SPECIAL EDITION TEGNIESE TECHNICAL BULLETIN. Dealing with drought and water stress

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1 SPECIAL EDITION TEGNIESE TECHNICAL BULLETIN Dealing with drought and water stress SEPTEMBER 2017

2 INHOUD / CONTENTS Is waterskaarstes voortaan deel van ons landskap? 1 Min reën, lae damvlakke bied wyd rede tot kommer Klimaat van verandering? 4 Só raak klimaatsverandering produsente Lessons from Down Under 5 Water budgets 'critical' for producers - scientist Water stress and vines: explore the 'magic window' 8 Irrigation methods and technologies for efficient water use Farming for the future 9 How to manage soil and irrigation for efficient water use *The content of this edition is based on presentations delivered at the 2017 SASEV WineTech symposium in a session sponsored by SATI. Content compiled by Jorisna Bonthuys. For any enquiries, comments and feedback, please contact: Tarryn Wettergreen: Dawie Moelich: Clayton Swart: tarryn@satgi.co.za dawie@satgi.co.za clayton@satgi.co.za

3 Is waterskaarstes voortaan deel van ons landskap? Min reën, lae damvlakke bied wyd rede tot kommer Die droogte het produsente in n wurggreep en in dié stadium lyk dit of daar nie veel verligting op die horison is nie. Só het John Roberts, assistent-direkteur van die Wes- Kaapse departement van waterwese en sanitasie, op die onlangse SAWWV/Winetech-konferensie gesê. Op dié konferensie is onder meer bestek opgeneem van hoe produsente doeltreffender te midde van droogtetoestande kan boer. Roberts meen daar is sterk aanduidings dat boere hul moet staal vir nóg strenger waterbeperkings dié seisoen (2017/2018). Die Wes-Kaapse regering hiersien tans alle waterbeperkings in die provinsie, inaggenome die voorrade wat drasties krimp. Die gemiddelde inhoud van Wes-Kaapse damme was begin September slegs 33,6% - in die eerste week van September laas jaar was dit 61%. Reënvalsyfers wat by die Kaapstadse Internasionale Lughawe aangeteken is, toon reënval is tot dusver vanjaar 40% tot 50% onder die gemiddelde op lang termyn. Hoewel normale of bonormale reënval vanaf September tot Desember voorsien word, is die provinsie se watersituasie nog lank nie rooskleurig nie. Omdat die opvangsgebiede baie droog is, beteken dit ook nie dat dam- en riviervlakke dadelik sal styg as die reën wel kom nie. Waterbeperkings van 50% (en tot 80%) vir die landbousektor en van 30% (tot 50%) vir ander verbruikers word genoem sou dit nie voor 1 November genoegsaam reën nie. Dit bly onmoontlik om die toekoms te voorspel en produsente moet daaarom voorbereid wees op die ergste, het hy gesê. "Selfs weervoorspellers sukkel om reënval te voorspel. Nie eens klimaatmodelle kan akkurate voorspellings bied nie," het Roberts gesê. "Tans beleef ons die derde droogtejaar agtereenvolgens. Vanjaar is moontlik nóg droër as 2016 en 2015, te oordeel aan reënvalsyfers tot nou." Die huidige weerkundige en hidrologiese droogte kan ook n sosiaal-ekonomiese droogte ontketen wat n groot impak op die Wes-Kaapse landbousektor kan hê, het hy gewaarsku. "Water is krities belangrik vir groei en ontwikkeling. Ons word daarom deur groot risiko s in die gesig gestaar weens die impak van die huidige droogte." Droogte is egter niks nuuts in die streek nie en produsente moet dit in hul beplanning verreken, sê hy. Suid-Afrika is een van die 30 droogste lande ter wêreld, met n jaarlikse gemiddelde reënval van minder as 500mm. Dit is aansienlik minder as die wêreldwye gemiddelde van 860mm. "Suid-Afrika is grootliks n droë land met wisselvallige reënvalpatrone. Droogtes is onafwendbaar en kom gewoonlik ongeveer elke tien jaar hier voor, wanneer dit dan twee of drie jaar lank kan duur. Boonop word Suid-Afrika se reënvalpatrone deur groot veranderlikheid gekenmerk." Navorsers voorsien dat groot dele van Suider-Afrika in die komende dekades droër en warmer sal word te midde van eietydse klimaatsverandering. Uitdagings met beperkte waterbronne word vererger omdat die aanvraag na water reeds plekplek die aanbod daarvan oorskry. Twee-derdes (66%) van alle waterverbruik landwyd is deur boere wat die grootste direkte verbruikers is. Roberts het gesê dit is beter om vir verskillende toekoms scenario s te beplan as om inderhaas by onvoorsiene toestande aan te pas. "Waterbeperkings is nie n vloekwoord nie," het hy gesê. "Dit is n manier om beskikbare waterbronne te bestuur om die beskikbaarheid daarvan te verseker. Ons het n hele aantal gebruikers wat van dieselfde bronne afhanklik is." Roberts het n