Grapevine Rows Research Articles

Does a native and introduced cover crop species differ in their ability to suppress weeds? A study in a table grape vineyard

This study compared the weed suppression ability of a native cover crop species phacelia (Phacelia tanacetifolia), an introduced cover crop species rye (Secale cereale L.), and a no cover crop (herbicide‑managed) system in a vineyard. Cover crops were sown in the interrow spaces of the grapevine rows. Percent weed cover after the cover crop termination was lower in the interrow of the phacelia than the no cover crop plots. During the cover crop growing season, phacelia suppressed weeds more than rye. However, the weed seedbank of the cover crop plots was greater than that of the no cover crop plots.

Versatile method for grapevine row detection in challenging vineyard terrains using aerial imagery

Accurate detection and differentiation of grapevine canopies from other vegetation, along with individual grapevine row identification, pose significant challenges in precision viticulture (PV), especially within irregularly structured vineyards shaped by natural terrain slopes. This study employs aerial imagery captured by unmanned aerial vehicles (UAVs) and introduces an image processing methodology that relies on the orthorectified raster data obtained through UAVs. The proposed method adopts a data-driven approach that combines visible indices and elevation data to achieve precise grapevine row detection. Thoroughly tested across various vineyard configurations, including irregular and terraced landscapes, the findings underscore the method’s effectiveness in identifying grapevine rows of diverse shapes and configurations. This capability is crucial for accurate vineyard monitoring and management. Furthermore, the method enables clear differentiation between inter-row spaces and grapevine vegetation, representing a fundamental advancement for comprehensive vineyard analysis and PV planning. This study contributes to the field of PV by providing a reliable tool for grapevine row detection and vineyard feature classification. The proposed methodology is applicable to vineyards with varying layouts, offering a versatile solution for enhancing precision viticulture practices.

UAV-based individual plant detection and geometric parameter extraction in vineyards.

Accurately characterizing vineyard parameters is crucial for precise vineyard management and breeding purposes. Various macroscopic vineyard parameters are required to make informed management decisions, such as pesticide application, defoliation strategies, and determining optimal sugar content in each berry by assessing biomass. In this paper, we present a novel approach that utilizes point cloud data to detect trunk positions and extract macroscopic vineyard characteristics, including plant height, canopy width, and canopy volume. Our approach relies solely on geometric features and is compatible with different training systems and data collected using various 3D sensors. To evaluate the effectiveness and robustness of our proposed approach, we conducted extensive experiments on multiple grapevine rows trained in two different systems. Our method provides more comprehensive canopy characteristics than traditional manual measurements, which are not representative throughout the row. The experimental results demonstrate the accuracy and efficiency of our method in extracting vital macroscopic vineyard characteristics, providing valuable insights for yield monitoring, grape quality optimization, and strategic interventions to enhance vineyard productivity and sustainability.

Grapevine row orientation, vintage and grape ripeness effect on anthocyanins, flavan-3-ols, flavonols and phenolic acids: I. <i>Vitis vinifera</i> L. cv. Syrah grapes

Phenolic concentrations are affected by environmental factors and grape cultivar, as well as viticultural practices, which should be considered when a specific phenolic profile is intended. The effect of microclimate induced by row orientation on phenolic compounds of Vitis vinifera L. cv. Syrah/101-14 Mgt grapes was investigated. Grapes were harvested from four vintages at 22 °Brix, 24 °Brix and 26 °Brix from N-S, E-W, NE-SW and NW-SE orientated grapevine rows. Phenolics were quantified in freeze-dried grape skins using an HPLC method. A vintage effect was only evident for specific individual phenolics for the four vintages. Grapes from NE-SW rows at 22 °Brix had the highest total flavonols and anthocyanins. Catechin was highest in grapes from N-S rows at 24 °Brix, whereas total phenolic acids, caffeic acid and total flavonols were highest from NW-SE rows at 24 °Brix and 26 °Brix. Isoquercetin was highest from NE-SW rows at 22 °Brix and 26 °Brix, whereas kaempferol and quercitrin were highest from E-W rows at 24 °Brix. The majority of phenolics was highest from NW-SE rows at 24 °Brix and 26 °Brix. The results indicate that row orientation affects phenolic development in Syrah grapes, but that vintage has a limited effect on phenolics. Light induced in the fruit zone positively affected the grape phenolic development of NE-SW rows at 22 °Brix and that of NW-SE rows at 24 °Brix and 26 °Brix. However, it is unlikely that a single index can be applied to all growing conditions and grape cultivars. Rows that allow moderate radiation intensity in the canopy (i.e., NE-SW and NW-SE during the day) seem more favourable for the development of phenolics than N-S and E-W rows. The light and berry temperature conditions in the fruit zone resulting from row orientation have the potential for widening the range of Syrah wine styles. In practice, a desirable row orientation may not be applicable to all environments. Management of the fruit zone remains an option for increasing or decreasing grape light exposure, irrespective of row orientation.

