.28 | 30.40 | 14.12 | 118.25 | 13.73 | 29.80 |
May | 17.43 | 23.80 | 19.04 | 14.00 | 17.16 | 61.09 | 19.29 | 37.02 |
June | 24.10 | 2.80 | 21.62 | 28.60 | 22.08 | 47.42 | 22.03 | 63.56 |
July | 26.94 | 23.80 | 24.39 | 33.80 | 23.83 | 45.14 | 26.41 | 0.00 |
August | 26.16 | 2.20 | 24.97 | 80.80 | 25.13 | 0.69 | 25.98 | 6.54 |
September | 22.79 | 19.00 | 21.22 | 61.40 | 20.86 | 57.32 | 22.75 | 45.82 |
October | 18.19 | 18.80 | 18.23 | 30.80 | 17.79 | 111.08 | 17.50 | 137.85 |
The experimental design adopted in the trial was a randomized block design, with three blocks, each one consisting of 15 vines characterized by uniform crop load and canopy. For the phenological stages, the BBCH scale was used (
The grapevine material sampled for N analyses was collected from:
Summer and winter pruning residues in the 4 years of trial (leaf removal at BBCH 60–85; cluster thinning at BBCH 75–77; berry thinning at BBCH 75–77; fallen leaves at BBCH 93–97; and pruned wood at BBCH 99);
Different annual organs of the vines (leaves of the primary and secondary shoots, clusters, and primary and secondary stems) sampled from the middle position of selected fruiting canes during the main phenological stages of the seasons (BBCH 65; 71 75; 79; 83; and 89);
A representative sample of table grape clusters at harvest (BBCH 89).
The leaves of the primary shoots and the leaves of the secondary shoots are mentioned hereafter in the text as primary and secondary leaves, respectively.
A middle shoot of the cane from each vine was taken from the field at each phenological stage (15 shoots/block), placed in large plastic bags, and was quickly carried to the lab for all the following analyses:
Leaf area measurement, by using a leaf area meter (LI-3100 area meter, LI-COR Inc., United States). Leaf area of the shoots was expressed as cm2, whereas the leaf area of the vine was expresses as m2 and was determined by multiplying the mean total leaf area per shoot by the mean number of shoots per vine in the different phenological stages;
Soil-Plant Analysis Development (SPAD) measurements of the leaf opposite to the cluster. Five readings were carried out for each completely expanded leaf and values were averaged in order to determine the mean SPAD value (Chlorophyll Meter SPAD-502, Konica Minolta);
Vegetative parameters on the middle shoots (primary and secondary) of the cane (number, length, nodes, number and weight of the leaves, weight of both primary and secondary stems);
Measurement of fresh and dry (65°C) weight of all the vine material (ORMA, model BC).
At harvest, the following quantitative and qualitative parameters were measured:
Yield/vine and cluster average weight;
Berry size and weight;
Detachment force was measured with a mechanical gauge PCE-FM1000 (PCE Italia s.r.l., Capannori, Italy), and compression of the berry was measured by using FirmTech 2 Fruit Firmness Tester (Bioworks, United States);
Colorimetric parameters (
Total Soluble Solids (TSS, °Brix) by using a hand-held, temperature compensating digital refractometer HI96814 (Hanna Instruments, RI, United States);
Titratable acidity (grams of tartaric acid per liter of juice) to final pH of 8.1 and pH with an automatic titrator (PH-Burette 24, Crison Instruments, Barcelona, Spain).
All the fresh material was analyzed in 1 day or on the successive day (storage at 4°C). After the analyses, all the material was oven dried (65°C) until constant weight was achieved for the determination of dry weight (d.w.) and water content (w.c.) of the organ. Successively, an aliquot of each sample was stored at -20°C to be used for the subsequent N determination. Clusters to be analyzed for N were lyophilized and stored at -20°C.
Summer and winter pruning residues, clusters at harvest and fallen leaves were collected and fresh weighed in the vineyard (15 vines/block) with a scale in order to determine the weight of the materials for each vine. Successively, a sample for each material was placed in plastic bags and carried to the lab for the analyses (weight and water content). Finally, the samples (clusters after lyophilization) were stored at -20°C for N determination in the successive weeks.