oorsig gebied oor onder meer die stand van waterbronne in die Gourits-, Olifants/Doorn-, Breede- en Berg-opvangsbestuursgebied. In die Gourits-, Olifants- en Breede-opvangsbestuursgebied gebruik die landbousektor onderskeidelik 75%, 95% en 91% van die beskikbare waterbronne. In die Bergrivier-opvangsbestuursgebied gebruik landbou en verbruikers in dorpsgebiede ongeveer ewe veel waterbronne. Owerhede werk hard om te verseker dat water vir alle gebruikers geredelik beskikbaar is. "Waterbeperkings is belangrik vir beplanning en om te verhoed dat 'Dag Nul' aanbreek wanneer daar dan nie meer water beskikbaar is nie." Tans geniet huishoudelike en nywerheidsverbruikers 97% versekering van die watervoorraad, het hy gesê. "Dit beteken dat verbruikers elke drie uit honderd jaar watertekorte kan ondervind en gevolglik 70% of minder water kan kry." 1

4 Hierteenoor geniet die landbousektor 91% versekering van watervoorraad. "Dit beteken dat produsente sewe uit elke tien jaar lank 100% van hul wettige toewysing kan kry, maar vir drie jaar lank (uit elke tien jaar) 70% of minder. Daar kan jare wees wat produsente ongelukkig niks kry nie." Risikobestuur is onderliggend aan die provinsie se beleid oor watervoorsiening, het Roberts aangedui. Die Wes-Kaap se geïntegreerde watervoorsieningstelsels is geleë in n winterreënvalgebied wat gekenmerk word deur nat winters en droë somers. Die ses grootste damme in die provinsie word gevul in die nat wintermaande (vanaf Mei tot Oktober) wanneer ongeveer 90% van die jaarlikse afloopwater voorkom. Gedurende die droër maande (vanaf November tot April) is daar min invloei in die damme terwyl besproeiingsbehoeftes, en stedelike gebruik hoog is. Gewoonlik kry die Wes-Kaap gemiddeld tussen mm reën per jaar. "Sedert 2003 het afsny-hoogdrukstelsels veroorsaak dat groot volumes water dikwels in n baie kort tydperk oor dele van die provinsie uitgesak het, wat onder meer groot vloedskade in die Suid-Kaap en die Breede-opvangsbestuursgebied veroorsaak het." Meer intense buie op ongewone tye van die jaar kan ook oesskade meebring. "Ons (Wes-Kaapse) produsente is gewoond aan nat winters en droë somers, maar dit is moontlik aan die verander. Dit is byvoorbeeld nie nou die tyd om damme te bou nie - daar is nie water om dit mee te vul nie." Die tyd wanneer buie uitsak, het ook dramaties verander oor dele van die provinsie, het hy uitgewys. "In gebiede soos die Suid-Kaap vloei riviere soos Maalgate (naby George) wat tevore heeljaar gevloei het, tans glad nie. Produsente is gewoond aan reën wat op sekere tye uitsak en hul gewasproduksie onderhou. Nou reën dit op ander tye, wat uitdagings bied wat waterberging betref." Die departement van waterwese en sanitasie het stoorplek vir 900 miljoen m 3 se watervoorraad, maar tans net kapasiteit vir n derde daarvan. In die winter word ongeveer 50% van die provinsiale damme se kapasiteit benodig om genoeg water vir die somermaande te stoor. "Die res van die damme se stoorvolumes is nodig om op lang termyn oordrag-stoorkapasiteit vir droogtetydperke te verseker. "Die afgelope drie jaar het ons egter in hierdie reserwe-stoorkapasiteit ingedelf." Op n plaaslike vlak is die impak van die droogte groot. Die Clanwilliamdam naby Citrusdal is byvoorbeeld tans net 36% vol, vergeleke met 99% laas jaar dieselfde tyd. Na verwagting sal die Clanwilliamdam byvoorbeeld net 45% vol wees teen die begin van die besproeiingseisoen. As die dam se vlakke byvoorbeeld nie oor die komende paar maande tot 60% of meer styg nie, kan 80% se inkortings boere se voorland wees. Dit kan verreikende gevolge inhou vir die sowat 860 kommersiële boere en permanente werkers (en ongeveer net soveel seisoenale werkers) wat daarvan vir hul bestaansmiddelle afhanklik is. Landbou ding toenemend mee met ander verbruikers, onder meer die Stad Kaapstad en munisipaliteite aan die Weskus. Naas verbruikers in dorpe en die stad wat water benodig, moet owerhede ook uit n strategiese oogpunt verseker dat die Koeberg-kernkragsentrale water kry. Sonder water kan Koeberg nie funksioneer nie en is n kragkrisis moontlik, het hy gewaarsku. Die Stad Kaapstad het volgens hom die afgelope paar jaar hard gewerk om die presentasie waterpype wat elk te herstel en vergelyk goed met die wêreldgemiddeld hiervoor (van 18%). Hoewel die stad se inwonertal dramaties uitgebrei het oor die laaste paar jaar gebruik dit tans net soveel water soos in 2005 (12 jaar gelede). Wat die impak van eietydse klimaatsverandering op die stand van waterbronne betref, het Roberts