Fertilization with different soil types in viticulture: a three-year experience in Trentino Alto Adige

The work aimed at investigating the impact of various good quality soils of on vineyard productivity. Manure matured with a fast and controlled process and compost obtained from digestate of an organic fraction of municipal solid waste (OFMSW) were applied one time on a grapevine row, in two CAVIT vineyards. A physico-chemical characterization of the soils was carried out and biological quality indices QBS-ar (Arthropodological Biocenosis) were calculated. The vegeto-productive monitoring was performed by foliar nutrients analysis and measuring NDVI and SPAD indices. The organic source had a significant fertilizing effect, especially manure, which determined a nutrient increase in soil (P, K and Mg), a rise in photosynthetically active biomass, available nitrogen and potassium in plants. The effects on the biological community of soils and musts quality were negligible. The use of soil improvers could be an efficient strategy for the nutrition of not vigorous vineyards, which do not require high nitrogen inputs.

Grapevine row orientation mediated temporal and cumulative microclimatic effects on grape berry temperature and composition

Ambient radiation and temperature are global drivers of grapevine growth, grape yield and composition, and wine quality. Knowledge of the implications of vineyard row orientation/microclimate is required for decision-making in current and future macro- and mesoclimates. Temporal and cumulative microclimatic changes, induced by vine row orientation (NS; EW; NE-SW; NW-SE) of vertically trellised Shiraz grapevines, on berry pulp temperature and composition at different ripeness levels were investigated. Berries dynamically gained heat energy relative to: ambient climate/weather; direct canopy wall/bunch irradiance; and berry skin colour development. Berries exposed to direct solar radiation during the morning, leading to higher pulp temperatures than ambient, but having a cooling profile after that, resulted in slightly advanced sugar ripening and generally higher skin total anthocyanins and phenols, without significant effects on pH and titratable acidity, at the respective ripeness levels. In contrast, excessive exposure of bunches and those that built up heat, reaching highest temperatures during late afternoon, seemed not conducive to grape composition associated with higher quality. The S, SE, E and NE canopy sides showed consistently higher skin total anthocyanin and phenol contents than their counter sides. Except for acylated forms of peonidin-glucoside, anthocyanin (mono-, acetyl- and coumaroyl-glucosides) accumulation was mostly favoured in berries exposed to exterior canopy sides, but differences in acylated anthocyanins between exterior-facing and interior-facing berries were less than for mono-glucoside anthocyanins. Over-exposure and heat peaking during late afternoon seemed detrimental. Novel information on berry pulp temperature variation in a developing composite grape bunch, exposed to weather and microclimate fluctuation, is provided. An ostensibly homogeneous bunch in reality represents a dynamic berry pulp thermal range at any point in time. Cumulative thermal and radiation impact was evident. This is the first comprehensive attestation on the role of grapevine row orientation (or any viticulture practice) in the management of seasonal nocturnal- and diurnal berry temperature and concomitant composition.

