Technical Yearbook 2024

2024

Technical Yearbook

Contents

VITICULTURE Promotion of wild bees in South African and Austrian vineyards by plants with diverse floral traits ........................... 7 Mapping individual vines using drone imagery ....................10 Treated municipal wastewater for irrigation (Part 1): Irrigation application and water quality .................................13 Treated municipal wastewater for irrigation (Part 2): Grapevine water status and vegetative responses .................17 Treated municipal wastewater for irrigation (Part 3): Yield and juice characteristics ..................................................21 Treated municipal wastewater for irrigation (Part 4): Soil chemical responses ............................................................28 Treated municipal wastewater for irrigation (Part 5): Soil hydraulic conductivity .......................................................33 Biosand reactors as a feasible solution for the treatment of winery wastewater (Part 1) ......................................................36 Biosand reactors and anaerobic digestion – a zero-waste model for winery wastewater (Part 2) ....................................40 The quest for new Pinotage clones ..........................................43 In-field fractional use of winery wastewater with raw water (Part 1): Plot selection, augmentation and climatic conditions ....................................................................46 In-field fractional use of winery wastewater with raw water (Part 2): Irrigation application, water quality and nutrient load ...............................................51 In-field fractional use of winery wastewater with raw water (Part 3): Soil responses ..........................................56 In-field fractional use of winery wastewater with raw water (Part 4): Grapevine and wine responses ..............62 In-field fractional use of winery wastewater with raw water (Part 5): Assessment of the below and above-ground chemical status of grapevines in the lower Olifants River region ......................................................68 High(er)-throughput evaluation of novel grapevine material for important traits ....................................................73 Understanding and controlling Phomopsis (‘streepvlek’) in Western Cape vineyards ...............................75 The grapevine collection at ARC Infruitec-Nietvoorbij ........78 Biocontrol in viticulture ............................................................81 Impact of GHS on evaluation of IPW spray programmes ....................................................................84

OENOLOGY Hydrogen sulphide formation in canned wines – the role of liners and wine composition .................................86 Bioprotection as an alternative to SO 2 in the pre-fermentation phase ............................................................88 Yeast cell density and the effect on volatile thiol formation ......91 Calcium tartrate instability ......................................................93 Electronic noses .........................................................................96 Towards a circular economy in winemaking – re-utilisation of yeast lees .........................................................98 Plant-based proteins in oenology ..........................................100 The use of carrageenan in calcium tartrate and protein stabilisation of wines ...............................................................105 Stirring things up – Sauvignon blanc juice stabulation .....107 PRACTICAL IN THE VINEYARD Under-vine living mulches .....................................................110 Waterlogged conditions in vineyards ...................................112 Vineyard response to the floods in the Olifants River region during 2023 .................................................................115 Centennial celebration and congress of the International Union of Soil Science ..............................................................119 Suitable rootstock for soil and wine goal ..............................123 Mechanical pruning in the Orange River – a viable alternative ..................................................................126 The vine’s reserve bank ..........................................................129 PRACTICAL IN THE CELLAR The influence of consumers’ preferences on the wood character of wine .....................................................................133 What is a ‘microbiome’, and how does it relate to wine? ...134 Practical considerations concerning wine hoses .................136 Tips for additions ....................................................................138 E-aphrom – a digital sensor for secondary fermentation ......141 Organise your store .................................................................145 GENERAL Opstal Estate – rock-solid between the Slanghoek and Badsberg Mountains ..............................................................148 Carbon Heroes launches personalised QR codes and landing pages ...................................................................................149 Case study – Achtertuin Farm’s sustainability story unveiled through the CCC carbon calculator .............................152 Confronting Climate Change’s Workshops ................................155

IMAGES COPYRIGHT: Individual authors, Shutterstock or WOSA library. DTP LAYOUT: Avant-Garde South Africa | 021 863 3165 | COVER: Shutterstock, Pixabay | PRINTING: ABC Press

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Authors / Contributors

Callie Coetzee Vinpro callie@vinpro.co.za

Johan de Jager Vinpro johan@vinpro.co.za Karien O’Kennedy South Africa Wine karien@sawine.co.za

Carien Coetzee Basic Wine carien@basicwine.co.za

Carolyn Howell Senior researcher, ARC Infruitec-Nietvoorbij howellc@arc.agric.za

Lida Malandra Enartis lida.malandra@enartis.co.za Melané Vivier SAWGRI, Stellenbosch University mav@sun.ac.za Matthew Wrensch Geography Environmental Studies,

Charl Theron Private consultant charltheron495@gmail.com Etienne Terblanche Vinpro etienne@vinpro.co.za Francois Halleen RDI, VillaCrop Protection fhalleen@villacrop.co.za

Stellenbosch University mwrensch98@gmail.com

Pieter Badenhorst Private consultant pieterb@fortheloveofwine.co.za

Gert Engelbrecht Vinpro gerte@vinpro.co.za

Phyllis Burger Senior researcher, ARC Infruitec-Nietvoorbij burgerp@arc.agric.za

Gareth Holtman Department of Civil Engineering, CPUT gareth@holtman.co.za

René Gaigher Conservation Ecology & Entomo​logy​, Stellenbosch University reneg@sun.ac.za

