South Africa Wine Technical Yearbook 2025

Technical Yearbook

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TECHNICAL YEARBOOK 2025

Contents

OENOLOGY

81

Authors / Contributors................................................................3 Foreword....................................................................................... 4 VITICULTURE 6 Winery wastewater irrigation (Part 1): Annual dynamics of volumes and quality at two wineries.....7 Winery wastewater irrigation (Part 2): Soil chemical responses on poorly drained soils....................14 Winery wastewater irrigation (Part 3): Soil chemical responses on a well-drained soil......................20 Winery wastewater irrigation (Part 4): Evaluation of a pot experiment on four differently textured soils...............................................................................27 Winery wastewater irrigation (Part 5): Effect on soil K, Na and pH (KCl) ................................................. 31 Winery wastewater irrigation (Part 6): Effect on soil phosphorus .......................................................... 38 Winery wastewater irrigation (Part 7): Effect on soil enzyme activities ................................................. 41 Winery wastewater irrigation (Part 8): Vulnerability of selected soils in areas with different rainfall .......................................................................... 46 Grape marc – a game-changer for greener dairies?..............53 The fascinating world of terroir in winemaking (Part 1): How nature, tradition and science come together ................. 55 The fascinating world of terroir in winemaking (Part 2): How nature, tradition and science come together ................. 58 Resistance of grapevine rootstocks to nematodes – the status quo in South Africa...................................................61 Near-real-time characterisation of vines ................................. 63 Rooted in research – what science says about regenerative viticulture. Part 1: Organic soil amendments, biostimulants and biological control agents...........................65 Rooted in research – what science says about regenerative viticulture. Part 2: Cover cropping and weed management.............................................................69 Rooted in research – what science says about regenerative viticulture. Part 3: Functional biodiversity enhancement.........................................................73 Soil texture’s influence on soil biological health indicators –implications for vineyard management.............77 Sunscreen for Sauvignon blanc................................................79

Cultural insights in wine aroma descriptions in South Africa, France and Portugal . ..................................... 82 OTR and long-term ageing of Sauvignon blanc wines..........84

Specific bioprotection against Brettanomyces : Naturally controlling Brettanomyces at the onset

of wine production with LEVEL 2 SALVA™............................ 87 Wine yeasts and energy saving in wineries............................94 Yeast-derived acidification of red wines .................................. 96 Q&A. Tackling calcium crystals in wine................................100 PRACTICAL IN THE VINEYARD 103 Post-harvest strategy for maximum reserve accumulation in grapevines....................................................104 Irrigation duration – time to give water... but how much is enough?.......................................................108 Profile pit stories with Johan ..................................................111 Watt’s up with row direction?.................................................115 Grapevine fanleaf virus............................................................117 Sunburn in the Paarl and Swartland regions........................119 Grapevine-associated Aspergilli .............................................122 PRACTICAL IN THE CELLAR 124 Tips to avoid the most common cellar mistakes (Part 1)...125 Tips to avoid the most common cellar mistakes (Part 2)...128 Guidelines for the management of barrel storage rooms....130 Post-harvest cleaning of equipment......................................132 Post-harvest reflection .............................................................134 Who is ultimately responsible for a task?.............................136 Checklists. .................................................................................138 New life ......................................................................................140 Benefits of ergonomics . ...........................................................142 GENERAL 144 Understanding CCC: South Africa’s trusted carbon footprint calculator for the fruit and wine industry.............145 Haygrove case study. Maximising sustainability: The synergy between SHERPA and CCC . ............................148

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

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Authors/Contributors

Amandine Deroite Lallemand ploubser@lallemand.com Ana Hranilovic Laf fort morne.kemp@laffort.com Anton Nel Cape Peninsula University of Technology Senior Lecturer nelap@cput.ac.za Carien Coetzee Basic Wine carien@basicwine.co.za Carlos Poblete-Echeverria Stellenbosch University SA Grape and Wine Research Institute Associate Professor cpe@sun.ac.za Gert Engelbrecht Vinpro gerte@vinpro.co.za Hanno van Schalkwyk Vinpro hanno@vinpro.co.za Heinrich Schloms Vinpro heinrich@vinpro.co.za Hennie Visser Vinpro hennie@vinpro.co.za Johan de Jager Vinpro heinrich@vinpro.co.za

Klaas Coetzee Vinpro klaas@vinpro.co.za Lucinda Heyns Private Consultant lucindaheyns@gmail.com

Pieter Badenhorst Private Consultant pieterb@fortheloveofwine.co.za Reckson Mulidzi ARC Infruitec-Nietvoorbij Research Team Manager mulidzir@arc.agric.za Rinus Knoetze ARC Infruitec-Nietvoorbij Senior Researcher knoetzer@arc.agric.za Dr Roeline van Schalkwyk Stellenbosch University Department Soil Science Post Doctoral Researcher Post Doctoral Fellow fiarbairn@sun.ac.za Sami Yammine Laf fort morne.kemp@laffort.com Wilmie Cronjé Blue North wilmie@bluenorth.co.za roeline@sun.ac.za Samantha Fairbairn Stellenbosch University SA Grape and Wine Research Institute