The total N content was carried out on micronized and homogenized samples using an elemental analyzer (Flash 2000 CHNS/O, Thermo Fisher Scientific, United Kingdom) operating according to dynamic flash combustion method (modified Dumas method). The instrument was calibrated with standard BBOT [2,5-Bis (5-tert-butyl-benzoxazol-2-yl)-thiophene] (Thermo Fisher Scientific, United Kingdom), and the samples were analyzed in triplicates. The results were reported based on the dry weight of the material.
Analysis of variance (ANOVA) was performed with XLSTAT-Pro software (Addinsoft, Paris, France) at the 0.05 P level. The assumptions of variance were verified with the Levene test (homogeneity of variance) and the Lilliefors and Shapiro-Wilk tests (normal distribution). The mean values obtained for the different factors were statistically separated by using the REGWQ test. In the case of heteroscedasticity, Kruskal-Wallis non-parametric test was used, followed by the Conover-Iman test to determine differences between phenological stages for each season.
Mean data of phenological growth stages for the vine growth, N content/concentration, and biomass were also subjected to Principal Component Analysis (PCA).
The distribution of N in the different organs of the shoot is shown in Figures
Nitrogen concentration (g/kg of dry weight) in the leaves of the primary
Nitrogen concentration (g/kg of dry weight) in the stems of the primary
Nitrogen concentration
The N concentration in the secondary leaves during the different phenological stages (Figure
Figure
The N concentration in the secondary stems (Figure
The N concentration in the inflorescences/clusters is shown in Figure
The N concentration in the materials removed with summer and winter pruning, fallen leaves, and harvested clusters from 2012 to 2015 are shown in Figure
Nitrogen concentration
The pruning operation that mostly affected the N concentration was leaf removal (mean value 27.1 g/kg), when compared to the other pruning practices carried out during the season. If we looked at the data as N content/vine (Figure
Results of PCA for N content/concentration (Figure
Principal component analysis plot of N content/concentration in materials removed with viticultural practices and fallen leaves in the different seasons
The vine growth values of the seasons 2013, 2014, and 2015 are reported in Tables
Vegetative parameters in 2013.
Stage | Primary shoot length (cm) | Nodes (n.) | Primary shoot f.w. (g) | Primary shoot leaves (n.) | Primary shoot leaves f.w. (g) | Secondary shoots (n.) | Secondary shoots length (cm) | Secondary shoots f.w. (g) | Secondary shoots leaves (n.) | Secondary shoots leaves f.w. (g) |
---|---|---|---|---|---|---|---|---|---|---|
Flowering | 136.0 | 15.8 c | 68.1 b | 10.1 b | 48.4 c | 5.2 c | 40.0 b | 2.6 b | 8.0 c | 3.9 c |
Berry-set | 151.8 | 17.6 bc | 82.1 b | 15.2 b | 100.4 ab | 9.4 ab | 138.0 a | 12.6 ab | 23.9 b | 39.2 b |
Berry growth | 160.5 | 20.9 bc | 116.4 b | 16.6 b | 127.3 a | 9.2 ab | 109.4 ab | 24.8 ab | 29.6 b | 68.1 b |
Veraison | 202.5 | 31.1 ab | 181.1 a | 25.8 a | 116.3 ab | 10.5 ab | 171.3 a | 39.1 a | 46.4 a | 101.1 a |
Ripening | 204.5 | 36.2 a | 175.9 a | 24.0 a | 104.9 ab | 12.2 a | 162.3 a | 28.0 a | 43.0 a | 62.2 b |
Harvest | 179.1 | 25.4 ac | 173.9 a | 16.1 b | 79.9 bc | 6.6 bc | 124.4 a | 30.6 a | 23.9 b | 51.9 b |
Vegetative parameters in 2014.