Heinrich Schloms Vinpro heinrich@vinpro.co.za

Santi Basson Private consultant santib@mweb.co.za

Hanno van Schalkwyk Vinpro hanno@vinpro.co.za

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FOREWORD

A knowledge-driven future for South African Wine

The foundation of a thriving and competitive wine industry lies in continuous learning, research, and innovation. At South Africa Wine, our Research, Development, and Innovation (RDI) department is dedicated to ensuring that the latest scientific advancements are not only accessible to our industry but also applied in ways that drive meaningful progress in grape growing and winemaking. The Technical Yearbook is an essential resource in this undertaking. By consolidating an entire year’s worth of research driven technical articles, we provide industry professionals with a guide to the latest research results and best practices that can help shape the future of South African wine. This publication represents the expertise, dedication, and forward-thinking approach of the researchers, viticulturists, and winemakers committed to quality grape growing and winemaking. With topics ranging from new clones for Pinotage and the effective utilisation of winery wastewater to bioprotection and calcium tartrate instability, the Technical Yearbook bridges academic research and practical application. By translating science into actionable knowledge, we empower industry stakeholders to make informed decisions that enhance sustainability, efficiency, and quality. As we print and distribute this book for the second year under the auspices of South Africa Wine, we reaffirm our commitment to creating and maintaining a knowledge-sharing culture. We aim to ensure that the South African wine industry remains at the forefront of global innovation, equipped with the tools and insights to navigate present challenges and future opportunities. I encourage every reader to engage with the content, apply the findings, and contribute to the collective growth of our industry. Ultimately, this contributes to our strategic goal of building a more resilient, sustainable, and prosperous future for South African wine. 

Gerard Martin Research, Development, and Innovation Executive South Africa Wine

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Viticulture 1

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JANUARY/FEBRUARY

Promotion of wild bees in South African and Austrian vineyards by plants with diverse floral traits By René Gaigher, Silvia Winter, Sophie Kratschmer & Temitope Kehinde The aim of this study was to gain a better understanding of how the plant community in vineyards could potentially be manipulated to improve bee diversity.

Global declines in pollinating insects Wild pollinating insects are declining in abundance and diversity worldwide. This is due to many interacting stressors such as climate change, pathogens, intensive farming practices with high levels of agrochemical inputs, and landscape transformation, which leads to a loss of pollinator habitats. 1 More than 75% of global food crops and more than 85% of wild flowering plant species rely on pollination provided by animals, mainly insects. Therefore, the decline in pollinators is of major concern for food security and the continued functioning of natural ecosystems. 3 Even though wine grapes do not depend on insect pollination, vineyards that are managed in an ecologically

sensitive way can provide pollinator-friendly habitats and, in doing so, support this important group of insects in farming landscapes. Factors that promote them include flowering plants in vineyard cover crops that provide essential food sources such as nectar and pollen, 4 reduced disturbance in vineyard inter-rows which promotes ground-nesting pollinators, 7 and semi-natural features in the landscape such as fallows and solitary trees which provide nesting habitats. The potential contribution of viticultural landscapes to pollinator conservation is significant because conservation in farmland is becoming an increasingly important part of global conservation strategies. 3

Hypothetical plant assemblages illustrate the difference between taxonomic and functional richness:

FIGURE 1 – ASSEMBLAGE A. High taxonomic richness (many different species) but low functional richness (they are all ecologically similar and belong to the same plant family).

FIGURE 1 – ASSEMBLAGE B. High taxonomic richness and high functional richness (a wide variety of ecological, morphological, and life-history traits among species).

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bees. 6,7 This study followed this work to focus on the influence of flowering plant taxonomic and functional richness on bee diversity. Taxonomic richness refers to the number of species in an assemblage, whereas functional richness refers to the variety of ecological, morphological, or life-history traits (for example, flower colour, shape, longevity, and flowering season) among species in an assemblage. In the hypothetical plant communities in Figure 1, Assemblages A and B have equal taxonomic richness, but Assemblage B has higher functional richness. Plant and animal communities with high functional diversity support more diverse ecological functions and more diverse responses to disturbance, which improves the functioning and

FIGURE 2. Data collection of plant assemblage in an Austrian vineyard.

How do flowering plants in vineyard inter-rows influence wild bees? A collaborative study during 2019 - 2020 between Stellenbosch University and the University of Natural Resources and Life Sciences, Vienna, assessed how different aspects of the plant community in vineyards influence wild bee diversity. 5 Previous work highlighted the importance of floral abundance (total coverage of flowers) in vineyards for

resilience of these communities. 10 We used data that were previously collected from the Stellenbosch region in South Africa and from Carnuntum and Neusiedlersee-Hügelland in Austria (Figure 2). For plants and bees, we selected traits that are relevant to pollination (Figure 3) and then calculated the functional richness of plants and bees for each site based on these

Lecty a) Uses pollen from many plant groups b) Specializes on pollen from 1 plant group

Flowering period a) Spring b) Early summer c) Summer d) Late summer e) Whole season

Nesting a) Ground nesting b) Above-ground nesting

Flower shape

a) Bell and funnel b) Disk c) Flag blossom

Mouthpart length

Sociality a) Solitary b) Colonies

Nectar presence a) Yes b) No

Flower colour a) Pink

Traits used to calculate bee functional richness

Traits used to calculate plant functional richness

b) Purple c) Yellow d) White e) Etc.

Pollen collection type

Flower symmetry a) Radial symmetry b) Bilateral symmetry

Activity period a) Spring b) Early summer c) Summer d) Late summer e) Whole season

Body size

Nectar accessibility a) Nectar openly available b) Nectar hidden

a) Abdomen b) Leg c) Crop

FIGURE 3. Traits used to calculate wild bee and flowering plant functional richness.

