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1 Professor of Viticulture, 2 Graduate Student, and 3 Technician, Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, Ontario, Canada.
* Corresponding author [Email: areynold{at}brocku.ca];
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Abstract |
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Key words: methyl anthranilate, transpiration, Vitis labruscana, volatile esters
Both field-grown (Smart and Coombe 1983) and potted grapevines (Reynolds and Naylor 1994) usually respond favorably to added irrigation water in terms of increased yields and improved fruit composition. Vitis vinifera (Smart 1974, Smart and Coombe 1983) as well as most fruit trees (Chalmers et al. 1986, Ebel et al. 1995) are by necessity irrigated in arid climates such as those in California and Australia. However, vigorous V. vinifera grapevines frequently produce dense, shaded canopies that may reduce winegrape quality (Smart et al. 1985). That has been remedied by imposing a mild water stress through irrigation deficits (Caspari et al. 1997, Matthews and Anderson 1988, Matthews et al. 1987), which may reduce vine vigor and reduce competition for carbohydrates by the growing tips and is likely to increase fruit quality. Specifically, there is some evidence that reducing irrigation may lead to increased concentration of flavor compounds in the fruit (McCarthy and Coombe 1985), whereas other work suggests that irrigation deficits applied at postbloom or lag phase may reduce berry monoterpenes (Reynolds and Wardle 1997).
Grape cultivars used for juice (V. labruscana cvs. Concord and Niagara) in the Niagara region of Ontario tend to be low in vigor, and hence provide a problem opposite to that of many winegrape vineyards. Low vigor and attendant low yields have become commonplace in the past few years. Moreover, V. labruscana cultivars are very sensitive to water stress (Naor and Wample 1994), such that decreased leaf water potentials (
) usually are accompanied by significant decreases in stomatal conductance and net assimilation rate. The rapidly falling yields in the Niagara region have been attributed to changes in weather patterns and, specifically, to drought conditions during the fruit maturation phase (stage III) of grape berry development (OGGMB 2002). Vitis labruscana yields tend to be based upon many small clusters containing few, but relatively large (3 to 4 g) berries. Berry weight is highly dependent upon water uptake during stage III of berry growth. Providing V. labruscana vines with sufficient water during this developmental stage should therefore have a significant impact upon their yield.
Use of irrigation for V. labruscana in Ontario and the northeast and midwest United States has received little attention. In Arkansas researchers (Spayd and Morris 1978) increased yield of Concord by 2 t/ha by using irrigation. Subsequent studies showed that irrigation could increase both yield and soluble solids in Concord during drought seasons (Morris and Cawthon 1982). In Ontario, Cline et al. (1985) measured high soil water tension using tensiometers installed in clay soils and found that irrigation increased yields of Geneva double curtain-trained Concord by 13% and also increased berry and pruning weights. In New York, Liu et al. (1978) measured < –16 bars in field-grown Concord vines; however, leaves at these did not experience stomatal closure. Recently, Lakso and Pool (2001) began to investigate irrigation management for Concord and Niagara in the gravelly soils adjacent to the south shore of Lake Erie. Preliminary data indicate that Niagara responds more favorably to supplemental irrigation than Concord; however, under intensive management that may include minimal pruning, irrigation is considered an essential adjunct.
Fertigation, or the provision of fertilizers in irrigation water, is a relatively recent innovation. Bravdo and Hepner (1987) showed that nitrogen, phosphorus, and potassium (NPK) fertigation increased uptake of these elements compared to conventional fertilization, increased juice P and monoterpenes, and improved wine quality. However, very little fertigation research on grapevines has been done in the last 10 years. Impact of fertigation on fruit trees, on the other hand, has been intensively studied. Neilsen et al. (1997) showed that varying the rate of fertigation to high-density apple orchards produced significant differences in soil and tissue N, P, and K. Uptake and tissue concentrations of other major and minor elements were also positively impacted by fertigation management (Neilsen et al. 1993).