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FOREWORD

Advancing South African Wine through knowledge and innovation A resilient, competitive, and future-focused wine industry is built on a strong foundation of science, skills development, and innovation. At South Africa Wine, the Research, Development and Innovation (RDI) department remains committed to ensuring that credible, relevant research is not only generated but effectively translated into practical solutions that support grape growers and winemakers across the diverse South African production context. The Technical Yearbook continues to play a critical role in this mandate. By compiling a year’s worth of research-driven technical articles into a single, accessible publication, it provides industry professionals with a consolidated reference to the latest scientific insights, technological advances, and best-practice recommendations shaping modern viticulture and oenology in South Africa. This year’s edition reflects the breadth and depth of research underpinning the industry, addressing both persistent and emerging challenges. The topics presented, including a series on winery wastewater irrigation, regenerative viticulture and cultural perspectives in wine aroma descriptions, once again span both vineyard and cellar. This demonstrates how targeted research can improve production efficiency, product quality, sustainability, and resilience in the face of climatic, economic, and regulatory pressures. By bridging the gap between academic research and on-farm or in cellar applications, the Technical Yearbook supports informed decision making and encourages the adoption of evidence-based research outcomes. It also stands as a testament to the collaborative efforts of researchers, technical specialists, and industry practitioners advancing the South African wine industry. As we continue to strengthen a culture of knowledge sharing under the South Africa Wine umbrella, this publication reinforces our long term commitment to innovation, capacity building, and continuous improvement. Readers are invited to explore the insights, translate ideas into practical action and foster continuous learning in their own organisations and regions. Each step brings South African wine closer to a sustainable, adaptable and globally competitive future.

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

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TERTIUS GOUS, SKILPADVLEI

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SHUTTERSTOCK

VITICULTURE 1

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JANUARY/FEBRUARY

Winery wastewater irrigation (Part 1): Annual dynamics of volumes and quality at two wineries By Reckson Mulidzi & Carolyn Howell

Abstract In wineries, the composition and volume of their wastewater changes throughout the year. The quality thereof is usually at its worst when vintage operations are dominated by the production of red wines. Taking the above-mentioned into consideration, the objective of the study was to investigate the annual dynamics of winery wastewater (WWW) quality and volumes at: (i) an existing grazing paddock at a winery near Rawsonville where WWW has been disposed of for many years and (ii) a new paddock at a winery near Stellenbosch where no WWW had previously been Introduction Increasing wine production over the last two decades has necessitated wine-producing countries to find sustainable winery wastewater (WWW) management practices that address environmental concerns. The use and availability of WWW for irrigation has increased globally and the disposal of wastewater is governed by stringent legislation. Most wineries in South Africa dispose of their wastewater through land application. This is carried out by irrigating small areas of cultivated pasture with the wastewater or ponding, with the former being the more general practice. The use of WWW for wine grape production is increasing, and it is therefore important to understand the environmental implication of such a practice. Where wineries use sodium (Na + ) -based cleaning detergents such as sodium hydroxide, the WWW will contain high levels of Na + . The current trend to replace sodium hydroxide with potassium (K + ) -based cleaning detergents in cellars may increase K + levels in the WWW. In terms of the General Authorisations for legislated limits for irrigation using wastewater in South Africa, most South African wineries would not qualify to discharge their untreated WWW into natural water resources. Where the disposal of winery wastewater is through land application, the following requirements, as stipulated in the General Authorisations, must be met (Table 1).

applied. The study was conducted over two and a half years. Although the quality and volume of WWW varied between the two wineries, WWW contained high levels of potassium (K+) for both wineries, whereas the sodium (Na+) levels were only high at the winery near Rawsonville. The study showed that WWW did not always comply with national legislation in terms of chemical oxygen demand (COD) and pH throughout the study period, while some prominent spikes for non-compliance for sodium adsorption ratio (SAR) and electrical conductivity (EC) were observed for both wineries. TABLE 1. General Authorisations for legislated limits for chemical oxygen demand (COD), faecal coliforms, pH, electrical conductivity (EC) and sodium adsorption ratio (SAR) for irrigation using wastewater in South Africa. Parameter Maximum irrigation volume allowed (m 3 /day) <50 <500 <2 000 COD (mg/L) 5 000 400 75 Faecal coliforms (per 100 mL) 1 000 000 100 000 1 000 pH 6 - 9 6 - 9 5.5 - 9.5 EC (mS/m) 200 200 70 - 150 SAR <5 <5 Other criteria apply The composition of WWW changes throughout the year. The large variability in volume and quality of WWW is associated with different practices that occur during different times of the year. Winery wastewater quality is usually at its worst when vintage operations are dominated by the production of red wines. High pollution loads from July to November are associated with bottling of white wines, putting red wines to barrel and filtering of the previous year’s red wines. In the Southern Hemisphere, harvest is from the end of January until beginning of April. Winery wastewater produced during harvest will contain higher levels of chemical oxygen demand (COD) and salts than wastewater produced outside the harvest period. Levels of COD and salts in WWW fluctuate according to winery operations, and reach a maximum when grapes

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FIGURE 1. Rain gauge with an attachment to catch the overflow for measuring the volume of wastewater applied to a replication plot at a winery near Rawsonville.

