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Use of Winery Wastewater as a Resource for Irrigation of Vineyards in Different Environments.

by | Oct 25, 2020 | Viticulture

Project Number
P04000022

Project Title
Use of winery wastewater as a resource for irrigation of vineyards in different environments.

Project Leader
Howell, C L

Team Members
Mdlambuzi, T

Malan, G

Myburgh, P

Mulidzi, R

Baron, F

Harris, T

Freitag, K

Completion date

2022

EXECUTIVE SUMMARY

Objectives and Rationale
Since climatic conditions and soil type range considerably in the Western Cape, it was possible to assess the fitness for use of winery wastewater for irrigation of different soil types in regions with varying rainfall on soil and vineyard performance. Wine grapes are an important crop in regions such as the Western Cape and the Lower Orange River in the Northern Cape. However, wineries produce large volumes of poor quality wastewater, particularly during the harvest period. On the other hand, the Western Cape has experienced a drought. In August 2017, the level in the Theewaterskloof Dam was 25.1%. Therefore, the City of Cape Town had to introduce water restrictions and at once stage, residents were subjected to Level 5 water restrictions. This meant that residents were allocated 87 L of water per person per day. More recently, as of 19 August 2019 the level of water in the Theewaterskloof Dam was 81.7%, and water restrictions are at Level 1. As of 5 October 2020, the dams in the Western Cape were filled to capacity. Taking the afore-mentioned into consideration, it is clear that the Western Cape has experienced severe drought recently, which means that water resources for urban and agricultural uses are extremely limited. The drought also severely restricted the irrigation sector, and will change the way things are done in the future. Wine grape producers will therefore have to use water resources judiciously to produce grapes. In addition to this, it is important that the sustainable use of alternative water sources for vineyard irrigation be investigated. The use of augmented winery wastewater was investigated in a previous WRC and Winetech funded project. However, this project only addressed the suitability of using winery wastewater for grapevines in a sandy soil under one set of climatic conditions. Results of a pot experiment showed that soil type and winter rainfall have a pronounced effect on salt accumulation where winery wastewater is used for irrigation. Therefore, a field study was necessary to investigate the use of winery wastewater for vineyard irrigation to determine the sustainability of such a practice in other environments. Since climatic conditions range considerably in the Western Cape, it would be possible to investigate the effect of climatic factors such as magnitude of rainfall on the possibility of using winery wastewater for vineyard irrigation. Therefore, three different regions were to be selected where grapevines would be irrigated with winery wastewater. In addition to climatic differences, there are also different soil types. Since it is well known that soil type can influence nutrient element adsorption and accumulation, it would also be possible to investigate different soil types within the same climatic zone. Experience from a previous study showed that it would be impractical to augment winery wastewater to a pre-determined level before each irrigation, i.e. specifically at the commercial level because it would be difficult to monitor the winery wastewater quality continuously in order to adjust the volumes of raw and wastewater to obtain a required level of augmentation. Therefore, a more practical approach would be applied in this project to use the in-field fractional use (augmentation) of winery wastewater with raw water. According to this approach, grapevines would be irrigated as follows. For each irrigation, a certain percentage of the irrigation requirement would be applied as undiluted winery wastewater. Raw water would then be applied for the other part of the irrigation requirement. All vineyards in the project would be irrigated with micro sprinkler irrigation to ensure that the full soil surface is wetted as well as reduce the risk of clogging of the irrigation pipes. It should be noted that experimental grapevines would be irrigated so that optimum wine quality would be obtained. Therefore, stem water potential thresholds for optimum wine quality for the specific cultivars would be used to set up the refill points. In this regard, grapevines would therefore be under-irrigated rather than over-irrigated because better wine quality is obtained when grapevines receive less water. Considering the foregoing, winery wastewater could be an important resource for irrigation of vineyards. Previous studies have used artificial “winery wastewater”, mostly on a laboratory scale or the winery wastewater has been diluted before being used to irrigate vineyards. Until now, the impact of in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation has, however, not yet been studied and this study is the first where vineyards would be irrigated with undiluted wastewater from a commercial winery followed by an equivalent amount of raw water at the field level. Thus, to know the impact of in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation on the chemical composition, in particular potassium (K) and sodium (Na), of the soil as well as grapevine performance and wine quality is indispensable. Furthermore, the study would generate information and guidelines on using winery wastewater as a resource for vineyard irrigation in different environments. The users and beneficiaries of the information are wine makers, farmers, technical advisors, government department officials and legislators. A research project to investigate the use of winery wastewater as a resource for irrigation of vineyards in different environment was initiated and funded by the Water Research Commission of South Africa. The project was co-funded by Winetech and the Agricultural Research Council. Three different regions in the Western Cape were selected where grapevines would be irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation for four seasons (2017/18, 2018/19, 2019/20 & 2020/21). Given that soil type can influence nutrient element adsorption and accumulation, two different soil types were selected within the same climatic zone.