gesê daar is n "ingewikkelde verhouding" tussen reënval en beskikbare waterbronne. "As minder reën voortaan in die winter gaan uitsak, kan dit meebring dat grondwaterbronne minder aangevul word. Meer intense reënbuie veroorsaak ook dat baie water verlore gaan, omdat dit gewoon wegspoel en nie in die damstelsel beland nie." Nuwe en alternatiewe waterbronne sal voortaan toenemend ontgin moet word, het hy gesê. Dit sluit in om afvalwater te herwin, asook om grondwaterbronne te ontsout. In Israel word altesame 85% van gesuiwerde rioolwater byvoorbeeld in die landbousektor gebruik. Bykans die helfte van alle water wat in Israel in die landbousektor gebruik word, is van afvalwaterbronne afkomstig. n Soortgelyke tendens word in Spanje bespeur, waar sowat n kwart van afvalwater (25%) reeds herbenut word. Wat ontsouting betref, het die tegnologie reeds sodanig verbeter dat dit keuses vir die landbousektor bied. Nuwe varswaterbronne sal ook ondersoek moet word, het hy gesê. Die landbousektor word uitgesonder as een wat in terme van die Nasionale Ontwikkelingsplan uitgebrei moet word en werk in die landelike ekonomie moet skep. Ambisieuse teikens vir werkskepping sal beleggings in besproeiingsinfrastruktuur noodsaak, meen Roberts. "Ons benodig n omgewing waarin landbou te midde van beperkte waterbronne bemagtig eerder as die sondebok gemaak word. Vennootskappe hieroor is nodig." 2

5 STAND VAN WES-KAAPSE DAMME op 28 August NOMMER DAM Voëlvlei BergRIVIER Theewaterskloof BO-Steenbras ONDER-Steenbras Wemmershoek Brandvlei Kwaggaskloof Clanwilliam Roode Elsberg Ceres-Koekedouw Eikenhof Elandskloof Calitzdorp INHOUD VAN DAMME % % 3

6 Klimaat van verandering? Só raak klimaatsverandering die Wes-Kaap Landbou kan te midde van klimaatsverandering steeds aanpas en blom. Só het Dr. Hannes Rautenbach, spesialis-wetenskaplike van die Suid-Afrikaanse Weerdiens, gesê. Hy was n genooide spreker op die onlangse SAWWV/Winetech-konferensie wat onlangs op Simondium gehou is. As die heersende koers van mensgemaakte kweekhuisgasvrystellings in die Aarde se atmosfeer voortduur, word voorsien dat oppervlaktemperature teen 2100 met ongeveer 5ºC wêreldwyd kan styg, het hy uitgewys. Die warmste 10 jaar wat die afgelope 136 jaar aangeteken is, was almal sedert Die jaar 2016 was boonop die warmste nóg wêreldwyd sedert betroubare rekords hieroor gehou word. Wes-Kaapse boere kan hulle gereed maak vir droër toestande op die lang termyn, maar dit betekennie alles is verlore vir die landbou nie. Die koers van klimaatsverandering in Suider-Afrika is volgens Rautenbach nie tans so vinnig soos in ander wêrelddele nie en die streek sal steeds geskik vir landbou bly. Skuiwe in reënvalpatrone word bespeur, maar dit is inkrementeel en laat genoeg ruimte vir tydige landbou-aanpassings. Rautenbach meen te veel verwysings na klimaatsaanpassings, byvoorbeeld in dokumente soos die Wes-Kaapse Strategie vir Klimaatsverandering, bevat veralgemenings oor klimaatsverandering wat produsente kan verwar. "Wat baie mense doen, is om onmiddellik te beplan vir n 5ºC-styging sonder om te besef dit kan eers teen 2100 n werklikheid word. In ons geval praat ons van n 0,5ºC-styging per dekade. Ons moet historiese rekords in ag neem om by toekomstige veranderings te pas." Gestandardiseerde reënvalindeks (Julie 2016-Junie 2017) Sleutel Uiters droog Baie droog Taamlik droog Ietwat droog Volgens Rautenbach is daar nog onsekerheid oor presies hoe klimaatsverandering reënval in die streek gaan beïnvloed, hoewel meer ekstreme weerstoestande waarskynlik voorsien word. Hy meen klimaatsverwante aanpassings moet die weer en klimaat in ag neem. Daar is aanduidings dat winterreënval oor dele van die provinsie afneem en dit lyk asof die reënseisoen voortaan later sal begin as waaraan produsente gewoond is. Daar is deesdae ook minder reëndae van Januarie tot April, terwyl n toename daarin bespeur word vanaf November tot Desember. Droogtetoestande is van tyd tot tyd n gegewe, met inagneming van Suid-Afrika se ligging, die faktore wat weerstoestande beïnvloed, asook die hoogs veranderlike aard van weerstoestande hier. Die Wes-Kaap is oor die algemeen eintlik n droë provinsie buiten in hoogliggende gebiede waar dit meer reën. "In die beginjare van die Kaap het handelskepe reeds by die suidpunt van Afrika verbygevaar en by Mosselbaai eerder as Kaapstad anker gegooi om hul watervoorraad aan te vul," het hy gesê. "Selfs in daardie jare het mense geweet die Kaap is droog." Wêreldwyd word n gemiddelde temperatuurstyging van 