Stage | Primary shoot length (cm) | Nodes (n.) | Primary shoot f.w. (g) | Primary shoot leaves (n.) | Primary shoot leaves f.w.(g) | Secondary shoots (n.) | Secondary shoots length (cm) | Secondary shoots f.w.(g) | Secondary shoots leaves (n.) | Secondary shoots leaves f.w. (g) |
---|---|---|---|---|---|---|---|---|---|---|
Flowering | 81.9 b | 13.8 c | 58.7 d | 12.4 c | 45.7 d | 8.0 b | 36.8 b | 4.4 d | 13.3 d | 5.9 d |
Berry-set | 134.8 ab | 18.7 bc | 92.1 c | 15.1 bc | 96.4 b | 10.1 ab | 130.0 a | 19.8 b | 25.3 c | 29.2 c |
Berry growth | 151.4 ab | 19.6 bc | 116.9 b | 17.4 b | 103.2 ab | 9.9 ab | 100.7 a | 20.3 b | 27.4 c | 53.3 b |
Veraison | 191.4 a | 31.9 ab | 100.1 c | 28.2 a | 109.9 a | 14.0 a | 115.9 a | 23.1 a | 57.1 a | 67.8 a |
Ripening | 215.2 a | 38.2 a | 127.0 b | 29.6 a | 110.4 a | 14.1 a | 149.2 a | 20.7 b | 45.2 b | 54.2 b |
Harvest | 164.1 a | 24.4 bc | 149.1 a | 14.7 bc | 73.1 c | 8.3 b | 120.2 a | 15.3 c | 21.9 c | 31.1 c |
Vegetative parameters in 2015.
Stage | Primary shoot length (cm) | Nodes (n.) | Primary shoot f.w. (g) | Primary shoot leaves (n.) | Primary shoot leaves f.w. (g) | Secondary shoots (n.) | Secondary shoots length (cm) | Secondary shoots f.w.(g) | Secondary shoots leaves (n.) | Secondary shoots leaves f.w. (g) |
---|---|---|---|---|---|---|---|---|---|---|
Flowering | 86.8 c | 14.7 d | 61.7 e | 10.7 c | 43.9 f | 5.9 c | 41.7 c | 4.2 c | 8.9 c | 6.3 d |
Berry-set | 142.9 b | 20.8 c | 79.6 d | 15.2 b | 93.4 b | 9.7 ab | 143.9 b | 15.5 b | 24.1 b | 36.5 c |
Berry growth | 145.7 b | 22.0 c | 88.1 d | 17.6 a | 106.8 a | 10.9 a | 176.7 a | 23.8 a | 37.8 a | 76.1 ab |
Veraison | 157.8 b | 25.1 b | 100.9 c | 16.1 b | 89.3 c | 8.1 b | 183.9 a | 24.4 a | 34.0 ab | 72.0 ab |
Ripening | 193.1 a | 33.4 a | 133.0 b | 15.7 b | 75.1 d | 9.3 ab | 192.9 a | 24.3 a | 31.1 ab | 70.4 b |
Harvest | 205.9 a | 34.0 a | 143.2 a | 11.9 c | 63.7 e | 10.1 ab | 208.3 a | 26.3 a | 31.9 ab | 80.1 a |
Total vine biomass (as g of d.w.) increased with a similar pattern in all the three seasons (Figure
Total vine biomass growth from flowering to harvest (g of dry weight) of Italia table grape throughout the seasons of 2012, 2013, and 2014 as a function of the different phenological growth stages. Bars represent standard deviation. For each season, data points followed by a different letter are significantly different at
Leaf area was measured from 2013 to 2015 during the main phenological stages (Table
Leaf surface area of Italia table grape throughout the seasons of 2013, 2014, and 2015.