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A

B

FIGURE 4. Effect plots showing the influence of flowering plant functional richness on a) wild bee taxonomic richness, and b) wild bee functional richness. The shaded area indicates 95% confidence intervals.

functional richness promoted wild bee taxonomic and functional richness across management regimes and regions (Figure 4). This means that a wide range of flowering plant species that vary in their traits best promote a wide variety of wild bee species and traits. This positive relationship may be explained by the fact that individual bee traits were associated with distinct plant traits. For example, in Austrian vineyards, short-tongued bees benefited from yellow flowers with radial symmetry and hidden nectar, likely because their mouthpart morphology allows them to easily access hidden nectar compared to other insects such as flies (Figure 4). This type of trait matching between flowering plants and flower-visiting insects is important for effective pollination of the plant, and for the insect to access its food resource, pollen and/or nectar (Figure 5). 2 Management implications Increasing the functional diversity of flowering plants in and around vineyards promotes wild bee diversity. This could be done by selecting cover crop mixtures with diverse floral traits (e.g., by selecting plants from different plant families) and by reducing tillage that favours a wide variety of plant traits. This work shows potential to fine-tune vineyard practices to enhance pollinator diversity and plant-pollinator networks in viticultural landscapes. It would be supported by further research on how this could be optimised for different conditions in the South African context. 

FIGURE 5. An example of trait matching between pollinators and flowering plants: Short-tongued bees are effective pollinators of radial, yellow flowers with hidden nectar, which often belong to the Asteraceae family. traits. Additional factors were considered in the analyses, including vineyard management approach (organic vs non-organic), total vegetation cover in vineyards, amount of semi-natural vegetation in a 500 m radius around the sites, and number of woody structures (woodland patches, tree lines and solitary trees) in the surrounding landscape. The most prominent result was that high flowering plant

References https://www.wineland.co.za/promotion-of-wild-bees-in-south-african-and-austrian-vineyards/

For more information, contact René Gaigher at reneg@sun.ac.za.

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JANUARY/FEBRUARY

Mapping individual vines using drone imagery By Matthew Wrensch & Kyle Loggenberg This study proposes a new method of creating precision input data for precision viticulture and autonomous farming applications using remote sensing. Abstract Precision viticulture (PV) seeks to optimise the health and yield of vineyards by providing farmers with site-specific management schemes. Through these practices, the environmental impact of farming can be reduced. Remote sensing (RS) developments have risen through the years, and new data availability has revolutionised the PV field. While previous RS studies have attempted individual vine delineation, no industry standard exists. This study aims to delineate individual vine plants using drone-captured RGB imagery (red, green and blue waveband). The computer vision algorithm, region grow, has been investigated in a geographic object-based image analysis (GEOBIA) environment to extract individual vine plants. The model achieved an intersection over union (IOU) score of 0.54 and an area under curve (AUC) score of 0.59, representing the algorithm’s predictive performance against the ground truth. While the results indicate only moderate performance, they provide ground for further research.

Background Precision viticulture (PV) and autonomous farming (AF) have emerged as a dynamic duo, reimagining grape production. These transformative practices can bring automation to existing techniques and inspire the creation of new ones, thereby making invaluable improvements to the quality and yield of grapes and promoting more sustainable farming techniques. PV approaches and AF are highly reliant on accurate crop data. Remote sensing (RS) technologies, such as unmanned aerial vehicles (UAVs), commonly referred to as drones, with their ability to capture detailed measurements from a distance, provide crucial data and insights driving automation in farming. The model proposed by this study utilises RGB imagery (red, green and blue waveband) captured by UAVs and computer vision to detect individual vine plants. Accurate delineation of individual vines could contribute to more precise spraying of pesticides by autonomous vehicles or provide more detailed information on vine plants’ biophysical characteristics. This research demonstrates the potential of the region grow algorithm and RGB-UAV/RGB drone imagery for individual vine extraction. Materials and methods The process of extracting individual vine plants was achieved through a two-step workflow, which consisted of 1) extracting vine rows, and 2) delineating individual vines. The two-step workflow is detailed in the following sections.

Part 1: Vine row extraction Site and data

The data used was provided by Stellenbosch University’s Department of Viticulture and Oenology and consisted of drone RGB imagery captured at a 2 cm resolution. The imagery was collected over Thelema Mountain Vineyards in Stellenbosch, Western Cape of South Africa, during the 2020/2021 growing season. Additionally, ground control points (GCPs) were collected on-site, which served as a reference to digitise the outline of 13 vine plants. The digitised vines were crucial in the accuracy assessment process, as they were used to compare the model predictions with actual ground-truth values. The GCPs also provided a measurement of the average vine plant spacing in this vine parcel. Data preparation Three vegetation indices were created from the RGB imagery to allow for better vine row detection. The indices selected were the green leaf index (GLI), excess green excess red (ExG-ExR) and colour of vegetation (CIV). Recommendations by De Castro and other authors (2018) informed the selection of the vegetation indices. Row extraction and classification The row extraction and classification process were completed using the eCognition Developer 10.2 software (Trimble Geospatial, 2022). The drone images were classified into three categories: Vine, shadow, and inter row area (IRA) using two algorithms, multiresolution

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Buffer [50 cm]

Polygon to raster

Raster to polyline

Create random points

Thin

FIGURE 1. Centreline extraction workflow.

FIGURE 2. MRS segmentation at a high zoom level.

FIGURE 3. Resulting classification (three classes).

FIGURE 4. Creation of centreline (in red).

FIGURE 5. Seeds (red) generated along the centrelines.

FIGURE 6. Seeds (crosses) grown.

FIGURE 7. Final region grow objects outlined in red to the extent of the vine row.

segmentation (MRS) and the decision trees (DT) classifier, also known as classification and regression trees or CART.