are crushed. The lowest COD values in the WWW usually occur in December and January (pre-harvest) and June and July (mid-winter). Peak periods of wastewater generation, as well as maximum levels of COD, tend to coincide with peak harvest periods. Variation in the period of high COD reflected local differences in harvest period. This variation also depends on the production period, as well as the unique style of winemaking of different wines. Taking above-mentioned into consideration, the objective of the study was to investigate the annual dynamics of WWW volumes and quality at two different wineries. Materials and methods Experimental sites The experiment was carried out over two and a half years at two different sites, namely (i) at a winery near Rawsonville in an existing cultivated pasture grazing paddock where WWW had been applied for over 15 years (-33.4137.7° 19.1920.3°) and (ii) at a winery near Stellenbosch in a newly cultivated pasture grazing paddock where no WWW had been applied before (-33.4958.6° 18.4759.9°). Both sites were in the centre of wide flat plains. The grazing paddocks were considered to be representative of WWW disposal through land application as practised by most wineries in South Africa. The winery near Rawsonville crushes ca . 22 000 tons of grapes annually, whereas the one near Stellenbosch crushes ca . 16 000 tons. Both wineries produce white and red wines. Trial layout At both sites, three 2 m x 3 m replication plots were demarcated. Rain gauges were installed at a height of 0.5 m

at each plot to measure the amount of WWW applied. A two-litre plastic bottle was attached to each rain gauge in the irrigation site to collect the overflow WWW when the rain gauge was full (Figure 1). Three rain gauges were also installed outside each paddock for measuring rainfall. Application of winery wastewater (WWW) to the soils At both sites, all WWW was disposed of through overhead sprinkler irrigation. The amount of WWW applied, as well as rainwater, were recorded on a weekly basis. Field measurements commenced on 1 March 2011 and were terminated on 30 November 2013. Wastewater sampling and analysis Winery wastewater samples were collected from the rain meters once a week and analysed for chemical composition. The COD of the WWW was measured using a portable spectrophotometer. The samples were also analysed by a commercial laboratory according to methods previously described. The SAR of the wastewater was also calculated. Results Basic cations: The WWW contained high concentrations of K + and Na + which could have a negative impact on the soil (Figure 2A). On average, K + levels in the WWW were substantially higher than the levels of Na + . This indicated that the winery probably used more K + -containing detergents than Na + -based ones. The annual fluctuation in K + and Na + could not be related to specific seasonal activities in the winery, e.g. grape crushing or bottling. However, almost throughout the Winery near Rawsonville Chemical composition of WWW

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FIGURE 2. Temporal variation in (A) K + and Na + , (B) Ca 2+ and Mg 2+ , (C) sodium adsorption ratio (SAR) and (D) electrical conductivity (EC) in wastewater from a winery near Rawsonville. Shaded columns indicate the harvest periods. Dashed lines indicate the Na + , SAR and EC thresholds for irrigation water.

study period, the Na + was higher than 70 mg/L, i.e. the upper threshold for unrestricted use for sprinkler irrigation. The levels of calcium (Ca 2+ ) and magnesium (Mg 2+ ) in the WWW were substantially lower than the monovalent ions (Figure 2B). This was to be expected since chemicals containing Ca 2+ and Mg 2+ do not play a prominent role in winery processes. At these low levels the bivalent ions would not have any negative effects on soils or crops. However, the Ca 2+ and Mg 2+ could have some positive effect on the water quality by reducing the SAR. Sodium adsorption ratio (SAR): In 2011, the SAR of the WWW was frequently higher than 5, i.e. the legal limit for irrigation with wastewater as stipulated in the General Authorisations. During the remainder of the study period, the SAR was mostly equal to, or below the legal limit (Figure 2C). It should be noted that the wastewater SAR did not follow a distinct annual pattern that could be linked to specific activities in the winery. Electrical conductivity (EC): The EC of the WWW was below the permissible limit of 2 dS/m, i.e. as stipulated in the General Authorisation for irrigation with wastewater, except for prominent spikes in January 2012 and June 2013 (Figure 2D). Similar to the SAR, the EC did not follow a distinct annual pattern that could be linked to specific winery activities. Anions: Similar to the cations, the variation in levels of bicarbonate (HCO 3 - ), as well as sulphate (SO 4 2- ) and chloride (Cl - ), could not be related to a specific activity in the

winery (Figure 3A & B). During February and March 2013, the level of Cl - was above the recommended threshold of 150 mg/L for vineyard irrigation. Phosphorus (P): Since the levels of P were generally low throughout the study period (Figure 3B), land application of the WWW would not make a significant contribution to the P requirements of crops. pH: With the exception of November and December 2011, the WWW pH was generally equal to or less than six, i.e. the lower limit for wastewater irrigation as stipulated in the General Authorisation (Figure 3C). Annually, the pH tended to be higher in winter than during the harvest period. Since the pH was below the legal requirement for disposal through land application during these periods, it was not suitable for irrigation of crops. Based on the foregoing, the experimental plots were irrigated with acidic water throughout most of the study period. COD: Throughout the study period, the COD of the WWW was considerably higher than 400 mg/L, i.e. the upper limit for wastewater irrigation as stipulated in the General Authorisation (Figure 3D). Therefore, the WWW did not comply with the legislation for disposal through land application. Furthermore, the COD frequently exceeded 5 000 mg/L, i.e. the threshold above which wastewater may not be used for irrigation, or any other land application. Annually, the wastewater COD tended to peak during the harvest period (Figure 3D). This confirmed that the crushing and wine making generated wastewater with high COD.