0,99 C sedert 1880 bespeur. Volgens Rautenbach is die koers van temperatuurstygings taamlik stadig. "Ons gaan nie oornag n 5ºCstyging ondervind nie. Daar is tyd om met aanpassings vorendag te kom." Navorsing toon Suid-Afrika verhit sedert 1931 met gemiddeld 0.17 C per dekade. Historiese reëndata lewer interessante inligting oor gemiddeldes, ekstreme toestande en tendense, sê hy. Rautenbach reken klimaatsverwante aanpassingsmodelle moet daarom aansienlik meer gewig gee aan historiese waarnemings en datastelle as nou. Volgens reënvalrekords het die Wes-Kaap byvoorbeeld in die 1930 s en 1940 s droër tydperke beleef as nou, het hy uitgewys. Volgens die rekords word n toename die afgelope dertig jaar in reënval ondervind gedurende Junie, Julie en Augustus en die afgelope sewe jaar ook vanaf November tot Desember. Die afgelope 27 jaar word meer natter jare volgens die rekords ondervind vergeleke met die vorige drie dekades. Die prentjie lyk nie oral dieselfde in die provinsie nie. Dit blyk daar is n toename in die jaarlikse reënvalsyfers aan die oostelike dele van die Wes-Kaap en die westelike dele van die Oos- Kaap. Daar is aanduidings dat droë tydperke voortaan langer kan duur wanneer dit voorkom aan die westekant van die provinsie terwyl dit van korter duur kan wees aan die oostekant daarvan. Wat die voorspellings vir die res van die seisoen betref, het hy gesê die vooruitsigte lyk goed vir bonormale reënval vanaf November. Rautenbach ag dit uiters belangrik van mense in die landbou- en watersektor om hul te vergewis van die jongste navorsing en ook om behoorlik plaaslike toestande te monitor ten einde met toepaslike aanpassings vorendag te kom. 4

7 "Rig n weerstasie op en vind aanduiders van drempelpunte wat op jou plaas van toepassing is sodat jy beter voorbereid kan wees op veranderings. Hou n langtermyn-rekord van gemiddeldes asook veranderings wat uiterstes in jou konteks betref. Met behulp van historiese rekords kan jy meer toepaslik aanpas, waar nodig." Seisoenale voorspellings en historiese rekords moet in bestuursplanne ingebou word om te verseker boerderybedrywighede is klimaatsenstitief, het hy gesê. Maandelikse reënvalsyfers (30 jaar-tydperke) Gemiddelde reënval (mm) Jan Feb Mar Apr Mei Jun Jul Aug Sep Okt Nov Des WATEr budgets 'CRITICAL' FOR PRODUCERS Lessons from Down Under Water budgets are critical for wine and grape producers, says Dr Mark Krstic, business development manager at the Australian Wine Research Institute. Krstic said Australian farmers learned very valuable lessons regarding drought management in their vineyards in recent years. The Millennial Drought in Australia (from April 1997 till October 2009), for instance, had an enormous impact on producers, especially in the Murray Darling Basin. The region had below normal rainfall, and in some areas farmers experienced the driest conditions on record. This had a very negative impact on water storage capacity, similar to the situation that is currently unfolding in the Western Cape, he indicated. At one stage during the drought in 2007 one megalitre of water cost more than 100 Australian dollars on the Australian water market. The situation drove a lot of political focus on change and investing in infrastructure, he said. Many producers changed their water delivery systems from open irrigation systems with 30% water losses, to pressurised pipe systems with less losses. "People started looking over the fence, thinking long term and more about their catchment," he said. Key questions What is your water budget? How much water do you need? Where are you going to use it? When are you going to use it? Will it be enough? "The drought also got people benchmarking their water use. It made producers look closer at how they manage water on farms. It showed that how you manage your irrigation system is often more important than the actual system itself." Krstic said it is critical that farmers understand their yield response curves. "It is not always about giving more water. At some point, 5

