Handbook for Irrigation of Wine Grapes in South Africa

HANDBOOK FOR IRRIGATION OF WINE GRAPES IN SOUTH AFRICA

PA Myburgh

The book is in essence a summary of the wine grape irrigation research carried out in South Africa over a period of more than 50 years. The research was carried out to develop irrigation guidelines, particularly with respect to optimising wine quality and maximizing water use efficiency. Therefore, the primary focus of the book is on practical irrigation, rather than the physiology concerning grapevine water relations. In addition to irrigation strategies, and the scheduling thereof, related aspects such as climate, soil properties, water quality, irrigation systems, as well as frost protection are also addressed. It is envisaged that the book will be a useful guide for present and future generations of wine grape growers, as well as viticulture students.

HANDBOOK FOR IRRIGATION OF WINE GRAPES

IN SOUTH AFRICA

PA MYBURGH

Handbook for irrigation of wine grapes in South Africa All rights reserved Copyright © 2018 Agricultural Research Council 1134 Park Street, Hatfield Pretoria, PO Box 8783, Pretoria 0001 Tel: +27 (0)12 427 9700 E-mail: enquiry@arc.agric.za The author has made every effort to obtain permission for and acknowledge the use of copyrighted material. Please refer enquiries to the author. No part of this book may be reproduced or transmitted in any form or by any electronic, photographic or mechanical means, including photocopying and recording on record, tape or laser disk, on microfilm, via the Internet, by e-mail, or by any other information storage and retrieval system, without prior written permission by the author. First edition 2018

ISBN 978-0-620-80402-8 (print) ISBN 978-0-620-80405-9 (e-book) Set in Arial MT Light 9/12 LAYOUT AND DESIGN by VR Graphics, www.vrgraphics.co.za PRINTING by Shumani Mills Communications, Tygerberg

Cover Without cold, wet winters, neither man, nor grapevine can thrive in the long, dry summers.

Disclaimer Unless indicated otherwise, all photographs and graphic material belong to ARC Infruitec-Nietvoorbij.

2 IRRIGATION OF WINE GRAPES

I dedicate this book to the youth of today who will be responsible for the wine of tomorrow.

Philip Myburgh

IRRIGATION OF WINE GRAPES 3

Foreword

I met Philip Myburgh in 1976 and we worked together for a number of years on the irrigation of wine grapes. It was also my privilege to keep track with his outstanding research over a period of 42 years. He dedicated his whole career life to irrigation research and the result is clear for everyone to see and appreciate. In my opinion there is no one better equipped and experienced to have written this book on a topic of critical importance for South Africa. The Western Cape of South Africa is in the midst of the most serious drought since the recording of weather data started in the 19th century. The scarcity of water as well as

Dr Johan van Zyl

the competition for water between users other than agriculture forces everybody, including the wine industry to use this finite resource optimally. This book therefore comes at a most opportune time. “Handbook for irrigation of wine grapes in South Africa” brings together information that has been “fragmented” among many articles, projects, observations and reports and over a long period of time. But the book offers much more. The author succeeded in converting information into knowledge that he then presents as practical recommendations. The book is furthermore also testimony and a tribute to the excellent quality and growth in the volume of irrigation research for the wine industry in South Africa. A substantial portion of the contents is based on Dr Philip Myburgh’s own research, but also includes all other South African research and

4 IRRIGATION OF WINE GRAPES

Foreword

relevant international work. The work is up to date, relevant and fluently written in a very readable style. This new book covers the entire continuum from climate and soil through to the grapevine and finally to the wine in the bottle. It is a comprehensive work that addresses all the aspects that wine growers, advisors and planners would like to know. At an academic level, lecturers can use this handbook with confidence as study material for students. Over and above the chapters on irrigation systems and irrigation scheduling, the chapter on irrigation water quality deserves special mentioning. Waste water use for irrigation is becoming a reality to relieve the pressure on other water resources. Philip Myburgh gives us guidelines based on experimental data on how to use such water without harm to the grapevine, the wine or the environment. Although the author never loses sight of his end goal namely, practical recommendations, useful and interesting background information is given in all chapters. The reader will enjoy reading more about terms such as water potential, deficit irrigation, anisohydric water stress; terms often used, but not well-understood by us all. The astonishing ability of grapevines to adapt to a changing environment by varying the number of stomata that it forms, should amaze us all and is one of the unique findings in the book. It is not difficult to foresee that “Handbook for irrigation of wine grapes in South Africa” will become a standard reference book and a landmark in the often muddy waters of irrigation recommendations and practices. I wish to congratulate Philip on an excellent and valuable product. In my opinion this book is a must for everyone involved in some aspect of the irrigation of wine grapes.

IRRIGATION OF WINE GRAPES 5

VILLA AND MONASH: Bridging the agricultural skills gap in SA

South Africa, a world class educational institution dedicated to supporting South Africa and the continent to meet its diverse economic and educational needs by providing internationally recognised qualifications. THE ROLE OF AGRICULTURE IN THE SOUTH AFRICAN ECONOMY The South African economy is heavily reliant on the agricultural sector. Agriculture delivers more jobs per Rand invested than any other productive sector, and remains critical in the face of rural poverty and food insecurity (DAFF, 2016). The primary production component of the agricultural sector contributes about 3% to the country’s GDP, but if the entire value chain of agriculture is taken into account, its contribution to GDP increases to about 12%. Agriculture is often neither a study direction, nor a career, of first choice. Partly to blame for this reality is limited awareness and understanding of the vast number of agri-business and entrepreneurship career opportunities that exist along the entire length of the food and nutrition value chain. Much can be, and should be, done to change perceptions, which are currently evident at both school and higher education levels.