2022) using the vine row polygons as the bounding boxes and the generated vine plant location estimates as the seed pixels. The vine plant extraction process was iterated 50 times to ensure that the full extent of each vine was detected. Results Part 1: Vine row extraction The results from Part 1 of the process can be seen in Figures 2 and 3. Figure 2 depicts a zoomed-in view of the image objects generated in the segmentation process. Figure 3 shows the final row extraction results obtained through the DT classification. In Figure 3, green represents the vine, black represents the shadow and yellow represents the inter row area (IRA). The vine rows were extracted as polygons and used as input for Part 2 of the processing workflow. It should be noted that some post-processing was required to remove grainy misclassifications and to remove grass patches incorrectly classified as a vine.

Part 2: Individual vine delineation Centreline and seed extraction

The extracted vine rows were imported into ArcGIS Desktop 10.8.1 (Esri, 2020) for further processing. The workflow outlined in Figure 1 was followed to identify the centrelines of each vine row. An average vine length of 1.75 m, as determined by in-field GPS measurements, was used to generate seed points or pixels from these lines. Vine plant extraction The region grow algorithm was used to obtain the final vine plant delineation. Region grow is designed to take a seed pixel and expand it outwards to a specified bounding box threshold. The algorithm was implemented in the eCognition Developer 10.2 software (Trimble Geospatial,

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FIGURE 8. AUC curve.

Part 2: Individual vine delineation Figure 4 depicts the result of the penultimate phase of the workflow illustrated in Figure 1. This phase involved the creation of centrelines using the vine polygons from Figure 3. Figure 5 shows the final output of the Figure 1 workflow, showcasing the generation of seed points along the previously generated vine row centrelines. Each seed represents a prediction of a vine plant’s location. Figure 6 shows the seeds overlaying the generated individual vine objects. The final individual vine objects can be seen in Figure 7.

Accuracy assessment The intersection over union (IOU) accuracy assessment was used to validate the correctness of the detected vines. This approach measures the overlap between the predicted vine areas and the ground truth values. The model achieved an IOU score of 0.54, representing moderate predictive accuracy. An area under curve (AUC) score was also employed to assess predictive accuracy, with the model producing an AUC score of 0.59. Figure 8 shows that the AUC curve lies above the 0.5 line, indicating that the model does possess a level of predictive prowess.

Conclusion The results highlight the potential of drone imagery for the extraction of individual vines. The IOU and AUC scores of 0.54 and 0.59 show that the model is not ready for large-scale application. However, the research does provide grounds for future research. One of the major positives of the study’s results is the demonstrated utility of RGB imagery. While multispectral imagery is more commonly used than RGB imagery due to the usefulness of the near-infrared (NIR) band for vegetation indices, these multispectral sensors are more expensive than RGB sensors, making them less accessible, particularly for smaller farms. Using RGB drone imagery would provide affordable methods for improving farm management techniques, benefiting a broader spectrum of farmers. The developed methodology provides a point of departure for detecting accurate vine foliage areas and vine plant locations, allowing farmers to monitor the health of individual vine plants and detect missing or dead plants. Vine-level data could also assist with more accurate automated crop spraying. With continued research and enhancements, the model has the potential to achieve greater accuracy, robustness and automation. This progress could pave the way for widespread adoption within the viticulture industry. 

References https://www.wineland.co.za/mapping-individual-vines-using-drone-imagery/

For more information, contact Matthew Wrensch at mwrensch98@gmail.com.

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MARCH

Treated municipal wastewater for irrigation (Part 1): Irrigation application and water quality

By Carolyn Howell, Karla Hoogendijk, Philip Myburgh, Vink Lategan & Eduard Hoffman

Abstract Low annual rainfall, limited supply of fresh water that can be stored on farms and water restrictions imposed by authorities during drought highlighted the necessity for alternative water sources for vineyard irrigation for the South African wine industry. Therefore, the impact of irrigation with treated municipal wastewater (TMW) on soil and grapevines was assessed under field conditions in vineyards in the Coastal region of South Africa. Grapevines were uninterruptedly irrigated using TMW from the City of Cape Town over 11 years. Grapevines were either rain-fed, irrigated with TMW via a single dripper line, or received twice the volume via double dripper lines. As expected, the quality of the TMW used for the irrigation of the vineyards was below the minimum criteria stipulated by the General Authorisations to irrigate with wastewater in terms of pH, electrical conductivity (ECw), chemical oxygen demand (COD), faecal coliforms and sodium adsorption ratio (SAR). The mean sodium (Na+) concentration in the TMW exceeded the critical value of 100 mg/L for irrigating grapevines in South Africa. However, chloride (Cl-) levels were well below the threshold value of 700 mg/L, at which toxicity in grapevines could occur. The low N content in the TMW could not supply the annual N requirement of the grapevines. The annual amount of P applied via the single dripper lines was slightly below grapevine requirements, whereas double the TMW irrigation applied excessive amounts of P. Amounts of K+ applied via TMW irrigation were more than annual grapevine requirements for the double dripper line treatment, which could affect wine quality negatively. The amount of Ca2+ and Mg2+ applied via the TMW also exceeded annual grapevine requirements. Regular analyses of TMW are essential when using it as an alternative water source for vineyard irrigation. This will ensure that the legislated limits given in the General Authorisations are adhered to and that the chemical load conforms to recommended thresholds and norms. This study’s objectives were to assess the quality of treated municipal wastewater (TMW) used for irrigation of commercial vineyards and to quantify the amount of plant nutrients applied via TMW irrigation. In this regard, the study formed part of a long-term project to assess the sustainability of using TMW for vineyard irrigation in the Coastal region of the Western Cape.