8 you might even be wasting water. We need to understand our production systems better. It is all about understanding the seasonal water use patterns." Before During After What to do in a heat wave? Apply irrigation and refill as much of the root zone as possible ahead of the heat wave. If a deficit irrigation strategy is being employed, resupply irrigation. Consider applying a sunscreen spray. Reconsider any planned leaf removal or canopy manipulation strategy (for example foliage wires) that may lead to increased fruit exposure. Remember that if the heat wave does not occur, it is still very likely to be hot to very hot, so any preemptive action will not be wasted. Apply irrigation to maintain soil moisture at a level that enables vines to regain their turgor overnight in preparation for the next hot day. If using overhead irrigation, apply at night to avoid foliage burn (salinity). Irrigate to replace lost soil water and lower soil temperature. Monitor for pests and diseases that may have exploited heat damaged berries. Damage may take a few days to appear. If secondary invasion occurs, seek advice about chemical applications. Redo your irrigation budget. "Determine your water budget and monitor it very carefully. A water budget is a predicted plan that looks at these issues. It will help you consider: Do I need to make and implement management decisions now? "The key thing is to look at the economics of your business very carefully and monitor but at the same time see the opportunity in the chaos. Do you know the cost and returns on each block?" Producers also need to improve their understanding of heat wave management, he said. High-temperature stress in one region may be the normal growth temperature in another. "Absolute temperatures, the duration of the heat wave and humidity are important factors to consider. High vapor pressure deficit (VPD) will stress the vine at any temperature. "The key messages is be prepared for a big event. Make sure your soil profile is full before the heat wave arrives. Don t use a deficit irrigation strategy and avoid doing any plant leaf removal treatments to protect that fruit from direct sunlight. Make sure you have irrigation to maintain soil moisture levels. Under water deficit conditions, vines cannot cope with heat waves." In general water deficit (drought) exacerbates heat stress due to greater stomatal closure, resulting in higher leaf temperatures, reduced vine water status, increasing the risk of hydraulic failure and wilting. High temperature usually results in high VPD and increasing water loss, even with low stomatal conductance. Wilting of canopy also increases fruit exposure and temperature. The vine s ability to cope with heat waves is proportional to the water stress present, he explained. "There is a carry-over effect of severe water deficit on grapevine productivity." "Obviously, you need to avoid water deficit around flowering, otherwise you will affect the fruit set. If we skip on supplying water in certain phases, it affects future seasons growth." Understanding the water balance of a vineyard remains critical. "While you might be irrigating the system, only about 50% or 60% of that gets up going through the plant. There are still opportunities for improvement (in water use efficiency). Managing root zone salinity is also very important, he said. "Know your soil and consider your physical, chemical or biological constraints, including water tables. If your root zone is 1 meter deep and you are applying irrigation at a level of 1,5 meter deep, you are wasting water. Also, design your irrigation system with future needs in mind." The approximate annual percentage of water required by a grapevine at each growth stage varies depending on variety, rootstock and vigour, climate (rainfall, evaporation), soil type/depth and crop load. 6

9 "Schedule your irrigation appropriately to ensure the vines receive the right amount at the right time and consider using different irrigation management techniques." Some Australian farmers employ regulated deficit irrigation (RDI) as a management strategy. This strategy uses water stress as a tool to lower plant water potential and turgor, manipulate growth and save water (approximately 10-15%). "The aim is to apply less than the full irrigation requirement of the crop in a controlled, repeatable manner at critical growth stages of the crop." Partial rootzone drying and sustained deficit irrigation are techniques that are also employed (see illustration). Krstic says it is essential to understand the impacts of climate change and climate variability on the sustainable yield from the water source and future planning. This applies to issues of water access and new vineyard design. In future, variable rate irrigation technology will be used on small parcels, he believes. "Drought and water restrictions will magnify the importance of these questions and the management decisions that you have to make. Conditions are changing due to climate shifts. We are now adjusting ourselves for a new future at a catchment level." It is possible to apply less water than what the crop demands, he said. Research showed that it is possible to give vines 70% to 50% of the water it needs and still have relatively high yields. "Understand how far you can sustainably push your vines in relation to water use and associated impacts on yield and fruit or wine quality. You need to understand the yield response curve in your context." 7