The 2017 World Economic Forum Report states that Africa’s skills gap at secondary school level is high. In most African countries, local business executives are of the opinion that secondary school graduates do not possess, on average, the skills employers demand from a productive workforce. Add to this the fact that leading South African farming entities share the common sentiment that agricultural colleges are no longer delivering the well-rounded, technically skilled professionals that is critical in the role of not only production managers, but also lesser skilled workers. It’s clear that young Africans deserve urgent and tangible actions to be taken to adequately equip them for future roles in the agri-industry. They need an enabling environment that will prepare them for competing in the ‘global village’ where interconnectivity and technology-dense work environments define labour markets. State intervention and support on the African continent is generally slow and fraught with bureaucratic impediment. The logical solution is to involve private industry, i.e. the required skills, experience and funding – effective public-private collaboration can contribute to reduce skill-gaps at national and regional levels. VILLA IS TAKING ACTION It’s against this backdrop that Villa is introducing the new Monash / Villa partnership in training – a private enterprise partnership aimed at addressing some of the key issues highlighted above. The Villa Academy is joining forces with Monash

APPROPRIATELY TRAINED GRADUATES: SOUTH AFRICA

The NQF (National Qualification Framework) of South Africa abounds with registered qualifications in the field of agriculture, but they predominantly focus on primary production and research.

is skewed focus towards commercial agriculture; however, the reverse is true in certain other African countries, or perceived as more equitable. Where there is consensus, across all levels of agricultural endeavour, is that socio- economic aspects get too little attention. MORE PRACTICAL EXPOSURE NEEDED IN STUDENT STUDIES The South African agri-industry, over a prolonged period, has lamented the lack of practical exposure and experience of university graduates in particular. This unfortunate chasm in practical experience vested in graduates, which exist between university and industry, puts the brake, temporarily at least, on not only a company’s competitiveness but also that of the country. Funding for education is a contentious issue. In all forums where AET have been workshopped, the need for increased funding is raised – top of the item list slated for increased funding is “practical, vocationally relevant training”. Lack of funding is a debilitating factor for schools delivering agricultural science as a programme or subject. Shortcomings include lack of adequate infrastructure for practical training. Inefficient channelling and management of funding has been identified as problematic. FUNDING AND RESOURCE ALLOCATION

In light of the variety of components comprising the total agricultural supply chain, it should be recognized that not only skills linked with university degrees are required, but that skills should also come from a wider range of disciplines outside of the traditional agriculture- focused qualifications. The ‘boundary’ of agriculture is pliable – there are numerous qualifications and courses with links to the field of agriculture. In order to be relevant, Agricultural Education and Training (AET) needs to focus on building capacities not only for agricultural production, but also to equip a broader range of professionals and practitioners with the necessary skills to engage successfully with the key nodes (links) in the agricultural value chain. In addition to relevance, curricula should be multi- and transdisciplinary in order to build capacity for solving modern-day challenges such as evolving environments (e.g. climate change), new weeds and pests, resistance to pesticides, improved crops and livestock through classical breeding and genetic modification, etc. A challenge facing AET in South Africa and other countries on the continent is how to allocate scarce resources towards both commercial and small- scale farming. The argument, in particular for South Africa, is that currently there

The new partnership between Villa and Monash will go some distance to bridging not only the funding gap, but the skills gap as well… giving a vast number of young Africans the opportunity to pursue long and successful careers across all spheres of the agri-industry.

INSTITUTE FOR GRAPE AND WINE SCIENCES

The Institute for Grape and Wine Sciences (IGWS) is an initiative of the wine and table grape industries and Stellenbosch University. The aims of the IGWS are the establishment of world class training in grape and wine science, the promotion of research relevant to the local industry, as well as technology transfer to the wine and table grape industries. The initial focus was especially on the improvement of the infrastructure of training cellars and the purchase of modern research equipment. The establishment of critical human resources in training and research at the University, relevant to the wine and table grape industries, is a priority. Seven platforms have been established, and each platform is managed by a coordinator to give effect to the aims of the IGWS. These include an analytical, internship, sensory, viticulture, oenology, viticulture technology transfer, as well as an oenology technology transfer platform. One of the chief focuses of the IGWS is technology transfer and to communicate existing as well as new research and information to the industry. The purpose of this is to expand and reinforce the knowledge of people involved in the industry and thus improve the quality of South African viticulture and oenology. This contributes to an industry which is more competitive internationally. A needs assessment was done in the wine industry to identify priority themes for technology transfer. One of the great needs was the packaging of available information on the irrigation of wine grapes. As a result, the IGWS initiated and coordinated a project which led to the publication of this book. Due to the involvement of Netafim and Villa-Monash in technology transfer, they kindly also contributed financially to make the publication possible. In addition, in future the IGWS will focus on ensuring much closer ties between academics and the industry by initiating innovation projects and to further development initiatives originating from research. Specific attention will be given to projects which can have relevance for the industry if they can be developed into products, services or courses.

For more information on the IGWS, visit the website www.igws.co.za. The website also contains articles, e-books, fact sheets and a variety of information and resources for winemakers and viticulturists.

10 IRRIGATION OF WINE GRAPES

Acknowledgements

The Institute for Grape and Wine Sciences for initiating and co-funding of the book.

Lucinda Heyns for her skillful organisation and liaison to make this book possible.