The use of irrigation management on V. labruscana vineyards in the northeast United States and Canada may alleviate water stress during fruit maturation and lead to more optimal fruit composition. Moreover, at a time when water shortages are becoming critical, more definitive information is needed on the response of V. labruscana to irrigation in regions that have heretofore not used any form of water management. These experiments were designed to investigate the impact of different durations of irrigation and fertigation upon vine performance, fruit composition, and water relations of V. labruscana cvs. Concord and Niagara. They were also established to quantify the degree of water stress that Niagara Peninsula vineyards typically experience. There were three key issues we investigated with these experiments: (1) the effectiveness of irrigation on heavy clay soils; (2) the efficacy of fertigation with respect to increasing vine size and yield; and (3) the importance of timing of fertigation. A major focus in the final year of this project was to devise a method for calculating water budgets to precisely schedule irrigations. The Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith formula for calculating evapotranspiration (ET0) was used as a basis for irrigation scheduling. We hypothesized that supplemental irrigation and fertigation of V. labruscana cvs. Concord and Niagara would improve yield, overall vine performance, and berry composition through alleviation of water and nutrient stress. We furthermore hypothesized that the use of Penman-Monteith equation to calculate water budgets could be validated through measurement of vine and soil water status.
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Materials and Methods |
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The Concord experiment was established to specifically assess the impact of timing of fertigation (Table 1
). The experiment was a randomized complete block with six treatments and three blocks, consisting of 18 rows (200 vines long), each representing a specific treatment replicate. Two buffer rows bordered the plot. The fertilizer for the fertigation treatments was soluble 46-0-0 (urea), applied at a rate of 80 kg N/ha. The nonirrigated control and irrigated treatments were fertilized at 80 kg N/ha with granular 34-0-0 (ammonium nitrate). Twelve representative, equally spaced vines per row were designated for data collection. Irrigation or fertigation began each season shortly after bud-burst, at Eichhorn and Lorenz stage 12 (referred to as EL-12; typically around 15 May), when shoots were about 10 cm in length (Eichhorn and Lorenz 1977), and ceased at veraison (typically around 21 Aug).
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). Nine treatments were included in a randomized complete block, with three blocks, and each treatment replicate assigned to a row. Buffer rows were established on the perimeter of the experiment. As with the Concord trial, the nonirrigated control and irrigated treatments were fertilized at 80 kg N/ha with granular 34-0-0 (ammonium nitrate). Irrigation or fertigation began each season either shortly after bud-burst, at EL-12 (typically around 15 May), or at bloom (typically 20 June). Fertigation treatments were fertilized with 80 kg N/ha as 46-0-0, but at the different timings specified in Table 2. The last two treatments (8 and 9) were supplemented with 20-20-20 fertilizer over the fruit-set to veraison period to examine the effectiveness of post-set P and K addition. Twelve representative, equally spaced vines per row were designated for data collection.
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). In 2002, measures were taken to optimize the amount of water applied at each scheduled irrigation in an attempt to better fulfill vine evaporative demand. The FAO Penman-Monteith equation was first used to calculate the daily reference evapotranspiration (ET0) for the site based on weather variables from the Niagara Agricultural Weather Network (NAWN). Soil heat flux was deemed to be negligible in the Niagara region and thus not included in the calculation. The ET0 between 1 June and 26 July 2002 varied between 1.35 and 9.03 mm/day. The ET0 was then used, along with a soil water storage factor and a crop coefficient (0.75), to calculate the amount of water required by the vines in L/vine/day (Van der Gulik and Eng 1987). This calculated amount was then applied to the vineyard the following week. During peak ET0, the daily calculated volume was 24.4 L/vine (4.8 mm/day).
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Yield components and vine size. At harvest, 100-berry samples from random clusters in each vine were collected and stored at –25°C until analysis. Berry weights were determined on these samples. Yield and cluster number were determined on a per vine basis. Cluster weight was calculated from yield per vine and clusters per vine data. Berries per cluster were calculated from cluster weight and berry weight data. Harvest dates (Concord) were 28 to 29 Sept (1998); 10 to 12 Sept (1999); 27 to 29 Sept (2000); 7 to 9 Sept (2001); 13 to 15 Sept (2002). Harvest dates (Niagara) were 2 to 4 Sept (1998); 6 to 8 Sept (1999); 20 to 22 Sept (2000); 10 to 13 Sept (2001); 10 to 12 Sept (2002). Each data vine was pruned in the dormant season, and weights of cane prunings were collected using a dairy scale as estimates of vine size.
