Orienting vineyards N-S on a flat terrain allowed for uniform canopy and cluster exposure to solar radiation, since radiation is approximately symmetric about the N-S axis . However, the berry temperature on the west side of the vine significantly increased in the afternoon compared to the east side because hysteresis in air temperature causes asymmetry about solar noon. On average, berry temperature on the west side of the vines was greater than 35◦C for about 1-2.5 hours longer than the east side . Interestingly, although there was temporal asymmetry due to air temperature and temperature extremes, the net daily accumulation of berry growing degree hours was virtually identical between each side of the vine . On flat terrain, rows oriented NW-SE increased light interception and fruit overexposure in the afternoon and E-W reduced light interception and fruit overexposure in the afternoon . The high exposure to direct sunlight in NW-SE oriented rows resulted in simulated berry temperatures up to 7.8◦C higher on the SE side compared to the NW side . Compared to rows oriented NE-SW, best indoor plant pots rows oriented NW-SE had an additional 3 hours of canopy light interception above 200 W m−2 between 14:00 and 17:00 and berry temperatures greater than 35◦C for 2 additional hours . Narrow spacing affected berry temperature by potentially reducing the duration of berry exposure due to shading from neighboring vines.
Compared to the wider row spacing, the berries in narrow row spacing in N-S rows on a flat terrain intercepted up to 36% less sunlight and reduced elevated berry temperatures on the west-facing side . In the E-W row orientation, the number of hours with berry temperatures greater than 35◦C was also reduced with the narrow row spacing due to the shading from neighboring vines . The most balanced sunlight exposure and growing degree hours between each side of the vine was achieved in the N-S row orientation, although notable hourly berry temperature differences were present for both narrow and wider row spacing. For example, west-facing berries exceeded35◦C for about 1 hour for the narrower row spacing and about 3.6 hours for the wider row spacing .Adding a 30◦ slope to each of the simulations had a considerable effect on berry temperature, and could significantly change its behavior relative to flat terrain. Furthermore, the conditional inference tree results showed that the slope aspect had the strongest effect on the imbalance in temperature between different sides of the vines . In general, sloping to the south or west tended to increase light interception, berry temperatures, and berry temperature imbalance relative to north- or east-facing slopes. For example, compared to the vines oriented NW-SE on flat terrain, the vines oriented NW-SE on a southwest-facing slope increased the number of hours of Tberry > 35◦C up to 1.25 h on the southwest side . In contrast, situating these vines on a northeast-facing slope decreased the number of hours of Tberry > 35◦C up to 2 h on the northeast side . 、
For N-S oriented vines, slope had a minimal effect on daily integrated quantities such as daily light interception and berry growing degree hours, but did significantly affect short-term increases in berry temperature. N-S rows on west-facing slope increased the number of hours of Tberry > 35◦C for west-facing berries by over 2 h relative to flat terrain. However, these effects tended to be averaged out in N-S rows to maintain good symmetry over a daily period. The NE-SW oriented vines maintained good protection from berry temperature spikes and relatively good symmetry between sides of the vine as slope was added. For NE-SW oriented rows, the northwest-facing slope had more hours with Tberry > 35◦C than for the southeast-facing slope, but the opposite was true for daily-integrated quantities. This illustrates that exposure due to partially western-facing slope was more effective at generating temperature extremes than a partially southern-facing slope, but the opposite is true for daily-integrated quantities.The efficacy of shade cloth in reducing or equalizing berry temperature strongly depended on the row orientation and slope aspect . In general, adding shade cloth to the side of the row with partial or full south or west exposure tended to produce a significant reduction in berry temperatures and heat accumulation, as is to be intuitively expected. Adding shade cloth to sides of the vine with partial or full north or east exposure typically had weaker effect, and could actually increase temperatures on north-facing berries due to trapping of energy transmitted from the south. While avoiding fruit overexposure reduces fruit temperature, in some cases, controlling the amount of direct radiation received by berries with shade cloths consistently maintained the berry temperature below 35 ◦C.