Jan Booysen for his guidance.

Leandri van Heerden for the design and layout of this book, as well as her patience.

Netafim and Villa-Monash for their financial support to make hard copies of the book possible.

The South African wine industry via Winetech, as well as the Water Research Commission for co-funding wine grape irrigation research projects. Growers for permission to work in their vineyards, as well as technical assistance. The ARC for the opportunity and infrastructure to carry out the research. The irrigation research team at ARC Infruitec-Nietvoorbij for their collaboration and assistance over the years.

Carolyn Howell for her dedicated review of the manuscript.

IRRIGATION OF WINE GRAPES 11

Contents

4.2.2 4.2.3 4.2.4

Micro-sprinklers .................................79 Moveable sprinklers ..........................85 Flood irrigation ...................................87 Subsurface irrigation systems .......91 Maintenance of irrigation systems ....95 Conclusive remarks ......................100 Introduction ....................................102 Comparing rain, river and municipal water quality .................103 Water quality norms ......................105 pH ....................................................105 Nitrogen ...........................................106 Phosphorus .....................................107 Sodium ............................................107 Calcium and magnesium ................109 Bicarbonate and carbonate ............109 Chloride ...........................................110 Fluoride ............................................110 Copper ............................................111 Boron................................................111 Iron ..................................................113 Manganese ......................................113 Zinc ..................................................114 Cadmium .........................................114 Chromium ........................................115 Lead ................................................115 Mercury ...........................................115 Molybdenum ....................................115 Other elements ................................116 Irrigation with saline water ...........116 Quantification and classification of water salinity/sodicity ..................116 Leaching salts from the root zone .....119 Dilution of saline water ....................120 Treatment of saline water ................120 Effect of irrigation systems ..............122 Recommendations ..........................122 On-farm water treatment ...............123 Using treated wastewater for irrigation ...............................................123 Municipal wastewater ......................124 Winery wastewater ..........................127 Conclusive remarks ......................144 Introduction ....................................146 Quantification of grapevine water status ..............................................151 Grapevine water potential ...............151 Carbon isotope discrimination ........152

1 Climate 1.1

Introduction ......................................14 Climate classification ......................15 Climatic indices for viticulture .......19 Growing degree days ........................19 Mean February temperature ..............20 Heliothermal index .............................22 Cool night index ................................23 Comparison between the Köppen- Geiger classification and viticulture- based indices ......................................24 Interaction between climate, wine quality and irrigation ..............24 Climate change ................................26

1.2 1.3

4.3 4.4 4.5

1.3.1 1.3.2 1.3.3 1.3.4 1.3.5

5 Irrigation water quality 5.1

5.2

5.3

1.4

5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 5.3.6 5.3.7 5.3.8 5.3.9

1.5 1.6

Conclusive remarks ........................28 2 The dynamics of water in and around vineyards 2.1 Introduction ......................................30 2.2 The hydrological cycle ....................32 2.3 The water balance in vineyards ........33 2.4 Evapotranspiration ..........................35 2.4.1 Evaporation from the soil ...................35 2.4.1.1 Factors that affect evaporation ..........36 2.4.2 Transpiration ......................................41 2.4.2.1 Factors that affect transpiration .........41 2.4.2.1.1 Viticultural aspects ............................41 2.4.2.1.2 Edaphic factors .................................45 2.4.3 Effect of wetted soil volume on evapotranspiration .............................47 2.5 Conclusive remarks ........................53 3 Water related soil properties 3.1 Introduction ......................................54 3.2 Texture ..............................................54 3.3 Bulk density .....................................59 3.4 Water content ...................................59 3.5 Matric potential ................................60 3.6 Soil water characteristic curves .......60 3.7 Water holding capacity ...................63 3.8 Infiltration rate .................................65 3.9 Permeability .....................................66 3.10 Hydraulic conductivity ....................68 3.11 Conclusive remarks ........................71 4 Irrigation systems 4.1 Introduction ......................................72 4.2 Surface irrigation systems .............74 4.2.1 Drip ....................................................74

5.3.10 5.3.11 5.3.12 5.3.13 5.3.14 5.3.15 5.3.16 5.3.17 5.3.18 5.3.19

5.4

5.4.1

5.4.2 5.4.3 5.4.4 5.4.5 5.4.6

5.5 5.6

5.6.1 5.6.2

5.7

6 Grapevine water status 6.1

6.2

6.2.1 6.2.2

12 IRRIGATION OF WINE GRAPES

Contents

8.2

Qualitative assessment of root systems ..................................236 Indirect estimation of evapotranspiration ........................238 Crop coefficients .............................240 Evapotranspiration models ..............241 Direct soil and plant based measurements ...............................250 Soil based measurements ...............250 Wetting front detectors ....................250 Gravimetric samples .......................251 Neutron probes ...............................253 EnviroScan ® sensors .......................256 Diviner 2000 ® probes ......................257 DFM ® probes ...................................258 Tensiometers ...................................260 Watermark ® sensors ........................265 Plant based measurements .............267 Grapevine water potential ...............267 Diurnal trunk shrinkage and expansion ........................................271 Infrared thermometry .......................273 Remote sensing ...............................277 Setting refill lines for irrigation strategies based on grapevine water status ......................................279 Conclusive remarks ......................282 Introduction ....................................284 Types of cold damage ...................285 Prediction of cold damage ............287 Measures to reduce the risk of cold damage ..............................293 Viticultural aspects ..........................293 Soils and tillage ...............................294 Overhead sprinkler irrigation ...........296 Other methods .................................297 Managing vineyards following cold damage ...................................298 Conclusive remarks ......................299