Fruit composition. The frozen 100-berry samples were heated to 80°C in a water bath, juiced in a juicer, and the clear juice was separated by vacuum aspiration. The resulting juice was used to measure Brix using an Abbé refractometer (model 10450; American Optical, Buffalo, NY), pH via an Accumet pH meter (model 25; Denver Instrument Company, Denver, CO), and titratable acidity with a PC-Titrate autotitrator (Man-Tech Associates, Guelph, ON).
In addition, an extra 500-berry sample was taken from each treatment replicate in 2001 and 2002 to measure concentrations of methyl anthranilate (MA) and total volatile esters (TVE) as described by Fuleki (1982). Samples were removed from the –25°C freezer and allowed to thaw for several hours. Following homogenization in a Waring blender for 30 seconds, eight subsamples of 50 g were then weighed out and distilled using a distillation apparatus (model 141–1660; Lurex Scientific, Vineland, NJ), consisting of a 2-L round-bottomed steam-generating flask, a 1-L distillation flask, and a Friedrich condenser. Each 100 mL distillate sample was collected in a Kohlrausch flask held in an ice bath. The same distillate was used to determine both MA and TVE concentration.
Methyl anthranilate concentration was determined via a luminescence spectrophotometer (model LS50; Perkin-Elmer, Boston, MA), set to an emission wavelength of 425 nm and excitation at 335 nm, with slit widths of 8.0 and 5.0 mm, respectively. The fluorescence of MA was read directly from the apparatus, while the MA concentration was determined through the use of a standard curve constructed using 0 to 10 mg/L standard solutions (Fuleki 1982). Total volatile esters values were determined through a colorimetric reaction (Hill 1946), followed by extrapolation from an ethyl acetate standard curve constructed using 0 to 125 mg/L standard solutions. Absorbance readings of all standards and samples were carried out on a Pharmacia Biotech Ultraspec 1000E UV/VIS spectrophotometer (Biochrom, Cambridge, UK) at 540 nm. Thereafter, TVE concentrations were read from the standard curve.
Plant tissue analysis. Petioles were sampled from leaves adjacent to basal clusters in late Aug 1999. About 50 g of petiolar material was sampled from the 12 designated vines in each treatment replicate. Samples were dry ashed for 2 hr in a muffle furnace at 550°C, digested with hydrochloric and nitric acids, diluted, and analyzed using an Optima 3000 inductively coupled plasma optical emission spectrometer (PerkinElmer, Shelton, CT). All plant tissue analysis was performed at Agri-Food Laboratories, Guelph, ON.
Statistical analysis. All data was analyzed using SAS statistical software (SAS Institute, Cary, NC), with the general linear models procedure. Duncan’s multiple range test was used for means separation. Dunnett’s t test was used to determine if differences existed between the controls and individual treatments. Orthogonal contrasts were used to establish whether differences existed between specific groups of treatments.
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Results |
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). On two dates, control leaves inexplicably had slightly higher transpiration rates than the fertigated treatment. In 2001, the transpiration rates for Concord leaves were higher in the fertigated treatment than in the control on the first two sampling dates (Figure 2B). The severe drought conditions later in the season provoked a steep decline in the transpiration of fertigated vines (4.94 to 0.87 µg H2O/cm2/s), to a point where they were actually transpiring less than the nonirrigated control on the last three sampling dates. In 2002, an increase in overall transpiration was seen in both treatments, but again, fertigated treatments displayed lower transpiration; there were only two dates (25 July and 16 Aug) on which differences between the treatments were observed (Figure 2C).
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). The fertigated from bloom treatment had higher transpiration than the fertigated from budburst treatment on three of six sampling dates. In 2001, Niagara vines transpired at low rates in all treatments tested, with values ranging from 0.73 to 1.76 µg H2O/cm2/s (Figure 3B). Neither the irrigated treatment (budburst to veraison/dry thereafter) nor the fertigated treatment (fertigated budburst to veraison/irrigated thereafter) showed higher transpiration rates than the nonirrigated control. In fact, the control actually transpired at a higher rate than the other two treatments on three sampling dates (25 July, 15 Aug and 6 Sept). As with Concord, the Niagara vines showed a late season decline in transpiration in 2000 and 2001 and an increase late in the 2002 season.
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). Overall, Niagara vines showed much higher transpiration rates in 2002 than in 2001 (2.60 to 5.07 µg H2O/cm2/s).