Stage | Primary shoot leaf area (cm2) |
Secondary shoots leaf area (cm2) |
Total shoots leaf area (cm2) |
Total vine leaf area (m2) |
||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
2013 | 2014 | 2015 | 2013 | 2014 | 2015 | 2013 | 2014 | 2015 | 2013 | 2014 | 2015 | |
Flowering | 1622.0 b | 1934.0 c | 1726.0 b | 309.6 c | 369.6 c | 336.2 c | 1931.6 c | 2303.6 d | 2062.2 c | 4.9 c | 5.9 d | 5.7 c |
Berry-set | 2694.0 ab | 3094.0 ab | 2671.8 ab | 1934.6 ab | 2134.6 bc | 1845.8 b | 4628.6 ab | 5228.6 bc | 4539.7 b | 11.8 ab | 13.4 bc | 12.6 b |
Berry growth | 3130.7 a | 3269.6 ab | 3384.6 a | 2650.6 ab | 2754.5 b | 2643.3 ab | 5781.3 a | 6024.1 b | 6027.9 a | 14.7 a | 15.5 b | 16.8 a |
Veraison | 3616.0 a | 3502.5 a | 3371.5 a | 2916.2 a | 4560.9 a | 3560.9 a | 6532.2 a | 8063.4 a | 6932.5 a | 16.6 a | 20.7 a | 19.3 a |
Ripening | 3512.0 a | 2371.7 bc | 2813.4 a | 2457.9 ab | 2062.2 bc | 2062.2 b | 5969.8 a | 4433.9 bc | 4875.6 b | 15.2 a | 11.4 bc | 13.6 b |
Harvest | 1898.9 b | 1637.8 c | 1669.9 b | 1247.2 bc | 1804.5 bc | 1582.2 b | 3146.0 bc | 3442.3 cd | 3252.1 c | 8.0 bc | 8.8 cd | 9.0 c |
The pattern of SPAD values (Figure
SPAD values of leaf opposite to the cluster of Italia table grape throughout the seasons of 2013 and 2014 as a function of the different phenological growth stages. Bars represent standard deviation. For each season, data points followed by a different letter are significantly different at
Results of PCA for N concentration/content and vegetative parameters at the different phenological growth stages in the 3 years showed that the two main components were responsible for 79.89% of the total variation (PC1 60.13% and PC1 19.76%). The variables were oriented toward the four PCA quadrants (Figure
The different parameters measured at harvest for all the seasons are shown in Table
Quality parameters of Italia table grape throughout the seasons of 2013, 2014, and 2015.
Yield (kg/vine) | Yield (t/ha) | Berry length (mm) | Berry width (mm) | Berry weight (g) | Cluster weight (g) | Detachment force (N) | Compression (N) | TSS (°Brix) | pH | Titratable acidity (g/L) | h° | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2013 | 35.3 | 58.2 | 30.4 a | 24.6 a | 12.2 a | 733.9 b | 8.4 | 1.81 | 17.0 | 3.68 | 3.69 | 41.2 b | 8.3 b | 104.8 b |
2014 | 33.8 | 55.8 | 28.2 b | 22.2 b | 9.6 b | 862.9 a | 8.0 | 1.53 | 17.2 | 3.51 | 4.06 | 41.9 a | 9.8 a | 108.7 a |
2015 | 34.0 | 56.1 | 28.3 b | 22.4 b | 9.7 b | 803.4 ab | 8.1 | 1.82 | 17.2 | 3.67 | 3.90 | 41.5 ab | 8.5 b | 105.9 b |
Among the colorimetric parameters,
This was the first 4-year trial where the distribution of N in both different annual vine organs and pruning materials was presented for field grown table grape vines (Figures
The pattern of N concentration in primary leaves was similar to the one reported for young Thompson Seedless vines (
The secondary leaves showed a general higher N concentration with respect to primary leaves, and from these leaves, N was partially translocated both toward the clusters and the storage organs (canes, cordons, trunk, and roots), starting from veraison-ripening, as previously reported for wine grape (
Most of the N that was taken up from soil or remobilized ended up in the leaves in the first part of the season (maximum N content at berry growth-veraison), whereas leaf N content declined after veraison, partly as a result of supplying cluster needs during this time, as reported for Pinot Noir (
The highest N concentration in the annual vegetative organs occurred between flowering and berry growth, as previously reported for young Thompson Seedless vines (
Stem N concentration reached the lowest values at veraison in all years with the exception of 2015, similar to what was found for Thompson Seedless vines in Australia (
From the closing of the cluster to veraison, when the active growth of the shoots begins to stop, most of the N absorbed from the beginning of the season is localized in the clusters, but a significant percentage is also accumulated in the primary and secondary leaves (Figure
With regard to the clusters, the N content in the berry mainly consists of amino acids (
The pattern of N concentration in clusters of Italia was similar to that of Pinot Noir, but at harvest we detected values of 5–7 g/kg whereas in Pinot Noir values were around 10 g/kg (