6.3

Factors affecting grapevine water status ....................................155 Cultivars ...........................................155 Atmospheric conditions ...................158 Soil water status ..............................160 Soil salinity .......................................161 Trellis system ...................................162 Canopy management ......................163 Crop load .........................................164 Leaf damage by pests ....................166 Grapevine water status classification ..................................168 Grapevine responses in relation to midday stem water potential ..........172 Class I – No water constraints .........173 Class II – Low water constraints ......173 Class III – Moderate water constraints .......................................173 Class IV – High water constraints ......175 Class V – Severe water constraints ...175 Conclusive remarks ......................175 Introduction ....................................178 Irrigation strategies .......................180 Irrigation of newly planted grapevines .......................................181 Low frequency irrigation ..................184 Medium frequency irrigation ...........189 High frequency irrigation .................193 Pulse irrigation .................................195 Deficit irrigation ...............................197 Different pre- and post-harvest irrigation frequencies .......................198 Partial root zone drying ...................206 Irrigation during the post-harvest and dormancy periods ....................209 Irrigation strategies during critical drought periods ...............................213 Practices to reduce unnecessary water losses .....................................214

8.3

6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6 6.3.7 6.3.8

8.3.1 8.3.2

8.4

8.4.1

8.4.1.1 8.4.1.2 8.4.1.3 8.4.1.4 8.4.1.5 8.4.1.6 8.4.1.7 8.4.1.8

6.4

6.5

6.5.1 6.5.2 6.5.3

6.5.4 6.5.5

8.4.2

8.4.2.1 8.4.2.2

6.6

7 Irrigation strategies 7.1

8.4.2.3 8.4.2.4

7.2

8.5

7.2.1

7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.2.7

8.6

9 Preventing cold damage in vineyards 9.1

7.2.8 7.2.9

9.2 9.3 9.4

7.2.10

9.4.1 9.4.2 9.4.3 9.4.4

7.2.11

7.2.11.1 Reducing evaporation losses ..........215 7.2.11.2 Reducing excessive transpiration ......221 7.2.11.3 Preventing irrigation system losses ....226 7.3 Possible ways to use irrigation water more efficiently ....................229 7.4 The water footprint of wine ..............233 7.5 Conclusive remarks ......................234 8 Practical irrigation scheduling 8.1 Introduction ....................................236

9.5

9.6

References ..................................... 300 Abbreviations, acronyms and symbols ........................................307

IRRIGATION OF WINE GRAPES 13

Chapter 1

Climate

1.1 INTRODUCTION Since elements such as incoming solar radiation and air temperature can affect wine quality or style in a positive way, the climate of a region is important in wine production. On the other hand, high levels of humidity can increase the occurrence of diseases and pests, whereas strong winds may cause physical damage to grapevines. Given that vineyards for wine production are primarily planted in a Mediterranean climate with hot, dry summers and limited rainfall (Table 1.1), their water requirements must be replenished by irrigation. For example, vineyards in the Breede River and Lower Olifants River regions depend totally on irrigation. In most cases, irrigation water is obtained from winter rainfall stored in on-farm dams, or large dams which feed irrigation schemes. Where possible, irrigation water is pumped from rivers or bore holes. TABLE 1.1. Long term mean annual rainfall in grape growing regions. Data supplied by the ARC Institute for Soil, Climate and Water in Pretoria.

Rainfall (mm)

Region

District

Autumn & winter Spring & summer Total

Coastal

Grabouw

645

366

1 011

Stellenbosch

490

254

744

Piketberg

580

263

843

Breede River

Tulbagh

392

182

574

Robertson

164

116

280

Little Karoo

Montagu

176

149

325

Barrydale

204

154

358

Lower Olifants River

Lutzville

93

47

140

Lower Orange River

Upington

56

183

239

It is only in some areas of the Coastal region where grapevines can be grown without irrigation, i.e. if they have deep, well-developed root systems. These dryland, or rainfed, vineyards survive on the winter rainfall stored in the root zone and rainfall in spring. Based on the foregoing, it is clear that winter rainfall is by far the most important climatic variable with regard to sustainable viticulture. The

14 CHAPTER 1 – CLIMATE

Chapter 1

dependency of rainfed grapevines on rainfall in the Coastal region is illustrated by the positive yield response to rainfall, particularly the cumulative rainfall in July and August (Fig. 1.1). Furthermore, the regression equation indicates that the yield will be almost zero if no rain occurs in July and August under the given conditions.

Figure 1.1

12

2014

10

8

2015

2017

6

2016

4

Yield (t/ha)

2018

2

y = 0.0625x – 0.0519 R² = 0.9925

0

0 20 40 60 80 100 120 140 160 180

Rainfall (mm)

FIGURE 1.1. The effect of rainfall during July and August on the yield of dryland Cabernet Sauvignon near Philadelphia in the Coastal region. The dashed vertical line indicates the 71-year mean rainfall.

1.2 CLIMATE CLASSIFICATION In South Africa, wine grapes are grown in two broad climatic regions. Most of the wine grape vineyards occur in the Western Cape which has a Mediterranean climate. Wine grapes are also grown under summer rainfall conditions in the Northern Cape and on a limited scale in the other provinces. However, if a more accurate climate classification is used, there are distinct climatic differences within the two broader climate regions. The internationally accepted Köppen-Geiger classification separates climates into five primary groups based on latitude, i.e. tropical, arid, temperate, cold and polar (Peel et al. , 2007). In South Africa, wine grapes are only grown under arid and temperate conditions (Table 1.2). Each of the primary groups are further divided into secondary and tertiary groups based on air temperature and precipitation relationships. Furthermore, the Köppen- Geiger classification uses a so-called precipitation threshold, which is calculated according to the annual rainfall distribution as described in Table 1.2. The climate types for South Africa are indicated in Figure 1.2, but it should be noted that limited climate variation may occur within the demarcated areas.