Soil moisture.
Soil moisture values were acquired for the Niagara and Concord plots on three sampling dates in 2001 and two sampling dates in 2002. The 2001 Concord data revealed that the single fertigation treatment was the only one to exceed the control (Table 3). On 5 July 2002, following an irrigation period, soil moisture values in Concord varied between 11.9% (fertigated; split application) and 13.9 % (variable rate fertigation). No substantial differences were found among the treatments. It is noteworthy, however, that all treatments were below the published wilting point of 18.7% for Toledo clay soil (Kingston and Presant 1989), even following the irrigation.
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). In 2001, no treatments exceeded the control on the first sampling date, and treatments 7 and 9 inexplicably had lower soil moisture than the control on the second sampling date, despite current application of water in both treatments. The 9 Aug 2002 soil moisture in the nonirrigated control treatment was lower than all other treatments (12%). The other irrigation and fertigation treatments showed higher values than those in the Concord treatments a month earlier. The irrigation until harvest treatment showed the highest soil moisture value at 16.3%.
Vine size.
Weight of cane prunings for Concord averaged 0.3 kg/m row before treatment in 1998 (Table 4). The pruning weights were numerically highest in the irrigated treatment in 3 of 5 years, although not significantly different from the control and three fertigated treatments in 1999, or different from two fertigated treatments in 2002. There were also no treatment effects in 1998 and 2001. The 5-year means suggested that neither irrigation nor fertigation was effective in increasing vine size. However, after five years of irrigation, the weight of cane prunings of the irrigated treatment was 215% higher in 2002 than the mean vine size in 1998, or about 0.6 kg/m row.
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). Niagara vine size was significantly lower in the dry control treatment than in some treatments in 1998, 2000, and 2002, while fertigated treatments 7, 8, and 9 had a tendency to produce the greatest pruning weights in most seasons. Treatment 8 was among the highest vine sizes in 4 of 5 years, while treatments 7 and 9, along with treatment 2 (all of which were irrigated until harvest), were among the highest in 3 of 5 seasons; treatment 7 was the only treatment that exceeded the control in terms of the 5-year means. Although not as responsive as Concord in terms of vine size, weight of cane prunings of irrigated Niagara vines were about 150% higher in 2002 than in 1998, or 0.23 kg/m row.
Yield components.
Except for 1998, the dry control yielded lowest in Concord (Table 5). Two irrigation and/or fertigation treatments exceeded the control in 1999, three in 2000, and one in 2001, but no differences were observed between treatments in 2002. No single treatment was dominant; however, fertigation involving either a single or split application (treatments 3 and 4) were among the highest yielding in 4 of 5 years as well as the 5-year mean. The fertigation contrast was also significant in 2 of 5 years, suggesting that fertigation was superior to irrigation in this respect and that the increases in yield were not simply due to application of water alone. A number of yield components including clusters per vine were enhanced by irrigation and fertigation, in particular, irrigation alone (1999, 2000, and the 5-year mean), the single fertigation application (1998, 2000, and the 5-year mean) and the variable rate treatment (2001 and the 5-year mean) (Table 5). The split and weekly fertigation applications also had higher clusters per vine than the control in one of five seasons (2000 and 2001, respectively). The significant contrasts in 1998 and 2000 suggested that both irrigation and fertigation increased cluster number per vine. Irrigation, single application fertigation, and the variable rate treatment all increased clusters per vine relative to the control in terms of the 5-year means.
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). Cluster weight was highest in each of the aforementioned seasons in the irrigated, split, and weekly fertigation treatments, although the 5-year means were not significant. No consistent pattern was observed for berry number, although in seasons in which treatment differences were observed, treatments with highest berries per cluster were split application and weekly fertigated, and the latter treatment exceeded all others in the 5-year means. Berry weight was increased by both irrigation and fertigation treatments only in 1999; in other seasons, either no differences were observed or the berry weights of the nonirrigated controls equaled or exceeded those of the other treatments. The irrigated treatment exceeded the berry weight control in terms of the 5-year means.