Row orientation effects on chemical composition and aromatic profile of Syrah winter wines

Abstract Sunlight and heating influence leaf and grape metabolism and therefore wine quality. As a recent management tool, no information exists on the effects of grapevine row orientation on the wine composition of Syrah vines within the context of double pruning management, a technique used to transfer the grape harvest from the wet summer to the dry winter season. This is a first attempt to investigate the wine composition from north-south- (NS) and east-west- (EW) oriented Syrah winter vines. EW wine samples had higher total acidity, residual sugars, alcohol and color hue, whereas NS wines exhibited higher content of color intensity, anthocyanins, total phenolics, total phenolic index, ashes and pH. The identification of volatile compounds was tentatively performed and demonstrated the presence of alkanes, volatile phenols and alkyl sulfide in NS wines, while butyrolactone and beta-damascenone were found mainly in EW wines. Row orientation contributed to wine composition and could be used as a management tool for obtaining individual wine styles.

Influence of parent material on organic phosphorus fractions in vineyard soils in Santa Catarina, Brazil

Phosphorus (P) is an essential element for vineyard productivity. This study assessed the influence of parent material on organic P fractions in vineyard soils of basaltic and rhyodacitic origin. The experiment was conducted in four municipalities located in mountainous regions in Santa Catarina, Brazil: Urubici, São Joaquim, Campos Novos, and Água Doce. Disturbed soil samples were collected between grapevine rows at depths of 0.00–0.05, 0.05–0.10, 0.10–0.20, and 0.20–0.40 m. Soil chemical attributes (pH in H2O, Ca2+, Mg2+, Al3+, P, K+, and H + Al), total organic carbon (TOC), available and residual P, labile P (extracted with sodium bicarbonate), moderately labile P (extracted with sulfuric acid), and moderately resistant P (extracted with sodium hydroxide) were determined. Soil parent material influenced the dynamics of phosphorus in vineyard soils. Both P forms (available and solution equilibrium P) and P organic fractions (labile, moderately labile, and moderately resistant P), are affected by the parent material. Basaltic soils had higher TOC, available and residual P, and moderately labile and moderately resistant P, whereas rhyodacitic soils showed higher labile P. The high levels of moderately labile and moderately resistant P fractions in basaltic soil were attributed to its high TOC, available P, and residual P contents. Parent material was found to influence organic P fractions in vineyard soils.

Grapevine physiological response to row orientation-induced spatial radiation and microclimate changes

Terroir factors and vineyard practices largely determine canopy and root system functioning. In this study, changes in soil conditions, multi-level (vertical, horizontal) light interception (quantitative, photographic, schematic, 3D modelled), leaf water potential and photosynthetic activity were measured during the grape ripening period on NS, EW, NE-SW, and NW-SE orientated (Southern Hemisphere) vertically trellised Shiraz grapevine canopies. It was hypothesised that the spatial radiation interception angle and radiation distribution of differently orientated and vertically trained grapevine rows would affect soil conditions and vine physiological activity. Soil water content showed an increase and soil temperature a decreasing gradient with soil depth. In the afternoon, soil layers of EW orientated rows reached their highest temperature. This, along with measured photosynthetic active radiation received by canopies, complimented the diurnally-captured photographic, constructed and 3D modelled images (also schematically) of canopy and soil exposure patterns. The top, bottom and outside of NS canopies mainly received radiation from directly above, from the E and the W; during midday, high radiation was only received from above. The EW rows received the highest radiation component from above and from the N. The NE-SW rows received high levels of radiation from above, from the SE until 10:00, and from the NW from 13:00. A similar profile can be described for NW-SE rows, but with high radiation received from the NE up to 13:00 and from the SW from 16:00. Overall, lowest leaf water potential occurred for NE-SW canopies, followed by those orientated NW-SE, NS and EW. Photosynthetic activity reflected the positive radiation impact of the sun azimuth during the grape ripening period; best overall performance seemed to occur for E and N exposed canopy sides. This was largely driven by the responsiveness of the secondary leaves to radiation. Photosynthetic output decreased from apical to basal canopy zones with low, erratic values in the light-limited canopy centre. The NS and EW orientated canopies generally showed the highest average photosynthesis, while it was lower for the sides facing S, SE and SW. The results provide a better understanding of the physiological functioning of horizontal and vertical leaf layers in differently orientated grapevine canopies, as affected by climatic conditions. The study contributes to the longstanding challenges of capturing the complexity of parallel microclimatic and physiological output of grapevine canopies under open field conditions. The results can be directly applied to the selection of vineyard practices and seasonal management to ensure the attainment of yield, grape composition and wine quality objectives.