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FIGURE 3. Temporal variation in (A) HCO 3 2- , (B) Cl - and P, (C) pH and (D) chemical oxygen demand (COD) in wastewater from a winery near Rawsonville. Shaded columns indicate the harvest periods. Dashed lines indicate Cl - , pH and COD thresholds. - and SO 4

Rainfall and volumes of wastewater applied Mean monthly rainfall was typical for a Mediterranean climate (Figure 4). However, the July rainfall was abnormally low in all the winters compared to the long-term average for Rawsonville (data not shown). Winter rainfall, i.e. from April to September, amounted to 380 mm, 420 mm and 685 mm in 2011, 2012 and 2013, respectively. During the harvest period from February until April, WWW irrigation amounts were substantially higher (Figure 5). During the peak period, in March, ca . 23 mm irrigation was applied per day. In December, the soil received only ca . 3 mm wastewater per day. The irrigation volumes also increased from mid-winter to reach a second peak in August when bottling occurred. Total irrigation applied from April to September, amounted to 1 475 mm, 2 600 mm and 3 285 mm in 2011, 2012 and 2013, respectively. Based on the foregoing, the soil received the

highest irrigation plus rainfall in the winter of 2013, followed by 2012 and then 2011. The application of WWW resulted in die-back of the grass on the irrigated area after only one month (Figure 6A). This could have been the result of oxygen depletion in the topsoil due to the high level of COD in the WWW. Most wineries that applied their WWW through land application do not measure how much wastewater they are applying, and their strategy is to irrigate an area until the plants die off and then move the sprinkler. The plants normally recover after three months. The soil also became totally waterlogged and the WWW ponded on the soil after irrigation was applied, particularly in winter. Due to the waterlogging, part of the water-soluble organic fraction of the WWW accumulated in the topsoil and in the ponded water on the soil (Figure 6B). The organic matter probably underwent anaerobic

FIGURE 4. Mean monthly rainfall during the study period at a winery near Rawsonville.

FIGURE 5. Mean monthly wastewater applied during the study period at a winery near Rawsonville.

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FIGURE 6. Waterlogging upon irrigation with wastewater caused (A) ponding and die-back of the grass, as well as (B) accumulation of organic matter on the surface of the Longlands soil form at a winery near Rawsonville.

seasonal activities in the winery, e.g. grape crushing or bottling. The levels of Ca 2+ and Mg 2+ in the WWW were lower than K + and Na + (Figure 7B). SAR: Except in April and May 2011 (Figure 7C), the SAR of the WWW was well below 5, i.e. the legal limit as stipulated in the General Authorisation. This indicated that sodic soil conditions were unlikely to develop under the prevailing conditions. Similar to Na + , the wastewater SAR did not follow a distinct annual pattern that could be related to specific activities in the winery. EC: Although the EC of the WWW was initially high

decomposition, which caused bad odours in the vicinity of the ponded water.

Winery near Stellenbosch Chemical composition of WWW

Basic cations: The wastewater contained high amounts of K + , but relatively low levels of Na + (Figure 7A). This indicated that the winery probably used more K + containing detergents than Na + based ones. Most of the time, the Na + was less than 70 mgL -1 , i.e. the upper threshold for unrestricted use with sprinkler irrigation. The annual fluctuation in K + and Na + could not be related to specific

FIGURE 7. Temporal variation in (A) K + and Na + , (B) Ca 2+ and Mg 2+ , (C) sodium adsorption ratio (SAR) and (D) electrical conductivity (EC) in wastewater from a winery near Stellenbosch. Shaded columns indicate the harvest periods. Dashed lines indicate the Na + , SAR and EC thresholds.

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FIGURE 8. Temporal variation in (A) HCO 3 2- , (B) Cl - and P, (C) pH and (D) chemical oxygen demand (COD) in wastewater from a winery near Stellenbosch. Shaded columns indicate the harvest periods. Dashed lines indicate Cl - , pH and COD thresholds. - and SO 4

(Figure 7D), it gradually declined and from January 2012 until the end of the study period, it was below, or equal to the legal limit of 2 dS/m, stipulated in the General Authorisation. This indicated that saline soil conditions were unlikely to develop under the prevailing conditions. It should be noted that the EC did not follow a distinct annual pattern that could be related to specific activities in the winery. Anions: The level of HCO 3 - in the WWW generally tended to decline over the study period (Figure 8A). However, the HCO 3 - content was relatively low during the harvest periods. Although irrigation with water containing high levels of HCO 3 - could affect soils, plants and irrigation equipment, there are no guidelines available. Given the high levels in the WWW (Figure 8A), negative effects could be expected over time if the water is used for irrigation. The level of SO 4 2- in the wastewater was substantially lower than the HCO 3 - (Figure 8A). Except for some spikes following the harvest period in 2013, the variation in SO 4 2- could not be related to a specific activity in the winery. Unlike the HCO 3 - , the Cl - tended to increase during the harvest periods (Figure 8B). The Cl - levels in the WWW showed two distinct peaks where the permissible maximum norm of 150 mg/L for continuous irrigation of grapevines was exceeded. One of these peaks occurred in November 2011, whereas the second coincided with the harvest period in 2013 (Figure 8B). P: The variation in P could not be related to a specific activity in the winery (Figure 8B). Since the levels of P in

the WWW were generally low throughout the study period, land application of the WWW would not make a significant contribution to the P requirements of crops. pH: Except during the harvest periods, the wastewater pH was within the legal requirement for wastewater irrigation as stipulated in the General Authorisations most of the time (Figure 8C). Based on the foregoing, the soil was irrigated with suitable water with regard to pH, except during the harvest periods when the wastewater became acidic. COD: Annually, the wastewater COD tended to peak during the harvest period (Figure 8D). This confirmed that the crushing and wine making processes generated WWW containing high levels of COD. The COD of the WWW was considerably higher than 400 mg/L throughout the study period (Figure 8D). Furthermore, the COD frequently exceeded 5 000 mg/L, i.e. the threshold where wastewater may not be used for irrigation, or any other land application according to the National Water Act. Rainfall and volumes of wastewater applied Mean monthly rainfall was typical for a Mediterranean climate (Figure 9). Similar to Rawsonville, the July rainfall was abnormally low in all the winters. Winter rainfall, i.e. from April to September, amounted to 325 mm, 500 mm and 590 mm in 2011, 2012 and 2013, respectively. As expected, WWW irrigation amounts increased from January until March (Figure 10). During the peak of the harvest period, in March, ca . 30 mm irrigation was applied

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FIGURE 9. Mean monthly rainfall during the study period at a winery near Stellenbosch.