Methods
Vineyards were selected in the three selected production areas, namely the Coastal, Breede River and Olifants River regions. The specific locations were selected due to their vast difference in climate and more specifically their difference in mean annual rainfall. The Coastal region represents a more temperate climate that also has higher rainfall. Vineyards were also selected in climatic regions that had lower rainfall and warmer climatic conditions, namely the Breede River and Lower Olifants River regions. In addition to climatic differences, there are also different soil types. Since it is well known that soil type can influence nutrient element adsorption and accumulation, it would also be possible to investigate different soil types within the same climatic zone. The specific soils were selected to represent soils commonly found within each production region. The two experiment plots within each region were selected to be located as close to each other as possible to minimise spatial variability. The two experiment plots were on the same farm for all of the production regions, with the
exception of the Lower Olifants River region where they were on separate farms. Both experiment plots at Backberg formed part of a newly planted commercial Vitis vinifera L. cv. Cabernet Sauvignon/US8-7 vineyard which was established in September 2017. Both experiment plots at Madeba were part of a commercial V. vinifera L. cv. Shiraz/SO4 vineyard which was established in 2001. In the Lower Olifants River region, a V. vinifera L. cv. Shiraz/Ramsey vineyard established in 2012, was selected near the Lutzville winery to represent the deep, sandy soil which is typically found in the Lower Olifants River region. At Spruitdrift, the experiment plot was a V. vinifera L. cv. Cabernet Sauvignon/99R vineyard established in 2001 in a shallow, sandy loam soil overlying Dorbank. Each of the six experiment plots compromised of two rows of ten grapevines each. A buffer row of grapevines was located on the one side of each of the experiment rows and two buffer grapevines at each end that also received the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Grapevines were irrigated throughout the growing season (from 2017/18 to 2020/21) with in-field fractional use (augmentation) of winery wastewater with raw water according to their water requirements under the given set of climatic and soil conditions. Grapevines were irrigated with winery wastewater from mid-February when suitable wastewater became available from vintage processes. The application of irrigations was stopped either in mid-April or the beginning of May each year when the winter rainfalls began. Irrigation was applied by means of micro-sprinklers in order to apply larger volumes of water. Soil and grapevine responses were measured.