For instance, in vines oriented N-S and NW-SE with wider rows, 50%and 70% shade cloth significantly reduced the time berry temperature was above 35◦C late in the afternoon in west facing berries . It was possible in several cases to achieve near-equal heat accumulation between sides of the vine while also minimizing berry temperature extremes by applying shade cloth to one side of the vine. For example, applying 70% shade cloth to the SE side of the vine in NE-SW oriented rows on flat terrain effectively balanced heat accumulation while also eliminating berry temperatures above 35◦C. E-W oriented rows always had high imbalance in heat accumulation regardless of shade cloth density or slope aspect.Comparisons between measured and modeled berry temperature indicated that the model is able to reproduce general spatial and temporal patterns of temperature, and can capture the additional effects of shade cloth. This is in addition to prior validation efforts demonstrating excellent model performance in the absence of shade cloth. Experimental validation of 3D, spatially explicit models is complicated by high sensitivity of localized model predictions to specifics of the canopy geometry. However, overall close agreement between measurements and model predictions in an average sense suggested that the model is robust to variation in vineyard architecture, topography, and the addition of shade cloth. For model validation purposes, local measurements of ambient berry microclimate were used to drive simulations. Effects of large-scale microclimatic variation was not included within this model, which could affect the predictive ability of the model as large-scale features are varied such as topography. Variation in topography could induce changes in wind speed or sensible heating of the air independent of vineyard structure, which was not represented in the model. However, radiation exposure is the primary driver of berry temperature deviations from ambient, and other microclimatic effects due to large-scale topography are likely to be secondary and establish the baseline temperature state similar to changing weather.The results of this study for flat terrain largely confirmed conclusions of previous work regarding design of vertically-trained vineyards for berry temperature management, but revealed some additional trade-offs for consideration. Similar to previous findings, the NE-SW row orientation on flat terrain is likely to be the best compromise between canopy and berry light interception, reduction of elevated berry temperatures, and balancing of heating between opposing sides of the vine, which was also argued by Tarara et al.. A trade-off of this vineyard design is that it modestly reduces overall vine light interception relative to the more common N-S row orientation. Additionally, there are still significant differences in berry heat accumulation and exposure between sides of the vine in a NE-SW row orientation. However, for VSP vineyards on flat terrain with no shade cloth, the NE-SW row orientation appeared to be the best overall at equalizing exposure between sides of the vine and reducing berry temperature extremes. For N-S oriented rows on flat terrain, previously well-documented imbalances in berry temperature between sides of the vine were also observed. It is intuitive to understand that the higher air temperatures and lower humidity that occur in the afternoon, blueberry container size when combined with berry exposure to the west sun, creates higher berry temperature than in the morning when ambient conditions are cooler. There is strong evidence that the accumulation of berry anthocyanin is a function of temperature and light Buttrose et al., Downey et al., Hunteret al., Spayd et al. and that the temperature difference between sides of the vine can create imbalance in the mass of the berries, as well as on tritable acidity, pH and phenolic compounds.
If row access by mechanical equipment is not a concern, decreasing row spacing could offer some protection against berry temperature extremes, although this is not effective at balancing opposing sides of the vine. Interestingly, results indicated that although there was high berry temperature imbalance localized to the afternoon, daily integrated metrics such as daily growing degree hours and daily berry light interception were almost perfectly balanced between sides of the vine in N-S rows. However, it is possible this was coincidental, or that abnormal diurnal temperature fluctuations such as that caused by clouds could break this symmetry. The NW-SE row orientation on flat terrain resulted in the most elevated berry temperatures. Berries on the southwest side of the vine spent nearly 4 hours above 35◦C, and shade cloth did little to mitigate these temperatures because the sun was nearly perpendicular to the shade cloth at the hottest time of day. Most previous work examining the effects of shade cloth does so for a single site and vineyard design, but results indicated that details of topography and vineyard architecture can have a significant effect on shade cloth performance. In N-S oriented rows on flat terrain, smaller row spacing relative to canopy height significantly reduced the hours of berry exposure to direct sunlight in the east and west side of the vine due to shading from neighboring vines. While berry temperatures were reduced in vineyards with narrower row spacing, grape and wine quality could decline at some point when row spacing is reduced due to excessive berry shading. Mechanical equipment access may be impeded below some threshold row spacing. Full-size equipment generally requires a minimum row spacing of around 3 m for single canopy systems. Thus, depending on the availability of equipment for mechanization and the vineyard design, shade cloth appeared to be a viable option for mitigation of berry overexposure in widely spaced rows. This study considered only VSP trellis systems at a single fruiting height, which resulted in the potential for high fruit exposure. Other trellis systems that reduce berry exposure are becoming more popular in warm climate regions. However, since it is usually undesirable to completely shade clusters because of its negative effect on berry quality, it is still necessary to understand the interaction effects between canopy architecture and berry exposure. While the results of this work can provide some initial guidance in this regard, future work analyzing different trellis types is still needed. Because of the spatially explicit nature of the model presented in this work, it is likely that only minimal adjustments to the model are needed to accommodate different trellis types.For most cases, it was observed that planting on a slope fully or partially facing south or west increased berry exposure and elevated temperatures relative to north- or east-facing slopes or flat terrain . Furthermore, a west-facing slope tended to increase temperatures more relative to a south-facing slope. This is intuitive given that the sun spends most of the day to the south, and the sun is to the west during the warmest time of a typical day. In several cases, slope had the negative effect of increasing the imbalance in heat accumulation between sides of the vine. This was especially true for the E-W row orientation, which caused very large imbalance that could not be effectively mitigated by shade cloth. For N-S and NE-SW oriented rows, the impact of slope on the berry temperature metrics was generally small. Shade cloth was able to mitigate the negative effects of slope in many cases. Applying 70% shade cloth in the sloped cases achieved excellent balance in heat accumulation between sides of the vine with N-S, NW-SE, and NE-SW orientations. The 70% shade cloth was also able to reduce the time above 35◦C to 1 hour or lower in all but the case with N-S rows on a west-facing slope, and NW-SE rows on flat terrain. The 3D model developed in this work was able to represent the effects of shade cloth on berry temperature and, thus, provided a viable tool for quantification of interactions between hypothetical vineyard designs and shade cloth on metrics related to berry temperature.