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14 TECHNICAL YEARBOOK 2024 On average, grapevines in the back and foot slope sites received comparable irrigation volumes, whereas those in the shoulder plot received slightly less (Table if applied via the irrigation water. In addition, irrigation using K + -rich wastewater may lead to excessive K + uptake by grapevines, potentially negatively affecting wine quality. 3 However, TMW usually has a high sodium (Na + ) and chloride (Cl - ) content that can affect soil’s physical, chemical and biological properties. Corrosive metals such as iron (Fe 2+ ) and manganese (Mn 2+ ), often present in municipal wastewater, can clog irrigation equipment. The presence of heavy metals, pathogens and pharmaceutical compounds can also limit the use of TMW since some of these elements can accumulate in plants and ultimately enter the biological food chain. Methods Site selection and vineyard characteristics The field trial was carried out in full-bearing, commercial vineyards on a farm near Philadelphia in the Coastal region Each of the three main experiment sites consisted of three treatment plots. Since the study’s primary objective was to obtain a range of soil and grapevine responses to irrigation with treated municipal wastewater, it cannot be regarded as a comparative study. Therefore, there were no treatment replications. It must be noted that several vineyard field trials investigating soil and vineyard responses to irrigation have followed a similar approach. The experimental plots consisted of one row of 15 experiment grapevines, a buffer row on each side and at least two buffer grapevines at each end of the experiment rows. In one treatment, the grapevines were rain-fed, i.e. grown under dryland conditions. It was included to compare soil and grapevine responses upon irrigation with TMW. This was considered a control treatment, given that no raw water was available for irrigation on the farm. Grapevines of the second treatment were irrigated with TMW via a single dripper line (SLD), which is the standard industry norm. Drippers were spaced 1 m apart in the grapevine row and had a flow rate of 2.3 L/h. Irrigation frequency and volumes of water were applied according to the grower’s irrigation schedule. Grapevines of the third treatment received irrigation via double dripper lines (DLD), which doubled the volume of wastewater compared to SLD. The purpose of the DLD was to accelerate any possible effects of the wastewater on the soil and grapevines. Irrigation volumes of the SLD plots were measured by means of water meters from the beginning of the study period. Since the lengths of the DLD plots were the same as the SLD plots, it was assumed that grapevines in the DLD plot received double the volume of irrigation compared to those in the SLD plots. The TMW was sourced by the farm from the Potsdam Wastewater Treatment Works (WWTW) near the City of Cape Town (CoCT). A sample of the TMW was collected annually on the farm at the beginning of each year (January) from the 2006/07 season. A commercial laboratory analysed the wastewater samples. The water was also assessed for its microbial status from 2008 to 2012. Results and discussion FIGURE 1. The landscape position of the experimental sites near Philadelphia. Application of treated municipal wastewater FIGURE 1. The landscape position of the experimental sites near Philadelphia. Introduction The climate of the Western Cape is particularly suitable for producing grapes and supports a very productive wine industry. 1 However, freshwater resources are generally limited in the grape-growing districts. Consequently, sustainable grape production in the province is highly dependent on winter rainfall and the application of irrigation in drier regions. In this regard, inconsistent rainfall and periodic droughts can severely impact the wine industry. Low annual rainfall, limited supply of fresh water that can be stored on farms, and water restrictions imposed by authorities have highlighted the necessity for alternative water sources for vineyard irrigation for the South African wine industry. Many arid and semi-arid countries use TMW as an alternative source of irrigation water. It is particularly suitable as an irrigation water source in Mediterranean countries with limited freshwater supplies during warmer months and high rainfall during winter. This can facilitate the leaching of salts applied via wastewater irrigation. However, no studies have yet assessed the feasibility of using TMW rather than fresh water for vineyard irrigation under South African conditions. Using TMW for irrigation has several potential benefits and disadvantages. 2 As a source of additional water, it can improve and sustain crop production. It often contains high amounts of essential macro-elements such as nitrogen (N), phosphorus (P) and potassium (K + ) that can be recycled vineyard on the foot slope was planted in 2001, whereas the one on the back slope was planted in 2002. All grapevines were grafted onto 99 Richter and planted at a spacing of 2.75 m x 1.2 m. The vineyards were managed according to the grower’s standard viticultural practices regarding cover crop, fertiliser and irrigation management.

of the Western Cape from 2006/07 until 2017/18 seasons. 4 The region has a Mediterranean climate. Given the hilly landscape where the vineyards were irrigated using TMW, three experimental sites were selected in different landscape positions. The first site was in a Sauvignon blanc vineyard located on the shoulder of a hill (Figure 1) and was planted in 2000. The second and third sites were in two Cabernet Sauvignon vineyards on a back and foot slope. The vineyard on the foot slope was planted in 2001, whereas the one on the back slope was planted in 2002. All grapevines were grafted onto 99 Richter and planted at a spacing of 2.75 m x 1.2 m. The vineyards were managed according to the grower’s standard viticultural practices regarding cover crop, fertiliser and irrigation management. Application of treated municipal wastewater Each of the three main experiment sites consisted of three treatment plots. Since the study’s primary objective was to obtain a range of soil and grapevine responses to irrigation with treated municipal wastewater, it cannot be regarded as a comparative study. Therefore, there were no treatment replications. It must be noted that several vineyard field trials investigating soil and vineyard responses to irrigation have followed a similar approach. 5,6,7 The experimental plots consisted of one row of 15 experiment grapevines, a buffer row on each side and at least two buffer grapevines at each end of the experiment rows. In one treatment, the grapevines were rain-fed, i.e. grown under dryland conditions. It was included to compare soil and grapevine responses upon irrigation with TMW. This was considered a control treatment, given that no raw water was available for irrigation on the farm. Grapevines of the second treatment were irrigated with TMW via a single dripper line (SLD), which is the standard industry norm. Drippers were spaced 1 m apart in the grapevine row and had a flow rate of 2.3 L/h. Irrigation frequency and volumes of water were applied according to the grower’s irrigation schedule. Grapevines of the third treatment received irrigation via double dripper lines (DLD), which doubled the volume of wastewater compared to SLD. The purpose of the DLD was to accelerate any possible effects of the wastewater on the soil and grapevines. Irrigation volumes of the SLD plots were measured by means of water meters from the beginning of the study period. Since the lengths of the DLD plots were the same as the SLD plots, it was assumed that grapevines in the DLD plot received double the volume of irrigation compared to those in the SLD plots. The TMW was sourced by the farm from the Potsdam Wastewater Treatment Works (WWTW) near the City of Cape Town (CoCT). A sample of the TMW was collected annually on the farm at the beginning of each year (January) from the 2006/07 season. A commercial laboratory analysed the wastewater samples. The water was also assessed for its microbial status from 2008 to 2012.