Effect of Grapevine Canopy Side on Selected Sensory Attributes of Pinotage and Cabernet Sauvignon Wines

Grapevine row direction, canopy exposure and grape maturity can define the sensory attributes of wine. From this perspective, canopy exposure that favours colour intensity, astringency, aroma intensity and balanced acidity could result in improved wine quality. The aim of this study was to examine the effect of canopy exposure on selected sensory attributes of Pinotage and Cabernet Sauvignon wines from Paarl, Durbanville and Darling in South Africa. Pinotage and Cabernet Sauvignon grapes were harvested from both sides of the canopy of vines planted to E-W and N-S directions. Wines were made from the harvested grapes. Grapes and wines underwent physicochemical and sensory analysis. Durbanville Cabernet Sauvignon from the south side had decreased alcohol content. Total acidity, residual sugar (RS) and pH were not different between sides. Wines from the east side had increased colour, aroma, mouthfeel and overall quality. Paarl Cabernet Sauvignon was not different between sides for any physicochemical characteristics, except TA. Wines from the south side had increased colour, aroma, mouthfeel and overall quality. Darling Pinotage was not different between sides for any physicochemical characteristics. Wines from the west side had increased intensity of aroma and acidity, whereas Durbanville Pinotage from the east side had increased alcohol, pH, TA, colour and aroma intensity, as well as overall quality. The results confirm that canopy exposure has an effect on the wine sensory attributes. This investigation illustrates the variation in sensory attribute scores of Pinotage and Cabernet Sauvignon wines from different canopy sides. Canopy exposure in a vineyard of a specific region, orientated to an E-W or N-S direction, which favours colour intensity, aroma intensity and/or mouthfeel, could result in improved wine quality. Future investigations should focus on samples collected over at least three consecutive vintages, as well as the monitoring of temperature and photosynthetic active radiation.

Row orientation effects on Syrah grapevine performance during winter growing season

ABSTRACT The sunlight and heating effects on leaves and grapes are directly influenced by row orientation in vineyards. Row orientation studies have not been addressed under double pruning management, a technique used to transfer the wine grape harvest from wet summer to dry winter season in Brazilian Southeast. Effects of grapevine row orientation (north/south - NS and east/west - EW) of vertically trellised and shoot positioned Vitis vinifera L. Syrah grafted onto 1103 Paulsen were investigated in the South of Minas Gerais State. The vegetative vigor was increased in NS oriented vines, probably due to high photosynthesis as suggested by the highest leaf starch accumulation. The leaf and stem water potential were slight affected by row orientation. NS orientation increased the cluster weight, but cluster number and yield per vine were not affected by treatments. Berries from NS oriented vines also showed the highest values of anthocyanins and total phenols. Under NS orientation there was a reduction on tartaric acid and soluble sugar in berries probably diluted by increased cluster weight. This study showed that vineyard under NS orientation improved grapevine vigor and promoted better phenolic maturity in wine grapes harvested during the winter season than EW orientation.