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). Several treatments, however, appeared to rank among the highest-yielding each season, including irrigated to harvest, irrigated to veraison, fertigated bloom to veraison/irrigated after, and fertigated variable rate + irrigation thereafter. Five of eight treatments outyielded the control in terms of the 5-year means; two of the three treatments that did not exceed the control were those in which irrigation ceased at veraison. Cluster number, similarly, did not exceed nonirrigated controls in two of five years (1998 and 2000) but certain treatments that were noteworthy and/or consistently among the highest in cluster number, included irrigated to harvest, irrigated to veraison, fertigated bloom to veraison/irrigated after, variable rate fertigation + irrigation thereafter. Four of eight treatments exceeded the control in terms of 5-year mean cluster number: irrigated to veraison, fertigated bloom to veraison/irrigated thereafter, and the two variable rate treatments. The large reduction in cluster number between 2001 and 2002 was most likely due to late spring frost injury. Clusters per vine varied between 79 and 97 in 2001, while no treatment showed a cluster number >35 in 2002.
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). Cluster weights in some irrigated and fertigated treatments exceeded those of the controls in 3 of 5 seasons, and both irrigated treatments, the fertigated bloom to veraison/irrigated thereafter treatment, and both variable rate fertigation treatments tended to produce highest cluster weights when the 5-year means were also considered. One of the irrigated treatments and both variable rate treatments produced highest 5-year mean cluster weights. A similar pattern occurred for berries per cluster; treatment differences existed in 3 of 5 seasons, and the irrigated, fertigated/irrigated after, and variable rate fertigation treatments produced consistently highest berry numbers. Berry weights increased over the control in 4 of 5 years in many of the irrigated and/or fertigated treatments including all eight treatments for the 5-year means.
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). The control treatment exceeded the other five treatments throughout the 5-year study by a maximum of 1.5 Brix in 2001; while in 2002 no differences among treatments were observed. Correlations between yield and Brix were not strong (data not shown). Total volatile esters did not differ substantially among the treatments, although the split application tended to produce highest TA (Table 9). Differences between treatments occurred for berry pH in 3 of 5 years (1999 to 2001), but no consistent pattern was discernible.
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). A completely opposite trend was observed in 2002, as the control and irrigated berries showed highest values, while all other treatments were lower than the control. Total volatile esters concentrations were very similar among treatments over both seasons (Figure 4B).
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). In the final year of study, the Brix of six treatments equaled that of the control, and higher overall Brix levels were measured that were more consistent across all treatments than in previous seasons. The contrasts suggested that both irrigation as well as fertigation were implicated in the reduction in Brix (Table 10). There were weak correlations between yield and Brix (r = 0.34) (data not shown). A slight elevation in berry TA over the control was evident in several irrigated or fertigated treatments in 4 of 5 seasons; irrigated to harvest, and fertigated bloom to veraison/dry thereafter consistently produced high berry TA. Berry pH was affected very little and no discernible pattern amongst treatments was apparent.
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). The control treatment was lowest in MA in 2001, as was the case with Concord (Figure 4A). Treatment 7 (bloom to veraison fertigated followed by irrigation) was consistently low in MA over both seasons (Figure 5A), which was noteworthy as this treatment showed highest yields in both those years (Table 7). Total volatile esters values for the control and irrigated treatments were similar for Niagara over both years (Figure 5B). No other consistent trends were noticeable for TVE values. An anomaly existed for treatment 4 (fertigation budburst to veraison/dry thereafter), such that it had the highest TVE values in 2001, but the lowest values in 2002.
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). Weekly fertigation increased petiole N, single application fertigation increased petiole P, but the apparent uptake of all other elements was not enhanced by either irrigation or fertigation. Niagara vines were somewhat more responsive than Concord in terms of nutrient status (Table 12). The two variable rate fertigation treatments increased petiole N, P, and Ca relative to the control. Irrigation alone increased petiole Cu and Fe (irrigated up to harvest), and P and Ca (irrigated up to veraison), while fertigation from EL-12 to veraison/dry thereafter increased petiole Ca and Mn.