Results and discussion On average, grapevines in the back and foot slope sites received comparable irrigation volumes, whereas those in the shoulder plot received slightly less (Table 1). Due to limited water resources, vineyards in the Coastal region generally receive relatively low irrigation volumes compared to regions such as the Breede and Olifants Rivers. In the latter regions, more water can be abstracted from large irrigation schemes along the rivers. It was previously shown that 129 mm per year was sufficient for drip-irrigated wine grapes near Wellington. 8,9 This indicated that the grapevines at Philadelphia received adequate irrigation. On the other hand, it implied that grapevines in the DLD plots were indeed over-irrigated for the purpose of the study. TABLE 1. The mean volume of TMW applied annually for grapevine irrigation employing single dripper lines near Philadelphia from 2006/07 until 2017/18. Landscape position Irrigation (mm) Shoulder 160±71 Backslope 168±70 Foot slope 172±68 The pH range of the TMW varied between 6.7 and 8.0 throughout the 11-year study period (Table 2). The pH variation was within the range of 6.5 to 8.4, recommended for irrigation water. 10 The pH of the TMW was within the legislated limits to irrigate with wastewater as prescribed by the General Authorisations 11 given in Table 3. The mean electrical conductivity (EC w ) (Table 2) slightly exceeded the critical value of 0.8 dS/m, the salinity threshold for water used to irrigate grapevines. 9 Like pH, the EC w was within the legislated limits 11 (Table 3). The mean total-N level (Table 2) was below the critical value of 5 mg/L at which crops sensitive to N (such as grapevines) might be affected. 9 The P concentration in the wastewater consistently exceeded the long-term critical value of 0.05 mg/L, which demarcates a risk for algal blooms and biofouling of the irrigation equipment. 10 Calcium (Ca2+) levels in the wastewater varied between 33.4 mg/L and 67.3 mg/L throughout the 11-year study period (Table 2). The magnesium (Mg 2+ ) levels in the TMW were relatively low. The mean level of K + in the irrigation water was 20.3 mg/L. The mean Na + concentration exceeded the critical value of 100 mg/L, the legal limit for irrigating grapevines in South Africa. The mean sodium adsorption ratio (SAR) of the TMW (Table 2) also met the criteria stipulated by the General Authorisations 11 (Table 3). According to the SAR values of 0 to 10 mmol/L 0.5 for grapevines, 11 the TMW had a low sodium hazard. The Cl - levels in the TMW (Table 2) were well below the threshold value of 700 mg/L at which toxicity

TABLE 2. Water quality parameters of the TMW used for vineyard irrigation near Philadelphia from 2006/07 until 2017/18. Parameter Minimum Maximum Mean pH 6.7 8.0 7.1±0.3 EC w (dS/m) 0.7 1.2 0.9±0.2 Total N (mg/L) 1.0 16.0 4.3±1.5 P (mg/L) 0.1 9.5 3.2±1.1 Ca 2+ (mg/L) 33.4 67.3 46.4±8.8 Mg 2+ (mg/L) 6.1 11.6 8.5±1.5 K + (mg/L) 14.8 32.6 20.3±6.2 Na + (mg/L) 100.7 173.6 120.9±18.1 SAR (mmol/L) 0.5 3.0 5.5 4.3±0.7 PAR (mmol/L) 0.5 0.3 0.6 0.4±0.1 Cl - (mg/L) 111.2 281.2 160.2±39.8 HCO 3 - (mg/L) 142.1 242.0 203.0±33.5 SO 4 2- (mg/L) 54.0 276.0 84.4±11.3 Fe 2+ (mg/L) 0.0 0.34 0.10±0.08 Mn 2+ (mg/L) 0.0 0.08 0.04±0.03 TABLE 3. General Authorisations for legislated limits for pH, electrical conductivity (EC w ), chemical oxygen demand (COD), faecal coliforms (FC) and sodium adsorption ratio (SAR) for wastewater used for irrigation in South Africa. 10

Maximum irrigation volumes (m 3 /day) < 50 < 500 < 2 000

Parameter

pH

6 - 9

6 - 9

5.5 - 9.5 0.7 - 1.5

EC w (dS/m) COD (mg/L)

≤ 2

≤ 2

≤ 5 000

≤ 400

≤ 75

FC (per 100 mL) ≤ 1 000 000 ≤ 100 000

≤ 1 000

SAR

≤ 5

≤ 5

Other criteria apply

problems in grapevines might occur. 9 The levels of HCO 3 - in the irrigation water ranged between 142.1 mg/L and 242.0 mg/L (Table 2). It should be noted that high levels of HCO 3 - in irrigation water may negatively impact crops, soils and irrigation equipment. 9 The mean COD measured from 2011 to 2018 was 15 mg/L. This met the criteria stipulated by the General Authorisations 11 for using wastewater for irrigation (Table 3). The mean E. coli was 27 per 100 mL and was within the legislated limits to irrigate with wastewater as prescribed by the General Authorisations 11 given in Table 3. The Fe 2+ concentration in the wastewater (Table 2) never exceeded