In-field high throughput grapevine phenotyping with a consumer-grade depth camera

Plant phenotyping, that is, the quantitative assessment of plant traits including growth, morphology, physiology, and yield, is a critical aspect towards efficient and effective crop management. Currently, plant phenotyping is a manually intensive and time consuming process, which involves human operators making measurements in the field, based on visual estimates or using hand-held devices. In this work, methods for automated grapevine phenotyping are developed, aiming to canopy volume estimation and bunch detection and counting. It is demonstrated that both measurements can be effectively performed in the field using a consumer-grade depth camera mounted on-board an agricultural vehicle. First, a dense 3D map of the grapevine row, augmented with its color appearance, is generated, based on infrared stereo reconstruction. Then, different computational geometry methods are applied and evaluated for plant per plant volume estimation. The proposed methods are validated through field tests performed in a commercial vineyard in Switzerland. It is shown that different automatic methods lead to different canopy volume estimates meaning that new standard methods and procedures need to be defined and established. Four deep learning frameworks, namely the AlexNet, the VGG16, the VGG19 and the GoogLeNet, are also implemented and compared to segment visual images acquired by the RGB-D sensor into multiple classes and recognize grape bunches. Field tests are presented showing that, despite the poor quality of the input images, the proposed methods are able to correctly detect fruits, with a maximum accuracy of 91.52%, obtained by the VGG19 deep neural network.

Effects of Glyphosate-, Glufosinate- and Flazasulfuron-Based Herbicides on Soil Microorganisms in a Vineyard

In a vineyard we examined the effects of broad-spectrum herbicides with three different active ingredients (glyphosate, glufosinate, flazasulfuron) on soil microorganisms. Mechanical weeding served as control treatment. Treatments were applied within grapevine rows and soil samples taken from there in 10–20 cm depth 77 days after application. Fungi were analyzed using classical sequencing technology and bacteria using next-generation sequencing. The number of colony-forming units (CFU) comprising bacteria, yeasts and molds was higher under flazasulfuron compared to all other treatments which had similar CFU levels. Abundance of the fungus Mucor was higher under flazasulfuron than glufosinate and mechanical weeding; Mucor was absent under glyphosate. Several other fungi taxa were exclusively found under a specific treatment. Up to 160 different bacteria species were found – some of them for the first time in vineyard soils. Total bacterial counts under herbicides were on average 260% higher than under mechanical weeding; however due to high variability this was not statistically significant. We suggest that herbicide-induced alterations of soil microorganisms could have knock-on effects on other parts of the grapevine system.

Diversity of arbuscular mycorrhizal fungi in no-till and conventionally tilled vineyards

The use of a permanent vegetation cover or frequent tillage in vineyards may affect soil water budget, nutrient availability, soil compaction, soil erosion and soil microbe biodiversity, and through all these and other factors also yield and wine quality parameters. The abundance and diversity of arbuscular mycorrhizal fungi (AMF) might also be influenced, but so far effects on AMF by permanent vege-tation cover (= no-tillage systems) or repeated chiseling and rotary-tillaging have rarely been compared in vineyards. The objective of this on-farm study was to determine AMF species richness and diversity in two adjacent vineyards in Palatinate (SW Germany). In both vineyards, grown on fertile Luvisols, the var. “Pinot Gris” was grown for 39 years, but with different soil cultivation and different fertilization strategies. In one vineyard, soil was maintained periodically without vegetation by passing rotatory cultivator and chiseling between the grapevine rows (‘inter-rows’) several times per year, preferably during spring and summer and in dependency of rainfall and ‘weed’ growth, and fertilization was mainly by organic fertilizers in the last ten years before soil sampling. In the other vineyard, a permanent vegetation has been established since planting, dominated by Lolium perenne, and mineral fertilizers were exclusively applied. Despite of similar high nutrient availability in both soils, in particular of phosphorus, astonishing high AMF species richness and diversity were found in both vineyards. In the no-tillage inter-rows, 34 AMF species were found, with a species composition typically for Central European permanent grasslands (Shannon diversity index 2.45). In the tillage system 24 AMF species were found with a composition as known for extensively used, cultivated Central European croplands (diversity index 2.26). We conclude that above all soil cultivation has affected AMF diversity in these Central European vineyards, while the level and type of fertilization affected the AMF communities only on a minor level.