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Discussion |
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). Rainfall data suggest that there may have been adequate precipitation in June and July and that irrigation was therefore of little benefit until the latter part of the growing season. Niagara appeared to respond as predicted to fertigation in 2000, with both fertigated treatments displaying highest transpiration rates throughout the season (Figure 3A). The transpiration rate trends for both V. labruscana cultivars in 2001 and 2002 appeared to be mainly a function of the weather patterns in the latter part of the growing seasons. Overall transpiration rates in 2001 were low in both Concord and Niagara, consistent with severe drought stress (Figures 2B, 3B). In fact, vines experienced a drought so severe that even the supplemental irrigation and fertigation could not raise transpiration levels, and the control treatment was actually transpiring at a higher rate than the irrigated and fertigated treatments. The 2002 season saw less late season drought stress, and hence there was a trend in Concord and Niagara toward an increase in transpiration rate as the season progressed (Figures 2C, 3C). Overall, transpiration data suggest that despite low vine size (hence low water demand), either insufficient water was being supplied by the irrigation system or vine water relations were not being substantially impacted by the irrigation and fertigation treatments. The small vine size increases in some of the irrigated and fertigated treatments in 1998 to 2000 may have increased water demand beyond the volume of irrigation water supplied.
The soil moisture data from 2001 was generally inconclusive and did not show higher moisture levels in irrigated plots. A comparison of both Concord and Niagara treatments in 2002, however, revealed that irrigated and fertigated treatments had higher overall soil moisture than the nonirrigated controls, as one would expect. Data nonetheless suggested that all treatments were very low in soil moisture (Table 3), even below the published wilting point for Toledo clay of 18.7% (Kingston and Presant 1989). However, these values are similar in magnitude to the 14.8% soil moisture value for drought-stressed Concord vines in Honeoye gravelly sandy loam soil in New York state reported by Poni et al. (1994). Toledo series clay soils are generally poorly drained, tend to crack when dry, and are thus difficult to re-wet (Kingston and Presant 1989). Therefore, even when the theoretical correct amount of water was added, it may not necessarily have been absorbed by the soil. Another possibility for the low soil moisture numbers may be that the Penman-Monteith equation may have simply underestimated the amount of water required by these vines growing on this particular soil. Evidence to support this view lies in the very low transpiration values (Figures 2, 3).
Vine size and yield components. Lower berry weights are often the objective in winegrape production. That is particularly the case with red winegrape cultivars, which are fermented on the skins. This increased skin:volume ratio in turn heightens the overall concentration of color and flavor-producing compounds (Ginestar et al. 1998, Williams and Grimes 1987). Water deficits increase phenolic compounds, such as anthocyanins, which contribute to astringency and wine aging characteristics (Bravdo et al. 1985). Vines with increased water stress have generally been shown to have lower berry weights than unstressed vines (Goodwin and Jerie 1989, Reynolds and Naylor 1994).
Juice grapegrowers generally get paid primarily on a weight basis, making larger berries desirable. Vitis labruscana berry weights are highly dependent upon water uptake during stage III of berry development, making late-season water stress problematic. The results in this trial suggested that irrigation and fertigation of V. labruscana growing on heavy, Toledo clay soils may slightly increase vine size and yields. The yield increase appeared to result from a combination of increased cluster number (enhanced berry set), larger berry size, and increased vine size. These data contradict those reported in New York by Lakso and Pool (2001), who found little response of Concord vines to irrigation and limited response by Niagara vines under conventional vineyard management. However, previous studies in Ontario (Cline et al. 1985) indicated that irrigated, Geneva double curtain-trained Concord vines benefited from irrigation in terms of increased yields and vine size, especially during dry seasons. Moreover, irrigated, Geneva double curtain-trained Concord vines in Arkansas had higher vine size and yield than nonirrigated treatments (Morris and Cawthon 1982, Spayd and Morris 1978). The enhanced yields in the Ontario and Arkansas studies were attributed to both increased berry weights and berries per cluster.
Berry composition. High Brix is an essential component to grape and wine quality and also represents a means by which growers are paid. A base Brix level must be achieved by juice grapes in Ontario before the grower is paid the negotiated price per tonne. Bonuses are awarded to those crops exceeding the base sugar level. Small decreases in soluble solids (0.7 and 1.3 Brix) were the noted 5-year mean trends in irrigated and fertigated Concord and Niagara treatments, respectively. Such small reductions in Brix in these cultivars would likely not prove economically significant, as all treatments were well above the base level required for acceptance by processors.