FIGURE 10. Mean monthly wastewater applied during the study period at a winery near Stellenbosch.

per day. The irrigation volumes remained relatively high in winter and began to decline from October to a minimum in December when the soil received only ca . 1 mm wastewater per day. Total irrigation applied during winter, i.e . from April to September, amounted to 2 670 mm, 4 200 mm and 3 820 mm in 2011, 2012 and 2013, respectively. Based on

the foregoing, the soil received the highest irrigation plus rainfall in the winter of 2012, followed by 2013 and then 2011. Similar to Rawsonville, application of high volumes of winery wastewater caused die-back of the grass in the study plot (Figure 11).

FIGURE 11. Disposal of volumes of winery wastewater caused die-back of the grass in the plot at a winery near Stellenbosch.

Conclusions It is important to note that this study represented the worst-case scenario, i.e. the WWW disposal was not carried out in a bigger paddock. The study focused on the real amount of WWW applied per week to the grazing paddocks and its direct environmental impact on a specific site. Consequently, high volumes of WWW were applied on a single plot, particularly in the harvest period and winter. The study confirmed that WWW from a winery near Rawsonville contained high levels of K+ and Na+, whereas WWW from a winery near Stellenbosch contained high levels of K+. These high levels of K+ and Na+ in the WWW reflected the cleaning detergents the specific winery used. Results confirm that WWW composition can vary substantially between wineries. The pH of the WWW tended to be below the legal limit. The study also confirmed that WWW did not comply with national legislations in terms of COD and pH. Soil responses will be presented in the next two articles. 

For more information, contact Reckson Mulidzi at mulidzir@arc.agric.za. Reference https://www.wineland.co.za/winery-wastewater-irrigation-part-1/

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MARCH

Winery wastewater irrigation (Part 2): Soil chemical responses on poorly drained soils By Reckson Mulidzi & Carolyn Howell

physicochemical soil properties. The application of WWW with high levels of K + and Mg 2+ reduced soil structural stability and hydraulic conductivity. 7 The current trend of replacing sodium hydroxide with K + -based cleaning detergents in wineries could lead to increased K + levels in WWW. 7 Accumulation of high levels of K + in the soil is regarded as a potential problem by regulators and wine industry, because of the effect on soil structure and the accumulation of salts. 8 Disposal of WWW through land application has the potential to increase levels of soluble K + and the potassium exchange percentage (EPP) in soils as most K + in wastewater is available immediately. 9 It was previously shown that soils with low clay content retained less K + in the exchangeable form, while soils with higher clay content retained K + to a much greater extent. 10 The application of WWW with K + and Na + levels of approximately 400 mg/L to pastures and woodlots over the long term resulted in the accumulation of soil K + levels of 1 400 mg/kg. 11 High levels of Na + in the soil cause soil dispersion. Dispersion actually occurs when high-Na soils are irrigated with fresh relatively low-salinity water. It was previously believed that problems occur only when the exchangeable sodium percentage (ESP) of the soil is above 15. However, research in various countries such as Australia and South Africa has shown that in some soils Na + causes problems

Abstract The use and availability of wastewater for irrigation have increased globally and the disposal of wastewater is governed by stringent legislations. Most wineries in South Africa dispose their wastewater through land application. The land application of winery wastewater (WWW) results in accumulation of soil potassium (K + ) and sodium (Na + ). This can reduce soil structural stability and hydraulic conductivity. Therefore, the objective of the study was to investigate the effect of WWW irrigation on soil chemical properties and potential environmental impacts at a new paddock at a winery near Stellenbosch where no WWW had previously been applied. Due to the high volumes of WWW irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particular K+ and Na+, beyond the 90 cm depth. Unfortunately, the leached elements are bound to end up in natural water resources in the long run. Irrigation with WWW did not have a pronounced effect on soil pH (KCl) . The study confirmed that injudicious irrigation with untreated WWW poses a serious environmental hazard, particularly where crops in sandy soils are irrigated. Land disposal can only be recommended where the wastewater application does not exceed the water requirement of the grazing crop, or any other agricultural crop. This means that the WWW needs to be distributed on an area of land that is big enough so that the daily applications does not cause over-irrigation. Soil chemical status should be determined at least annually.

Introduction The use and availability of wastewater for irrigation have increased globally and the disposal of wastewater is governed by stringent legislations. 1 Most wineries in South Africa dispose their wastewater through land application. 2 This is done by irrigating small areas of cultivated pasture with the winery wastewater (WWW) or ponding, with the former more general. 3 The land application of WWW results in accumulation of soil potassium (K + ) and sodium (Na + ). There is also leaching of calcium

(Ca 2+ ) and magnesium (Mg 2+ ), which leads to the long-term instability of soil structure. 2,4 This will affect the soil’s hydraulic conductivity. Long-term application of WWW on pastures resulted in the accumulation of soil K + that has the potential to leach into groundwater and other water sources. 5 Although the effects of using wastewaters with high K + concentrations for irrigation have not been researched extensively, irrigating with such K-rich wastewaters could be advantageous to overall soil fertility. 6 However, the long-term application thereof could result in the alteration of