10 Water stress and vines: explore the 'magic window' Irrigation methods and technologies for efficient water use Sometimes being thirsty can be a good thing for a vineyard. This is the view of Dr Mark Greenspan, president of Advanced Viticulture Incorporated in America. He gave an overview of irrigation methods and technologies for efficient water use in vineyards. Some of the water management topics he covered included monitoring technologies (old and new), soil moisture and scheduling based on evapotranspiration. Understanding the water requirements of the vines is critical for managing water stress and its effects on vineyards, he said. Water stress is not beneficial during canopy establishment and shoot growth, at fruit set or during the first phase of berry growth. This is also the case late in the season to prevent yield loss due to shrivel. It may, however, be beneficial near veraison to slow and stop shoot elongation. It is also beneficial before veraison to stimulate ABA production and promote pigment production in coloured varieties. During pre-veraison water deficits, for instance, accelerates berry colour change in Merlot grapevines. Water deficit alters metabolic pathways affecting important flavor and quality traits in grape berries of Cabernet Sauvignon and Chardonnay, he pointed out. Crimson seedless does seem to respond positively to water stress. Monitoring soil moisture in your blocks is critical, he said. Use evapotranspiration to calculate vine water requirements. "Soil moisture is not secondary to plant stress. It is necessary for precision irrigation scheduling, he emphasised. Producers have many options to measure soil moisture content and ensure that they use it effectively and intelligently," he said. "The way a plant uses water and how it is sucked up through the plant and up in the shoot is critical for producers. It is crucial to understand how this works and what your plant s needs are." "We really need to know what is happening in the soil. Understand the (water) supply of the soil. "Make sure you don t stress your plants early in the season. For table grapes, we do not want any water stress during bloom and fruit set. We want to continue the supply of moisture to the vine in that period. "After fruit set, at least in wine grapes, we want the vine to express more and more stress. Eventually we want the shoots to This window of time before veraison and through veraison I call the magic window. This is when big physiological changes happen in the fruit. You can impose a short stress period during veraison. Then relax after that, and your colour will benefit. stop growing." Before veraison, it can help to stimulate abscisic acid (ABA) production and promote pigment production in colored varieties. ABA has a well-known positive impact on grape ripening, especially color development. "We don t want extra canopy than what is necessary because it is expensive to prune it out," he said. "This window of time before veraison and through veraison I call the magic window. This is when big physiological changes happen in the fruit. You can impose a short stress period during veraison. Then relax (water stress) after that, and your colour will benefit." A vine experiencing stress will produce ABA and this hormone, in turn, will have some different expression of the ripening genes in the fruit. Researchers has shown that ABA and water stress will differentially express some of the genes associated with the ripening of the fruit. Girdling (ring-barking a strip of bark from the vine) will reduce leaf stomatal conductance of its leaves. Once the girdle heals, stomatal conductance increases to pre-girdle values. Girdling will reduce transpiration and water use of vines, he explained. The reduction in canopy transpiration will continue as long as the girdle remains open. Producers can use visual indicators to monitor how much stress the vines experience. This includes considering shoot growth and leaf temperatures. Many tools are available to measure the water status of the plants, including dendrometers and infrared devices. "If you stress the vines, they are going to use less water. The good news is that you don t have to supply 100% to table grapes to get the yield you want. The tendency for growers are to give more water, which is not always better. More water is not always better. Research has proved you can have a sufficiently packable yield at 80% of full water use throughout the whole season." 8

