Vineyard row orientation (Part 4) – growth and yield

Terroir factors, such as soil and climate, together with cultivation practices, have layered and integrated effects on growth, yield, grape and wine quality, and cost efficiency.

Introduction

Wrong choices and execution of viticulture practices may lead to or enhance erratic behaviour of the grapevine. This would make it difficult to obtain sustainability and consistency of products. In general, row orientation selection is dictated largely by climatic conditions and topography of the landscape. In this regard, mechanisation of cultivation activities would add another layer of complexity to decision-making and expected outcomes. Complications of these factors for physiological functioning of the grapevine on the one hand and practicality of production on the other hand, in a specific terroir, may often lead to opposing/sub-optimal row orientation decisions in terms of suitability for specific cultivars and product objectives, particularly in complex terrains. Despite the importance of row orientation as basic consideration in grapevine cultivation, scientific evidence on its implications is scarce. Guidelines for informed decisions regarding row orientation choices are required to ensure an optimal planting strategy for sustainable production and the required quality/style of grapes and wine per terroir.

Vineyard and measurements

The effect of row orientation [North-South (NS); East-West (EW); North-East-South-West (NE-SW); North-West-South-East (NW-SE), each replicated five times on a flat site of approximately 3 ha] at fixed row (2.7 m) and vine (1.8 m) spacing, on growth and yield of spur pruned (two buds) vertically trellised Shiraz/101-14 Mgt, was determined at the Robertson Experiment Farm of ARC Infruitec-Nietvoorbij in the Breede River Valley, a region that experiences semi-arid macroclimatic conditions. Due to low precipitation and inconsistent rain events in summer, vines were irrigated weekly at a volume of 14 mm during the high season period. A cover crop (rye) was sowed after harvest and killed before budding. Vines were uniformly managed and were only vertically shoot positioned and topped; both actions were performed on average three times per year. Climate of the semi-arid region and experiment terroir at macro-, meso- and micro-levels was fully described in the companion popular articles. Shoots (including bunches) were sampled at three grape ripeness level stages (approximating 23°B, 25°B and 27°B, respectively) from each of the canopy sides per treatment replicate and used for determination of vegetative and reproductive growth characteristics. Cane mass was measured in winter. These measurements were done for seven consecutive years.

Results

Vegetative growth

Primary and secondary shoot characteristics showed minor differences between row orientations and different canopy sides. Primary shoot lengths and primary leaf area:secondary leaf area ratios averaged 110 – 120 cm and 0.80 – 0.90, respectively. This indicates a good canopy height and leaf age composition (as judged by the primary and secondary leaf area in the canopy). Each primary shoot had approximately 11 leaves and nine secondary shoots. Since vines were topped pre-véraison, primary growth was controlled and secondary shoot growth would have been stimulated as compensation mechanism for excess vigour. Secondary leaf area of primary shoots on S and SW sides tended to be lower. The SW canopy side displayed generally lower values for most characteristics. The EW-orientated vines showed a higher total leaf area/leaf mass, mainly attributed to a significantly higher secondary leaf area/leaf mass. The NS and EW orientations had higher cane mass. Average cane mass per vine was approximately 1.8 kg.

Reproductive growth

Although bud fertility, berry set and general morphology of bunches were largely unaffected by row orientation, less than two bunches per shoot were generally found for EW-orientated vines. Canopies were clearly not fully developed during the period of inflorescence primordia formation, initiation and differentiation, and vines were also already suckered during this time. Row orientation (and therefore total light intensity and light quality) may therefore not have had pronounced impact on these processes. Bunch and berry mass and volume progressively decreased during ripening for all row orientation treatments. Over the period of increasing grape ripeness levels, rachis mass (average of all orientations = 9.7 g) decreased by only 5%, whereas bunch mass (average of all orientations = 196 g) decreased by 15%. Berry mass at approx 23°B, 25°B and 27°B was 1.51 g, 1.38 g and 1.27 g. Berry mass of the EW orientation was respectively 5%, 7% and 6% higher than the average of the rest of the row orientation treatments at the different ripeness levels. The EW row orientation (south side in particular) resulted in consistently higher berry mass and volume. Diurnal canopy radiation profiles (discussed in the companion article on climate profiles) at critical times during the day (and season) were most likely impacting factors on berry size and in the case of the EW orientation, the more favourable whole vine water relation status may have been a primary causal factor. Total leaf area (10 – 12 cm²)/g fresh mass values showed equal balance for differently orientated vines, aligned with generally acknowledged viticulture criteria; secondary leaf area was the largest contributor to the ratio. Primary, secondary and total leaf area values per gram of fresh berry mass confirmed the significant role that secondary leaves may play in overall capacity of the canopy, in extending the harvesting window and in the build-up of reserves after harvest, irrespective of row orientation.

Yield

Overall average yields (over ripeness levels) of NS, EW, NE-SW and NW-SE orientations were 18.2, 17.1, 17.1 and 17.4 ton/ha, respectively (Table 1). Average yields (over treatments) for the seven-year monitoring period varied from 19.2 ton/ha at ripeness level 1 (approx 23°B) and 17.4 ton/ha at ripeness level 2 (approx 25°B), to 15.9 ton/ha at ripeness level 3 (approx 27°B). Total yield losses (over treatments) from ripeness level 1 – 2 and from ripeness level 2 – 3 averaged 9.5% and 8.6%, respectively, whereas from ripeness level 1 – 3 it averaged 17.3%. Given the reproductive growth findings and decrease in berry mass:rachis mass ratios with an increase in ripeness level, this yield loss with time is mainly attributed to a decrease in berry mass. The EW orientation maintained highest berry mass:rachis mass ratios (almost 5% higher than the average of the rest of the orientations). These trends may have significant economic impact, as producers (income based on bunch yield) and wineries (income depending on berry yield) alike would gain or suffer losses depending on timing of harvest and yield price point, especially in a region in which environmental factors (such as dry and hot conditions) favour high plant water deficits. Yields would decrease with longer bunch hang time and harvesting at a lower ripeness level would yield higher berry mass per total bunch mass; this would progressively decrease with an increase in ripeness level.