Key Results
Irrigation with the in-field fractional use (augmentation) of winery wastewater with raw water did not lead to a long-term accumulation of salts in the Backsberg sand and clay soils in the region with higher mean annual rainfall. Given that soil ECe levels at the Madeba clay loam experiment plot was higher at the end of the trial in September 2021 compared to the baseline values, this suggested an accumulation of salts during the grapevine growing season partly due to irrigation in-field fractional use (augmentation) of winery wastewater as well as less effective leaching in the heavier soil. The accumulation of soil K was substantially higher in the Backsberg clay experiment plot compared to the sand one. Similarly, the accumulation of K was substantially higher in the Madeba clay loam compared to the sandy loam. The greater accumulation of K in the soil in the Lower Orange River region was a result of higher amounts of K applied via the irrigation water in conjunction with lower winter rainfall. These K increases could have a negative impact on wine colour stability should it be taken up by the grapevine in sufficient quantities. Results from the Spruitdrift experiment plot showed that calcium (Ca), magnesium (Mg), K and Na had accumulated to such an extent that the wastewater irrigation had to be terminated after two seasons. Each of the vineyards had an experiment plot that was irrigated with winery wastewater and this was compared to the rest of the surrounding block which acted as the control at the end
of the project in September 2021. Soil pH(KCl) was higher for the experiment plots irrigated with wastewater compared to their respective controls but was still within the norm of 5.0 to 7.5 recommended for optimal grapevine growth. The electrical conductivity of the saturated soil extract (ECe) of the Backsberg sand experiment plot was similar to that of the control whereas for the Backsberg clay experiment plot, soil ECe of the experiment plot was slightly higher compared to its respective control. Consequently, rainfall must have leached some of the salts applied via irrigation with augmented wastewater salts from the soil in this particular region. However, this does not rule the possibility that winter rainfall could have leached salts beyond the measured depth. Soil ECe of the Madeba clay loam experiment plot was higher compared to its respective control which indicated an accumulation of salts during the grapevine growing. Furthermore, in heavier soils, less effective leaching is more likely to result in salt accumulation. Soil Ca and Mg was higher for the Backsberg clay and Madeba clay loam experiment plots compared to their respective controls. Soil K was substantially higher for all of the experiment plots compared to their respective controls regardless of mean annual rainfall. In contrast, soil Na of all the experiment plots irrigated with wastewater was similar or lower compared to their respective controls. This indicated that there was sufficient leaching of Na at all the experiment plots, regardless of soil texture. However, where more Na is applied via the irrigation water, Na could accumulate to levels where it could impact negatively on soil physical conditions or grapevine growth and yield. Despite substantial amounts of K applied via the in-field fractional use (augmentation), grapevines did not contain excessive K levels in their leaves. On the heavier textured soil at Madeba, there was an accumulation of Na in the leaves. Furthermore, this particular experiment plot had higher leaf blade Na than the control. This suggested that under the prevailing conditions of this particular climate/soil combination that the amounts of elements applied via the in-field fractional use (augmentation) of winery wastewater with raw water as well as less effective leaching caused the Na to accumulate in the grapevine. Leaf blade Na levels at the Spruitdrift experiment plot was substantially higher compared to the other experiment plots. The Madeba clay loam experiment plot had substantially higher permanent wood Na levels compared to the control. Given the accumulation of Na in the leaves and permanent wood parts, this is a likely explanation for the poor performance of the Madeba clay loam experiment plot. At the end of the trial, cane mass of the Lutzville deep sand and Madeba sandy loam experiment plots was comparable to baseline values measured at the beginning of the trial whereas the cane mass at the Madeba clay loam and Spruitdrift experiment plots were lower than the baseline values. This suggested that the in-field fractional use (augmentation) of winery wastewater with raw water had adverse effects on the vegetative growth of these grapevines and was likely related to the accumulation of Na in grapevine parts. Under the prevailing conditions at the Spruitdrift experiment plot, i.e. lower mean annual rainfall and shallow sand, the yield was so low at that not enough grapes could be harvested to make experimental wine after the second year of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. The extremely low yield measured at the Spruitdrift experiment plot was most likely due to the very low rainfall in the region due to drought as well as the excessive amount of elements applied via the irrigation water which were not leached. Higher berry mass and bunch mass of some of the experiment plots reflected in higher yields for some of the experiment plot compared to the controls. Results indicated that the grapevines at the Spruitdrift experiment plot had recovered to a certain extent after only receiving raw water for the last two years of the study. This indicated that the grapevines could recover from the detrimental effects that they had incurred from the in-field fractional use (augmentation) of winery wastewater with raw water for the first two seasons of the study. The yield of the Madeba clay loam experiment plot was still substantially lower compared to the control and was likely due to the accumulation of salts in the heavier soil as well as the lower mean annual rainfall. Irrigation of grapevines using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation did not have detrimental effects on juice characteristics with regards to ripeness parameters and ion content under the prevailing conditions. Sodic soil conditions caused high concentrations of Na in grape juice with concomitantly reduced Ca concentrations at the Spruitdrift experiment plot. Wine sensorial quality was not affected by the in-field fractional use (augmentation) of winery wastewater with raw water. Under the prevailing conditions, wines produced where grapevines were irrigated using in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation did not always conform to statutory requirements with regard to their Na content. This was specifically notable in regions with lower rainfall.