The frequently observed reductions in soluble solids in many irrigation studies are often associated with increased yields. There were no significant yield:Brix or berry weight:Brix correlations for Concord in this trial and only a weak one (R2 = –0.38, p < 0.05) for yield:Brix in Niagara, likely in all cases to the relatively low yields. In Concord, yield:Brix correlations are weak in low- to moderate-capacity vines, especially if yield is below 10 t/ha (Miller and Howell 1997). As to other studies with V. labruscana, Stevenson (1975) in British Columbia found no differences in soluble solids in Diamond plots irrigated at different rates. Cline et al. (1985) in Ontario showed that irrigated Concord vines had higher soluble solids concentrations, even with increased yield. However irrigated Concord vines in Arkansas tended to have soluble solids values that were >2 Brix lower than nonirrigated treatments (Morris and Cawthon 1982, Spayd and Morris 1978).
Some irrigation trials with winegrapes have also resulted in increased yields with little effect on soluble solids (Ginestar et al. 1998, Goodwin and Jerie 1989, Williams and Grimes 1987). Balo et al. (1999) demonstrated a 20 to 25% yield increase in Chardonnay by irrigation and fertigation treatments over a control, accompanied by only a slight decrease in must soluble solids concentrations, no reduction in volatile components, and no differences between wines. Similar results were obtained for Cabernet Sauvignon vines in Colorado (Hamman and Dami 2000). Imposing mild water stress via irrigation deficits has been shown to increase Brix in many cases as well (Reynolds and Naylor 1994). Nonirrigated treatments typically become overly water stressed, resulting in low soluble solids, low yield, and poor wines (Ginestar et al. 1998). Timing of irrigation has also been shown to affect soluble solids concentrations. For example, irrigation at the end of veraison increased yield slightly, but Brix was not affected (Ruhl and Alleweldt 1985).
Titratable acidity and pH values for Concord and Niagara were all within acceptable ranges, with no trends evident from the data. In prior studies with V. labruscana, reductions in irrigation frequency led to reduced TA in Diamond (Stevenson 1975), but studies with Concord generally showed that both TA and pH were unresponsive to irrigation (Cline et al. 1985, Morris and Cawthon 1982, Spayd and Morris 1978). Water deficits have been shown to moderately reduce TA in winegrapes (Matthews and Anderson 1988), with early season deficits showing greater reduction than postveraison deficits. Conversely, supplemental irrigation has been shown to increase must acidity, leading to improvements in potential wine quality (McCarthy and Coombe 1985). Other studies showed little to no effect of irrigation on TA and pH (Ginestar et al. 1998, Goodwin and Jerie 1989, Hamman and Dami 2000).
Methyl anthranilate and volatile esters. Vitis labruscana cultivars have evolved the ability to produce large amounts of "foxy" aroma compounds, mainly MA and other volatile esters, most likely in an attempt to attract seed-spreading vectors (Fuleki 1982). Methyl anthranilate is one of the main volatile esters found in V. labruscana (Fuleki 1982). These compounds are undesirable in winegrapes, but are welcomed in V. labruscana grapes bound for juice. Methyl anthranilate might be produced by a simple methylation of anthranilic acid as a side reaction of the shikimate pathway, or it may accumulate in grapes during the latter period of fruit maturation as a tryptophan breakdown product. Under periods of drought and nitrogen stress, MA and other tryptophan breakdown products are produced in grapes in substantial amounts that are sensorially noticeable (Hoenicke et al. 2001).
The MA and TVE concentrations are worthy of brief speculation with respect to their responses to treatments over the 2001 to 2002 seasons. In the extremely dry 2001 season, Concord MA values were highest in the fertigated treatments (Figure 4A), suggesting that alleviation of water and nitrogen stress by the fertigation, especially between veraison and harvest, increased the ability of berries to accumulate flavor compounds. Niagara berries also showed a low MA concentration in the control in 2001 (Figure 5A). However in 2002, an opposite trend was noted; the unirrigated control had the highest MA values in Concord (Figure 4A), and Niagara controls also showed higher MA values compared to other treatments (Figure 5A). This trend is consistent with research into atypical aging (Hoenicke et al. 2001), suggesting that water and nitrogen stress can increase concentrations of MA and other tryptophan metabolites. It may be that stress during fruit maturation, as in 2001, may impede the biosynthesis of these key aroma compounds, whereas water and nitrogen stress during the cell division stage, as was experienced in 2002, may result in enhanced MA synthesis. Another explanation might be that these vines actually become more stressed under the conditions provided by fertigation in 2001. Transpiration data suggested that in some instances the control treatment actually transpired at a similar or higher rate to the fertigated vines, suggesting vines were under similar levels of stress (Figures 2B, 2C, 3B, 3C). There also appeared to be an inverse relationship between MA and yield in Niagara; in both seasons, the treatment showing the greatest yield (treatment 7) produced relatively low concentrations of MA (Figure 5A).