IRRIGATION OF WINE GRAPES 15

TABLE 1.2. Description of Köppen climate symbols and defining criteria according to Peel et al. (2007).

1st 2nd 3rd Description

Criteria

A

Tropical

Not applicable to South African grape growing regions Mean annual precipitation < 10 x precipitation threshold (1) Mean annual precipitation < 5 x precipitation threshold Mean annual precipitation ≥ 5 x precipitation threshold

B

Arid

W – Desert

S

– Steppe

Mean annual temperature ≥ 18

h – Hot

k – Cold

Mean annual temperature < 18

> 10 and 0 < coldest month

C

Temperate

Hottest month T mean

mean temperature < 18

s

– Dry summer

Precipitation in driest month of summer < 40 and precipitation in driest summer month < (precipi- tation in wettest winter month ÷ 3) Precipitation in driest winter month < (precipita- tion in wettest summer month ÷ 10)

w

– Dry winter

f

– Without dry season Not (Cs) or (Cw)

Hottest monthly mean temperature ≥ 22

a – Hot summer

b – Warm summer

Not (a) and number of months where mean tem- perature is above 10 ≥ 4 Not (a) or (b) and 1 ≤ number of months where T mean is above 10 < 4 Not applicable to South African grape growing regions Not applicable to South African grape growing regions

c – Cold summer

D

Cold

E

Polar

(1) Precipitation threshold (P threshold

) varies according to the following rules: If 70% of mean

annual precipitation (MAP) occurs in winter then P threshold (MAT), if 70% of MAP occurs in summer then P threshold

= 2 x mean annual temperature = 2 x MAT + 28, otherwise P threshold =

2 x MAT + 14.

16 CHAPTER 1 – CLIMATE

Chapter 1

Hot semi-arid steppe Cold semi-arid steppe

Hot & dry summer (Mediterranean) Warm & dry summer (Mediterranean)

Humid subtropical with dry winter Subtropical highland with dry winter

Humit subtropical without dry season Temperate oceanic without dry season

Hot arid desert

Cold arid desert

FIGURE 1.2. Climate types for South Africa according to the Köppen-Geiger classification with average summer and winter temperatures in major cities and towns (downloaded from https://maps-southafrica.com/weather-map-south-africa).

Using the Köppen-Geiger classification can be explained by means of the following examples for Stellenbosch, Robertson and Lutzville: (i) At Stellenbosch less than 70% of the annual precipitation occurs in winter (Table 1.3). Therefore, the P threshold = (2 x mean annual temperature) + 14 = (2 x 17.3) + 14 = 48.7. Since the mean annual precipitation is more than 487 mm (= 10 x 48.7), it is not an arid climate. Given that the temperature of the hottest month is more than 10°C, and the temperature of the coldest month is between 0° and 18°C (Table 1.3), it is a temperate climate. Since precipitation in the driest summer month is less than 40 mm, and less than the precipitation in the wettest winter month divided by 3 (122.3 ÷ 3 < 40), it is regarded as a dry summer. Furthermore, the locality has a warm summer since the hottest monthly mean temperature is less than 22°C (Table 1.3), and the monthly mean

IRRIGATION OF WINE GRAPES 17

temperature is above 10°C for at least four months. Based on the foregoing, the climate at Stellenbosch is temperate with dry, warm summers, i.e. “Csb” in short. TABLE 1.3. Long term mean monthly air temperature (T n ) and total precipitation (P tot ) recorded at three localities in the Western Cape. Month Stellenbosch Robertson Lutzville T n (°C) P tot (mm) T n (°C) P tot (mm) T n (°C) P tot (mm) January 21.5 21.0 23.2 12.2 22.3 2.1

February

21.8

23.6

23.0

16.4

23.0

3.3

March

20.3

41.6

21.5

15.7

22.0

6.9

April

18.4

62.0

18.4

30.4

20.2

10.5

May

15.9

98.9

15.1

32.5

17.6

17.9

June

13.9

122.3

12.6

31.9

15.5

24.8

July

13.1

103.0

12.0

26.9

14.6

19.6

August

13.5

104.1

12.8

41.8

15.0

19.8

September

14.4

67.4

14.9

19.8

16.3

11.5

October

16.4

40.1

17.5

21.5

18.2

7.7

November

18.7

29.3

20.0

18.4

20.2

6.6

December

20.2

31.0

22.0

12.2

21.3

8.6

Mean

17.3

17.8

18.9

Total

744.3

279.7

139.3

(ii) At Robertson, less than 70% of the annual precipitation occurs in winter. Therefore, the P threshold = (2 x mean annual temperature + 14) = 49.5. Since the mean annual precipitation is less than 495 mm (Table 1.3), it is an arid climate. Given that the mean annual precipitation is more than five times the P threshold , it is regarded as steppe. Furthermore, the temperature is regarded as cold, since the mean annual temperature is less than 18°C (Table 1.3). Therefore, Robertson has an arid, steppe, cold or “BSk” climate. (iii) Since less than 70% of the annual precipitation occurs in winter at Lutzville, the P threshold is 51.7 as calculated from the mean annual temperature. Given that the mean annual precipitation is way below 517 mm (Table 1.3), it is also an arid climate. Since the mean annual precipitation is less than five times the P threshold , it is desert. Furthermore, the locality is regarded as hot, since the mean annual temperature exceeds 18°C (Table 1.3). Therefore, Lutzville has an arid, desert, hot or “BWh” climate.