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the critical value of 5 mg/L, which is the recommended maximum concentration of Fe 2+ in irrigation water used for irrigation of grapevines. 12 Levels of Mn 2+ in the TMW varied from being absent to a maximum concentration of 0.08 mg/L (Table 2). According to South African guidelines, 13 levels of Mn 2+ should not exceed 1.5 mg/L since Mn 2+ may cause clogging of irrigation pipelines, i.e. similar to Fe 2+ . No arsenic (As 3+ ) and mercury (Hg 2+ ) were detected in the TMW from 2008 to 2013. Chromium was present every season up to 2012/13, with concentrations ranging between 0.000 mg/L and 0.023 mg/L. Concentrations of cadmium (Cd 2+ ) and lead (Pb 2+ ) in the TMW were less than 0.003 mg/L and 0.0002 mg/L, respectively. Due to the low concentrations of the heavy metals and the cost implications, analyses of heavy metals were terminated in 2013/14. The concentrations of each element applied via the TMW in the vineyard, as well as the amount of irrigation water applied, were used to calculate the amount of each element applied on average SLD plots for the three landscape positions’ plots. Annually, 7 kg/ha, 5 kg/ha and 33 kg/ha of

N, P and K + , respectively, were applied. Annual amounts of 77 kg/ha, 14 kg/ha, 201 kg/ha and 267 kg/ha of Ca 2+ , Mg 2+ , Na + and Cl - , respectively, were applied via the irrigations with TWM. The low N content in TMW was insufficient to supply the annual N requirement of grapevines. The TMW provided adequate amounts of P to meet annual grapevine requirements when double the amount of irrigation water was applied. The K + applied via the TMW irrigation to the DLD treatment exceeded grapevine requirements. The amount of Ca 2+ and Mg 2+ applied via the TMW also exceeded annual grapevine requirements. Acknowledgements • The project was funded by the Water Research Commission (WRC), Winetech and the Agricultural Research Council (ARC). • ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for technical support. • Messrs Pierre Blake for permission to work in his vineyard, and Egbert Hanekom for managing the vineyard and technical assistance.

Conclusion The quality of the TMW used for vineyard irrigation met the minimum criteria stipulated by the General Authorisations for pH, EC w , COD, faecal coliforms and SAR for irrigation with wastewater in South Africa. The P concentration in the TMW consistently exceeded the long-term critical value of 0.05 mg/L, which demarcates a risk for algal blooms in water storage facilities, as well as biofouling of irrigation equipment. The mean Na + concentration of 120.9 mg/L in the TMW exceeded the critical value of 100 mg/L for irrigating grapevines in South Africa. Chloride levels in the TMW were well below the threshold value of 700 mg/L, at which toxicity in grapevines might occur. Considering the above-mentioned, regular analyses of TMW are essential when using it as an alternative source of water for vineyard irrigation. This will ensure that the legislated limits given in the General Authorisations are adhered to. Furthermore, the analyses will ensure that the chemical load conforms to recommended thresholds and norms. In doing so, irreversible damage to irrigation equipment, soils and grapevines can be avoided. The low N content in the TMW was insufficient to supply the annual N requirement of grapevines. Where double the normal irrigation volume was applied, TMW supplied adequate amounts of P to meet annual grapevine requirements. The amounts of K + applied via TMW irrigation to the DLD treatment were more than grapevine requirements and could negatively affect wine quality. The amount of Ca 2+ and Mg 2+ applied via the TMW also exceeded annual grapevine requirements. In general, using TMW irrigation can supply grapevine nutrients in a plant-available form, but some nutrient amounts may be insufficient, whereas others may be excessive. Consequently, growers are recommended to use an integrated fertiliser program by adjusting fertiliser amounts according to the amount of nutrients applied via the wastewater. Growers could also consider diluting the wastewater with raw water to reduce the oversupply of certain elements if indicated by analysis. Grapevine and soil responses will be presented in subsequent articles. 

References https://www.wineland.co.za/treated-municipal-wastewater-for-irrigation-part-1/

For more information, contact Carolyn Howell at howellc@arc.agric.za.

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APRI L

Treated municipal wastewater for irrigation (Part 2): Grapevine water status and vegetative responses By Carolyn Howell, Karla Hoogendijk, Philip Myburgh, Vink Lategan & Eduard Hoffman

landscape where the vineyards were irrigated using TMW, three experiment sites were selected in different landscape positions. The first site was in a Sauvignon blanc vineyard on the shoulder of a hill. The second and third sites were in two Cabernet Sauvignon vineyards on a back- and a footslope, respectively. Details of the characteristics of the vineyards, irrigation treatments and application, and an assessment of the water quality and nutrient load, were reported previously. 2,3,4 Grapevine water potential was measured during the 2017/18 season using the pressure chamber technique 5 according to guidelines described previously. 6 The stem water potential ( Ψ S ) was measured at each treatment plot in three mature, unscathed leaves opposite a bunch. At véraison of the 2017/18 growing season, 30 mature leaves opposite a bunch were collected per treatment plot at each landscape position. Leaf blades were analysed by a commercial laboratory. Over the last four years of the study period, i.e. 2015 to 2018, grapevine vigour was quantified by measuring pruning mass in winter. Due to the nature of the project, no statistical data analyses were initially planned. However, in discussions with statisticians, it became clear that comparing results obtained with the different irrigation strategies was possible. Different seasons were considered replications. Fisher’s least significant difference was calculated at the 5% level to compare treatment means.