Petiole analysis. Uptake of mineral nutrients over the growing season is dependent upon environmental conditions as well as phenological stage (Conradie 1981, 1991, Keller et al. 1998). The greatest demand for nutrients occurs early in the growing season, during the production of vine biomass, including new roots, foliage, and fruit growth (Conradie 1981, 1991). Berry growth rapidly increases following fruit set, thus calling for an enhanced uptake of many key nutrients, especially K, as the fruit develops. Factors that increase nutrient uptake early in the season include warming temperatures, increased metabolic activity, and increased transpiration (Conradie 1981, 1991). Limiting environmental factors include prolonged cool temperature periods, restricted soil drainage, soil compaction, and presence of soil-borne pest populations (Conradie 1991). Deficit irrigation can limit nutrient uptake because of reduced soil moisture and imposed water stress. A study by Balo et al. (1999) concluded that nutrient uptake in Chardonnay was limited mainly by insufficient water supply rather than lack of nutrients in the soil.
Nitrogen uptake peaks between veraison and harvest, but can continue until the onset of leaf fall (Keller et al. 1998). In this study, weekly fertigation of Concord vines increased petiole N, and single application fertigation increased petiole P, but most other elements were unaffected by irrigation and fertigation. In Niagara, the two variable rate fertigation treatments increased petiole N, P, and Ca relative to the control, suggesting that this variety is more responsive to fertigation than is Concord. In previous studies, irrigation of Concord vines was found to reduce petiole N, likely as a result of leaching and/or dilution (Cline et al. 1985). However, no differences in petiole N were noted in Diamond grapevines in response to irrigation or method of nitrogen application (Stevenson 1981). Potassium uptake tends to be more sensitive to soil moisture than other nutrients (Williams 1991). Potassium redistribution from vegetative structures of the vine to the fruit during ripening can reduce wine quality (Smart et al. 1985); these authors theorized that K cations are exchanged for hydrogen ions in the berries, thus increasing juice pH and lowering wine quality. Potassium uptake by Concord vines was not impacted by irrigation in Ontario (Cline et al. 1985) or Arkansas (Morris and Cawthon 1982). However, Mg uptake was reduced by irrigation (Cline et al. 1985, Morris and Cawthon 1982) and Ca uptake was enhanced (Morris and Cawthon 1982).
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Conclusions |
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TopAbstractMaterials and MethodsResultsDiscussionConclusionsLiterature Cited |
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Methyl anthranilate concentrations were very sensitive to drought and nutrient stress. Under severe stress experienced during fruit maturation in 2001, fertigated treatments had higher MA, while drought stress during stage I of berry development the following season resulted in nonirrigated control berries with highest MA concentrations. In both years of study, the treatments with the highest yields had the lowest MA concentrations, suggesting that minimized water stress and larger berries reduce MA accumulation.
Vitis labruscana vines showed small differences in transpiration rate between control and irrigated or fertigated treatments except for Niagara in 2000, possibly because irrigation early in the season increased canopy size above a point at which irrigation was inadequate. Low soil moisture values suggested that no matter how much water was added, the Toledo clay soil was not adequately re-wetted. The use of the Penman-Monteith method of irrigation scheduling also needs to be evaluated over several seasons and validated using both plant and soil moisture monitoring. The evapotranspiration values and crop coefficients may require adjustments to better tailor the needs of V. labruscana during severe drought stress. Studies incorporating data from seasons with higher precipitation may be advantageous in fine-tuning the formula and determining the best crop coefficient value to use. A method of employing an increasing crop coefficient based on canopy volume is currently being tested in field trials conducted by our research group.
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Footnotes |
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Manuscript submitted August 2004; revised January 2005
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0.05, 0.01, 0.001, 0.0001, or not significant, respectively.