Key Conclusion of Discussion
Results indicated that winery wastewater can be a beneficial source of irrigation water, particularly where grapevines are normally grown under dryland conditions, as well as during times of drought. Young grapevines were established successfully with the in-field fractional use (augmentation) of winery wastewater with raw water in the Coastal Region. The in-field fractional use (augmentation) of winery wastewater with raw water can be used for vineyard irrigation under certain prevailing conditions. In the Coastal Region, the in-field fractional use (augmentation) of winery wastewater can be applied on sand and clay soils. A ratio of winery wastewater to raw water of 1:1 or lower should be used. In the Breede River Region, the in-field fractional use (augmentation) of winery wastewater can be applied on sandy loam but should not be applied on clay loams over the long term in this particular region. In the Lower Olifants River Region, the in-field fractional use (augmentation) of winery wastewater for vineyard soils should not be applied on shallow sandy soils over the long term but can be used on deep sandy soils.

Take Home message for Industry
The in-field fractional use (augmentation) of winery wastewater with raw water can be used for vineyard irrigation under certain prevailing conditions. In the Coastal Region, i.e. a region of higher mean annual rainfall of c. 469.1 mm, the in-field fractional use (augmentation) of winery wastewater can be applied on sand and clay soils using undiluted winery wastewater with chemical oxygen demand (COD) and electrical conductivity (EC) levels of 2 600 mg/L and 1.20 dS/m or lower, respectively. A ratio of winery wastewater to raw water of 1:1 or lower should be used. In the Breede River Region, i.e. a region of lower mean annual rainfall of c. 152.9 mm, the in-field fractional use (augmentation) of winery wastewater can be applied on sandy loam soils using undiluted winery wastewater with COD and EC levels of 3 400 mg/L and 1.30 dS/m or lower, respectively. A ratio of winery wastewater to raw water of 1:1 or lower should be used. However, the in-field fractional use (augmentation) of winery wastewater for vineyard soils should not be applied on clay loams over the long term in this particular region. In the Lower Olifants River Region, i.e. a region of lower mean annual rainfall of c. 93.6 mm, the in-field fractional use (augmentation) of winery wastewater for vineyard soils should not be applied on shallow sandy soils over the long term but can be used on deep sandy soils using undiluted winery wastewater with COD and EC levels of 5 500 mg/L and 3.00 dS/m, respectively. A ratio of winery wastewater to raw water of 1:1 or lower should be used. The sodium adsorption ratio (SAR) of the wastewater must be less than 5. Given that winery wastewater has high K contents, the K contents of the winery wastewater as well as the potassium adsorption ratio (PAR) should be considered as a water quality parameter when using winery wastewater for vineyard irrigation. The raw water irrigation should follow the application of the undiluted winery wastewater immediately to avoid unpleasant odours in the vineyard while irrigations are applied. The internal drainage in the root zone must be unrestricted. Only micro-sprinklers should be used, since drippers have narrow flow paths and/or small orifices and are more susceptible to clogging. Irrigation must be applied with micro-sprinklers in such a way that the bunches are not wetted. At least 50% plant available water depletion should be allowed between irrigations to allow sufficient aeration for oxidation of organic material applied via the irrigation water. The irrigation frequency and volumes (schedule) should enhance, rather than negate, wine quality characteristics. A summer interception crop of Pearl millet should be cultivated on the sandy soils in the Coastal Region to intercept substantial amounts of K applied via the in-field fractional use (augmentation) of winery wastewater with raw water if growing conditions are favourable. However, the contribution of the slash and removal costs production costs of vineyards which are already high is a further aspect that would need consideration.

Final Report.pdf

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