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FIGURE 1. The Kroonstad soil form which exhibited duplex character at a winery near Stellenbosch.

at much lower ESP values, even as low as 5, with the critical value varying between soils. 9, 12, 13 Therefore, the objective of the study was to investigate the effect of WWW irrigation on soil chemical properties and potential environmental impacts at a new paddock at a winery near Stellenbosch where no WWW had Details of the experimental site at a winery near Stellenbosch where no WWW had yet been applied were previously reported. 1, 2 The trial layout, description of the application of the WWW to the experimental site, as well as water quality have also been given previously. Characteristics and properties of the soil at the Stellenbosch site The soil was classified as a Kroonstad (orthic A-E-G horizon) 14 soil form previously been applied. Materials and methods

which is commonly found in the Stellenbosch winelands region. This specific Kroonstad soil had a bleached light grey structureless apedal sandy horizon (E horizon) beneath the topsoil to a depth of 50 cm. The grey E horizon of the Kroonstad soil turned yellow when moist (Figure 1). Below this horizon was a sticky gleyed clay layer, which indicated a zone of prolonged wetness. Thus, the soil was very poorly drained. In the 0-30 cm soil layer, the soil contained 7% clay, 6% silt and 87% sand. Soil sampling and analysis Soils were collected at the demarcated plot before the start of the study in March 2011. Thereafter, samples were collected twice a year. Samples were collected in May, before the winter rainfall began and in November, after the winter rainfall season. Soil samples were collected at 0-10 cm, 10-20 cm, 20-30 cm,

30-60 cm and 60-90 cm depth layers. All analyses were carried out by a commercial laboratory according to methods described previously. 2 Extractable K + percentage (EPP ' ) and extractable Na + percentage (ESP ' ) of the soil were calculated. Results Initial soil chemical status At the beginning of the study, the soil was acidic with average pH (KCl) of 4.6 for the profile (Table 1). The P level was acceptable throughout the soil profile, but seemed slightly high for a sandy soil. The Na extr was relatively low throughout the profile compared to K extr and Ca extr which seemed to dominate the exchange capacity. The EPP’ was relatively high compared to the ESP’ which was less than 10% throughout the profile. Soil potassium, sodium and pH High amounts of WWW irrigation

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TABLE 1. The chemical status of the Kroonstad soil near Stellenbosch before the study began. Depth (cm) pH (KCl) P (mg/kg) Basic extractable cations (cmol c .kg -1 )

EPP’ (%) 28.1 31.4 35.6 29.8 30.4

ESP’ (%)

K

Ca

Mg

Na +

+

2+

2+

extr

extr

extr

extr

10 20 30 60 90

4.4 4.6 4.4 4.7 5.0

50 54 55 42 31

0.17 0.13 0.10 0.10 0.12

0.6 0.5 0.4 0.4 0.5

1.1 0.7 0.5 0.6 0.8

0.3 0.2 0.1 0.1 0.1

8.2 8.4 9.2 8.1 7.6

were applied in the course of the study (Figure 2A). Almost immediately, the application of WWW (May 2011) doubled the K extr in the 0-10 cm layer, after which it remained almost constant throughout the study period (Figure 2B). The K extr increased steadily up to May 2012 at 10-20 cm depth, after which it decreased again, to end up at almost the same level as before the start of the study. During 2013, there was an accumulation of K + in the 90 cm soil depth indicating that K was leaching to the deeper horizons. Substantial amount of applied K + via the WWW from November 2011 until May 2012 could be the reason for the relatively high soil K + concentrations recorded at all depths in May 2012. The potential for K + accumulation in soil after WWW is high, because it has a low leachability and K + ions that are not adsorbed by plants are then adsorbed by soil particles thereby reducing the risk of leaching. 9 This happened to some extent in the 0-10 cm layer in this study. The actual value is still low, probably due to the low cation exchange capacity (CEC) of the soil and thus its low capacity to retain cations. In the present study, high levels of K + were recorded in the 90 cm depth (Figure 2B) towards the end of the sampling period, which showed that K + had leached into the subsoil and then possibly to the water table and nearby streams through lateral flow. This also indicates a low capacity for retaining cations in the soil. The effect of K + ions on soil structure relative to Na + is well documented, 15 but limited research

FIGURE 2. Temporal variation in (A) rainfall and winery wastewater irrigation, (B) soil K + , (C) soil Na + , and (D) soil pH (KCl) where winery wastewater was applied to a Kroonstad soil near Stellenbosch.

data on the effect of high levels of K + in soil due to WWW irrigation on soil structure stability is available. 9 Application of WWW immediately after the start of the study in May 2011 more than doubled the soil Na extr in the 0-10 cm layer (Figure 2C). In the 10-20 and 20-30 cm layers, it also increased somewhat. Thereafter, it dropped down to its original level for the duration of the rest of the

study. The Na extr trend is in line with the Na + content in the WWW, which decreased after July 2011 and remained low during 2012 and 2013 where the average Na + concentration in the WWW was 41 mg/L and 46.2 mg/L, respectively. 2 As Na + is not an essential element, this trend is good for environmental sustainability of WWW management. The soil pH increased at all soil