18 CHAPTER 1 – CLIMATE

Chapter 1

1.3 CLIMATIC INDICES FOR VITICULTURE Climate classifications such as the Köppen-Geiger system only provide a broad regional to global generalization of climates. Unfortunately, they do not provide specific details on atmospheric variables that are important for viticulture and wine production. Atmospheric variables that affect grapevine growth, yield and wine quality are solar radiation, air temperatures, day-night temperature fluctuations, heat accumulation, wind speed, precipitation and humidity. Consequently, the following classification systems have been developed specifically for viticulture potential. 1.3.1 GROWING DEGREE DAYS This index describes the potential for wine quality based on heat summation (Amerine & Winkler, 1944). The criteria were adapted for the Western Cape wine producing regions by Le Roux (1974). The growing degree days are calculated as the summation of the daily mean air temperature above 10ºC through the seven months growing season, i.e. from September to March (Table 1.4). The GDD can be used to identify different areas for potential wine quality within a wine region (Fig. 1.3). For instance, wine quality potential in the Lower Olifants River improves as the distance to the Atlantic Ocean decreases (Bruwer, 2010).

TABLE 1.4. Wine quality potential classification according to the GDD as proposed by Le Roux (1974).

GDD

Class

Wine quality potential

< 1 389

I

Quality red and white table wine

1 389 - 1 666

II

Good quality red and white table wine

1 667 - 1 943

III

Red and white wine and port

1 944 - 2 220

IV

Dessert wine, sherry and standard wine

> 2 220

V

Dessert wine and brandy

IRRIGATION OF WINE GRAPES 19

Figure 1.3

1 500 1 700 1 900 2 100 2 300 2 500 2 700 2 900

Klawer

Region V

Vredendal

Lutzville

Region IV

GDD (ºC)

Ebenaeser

Region III

R 2 = 0.9529

0

10

20

30

40

50

Distance (km)

FIGURE 1.3. Effect of distance to the Atlantic Ocean on wine quality potential in the Lower Olifants River region according to the GDD as proposed by Bruwer (2010).

1.3.2 MEAN FEBRUARY TEMPERATURE Since temperature plays an important role in determining wine quality, analysis of long term weather data can be used to demarcate the potential wine quality of a region (Bruwer, 2010 and references therein). The MFT classification, i.e. for the warmest month of the year, was adapted by De Villiers et al . (1996) for the Western Cape wine regions (Table 1.5). The variability of MFT in the Coastal region of the Western Cape is shown in Figure 1.4.

TABLE 1.5. Wine quality potential classification for the Western Cape according to the MFT as proposed by De Villiers et al . (1996).

MFT (ºC)

Region

Wine quality potential

17 - 18.9

Cold

High quality white table wine

19 - 20.9

Cool

High quality white and red table wine

21 - 22.9

Moderate

High quality red table wine

23 - 24.9

Warm

Low acid, high pH

> 25

Very warm

Low acid, high pH

It was also shown that altitude and the proximity of the Atlantic Ocean affect the MFT in the Western Cape Coastal region over distances as far as ca. 60 km inland (Myburgh, 2005). The effects of sea breezes play a prominent role in the

20 CHAPTER 1 – CLIMATE

Chapter 1 t r 1

temperature variation of the Coastal region (Bonnardot et al. , 2002). The altitude and distance to the ocean can be used to estimate MFT for localities where there are no weather stations by means of the following equation: MFT = 20.9 - 0.0052341A + 0.06369D (R 2 = 0.9983; s.e. = 0.04°C) Eq. 1.1 where A is the altitude (m) and D is the distance to the Atlantic Ocean (km). In practical terms, the model shows that MFT declines at a rate of ca. 0.5°C with a 100 m increase in altitude, and that air temperature increases by ca. 0.6°C per 10 km increase in distance to the ocean. According to Equation 1.1, the MFT at the Atlantic Ocean coastline is estimated to be around 20.9°C. t r t r ri ti f t t l r i ( r t t l. , ). ltit i t t t t ti t f r l liti r t r r t r t ti f t f ll i ti : . - . . (R 2 . ; . . . ° ) . . r i t ltit ( ) i t i t t t tl ti ( ). I r ti l t r , t l t t li t r t f . . ° it i r i ltit , t t ir t r t r i r . . ° r i r i i t t t . r i t ti . , t t t

tl ti

tli

i ti

t t r

. ° .