Several studies reported that the vine accumulates most of the N between flowering and veraison as a result of being associated with cell division and growth that require N for the synthesis of chlorophyll, nucleotides, nucleic acids, and proteins (
At harvest, the N was distributed according to a constant pattern among different varieties: about a third accumulated in clusters and, of the remaining two-thirds, most of it was accumulated in the leaves and stems, while a smaller percentage was found in the roots, trunk, and branches (
Nitrogen concentration of the vine organs decreased throughout the current season in each year because of the mass growth, but an increase of N content was measured particularly for clusters. This was the consequence of the faster dry weight accumulation with respect to N accumulation, owing to the change of the growth model from cell division and cytoplasm rich cells toward cell wall material and non-growing tissues (
Nitrogen movement toward permanent vine parts did not occur until after fruit harvest in 23-year old Pinot Noir vines (
We can assume a similar amount (8–15 g/vine) to be accumulated in the aboveground organs and it should be mobilized from the permanent structures, mainly canes and older wood, and from roots, in the successive season at bud-break. If we add these values to the N accumulation in the annual organs previously reported (≅42 g, including summer pruning) we have an N accumulation of ≅50–55 g/vine during the season. The materials removed with summer and winter pruning and fallen leaves accounted for 29–31 g/vine, and will be partly available for the vine in the successive seasons if the residues are trimmed (pruned wood) and incorporated in the soil, while successively undergoing mineralization. Hence, summer and winter pruning and fallen leaves are only temporary N removals. It is unknown how rapidly these tissues mineralize and how much N will be used by vines during the following season, but we could consider realistic 10 g/vine (≈30%) as reported for other species (
In our study, we detected N concentration in fallen leaves of Italia vines of around 9–10 g/kg, slightly lower than the value (12.5 g/kg) reported for Thompson Seedless vines (
The N concentration in the pruned wood was in the range of 6.0–7.9 g/kg, very similar to what found (7.5 g/kg) for Thompson Seedless vines in California (
In the trunk, a lower N concentration has been reported (2–5 g/kg) with respect to N in 1 to 2-year old wood (
All these data suggest that the vine should contain an appropriate amount of N in the storage organs to be used at bud-break to sustain the early shoot growth. Nitrogen is extremely essential in the first phenological growth stages (flowering and berry growth), and an N fertilization after bud-break (i.e., fertigation) is necessary for the development of clusters with excellent quality and size parameters. Taking into account the N content at harvest (35 g/vine), the fraction accumulated in the storage sites (8–15 g/vine) and the amount lost with summer pruning (7 g/vine), we could consider a whole accumulation of about 50–55 g/vine for a yield of ≅30 kg/vine. In a table grape vineyard of 1500 vines/ha and 40–45 t of grapes/ha, the N requirement to sustain the vineyard will account for ≅80 kg of N/ha. A fraction (20–30%) of the N lost with summer and winter pruning, and fallen leaves (25–30 g/vine) will be partly available in the successive season (if incorporated and mineralized in the soil). Nitrogen fertilizers show a wide range of recoveries in the plant (5–96%) depending on type of fertilizer, mode of application, climate, soil type, and crop management with a mean value of 50% for cereal crops (
Based on the PCA data, the different years were characterized for N content/concentration depending on the viticultural practice. In particular, in 2012, the highest amount of N was removed with berry and cluster thinning, whereas heavier leaf removal and pruning operations were done in 2013 and 2015, respectively. These data showed a certain variability of values of N removed from the vineyard depending on the season as a consequence of both physiology of the vine (crop load, vine vigor, percentage of shot berries, etc.) and type of human labor (intensity, ability, specialization, etc., of workers).