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depths in response to the application of WWW throughout the sampling period (Figure 2D). It increased from 4.6 to 5.0 in the topsoil and from 5.0 to 5.3 in the subsoil. Winter rainfall (Figure 2A) had an impact on soil pH. The pH values fluctuated during winter periods throughout the study period with the exception of the 60-90 cm depth wherein it remained constant from November 2011 until November 2013 (Figure 2D). After the winter rainfall seasons, soil pH decreased. This trend was observed throughout the study period with the exception of the 60-90 cm soil depth. The fact that pH was higher in the topsoil and in the subsoil implied that organic materials supplied by the WWW could be the source of the pH increase in the topsoil, while the leaching of salts to deeper soil layers increased soil pH there. It was previously reported that soil pH increased when organic anions were mineralised and H + ions were consumed after WWW application. 16 Although application of WWW increased soil pH by more than 0.2 units, the soil pH of the irrigated area remained acidic. Long-term application of WWW could lead to pH increase over time. It was expected that the G horizon would have had greater buffering capacity to pH increase than the sandy A and E horizons, but this was not the case. Soil EPP’ and ESP’ The EPP ’ showed an increasing trend throughout the sampling period (Figure 3A). The highest increase was in the 60-90 cm soil layer. The EPP’ showed similar trends to that of K extr (Figure 2B). Although no measurements were done beyond 90cm depth, it is possible that the EPP ’ could be higher at lower depth. These results indicate that the duplex Kroonstad soil did not retain the K + ions supplied via the winery wastewater. The soil ESP’ (Figure 3B) showed similar trends to Na extr (Figure 2C).

FIGURE 3. Temporal variation in soil (A) EPP’ and (B) ESP’ where winery wastewater was applied to a Kroonstad soil near Stellenbosch.

FIGURE 4. Temporal variation in soil (A) Ca 2+ and (B) Mg 2+ where winery wastewater was applied to a Kroonstad soil near Stellenbosch.

The reduction of ESP’ after May 2011 could be associated with low Na + in the WWW, as well as low soil Na + during a similar period (Figure 2C). Soil calcium and magnesium Application of WWW did not increase soil Ca extr during the study period although it fluctuated between sampling periods (Figure 4A). The WWW contained too low amounts

of Ca to make any significant impact in the soil to which it was applied. In addition, it should be noted that the application of WWW is unlikely to have any benefits of Ca 2+ supply to agricultural crops, because it is available in too small quantities from the wastewater. Results showed there was a slight increase of Mg extr only at 0-10 cm soil depth during November 2011,

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TABLE 2. Effect of winery wastewater application on soil P (Bray II) in mg/kg at a newly irrigated grazing paddock at a winery near Stellenbosch. Depth (cm) Season Mar 11 May 11 Nov 11 May 12 Nov 12 May 13 Nov 13 10 50 64 77 95 63 70 76 20 54 44 64 75 70 64 71 30 55 44 70 67 73 63 80 60 42 34 50 53 53 46 59 90 31 19 22 27 31 25 22 Mean 46c * 41c 57ab 63a 58a 54b 62a * Means in the same row followed by the same letter, do not differ at p = 0.05. TABLE 3. Seasonal soil K + balances in the 0-90 cm depth of a sandy Kroonstad soil that was irrigated with winery wastewater near Stellenbosch. Period Soil K + (kg/ha) Applied K + (kg/ha) K + loss (kg/ha) Leached K + (%) Beginning End Mar 11 - May 11 2 457 2 633 5 236 5 060 97 * May 11 - Nov 11 2 633 2 984 2 883 2 532 88 Nov 11 - May 12 2 984 4 154 17 030 15 860 93 May 12 - Nov 12 4 154 3 452 9 105 9 807 108 Nov 12 - May 13 3 452 3 686 15 751 15 517 99 May 13 - Nov 13 3 686 3 744 5 934 5 876 99 * Amount lost through leaching expressed as percentage of the amount applied, a figure of >100 indicating that more was lost through leaching than what was applied during that period.

years of irrigating with WWW, the soil P levels were still in the acceptable range for plant growth, i.e. the P levels were below 100 mg/kg. The magnitude of the increases in the top 60 cm within only three years indicates that irrigating with the WWW could lead to P reaching unacceptably high levels in a few more years. Soil nutrient balances Since there was little change in K + levels with depth throughout the profile, it suggested that most of the applied K + was leached beyond 90 cm. In fact, seasonal soil K + balances showed that substantial amounts of K + remained in solution, and were leached (Table 3). Furthermore, the cumulative leached K + was linearly related to the cumulative irrigation plus rainfall (Figure 5). Due to the low clay content of the soil, the exchange complex could not retain large amounts of K + . Therefore, leaching of K + beyond 90 cm was not inhibited. Although leaching of K + in sandy or coarse textured soils during winter rainfall reduces the risk of accumulation and dispersion, it increases environmental risks such as groundwater recharge and/or lateral flow into other freshwater resources. A previous study showed that the K + accumulation in soil upon WWW irrigation could be high if it is not absorbed by plants, but adsorbed to soil particles thereby reducing the possibility of leaching. 9 Visual observations revealed that the grassroots did not extend beyond 30 cm depth. This suggested that the large amounts of the K + that was applied via the wastewater could not be utilised by the grass, since it had died back. Since there was little change in Na + levels with depth throughout the profile, it suggested that most of the applied Na + was leached beyond 90 cm depth. Seasonal soil Na + balances confirmed that substantial amounts of Na + were leached (Table 4). Furthermore, the

FIGURE 5. Effect of cumulative (Σ) irrigation plus rain on cumulative K + losses beyond 90 cm depth where a Kroonstad soil was irrigated with winery wastewater for two and a half years near Stellenbosch.