11 FARMING FOR THE FUTURE How to manage soil, irrigation for water use efficiency Efficient irrigation water use is critical for the future of the grape and wine industry. Water resources are limited in most agricultural regions, and inconsistent rainfall causes periodic droughts. This scenario may worsen if climate change reduces rainfall and the mean annual temperature increases, said Philip Myburgh, a senior researcher in the Soil and Water Science Program at ARC Infruitec-Nietvoorbij. Myburgh spoke about soil and irrigation management as a tool to improve water use efficiency on farms. Currently, the long term annual rainfall mean in areas like Robertson, the Little Karoo, and the Lower Orange River is less than 400mm per year. It is also very low in the Lower Olifants region (approximately 140mm per year). "We cannot have sustained agriculture relying on rainfall alone. That is why dams and irrigation systems are so important," he said. "Agriculture uses a lot of water. The public is looking critically at this and asking why. The sector has to increase its water use efficiency." Already water resources are limited in most regions. Rainfall is inconsistent, and climate change is expected to decrease rainfall in parts of the Western Cape and the Northern Cape. "Also, higher irrigation water tariffs will increase wine and table grape production costs. That is a given. The Water Act enables catchment management agencies (CMAs) to terminate water use licenses if growers misuse their allocated water resources. The industry also needs to reduce its water footprint to convince the public that scarce water resources are being used responsibly. "In reality, water use efficiency can only be improved if more grapes are produced using the same volume of water, or if the same mass of grapes is produced using less water." Myburgh defined water use efficiency as the mass of grapes produced per unit volume of irrigation water applied (kg/m 3 ). "Luckily, farm management practices that reduce evaporation and transpiration losses are likely to improve water use efficiency. Farmers can improve their water use efficiency by doing soil and irrigation management and considering viticultural aspects," he said. Evaporation (ET) happens in three phases (including the liquid and vapour phase). It is driven by atmospheric conditions, soil properties and movement of water in the soil. High evaporation peaks occur after rain or irrigation. For high-frequency irrigation (at least once a week), evaporation is c. 80% of ET, and c. 20% of ET in the case of lowfrequency irrigation (approximately six times per season). Myburgh considers good soil management as 'critical' to ensure water use efficiency on farms. Yield will not increase indefinitely with the volume of irrigation water applied, he emphasised. "Identify the point where maximum yield for a specific cultivar can be obtained under a given set of climatic and soil conditions. Using more water will be a waste and may reduce wine quality." Improving irrigation water use efficiency is not rocket science, he said. "The irrigation system is as good as its maintenance. Make sure that the pipelines, the canals, the filters and everything else function properly. Set irrigation refill lines according to midday stem water potential." Permanent systems such as micro sprinklers or drippers will be more appropriate in situations where water resources are limited. There is very little that growers can do during a water crisis, he said. "You can, for instance, remove excessive shoots and cut back on fertilisers to reduce the transpiration. But it is important that correct long term practices should be in place on your farm. It will ensure that your vineyards are better buffered against severe water constraints during drought periods, such as the current drought situation." Producers can also benefit from choosing rhe right trellis system to increase bearing capacity. their trellis system used to increase bearing capacity, he indicated. Changing canopy management in vineyards can also make a difference to water use efficiency on farms. Research in the Robertson area on Shiraz blocks, for instance, showed that using mechanical pruning versus single cordon VSP produces more or less the same yield. Yet the water use efficiency was higher when using mechanical pruning than VSP. Furthermore, plant material can determine the mass of fruit produced per unit volume irrigation water. This has, for instance, been shown in research which studied the effect of plant material on water use efficiency on furrow-irrigated Thompson Seedless near Upington. 9