Figure 1.4

No Station

District

MFT (°C) 23.0 24.7 18.9 22.9 25.0 19.1 20.6 24.0 24.2 23.6 24.4 23.4 24.3 23.7 22.8 24.5 23.2

1 Lutzville

Lutzville Klawer

1

Lutzville

2 Klawer Winery

2

3 Nortier

Lamberts Bay

4 Graafwater Co-op Graafwater

3

5 Ideal hill 6 Heldervue

Piketberg Piketberg

4

7 Vredenburg Co-op Vredenburg 8 Mo P rreesburg Co-op Mo P rreesburg

9 Porterville Co-op

Porterville

10 Langgewens

Mo P rreesburg

St. Helena Bay

6 5

11 Riebeeck Wes Co-op Riebeeck Wes

7

12 Grasrug 13 Landau 14 HS Boland 15 Philadelphia 16 Nederburg

Malmesbury Wellington Agter Paarl Philadelphia

Vredenburg

9

Porterville

8 10

11

Paarl Paarl

12

17 Bellvue

13

Atlantic Ocean

14

15

18 Bien Donne 19 Elsenburg

Groot Drakenstein

22.6

18 16

17

Stellenbosch 21.8 20 Mountain Vineyard Groot Drakenstein 22.5 21 La Motte Franschhoek 22.8 22 Nietvoorbij Stellenbosch 21.5 23 Helderfontein Helderfontein 21.8 24 Bethlehem Groot Drakenstein 22.1 25 Welgevallen 4 Stellenbosch 22.1

19

22

24 20 21

Table Bay

23

25

False Bay

30

Kilometers 30

0

FIGURE 1.4. The variability in mean MFT as recorded at selected weather stations in the Coastal region of the Western Cape (after Myburgh, 2005). I 1.4. The varia ility in ean FT as recor e at selecte eather stations in the Coastal region of the estern Cape (after yburgh, 2005).

IRRIGATION OF WINE GRAPES 21

1

I I

I

I

1.3.3 HELIOTHERMAL INDEX The HI can be calculated to describe the thermal character of the climate with respect to potential for viticulture within a specific wine growing area (Bruwer, 2010 and references therein). In South Africa, the HI is based on the summation of the mean and maximum monthly temperatures from October to March (Table 1.6). The HI includes a length of day coefficient to compensate for the greater photosynthetic active radiation occurring during longer days at latitudes higher than 40º. For latitudes lower than 40º, a value of one is used. An example where thermal character of the Lower Olifants River region was analysed by Bruwer (2010) is presented in Figure 1.5. This classification clearly shows how the climate becomes warmer as the distance to the Atlantic Ocean increases. TABLE 1.6. The HI used to describe the thermal character of the climate (Tonietto & Cabonneau, 2004 and references therein). Viticultural climatic class Class code Class interval (ºC) Very cool HL -3 <1 500 Cool HL -2 > 1 500 < 1 800 Temperate HL -1 > 1 800 < 2 100 Temperate warm HL +1 > 2 100 < 2 400 Warm HL +2 > 2 400 < 3 000 Very warm HL +3 > 3 000

Figure 1.5

2 200 2 400 2 600 2 800 3 000 3 200 3 400 3 600 3 800

Klawer

Class HI +3

Vredendal

Lutzville

HI (ºC)

Class HI +2

Ebenaeser

R 2 = 0.9984

Class HI +1

0

10

20

30

40

Distance (km)

FIGURE 1.5. Effect of distance to the Atlantic Ocean on the thermal character in the Lower Olifants River region according to the HI (Bruwer, 2010). Figure 1.6

17

Klawer

22 CHAPTER 1 – CLIMATE

16

Chapter 1

1.3.4 COOL NIGHT INDEX The CI ′ is based on the minimum mean night temperatures during the month preceding harvest (Bruwer, 2010 and references therein). The objective of the CI ′ is to assess the qualitative potential of a wine region with respect to wine colour and aroma. The CI ′ is based on the minimum daily temperature during March (Table 1.7). An example where the CI ′ in the Lower Olifants River region was analysed by Bruwer (2010) is presented in Figure 1.6. Unlike the GDD and HI, only two regions could be demarcated according to the CI ′ . This suggests that the CI ′ might not be sensitive enough for viticultural purposes in South Africa. TABLE 1.7. The CI ′ used to classify the climate with respect to potential for viticulture based on night temperature in the month preceding harvest (Tonietto & Cabonneau, 2004 and references therein). Viticultural climatic class Class code Class interval (ºC) Warm nights CI ′ -2 > 18 Temperate nights CI ′ -1 > 14 < 18 Cool nights CI ′ +1 > 12 < 14 Very cool nights CI ′ +2 < 12 2 200 2 400 2 600 2 800 3 000 3 200 3 400 3 600 3 800 HI (ºC) Class HI +3 Class HI +2 Class HI +1 Ebenaeser Lutzville Vredendal Klawer R 2 = 0.9984 Figure 1.5

0

10

20

30

40

Distance (km)

Figure 1.6

17

Klawer

16

15

Class CI h -1

14

Lutzville

(ºCI h C)

Class CI h +1

13

Vredendal

Ebenaeser

12

Class CI h +2

11

10

0

10

20

30

40

Distance (km)

FIGURE 1.6. Effect of distance to the Atlantic Ocean on viticultural potential in the Lower Olifants River region according to the CI ′ (Bruwer, 2010).