Fruit sphere microenvironments and berry phenolic content of Cabernet Sauvignon (Vitis vinifera L.) cultivated under rain-shelter systems with coloured plastic film

Abstract Rain-shelter cultivation has been proven an important cultivation method for grape-plantings in continental monsoon climate zones, of which white plastic films are the most common shelter material. However, while this method and material reduces the occurrence of the disease, it can also decrease the grape berry quality. Five colours (including red, yellow, blue, purple, and white) of plastic films were covered above Cabernet Sauvignon (Vitis vinifera L.) grapevine rows before veraison. Rain-shelter cultivation reduced air temperature, wind speed, and total solar radiation and enhanced relative humidity in the fruit sphere of grapevines. For each particular colour plastic film, the irradiance of its corresponding spectrum band in the canopy of vines was higher than with other colour plastic films. Meanwhile, the blue plastic film treatment significantly promoted the accumulation of total phenolics, anthocyanins, flavonoids, tannins, and phenolic acids more than the other colours of plastic films. Blue plastic films are more beneficial for berry quality promotion of wine grapes, especially Cabernet Sauvignon, under rain-shelter cultivation in continental monsoon climate zones.

La richesse de la flore comme levier pour maintenir la biodiversité dans le vignoble ?

The intensification of crop management have led to an impoverishment of the biological diversity, resulting in the loss of ecosystem services. In viticulture, flora could play an interesting role because it can compensate the negative impacts of vine monoculture. The flora biodiversity favours fauna biodiversity, sustaining especially the presence of pollinating insects in the grapevine inter row sown with grass or legumes and area around grapevine plots. These aspects have been poorly studied until now. A grapevine experiment set in Alsace at INRA Colmar in the frame of the DEPHY-EXPE PEPSVI project was used to address these questions. Between 2014 and 2016, floristic survey was carried out on 4 sites, within an area of 500 m2 within each plot. On those sites, different grapevine systems based on integrated, biological, or biodynamic production were tested. The “presence/absence” method implemented to characterize flora composition and richness on the grapevine row, the inter-row sown with grass, and the tilled inter-row. Results showed that Asteraceae, Fabaceae and Poaceae were the most represented flora families. Asteraceae and Fabaceae may provide pollination ecosystem services if they are well managed and allowed to flower. Moreover, Fabaceae family increases soil fertility by symbiotic fixation. The role of environmental factors, i.e., semi-natural area like hedge or forest edge close to vineyard, and anthropic factors, i.e., soil cover management, were also characterized and shown as impacted on flora composition and richness under grapevine rows and between inter- rows. Flora characterization will continue in 2017 and 2018 to validate the present results and to assess the evolution of flora composition and richness in different climatic conditions.

Mapping Cynodon dactylon in vineyards using UAV images for site-specific weed control

In Spain, the use of annual cover crops is a crop management practice for irrigated vineyards that allows controlling vineyard vigor and yield, which also leads to improve the crop quality. Recently, Cynodon dactylon (bermudagrass) has been reported to infest those cover crops and colonize the grapevine rows, resulting in significant yield and economic losses due to the competition for water and nutrients. From timely unmanned aerial vehicle (UAV) imagery, the objective of this research was to map C. dactylon patches in order to provide an optimized site-specific weed management. A quadrocopter UAV equipped with a point-and-shoot camera was used to collect a set of aerial red-green-blue (RGB) images over a commercial vineyard plot, coinciding with the dormant period of C. dactylon (February 2016). Object-based image analysis (OBIA) techniques were used to develop an innovative algorithm for early discrimination and mapping of C. dactylon, which had the ability to solve the limitation of spectral similarity of this weed with cover crops or bare soil. As a general result, the classified maps of the studied vineyard showed four main classes, i.e. vine, cover crop, C. dactylon and bare soil, with 85% overall accuracy. These weed maps allow developing new strategies for site-specific control of C. dactylon populations in the context of precision viticulture.

Towards Automated Large-Scale 3D Phenotyping of Vineyards under Field Conditions.