12 Practical water management advice Deep tillage is essential. It creates deep root systems that require less frequent irrigation, which will reduce the number of evaporation peaks during the first phase of evaporation. Consider the soil s physical and chemical limitations. This includes factors like natural compactness, shallow weathered rock, acidity and salinity. Adapt your implements to suit specific soil types on your farm. Ridging increases the soil surface, and this will increase the soil evaporation losses. Ridging is only recommended if conventional subsurface drains are impractical, or where irrigation resources are unlimited. Wheel tractors can work to depths of 800 mm if limitations are not too severe. Rear wheels cause re-compaction in the furrows. Use a ripper behind the rear wheel. Use laser controlled equipment for surface levelling when preparing land for flood irrigation. This will improve water distribution when irrigation is being applied. Cover the soil surface using mulches consisting of tree bark, cereal straw or wood chips. This will reduce evaporation losses. Tillage is expensive and will damage the structure of the soil surface layer. Loosening the surface layer of the soil to create a mulch is not recommended. Mulches primarily reduce evaporation primarily during Phase I. The reduction obtained with mulching will be more pronounced in the case of high-frequency irrigation. Improve water infiltration by incorporating organic material into the soil while doing root pruning. This has a huge effect on water infiltration. Kill cover crops before bud break. Cover crops will compete for water. Weeds will also cause unnecessary transpiration losses. An irrigation system is as good as its maintenance. Make sure that the pipelines, the canals and the filters, for instance, work properly. Evaporation losses can be reduced considerably if the irrigation water is only applied to a fraction of the irrigated land. The volume of water that will evaporate will be less than with full surface wetting (for instance when using drip irrigation versus furrows). Subsurface drip does not seem to have any positive effects on water use efficiency compared to furrows and drippers. There is a high risk of clogging that will reduce the lifespan of the drip system. Do not irrigate when the wind is blowing. The pressure in irrigation systems should not be too high. Fine mist will increase evaporation losses. Irrigate during the night where strong winds usually prevail during the day. Evaporation losses will also be less when atmospheric conditions are cooler during the night. Weeds must not interfere with the water distribution pattern of micro-sprinklers. Excessive irrigation (and nutrients) will induce vigorous vegetative growth, causing unnecessary transpiration losses. Yield will not increase indefinitely with the volume of irrigation water applied. Identify the point where maximum yield for a cultivar can be obtained under a given set of climatic and soil conditions. Applying more water will be a waste and may reduce wine quality. Set irrigation refill lines according to midday stem water potential. Monitor your vineyards, including by using remote sensing technology for irrigation scheduling. Plant material can also determine the mass of fruit produced per unit volume irrigation water. 10

13 THE SATI TEAM Willem Bestbier CEO Eunice Avenant Training Manager Lindi Benic Trade/Market Access Affairs Manager WILTON SEPTEMBER Transformation Manager Clayton Swart Communications and PR Manager Stephen Terblanche Accountant THURIA LEVY Office Administrator JOSEPH LOMBARDT Information and Knowledge Manager DAWIE MOELICH Technical and Market Access Manager TARRYN WETTERGREEN Research and Technology Transfer Manager VALENCIA WATTS Receptionist Jacques Ferreira Technical Assistant (Project Manager)

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