IRRIGATION OF WINE GRAPES 23

1.3.5 COMPARISON BETWEEN THE KÖPPEN-GEIGER

CLASSIFICATION AND VITICULTURE-BASED INDICES According to the Köppen-Geiger classification, Stellenbosch, Robertson and Lutzville have three distinct climates as discussed in Section 1.2. This implies that grapevine growth, yield and wine quality are likely to be affected differently in the three localities. However, in the case of GDD, MFT, HI and CI ′ , some of the indices are the same in more than one region, although the climate differs (Table 1.8). This means that grapevines could respond differently in regions that have the same viticultural index. Furthermore, the viticultural indices only focus on the wine quality and do not give an indication of grapevine water requirements. In contrast, the Köppen-Geiger classification provides an indication of the intensity of irrigation needed. At Stellenbosch with its “dry summers”, low frequency irrigation, e.g. once a month, would be adequate for sustainable viticulture. In fact, vineyards with deep, well-developed root systems in sandy loam or clay loam soils might be able to produce economically viable yields and wine quality. On the other hand, vineyards in similar soils under “arid” conditions in the Breede River Valley will require irrigation at a medium frequency, i.e. every two to three weeks. Under the almost “desert” conditions in the Lower Olifants River region, grapevines will need high frequency irrigation, e.g. more than once a week, particularly in the sandy soils away from the river. TABLE 1.8. Comparison of the climate classification according to Köppen-Geiger and the climatic indices for viticulture at three localities in the Western Cape. Climate classification Stellenbosch (Coastal region) Robertson (Breede River Valley) Lutzville (Olifants River Valley) Köppen-Geiger Temperate, dry, warm summer (Csb) Arid, steppe, cold (BSk) Arid, desert, hot (BWh) Growing degree days III (1914°C) IV (2029°C) IV (2217°C) Mean February temperature Moderate (21.8°C) Moderate (22.4°C) Warm (23.0°C) Heliothermal index Temperate warm (HI +1 ) Warm (HI +2 ) Warm (HI +2 ) Cool night index Temperate nights (CI ′ -1 ) Temperate nights (CI ′ -1 ) Cool nights (CI ′ +1 )

1.4 INTERACTION BETWEEN CLIMATE, WINE QUALITY AND IRRIGATION

The climate plays a prominent role in the wine style or quality produced in a specific terroir. Comparing results obtained by means of irrigation studies carried out with Merlot near Wellington (Myburgh, 2011a & b), Ashton (Lategan & Howell, 2010b) and Lutzville (Myburgh, 2011i) showed that the sensorial overall wine quality seems to be better where the HI is higher and the CI ′ is lower (Fig. 1.7). However, within a

24 CHAPTER 1 – CLIMATE

Chapter 1

region, the opposite is also possible. Wine quality potential of Cabernet Sauvignon in the Lower Olifants River region tended to be better where the HI, as well as CI ′ , are lower near the coastline (Bruwer, 2010). This trend was probably due to the extremely high HI and cool CI ′ near Klawer (Figs. 1.5 & 1.6). Traditionally, the terroir concept was developed for non-irrigated vineyards. Therefore, hydraulic properties of the soil, such as water holding capacity, within a terroir also play an important role in the wine style or quality. This is probably the reason for the trend towards better overall wine quality of Merlot in a heavier soil near Wellington compared to a sandy soil on Dorbank near Lutzville (Fig. 1.8).

60

60

A

60

60

55

55

A

B

55

55

50

50

50

50

45

45

Wine quality (%)

Wine quality (%)

q

45

45

40

40

Wine quality (%)

Wine quality (%) Wellington Ashton Lutzville

Wellington Ashton Lutzville

40

40

Wellington Ashton Lutzville

Wellington Ashton Lutzville

FIGURE 1.7. The sensorial overall quality of Merlot wine (A) tends to increase where the heliothermal index is higher and (B) tends to decline where the cool night index is lower.

60

60

55

55

50

50

45

Wine quality (%)

45

40

Wine quality (%)

Wellington Ashton Lutzville

40

Wellington Ashton Lutzville FIGURE 1.8. The sensorial overall quality of Merlot wine tends to increase where the clay content of the soil is higher.

Basically, the wine characteristics within a terroir are induced by the prevailing climate and soil properties under non-irrigated conditions. Therefore, it is important to note that the climate and soil seem to have a general terroir effect on wine quality although the vineyards need to be irrigated in the above-mentioned regions. However, it is important to note that the level of irrigation will affect wine quality

IRRIGATION OF WINE GRAPES 25

irrespective of the climate or soil. Generally, more irrigation will produce more grapes with a concomitant decline in wine quality and vice versa if less irrigation is applied (Fig. 1.9). These effects of irrigation on wine quality at the various localities are discussed in more detail in Chapter 7. It is also interesting that the Merlot wine quality seems to better where the grapes were harvested earlier (Fig. 1.9). This was probably due to higher HI and CI ′ near Wellington (Fig. 1.7).

Figure 1.9

60

27 Feb

8 Feb

21 Feb

55

50

Wine quality (%)

45

40

Wellington

Ashton

Lutzville

FIGURE 1.9. The sensorial overall quality of Merlot generally tends to decrease where the harvest date is later at a specific locality. The arrows illustrate how less irrigation will improve wine quality, and vice versa if more irrigation is applied.

1.5 CLIMATE CHANGE Climatic changes have occurred in the history of the Earth and are bound to happen again. Various mathematical models indicate towards global warming which goes hand in hand with lower rainfall. Higher air temperatures and lower rainfall will have a huge negative impact on the sustainability of viticulture, particularly in terms of water supply to the grapevine. The dilemma will be aggravated if lower rainfall reduces the available irrigation resources. Furthermore, climate change will most probably result in reduced irrigation water allocations and increased water tariffs. Since mankind is unlikely to prevent or stop possible climate change(s), certain adaptations need to be made, particularly with respect to vineyard irrigation. Firstly, vineyards should not be established in low potential soils, i.e. with low water holding capacity and low cation exchange capacity. Secondly, soil preparation must be carried out properly to ensure deep, well-developed root systems that can absorb water from the largest possible soil volume. Since large volumes of irrigation water are lost to evaporation in the case of full surface wetting, growers will have

26 CHAPTER 1 – CLIMATE

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