Interaction statistics of the seven yielding years/seasons (environment) and vines with different row orientation treatment (genotype) showed that for ripeness levels 1, 2 and 3, the NS row orientation consistently yielded above average, while the EW row orientation performed below average at ripeness levels 1 and 2 and on average at ripeness level 3. The NE-SW orientation showed above average yield at ripeness level 1, whereas it performed far below average at ripeness levels 2 and 3. The NW-SE orientation showed more or less average yields for all ripeness levels. In general, producers would prefer predictable productions and income and stability is therefore crucial in addition to the specific yield quantity of a row orientation; the NS orientation was stable, as well as producing highest yield, while NW-SE was stable at an average level, and EW and NE-SW were variable. With respect to yield, the ideal row orientation should have highest mean performance and stability.

Generally highest yields over different seasonal time periods and overall, and at all ripeness levels, were obtained with NS-orientated rows. Yields of other row orientation treatments varied according to seasons and ripeness level; at ripeness level 1, NE-SW was followed by NW-SE and EW, at ripeness level 2, NW-SE was followed by EW and NE-SW, and at ripeness level 3, EW was followed by NW-SE and NE-SW. Yields from different canopy sides of row orientations showed minor differences that progressively diminished the higher the grape ripeness level. In line with berry mass and berry mass:rachis mass findings, EW-orientated vines showed lowest overall yield losses from low to high ripeness level. Considering cane mass, lowest ratio of yield:cane mass was also found for the EW row orientation treatment (4.48), increasing for NW-SE (4.82), NS (4.90) and NE-SW (4.91).

It stands to reason that different cultivars may vary in vegetative and reproductive response to the orientation of vineyard rows. It may be accepted that the reaction of a particular cultivar may depend primarily on its sensitivity to the main factor steered by row orientation, i e meso/microclimate (especially diffused and direct radiation, according to the solar path at any given latitude, as well as altitude). Energy/heat balances and concomitant canopy and grape physiological processes would be a natural consequence of such impact. For example, if a cultivar has high sensitivity to direct radiation and temperature, yields may be lower and loss in quantity with further grape ripening may be enhanced by management practices leading to canopies and grapes that are overly exposed for a given row orientation. Under such circumstances, the grape composition matrix and eventual taste and flavour profiles of grapes and wine of both red and white cultivars may change, most likely negatively.

The trellising system in particular (e g bush/goblet, vertical or horizontal architecture) may play a large role in mitigating or magnifying positive and negative viticultural (and potential oenological) effects of row orientation. The results point to the necessity of microclimatic-efficient and uniform canopies within the practical norms of the different trellising systems. The capacity for sustained and predictable yields, as well as the protection of bunches from extreme environmental/climatic events that may be detrimental to berries at physical/morphological, sanitary and physiological/biochemical levels, should be maintained.

Conclusions

• Summer and winter parameters indicated a change in partitioning of carbon (between photosynthesising, reproductive and perennial storage tissue) and/or depletion of carbohydrate reserves (starch) during grape development and ripening with different row orientations.
• Considering changes in yield:cane mass ratio found with differently orientated rows, it is clear that row orientation changed the growth balances of the vines.
• The importance of row orientation as viticulture practice and the significance of especially meso- and microclimate profiles in the performance of grapevines at physiological, vegetative and reproductive levels are confirmed.
• Haphazard row orientation choices would increase production costs and would have high cost implications to modify/reverse.
• A judicious, intelligent best practice strategy should be followed in order to obtain the true reflection of a chosen row orientation in final products.
• The ideal row orientation would depend on grape and wine style objectives/targets and thorough consideration of the relevant terroir conditions, including soil, climate, topography and cultivation practices.

Summary

Growth and yield characteristics of differently orientated vertically trellised Shiraz grapevines (NS, EW, NE-SW and NW-SE rows) were investigated at three grape ripeness levels (ca 23°B, 25°B and 27°B). The EW rows had higher total leaf area/leaf mass, mainly attributed to significantly higher secondary leaf area/leaf mass. The NS and EW rows had higher cane mass. Berry mass of the EW orientation was higher than that of the other row orientations. Over the period of increasing grape ripeness levels, rachis mass decreased by 5% and bunch mass by 15%. Yield losses over treatments from ripeness level 1 – 2 and 2 – 3 averaged 9.5% and 8.6%, respectively. Yields of NS were highest and most consistent. Row orientation changed the vine growth balances. Judicious selection of a row orientation per terroir is required to increase sustainability.

Acknowledgements

We would like to thank the Agricultural Research Council and South African wine industry (through Winetech) for funding. We would also like to extent our gratitude to personnel of the Viticulture Department (especially G.W. Fouché, A. Marais, C. Paulse and L. Adams) and farm personnel at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij for their diligence and devotion. Details of this popular script can be found in the following scientific article (and the references therein):

Reference

Hunter, J.J., Volschenk, C.G. & Booyse, M., 2017. Vineyard row orientation and grape ripeness level effects on vegetative and reproductive growth characteristics of Vitis vinifera L. cv. Shiraz/101-14 Mgt. European Journal of Agronomy 84, 47 – 57.

– For more information, contact Kobus Hunter at hunterk@arc.agric.za.