Abstract A long-term trial was conducted in commercial vineyards in the Coastal region of South Africa to assess the impact of treated municipal wastewater (TMW) irrigation on vineyards. Cabernet Sauvignon and Sauvignon blanc grapevines were irrigated using TMW from the Potsdam wastewater treatment works for 11 years. Grapevines were either rainfed (RF), irrigated with TMW via a single dripper line (SLD) or received twice the volume of wastewater via a double dripper line (DLD). Grapevine vegetative responses were measured from the 2014/15 to 2017/18 season. Although high amounts of K + , Na + and Cl- were applied via TMW irrigation, it did not result in excessive plant uptake and did not negatively affect vegetative growth. Irrigation reduced water constraints throughout the growing season compared to RF conditions, particularly for Cabernet Sauvignon. Consequently, SLD and DLD grapevines produced stronger vegetative growth. Results showed that the availability of irrigation water (albeit of relatively low quality) in regions where grapevines are usually grown under dryland conditions can sustain the vegetative growth of grapevines. However, TMW can vary in its availability, as well as its quality over a short period. Plant and soil water status should be monitored regularly to avoid over-irrigation. Irrigation water, soils and grapevine leaves should be analysed to ensure that chemical parameters conform to recommended thresholds and norms.

Introduction Treated municipal wastewater (TMW) is a suitable irrigation water source in Mediterranean countries with limited fresh water supplies during summer and high rainfall during winter. The latter can facilitate the leaching of salts applied via wastewater irrigation, leading to sodicity. Approximately 2 000 ha of vineyards in the Swartland and surrounding regions in South Africa are irrigated with TMW supplied by the City of Cape Town’s Potsdam wastewater treatment works and the Malmesbury municipality. 1 The study’s objective was to assess the sustainability of long-term irrigation with TMW on grapevine vegetative growth from the 2014/15 to 2017/18 seasons in commercial vineyards in

the Coastal region of the Western Cape, South Africa. The low winter rainfall in 2017 in this spesific region and the looming onset of drought and water restrictions highlighted the necessity for alternative water sources for vineyard irrigation for the South African wine industry. Therefore, in the last season of the study, i.e. the 2017/18 season, grapevine plant water status, leaf chemical status and canopy characteristics were also measured. Methods The field trial was carried out in full bearing, commercial vineyards on a farm near Philadelphia in the coastal region of the Western Cape from 2006/07 until 2017/18. The region has a Mediterranean climate. Given the hilly

Results and discussion Grapevine water status At the pea-size berry stage of the

RF

SLD

DLD

2017/18 season, except for the backslope double dripper line (DLD) and footslope single dripper line (SLD) plots, the irrigated treatments did not experience any water constraints according to thresholds reported previously (Figure 1). 7,8 However, grapevines at the rainfed (RF) plots experienced low water constraints at the shoulder and backslope and moderate constraints at the footslope site (Figure 1A - C). On 18 December 2017 (véraison), all of the grapevines at the shoulder site experienced moderate water constraints, with Ψ S varying between -0.9 MPa and -1.1 MPa (Figure 1A). In contrast, grapevines of the RF plot at the backslope site were already experiencing severe water constraints (Figure 1B). Before harvest, there was little difference between the treatments and all the grapevines experienced severe water constraints, except for the grapevines at the footslope DLD plot (Figure 1C). According to water constraint thresholds, the maximum Ψ S measured at the footslope DLD plot fell under Class IV, namely “high water constraints”, which is regarded as ideal for producing quality Cabernet Sauvignon wine on a clay soil. 8 The substantially higher Ψ S measured at the footslope DLD plot during véraison and harvest was most probably due to high volumes of TMW applied at this plot 4 and subsequent greater soil water content (Figure 1C). At the back- and footslope sites, Ψ S was consistently higher at the SLD and DLD plots when compared to the RF plots, albeit very slightly (Figure 1B - C). Similarly, lower Ψ S in non-irrigated grapevines was reported compared to those irrigated with SLD and DLD in the Swartland. This was attributed to greater soil water content in irrigated plots. 9 From the results of the current study, it is clear that irrigation with TMW was only beneficial in preventing water constraints up until véraison, whereafter irrigated grapevines experienced similar levels of water stress compared to non-irrigated grapevines. Similar results were

-2.2 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0

No

Low Moderate

Ψ S (MPa)

High Severe

A

Pea size Véraison Harvest

RF

SLD

DLD

No

Low Moderate High Severe

Ψ S (MPa)

B

Pea size Véraison Harvest

RF

SLD

DLD

No

Low Moderate

Ψ S (MPa)

High Severe

C

Pea size Véraison Harvest

FIGURE 1. Effect of rainfed conditions (RF) and irrigation with treated municipal wastewater via single (SLD) and double line drip (DLD) on the midday stem water potential (Ψ S ) in (A) Sauvignon blanc on a shoulder and Cabernet Sauvignon on (B) a backslope and (C) a footslope at pea size, véraison and harvest during the 2017/18 season. Figure 1.

reported for Tempranillo grapevines under RF and irrigated conditions during seasons with limited rainfall. 10 Vegetative grapevine measurements Leaf chemical status All experimental grapevines had leaf blade N levels (Table 1) exceeding the recommended norms of 1.5% to 2.4%. 11 No substantial differences were observed between treatments, but leaf N content tended to increase slightly

with the amount of irrigation water applied. Given that the N content of the leaves was above the recommended norm of 2.4%, care should be taken to avoid over-fertilisation that could lead to excessive vegetative growth and reduced fruitfulness. 12 The grapevine leaf blade P content (Table 1) was within the recommended range of 0.12% to 0.45%, 11 except for slightly higher concentrations in the shoulder SLD, DLD and footslope DLD plots. Irrigation with TMW significantly

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