Italia shoot length reached the maximum value of around 200 cm in all the 3 years around the time of ripening (end of August), when natural tipping of the shoots (breakage against the plastic cover) and manual operation of tipping reduced the length. Italia primary shoots length reached higher values (>200 cm) than the ones (≅120–160 cm) reported for Thompson Seedless vines measured over 3 years in California, but the pattern was quite similar (
The pattern of Italia leaf area surface was similar to Thompson Seedless unpruned vines, although with higher values, since Italia vines were 15-year old and Thompson vines were only 2-year old (
The leaf surface area of Italia vines reached values of 17–21 m2 at veraison, not far from values reported for 2-year old Thompson Seedless (18–24 m2) by
Although the leaf area significantly decreased from veraison, the weight of leaves was almost similar. This indicated that older leaves were heavier than younger ones because there was a significant reduction of water content from 82% (younger leaves) to 70% (older leaves) and to 50% in senescent ones. The PCA analysis confirmed the higher water content of the organs from flowering to berry-set (Figure
Total vine biomass growth in the different years clearly indicated two strong increases, before and after veraison. In particular, before veraison, we measured a significant growth of the shoots and leaves, whereas after veraison, the noteworthy growth of the clusters was evident. The lag phase generally detected before veraison (
With respect to SPAD measurements, values at berry growth (44.1 in 2013 and 38.6 in 2014) were similar to those reported by
The PCA analysis showed the changes of the vine during the season, with various significant steps in the different phenological stages. At flowering, N concentration was very high in sinks such as inflorescences and stems, thus, indicating an important requirement of such element at this stage to support the reproductive phase. Successively (berry-set and berry growth), there was a strong increase in the water content of the young and growing tissues, also suggesting the important role of irrigation in supporting absorption of elements and increase of vine biomass. During these stages, N concentration in the leaves was highest to sustain the intense metabolism of the vine (clusters and shoot growth). At veraison, the leaves reached the highest number and weight, whereas at ripening and harvest clusters reached the highest weight and content of N, thus, becoming the stronger sink for this element at the end of the season.
Data of the 3 years failed to show particular differences, since the vineyard was always managed according to local practices. The differences for some parameters such as cluster size were probably the consequence of climatic conditions (Table
In conclusion, the N concentration of Italia vines declined in all the annual vine organs (leaves, stems, and clusters) throughout the season with different patterns. The N content varied among the different annual organs, with the greatest accumulation observed in clusters with values ranging from 19 to 25 g/vine at harvest. Nitrogen content in both primary and secondary leaves reduced after veraison.
As expected, clusters accounted for the greatest N removal from the vine (21.4 g), followed by pruned wood and fallen leaves, with 13.6 and 8.7 g/vine, respectively. In the case of pruned wood and fallen leaves, it should be only a temporary removal from the vine, because part of N would become available after the mineralization of the incorporated residues in the soil. Taking into account these data, the overall N required by the vine was around 50–55 g/vine, which corresponded to about 80 kg of N/ha in a table grape vineyard with 1500 vines and a yield of 40 t/ha.
Based on N concentration and leaf area, primary leaves were important for N translocation toward clusters till veraison; successively, secondary leaves also played an important role for the translocation of N to clusters and stems. The reduction of N content in primary leaves after veraison suggested a translocation of N to stems and permanent organs. The final reduction of N in the fallen leaves also indicated a partial translocation of N to vine before abscission.
We think that a confirmation (with some obvious differences) of the results reported in the literature for wine grapes can be considered an important aspect of this research on table grape. Values of N concentration in clusters depended on the different crop load and cluster size of table grape varieties with respect to wine grape varieties. The different yield and canopy development can also explain the higher accumulation of N in the clusters of table grape with respect to wine grape. The results obtained in this study could be useful not only in Italy but also in many other countries where table grapes are cultivated, as we all know the importance of N fertilization. Data of this 4-year study would suggest N values of 50 g/vine should be more than appropriate for such type of vineyard, and even lower N values (40 g/vine) when pruned residues are also trimmed and incorporated in the soil undergoing mineralization (or cover crops are used). If we could reduce N application (with appropriate fertilization schedules), it would be very useful for the environment (lower pollution of soil, water, etc.) and for the balance of the farm (lower costs for the fertilizers, use of cover crops, etc.).
GF conceived and designed the study, analyzed the data, and wrote the paper. AMSM and AM performed the field and laboratory analyses, collected and analyzed the data, and wrote the paper. ADM performed the laboratory analyses and analyzed the data. DM performed laboratory analyses and analyzed the data.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank the Fanelli farm in the countryside of Conversano (Ba) for all the measurements and collections of samples carried out in the vineyard. The authors thank Prof. Matthew Fidelibus for his comments and suggestions on the manuscript.