In viticulture, phenotypic data are traditionally collected directly in the field via visual and manual means by an experienced person. This approach is time consuming, subjective and prone to human errors. In recent years, research therefore has focused strongly on developing automated and non-invasive sensor-based methods to increase data acquisition speed, enhance measurement accuracy and objectivity and to reduce labor costs. While many 2D methods based on image processing have been proposed for field phenotyping, only a few 3D solutions are found in the literature. A track-driven vehicle consisting of a camera system, a real-time-kinematic GPS system for positioning, as well as hardware for vehicle control, image storage and acquisition is used to visually capture a whole vine row canopy with georeferenced RGB images. In the first post-processing step, these images were used within a multi-view-stereo software to reconstruct a textured 3D point cloud of the whole grapevine row. A classification algorithm is then used in the second step to automatically classify the raw point cloud data into the semantic plant components, grape bunches and canopy. In the third step, phenotypic data for the semantic objects is gathered using the classification results obtaining the quantity of grape bunches, berries and the berry diameter.

Response of Vitis vinifera L. cv. Merlot to Low Frequency Drip Irrigation and Partial Root Zone Drying in the Western Cape Coastal Region – Part I. Soil and Plant Water Status

The impact of five drip irrigation strategies on water status in Merlot/99R was compared to a non-irrigated control (T1) in the coastal wine grape region of the Western Cape province, South Africa. Relationships between predawn (ΨPD), leaf (ΨL), stem (ΨS) and total diurnal (ΨTot) water potential made it possible to classify grapevine water status in terms of ΨL, ΨS, or ΨTot according to previous classifications derived from ΨPD. Around veraison, T1 grapevines already experienced moderate to strong water constraints (ΨS < -1.0 MPa), followed by strong to severe water constraints (ΨS < -1.4 MPa) prior to harvest. Irrigations at pea size, veraison and post-harvest, either applied in grapevine rows (T2) or work rows (T4), did not reduce water constraints compared to T1. However, irrigations at pea size, midway between pea size and veraison, at veraison, midway between veraison and harvest, and post harvest, either applied in grapevine rows (T3) or work rows (T5), reduced grapevine water constraints compared to T1. Irrigation in work rows did not affect grapevine water status compared to irrigation in grapevine rows. A partial root zone drying (PRD) strategy, obtained by switching subsurface irrigation in work rows between alternating rows at approximately 14-day intervals (T6), also reduced water constraints compared to T1. The water status in PRD grapevines clearly responded to the low plant available water (PAW) depletion levels in the alternating work rows in which irrigations were applied. There was minimal lateral flow of irrigation water from subsurface irrigation lines in the work rows towards the grapevine rows.

Response of Vitis vinifera L. cv. Merlot to Low Frequency Irrigation and Partial Root Zone Drying in the Western Cape Coastal Region – Part II. Vegetative Growth, Yield and Quality

The impact of five drip irrigation strategies on vegetative growth, yield and quality of Merlot/99R was compared to a non-irrigated control (T1) in the coastal region of the Western Cape province. Irrigations at pea size, veraison and post-harvest, either applied in grapevine rows (T2) or work rows (T4), tended to increase berry mass and yield compared to T1. More frequent irrigation at pea size, midway between pea size and veraison, at veraison, midway between veraison and harvest, and post-harvest, applied either in the grapevine rows (T3) or work rows (T5), increased berry mass and yield. A partial root zone drying (PRD) strategy, obtained by switching subsurface irrigation in the work rows between alternating rows at approximately 14-day intervals (T6), induced a similar trend. Under the given conditions, yield only increased when irrigation plus rainfall from bud break in September until harvest in February/March increased from ca. 200 mm to 400 mm. More water did not cause any further yield increases. Although low frequency irrigation increased yields compared to T1, it did not affect sensorial wine quality characteristics negatively. Non-irrigated grapevines produced the smallest berries, but did not necessarily produce wine superior in quality. The PRD strategy reduced wine quality, particularly when irrigation was applied at a high frequency between switches. The latter strategy only improved irrigation water productivity when compared to conventionally irrigated grapevines that received unnecessary high volumes of water. Subsurface irrigation applied in the work rows did not affect grapevine responses compared to irrigation in the grapevine rows.