May 2012 and November 2013 (Figure 4B). The WWW contained too low amounts of Mg 2+ to have any significant impact on the soil to which it was applied. Soil phosphorus Application of WWW over three years increased available soil P (Table 2).

It increased from 50 mg/kg to 76 mg/kg in the topsoil layer after three years of WWW applications, while for the 90 cm soil depth, it decreased from 31 mg/kg to 22 mg/kg. Although there was P build-up over time due to WWW application, the P had accumulated in the top 60 cm. At this stage, after three

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TABLE 4. Seasonal balances for soil Na + in the 90 cm depth increment of a sandy Kroonstad soil that was irrigated with winery wastewater near Stellenbosch. Period Soil Na + (kg/ha)

Conclusions Due to the high volumes of WWW irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particularly K + and Na + , beyond the 90 cm depth. Unfortunately, the leached elements are bound to end up in natural water resources in the long run. Irrigation with WWW did not have a pronounced effect on soil pH (KCl) . The study confirmed that injudicious irrigation with untreated WWW poses a serious environmental hazard, particularly where crops in sandy soils are irrigated. WWW by means of irrigation is definitely not the ultimate solution to the problem. Land disposal can only be recommended where the wastewater application does not exceed the water requirement of the grazing crop, or any other agricultural crop. This means that the WWW needs to be distributed on an area of land that is big enough so that the daily applications do not cause over-irrigation. Therefore, sound wastewater management can only be achieved by means of irrigation scheduling based on frequent soil water content measurements. Care should be taken that the irrigation water does not leach beyond the root zone. The soil chemical status should be determined at least annually. Soil samples must be collected as deep as practically possible to make sure that elements applied via the WWW do not accumulate below the root zone. Soil responses at a winery near Rawsonville will be presented in the next article.  Due to the risks involved as discussed above, disposal of

Applied Na + (kg/ ha)

Na + loss (kg/ha)

Leached Na + (%)

Beginning

End

Mar 11 - May 11 May 11 - Nov 11 Nov 11 - May 12 May 12 - Nov 12 Nov 12 - May 13 May 13 - Nov 13

366 514 411 283 221 155

514 411 283 221 155 221

1 645 1 497 1 331 1 459 1 262 1 324 1 139 1 205 1 713 1 647 333 436

91 * 131 110 105 106

96 * Amount lost through leaching expressed as percentage of the amount applied, a figure of >100 indicating that more was lost through leaching than what was applied during that period.

FIGURE 6. Effect of cumulative (Σ) irrigation plus rain on cumulative Na + losses beyond 90 cm depth where a Kroonstad soil was irrigated with winery wastewater for two and a half years near Stellenbosch.

cumulative leached Na + was linearly related to the cumulative irrigation plus rainfall (Figure 6). Similar to K + , the low clay content of the soil could not retain large amounts of Na + . Therefore, leaching of Na + beyond 90 cm was also not inhibited. Although, leaching of Na + from sandy or coarse-textured soils during winter rainfall also reduces the risk of accumulation and dispersion, it poses the same environmental risks as the large amounts of K + that were leached from the soil. Acknowledgements • This article is an output of WRC

by wineries on soils, crop growth and product quality”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC. • Goudini and Koelenhof wineries for their permission to work at their land and utilisation of their wastewater for research. • ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for their assistance, and in particular Mr. F. Baron for his dedicated technical support.

Project K5/1881, entitled “The impact of wastewater irrigation

For more information, contact Reckson Mulidzi at mulidzir@arc.agric.za. Reference https://www.wineland.co.za/winery-wastewater-irrigation-part-2/

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APRI L

Winery wastewater irrigation (Part 3): Soil chemical responses on a well-drained soil By Reckson Mulidzi & Carolyn Howell

Abstract Most wineries in South Africa dispose their winery wastewater (WWW) through land application, but this results in the accumulation of soil potassium (K + ) and sodium (Na + ). This accumulation can affect soil structural stability and hydraulic conductivity. Taking above-mentioned into consideration, the objective of the study was to investigate the effect of WWW irrigation on the soil chemical properties at an existing grazing paddock at a winery near Rawsonville where WWW has been applied for many years. Results showed that due to the high volumes of WWW irrigation plus rainfall, large amounts of cations, particularly K + and Na + , were leached beyond the 90 cm depth in the Longlands soils. Unfortunately, the leached elements will likely end up in natural water resources in the long run. Land application of WWW did not have a pronounced effect on soil pH (KCl) . The study confirmed that injudicious irrigation with untreated WWW poses a serious environmental hazard, particularly where crops in sandy soils are irrigated. Consequently, land disposal of WWW by means of irrigation is definitely not the ultimate solution to the problem and can only be recommended where

the WWW application does not exceed the water requirement of the grazing crop. Wastewater application according to the K + requirement of the crop is also very crucial. This means that the WWW needs to be distributed on an area of land that is big enough so that the daily applications do not cause over-irrigation. Therefore, sound wastewater management can only be achieved by means of irrigation scheduling based on frequent soil water content measurements. Care should be taken that the irrigation water does not leach beyond the root zone. The soil chemical status should be determined at least annually. Depending on the type of soil and quality of wastewater, each winery will need to determine the size of land needed for irrigation with WWW high in K + . The winery will also have to consider the electricity costs if wastewater needs to be pumped from nearby farms in order to be utilised for a crop requirement. The effects of K:Na ratio in diluted or undiluted WWW on soil structure stability, K + availability and leaching of elements also need to be addressed by continued research. Since the climate, particularly rainfall, will affect the accumulation and/ or leaching of the elements, it is important that the research is carried out in field studies.

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